Old skool fabrication part 2
Cont. 6.46 to 6.91
In this particular situation where we were using a thick cast aluminum inner primary, we noticed that the bolt boss on the outside of the cover, opposite the pencil shown in the picture, could potentially rub against the lower rail. After rechecking this area in more detail, we found that there would be slightly less than an eighth of an inch of clearance, so we just barely ground down the extreme end of the boss by a little over a sixteenth of an inch. Wherever possible we try to maintain at least an eighth of an inch clearance between components and frame members. An alternative would have been to make the frame a sixteenth of an inch narrower but in this case since there was only one point of potential interference it made more sense to just get out the grinder as the cast bolt boss was very thick.
Before we get back on track and start on the down tube notches it may be important to reemphasize the importance of building a welding jig one piece at a time while we're also building our first frame. A good frame can be built without using a conventional welding jig and all types of temporary jigs and fixtures can be made using wood, clamps, spacers and cribbing but it is far easier to just go ahead and build even a rudimentary jig out of two by fours than it is to rely on stop-gap temporary lash-ups that have to be disassembled and reassembled as you progress through the fabrication process. A jig, even a crude one, is your third hand and believe me there will be times when you wished that you hand four hands when you're trying to hold together three parts at one time and getting some good accurate tack welds into place without everything moving around.
To make the notches where the down tubes intersect the backbone (top tube) it's best to create some arrangement of temporary fixtures or use a jig to hold the backbone in its correct attitude as it would set on a finished frame. On our particular build the top tube slopes down towards the rear axle adjusters twenty-four degrees from true horizontal. The height is determined by the length of the seat post, the slant angle of the seat post and the width of the lower rails. If you've welded up the upper frame section with the seat post and seat post cross member you can simply set this assembly in place and hold it at the proper angle.
Place one of the bent lower rails in its correct position relative to the seat post cross member and let the down tube section lean in towards the top tube as shown in the pretty horrible snapshot of Figure 6.47.
Figure 6.47
As you can see, we're still moving into the new house so half of the garage is being used for storage. Access to the opposite side of the jig is blocked off by furniture so this frame will have to get by with only half of its lower rails for a few more weeks. No, that little Merry-Go-Round toy in the background isn't mine but it might look good as a gas tank on somebody's 'Theme' bike.
Once the tubes are in position, we need to mark a line on the down tube where it touches the backbone. Make the line parallel with the top tube and about one quarter of an inch higher than the actual point where the two pieces of tubing intersect. As we begin cutting the fish-mouth in the down tube it will begin to lean inwards even more and as this angle increases the notch will 'appear' to move downwards relative to the backbone, so we need to do the initial notching a little higher up on the tube to begin with. If you make the initial cuts to low, you'll end up with a big gap in the down tube notch, under the intersection point with the top tube, and you won't be able to make a nice tight joint for welding.
How you cut these notches in the down tubes is up to you and only limited by the number and types of tools you have at hand. Large shops usually use an end mill. Some places have built a separate fixture that holds a hole saw. You can do the cuts with a regular little disc grinder if you're careful. For custom work or one-offs, I usually use a die grinder with a metal cutting bit for the rough cuts and switch to abrasive stones for the cleanup work. Even using the grinder, it only takes about thirty minutes to make a very nice cut that's usually a lot more accurate than one cut with a hole saw.
Figure 6.48 shows the down tube and backbone with the first rough cut to give you an idea of what we're after and how the tube looks after the initial cut is started.
Figure 6.48
Note that we haven't cut off the upper end of the down tube where it extends over the backbone so it’s easier to see what this notch looks like. On this particular tube we have very little overhang but on others where we've left more excess material there can be several inches extending over the top tube.
In case you're interested the bungee cord allows me to quickly pull the frame out of the jig, yet it keeps it pulled tightly against the stops while I'm trial fitting parts. That wooden object in the picture is part of a piece of furniture behind the jig and doesn't have anything to do with what we're working on.
The goal for making these notches in the down tubes is to fit them into the backbone as tightly as possible so that the two separate down tubes in effect blend into the backbone tangent to its outer surface. To do this we simply keep cutting the notches deeper and deeper until the down tube finally leans in as much as possible yet blends into the side of the backbone at a point that's just about on the longitudinal centerline of the top tube.
Figure 6.49
In Figure 6.49 we've deepened the initial rough cut and trimmed off some of the excess tube that extended above the backbone. The black marker line indicates about how much more tube needs to be eliminated by deepening the fish-mouth.
Figure 6.50
Figure 6.50 shows the completed rough-cut notch in the down tube. It is hard to discern in this picture, but the upper rim of the down tube notch isn't a sharp knife-like edge but is instead a blunt surface equal in thickness to the tubing wall. This provides plenty of meat for the final weld and the bead will do the work of smoothly blending the two tubes together at this particular junction.
I usually work on both down tubes at the same time, alternating from one to the other as I'm deepening the notches.
Note that there's no notch for the steering neck yet since that'll be one of the last pieces installed in the frame.
Once we have the notches cut and the two down tubes trial fit together nicely at the backbone, we can finally measure the inward slope angles of these pieces and figure out how we need to place the lower rails in the bender to make the final bends where the tubing heads up towards the axle adjusters.
Part 7
We're getting very close to finishing up the basic frame now but there are a few more important points we need to cover before we can wrap up the lower rails.
In part Six we cut the fish-mouth notches in the down tubes at the backbone intersection and now we're ready to figure out how to make the last bend in the lower rails which isn't as simple as it looks. In fact, some of our visitors jumped ahead of me and tried to make those bends only to be surprised that their rails were pigeon-toed at the rear end of the frame as seen in Figure 6.51 below.
Figure 6.51
The lighting in this picture is pretty bad but if you look closely, you'll notice that the tail end of the lower rail is about two inches inward of lining up with the tail end of the left-hand wishbone. This is what I called pigeon-toed. The reason this happens is because the final upward bend in the lower rail was made in the same plane as the two small bends in the forward portion of the rail where it sweeps up into the down tube. If you sight down the lower rail you can see that all three bends are in the same plane. If you were to rotate the down tube until it was perfectly vertical the back end of the lower rail would match the upper wishbone perfectly.
The final rear bend in the lower rails can't be properly made until we know what the inward slope angle is on the down tube because that slope causes the centerline of the rail, drawn on the uppermost surface of the tube, to shift about one quarter of an inch to the left or right depending on the rail being measured.
Figure 6.52 illustrates what I'm trying to describe.
Figure 6.52
If you look closely, you can see a felt marker line drawn on the uppermost surface of the lower rail tube while the down tube is perfectly vertical. This black line represents the centerline of the tube we used in the bender when we made the two 40-degree bends (seen in the top portion of the photo) where the down-tube and lower rail transition into each other. For the purposes of making the final upward bend on the lower rails however this line is a ‘false’ centerline, as we’ll soon see.
Figure 6.53
In Figure 6.53 however we have tilted the down tube over into its actual position and we'll note that the black marker line is rotated inward towards the right and that the new uppermost surface of the lower rail, indicated by the red marker line, is about one quarter of an inch away. That red marker line represents the control line we need to use in the bender when we make the last rearward bend in the rail. In other words, the last bend will be pointing straight up relative to the lower rail and not in line with, or in the same plane, as the down tube. This is a classic example of a typical ‘rotated’ bend, which you’ll be hearing a lot about when you start building wide-tire frames.
This last statement brings us to the subject of learning how to find up, down and sideways on round tubing. This is the question I am asked most often, and my standard reply is to buy a good book on pipefitting because there you will find literally hundreds of handy methods of dealing with angles on cylindrical structural members and round pipe or tubing. You'll also learn how to use a few special tools designed just for pipe and tubing work, but the tool used most often is the little nine-inch magnetic torpedo level.
The key to successful tubing work is to be sure that all of your horizontal tube runs and the base plate, jig or frame table, and your bender, are absolutely level in all directions. You cannot work with tubing unless you have total confidence in the levelness of your horizontals. In the same vein all of the vertical members should be plumb. For instance, the seat post even though it slants to the rear of the frame should be plumb left to right, at a perfect ninety-degree angle to the frame cross members. If everything is level and plumb you can find virtually any angle, distance, offset, or measured point anywhere on the frame just by using a level and a measuring tape.
One of the handiest books to have on hand is the "Pipe Trades Pocket Manual" by Thomas W. Frankland. This little book explains in lay terms how to do anything including how to find angles by using your wristwatch just in case you've lost your angle finder. It explains is easy to understand terms how to calculate arc lengths, offset bends and how to cut miters just to highlight a few points. It's also loaded with dozens of handy charts, graphs and tables including all of the trig functions.
Even without such reference guides it's pretty easy to navigate around frame tubing.
Figure 6.54
You can use a simple combination square with a built-in level bubble to find the top center point and side centers ninety degrees opposite top center on a tube. If you locate these points at two different places on a tube run, you can scribe control lines between them using a straightedge. It's almost as easy as working with square or rectangular tubing once you get the hang of it.
Figure 6.55
Welding supply shops also sell a host of measuring devices and tools specifically designed to be used on tubing but in most cases all we really ever need to know is where the surface centerline is on any given piece of tubing.
Before going much further I have to apologize for the poor quality of the pictures and the total mess in the garage which makes it hard to see things but I'm using our second-tier camera as we can't find the good one and the garage/shop looks like it's going to be used for storage for at least another month before I can get the tools and benches unpacked. One thing is for certain though and that is if I can work on a frame in this cramped space, you probably can as well.
Looking at our lower frame rails again take a gander at Figure 6.56.
Figure 6.56
In this shot I've propped-up the down tube at pretty close to the actual installed angle and even though the vantage point is off-center you can see how the upward bend in the rear portion of the rail, at the bottom of the image, lays in a true straight up and down plane and not canted to the left or right. It's almost impossible to make this bend correctly unless your bender is level and plumb.
Figure 6.57 shows this lower rail in position. Note that we haven't trimmed off the excess tubing heading out past the location of the axle plate, and we haven't bent another tube to replace the pigeon-toed rail on the opposite of the frame.
Figure 6.57
Figure 6.58 shows the frame as it now stands.
Figure 6.58
We need to finish up with fine fitting on the down tube miters at the backbone, bend another left-hand rail, trim off the end of the right-hand rail and then we'll be ready to do some initial tack welds and start on the axle plates and steering neck.
In case you're interested I messed up the left handrail by putting it in the bender pointing in the wrong direction and doing the bend at the same time that I was trying to carry on a phone conversation with another frame builder who probably did the very same thing as we were comparing notes on exactly how to best describe this particular bend to others. In the end it all worked out pretty well as I ended up with a sample of tube that shows perfectly how not to do something.
Within seconds of posting this page on the site I was already getting calls about the 'backdrop' for Figure 6.58 and for those who might be interested the grayish clamshell-looking thing is an old Edison Mutoscope that shows dirty pictures if you crank the handle and peek through the viewer. It's in the shop for welding on the case which is busted at the base. The orange thing is a 1937 Rockola jukebox that we haven't had time to move into the house yet. The big white slabs are the doors from inside the house that were supposed to be re-hung three weeks ago. The other pieces of bent tubing laying around are parts of a Sportster chopper frame for Tom Toby that were supposed to be shipped out in January.
Part 8
In part 7 we bent the lower rails to form the upsweep to the area of the axle plates and now we're ready to cut and install these plates but before we do it's a good idea to understand exactly how the axle adjusters came into being and what it is exactly that they do for us.
On modern bikes the axle plates house the axle adjusters and in almost 99% of all cases bike owners and professional bike mechanics believe that the axle adjusters are used primarily to tension the final drive chain (or belt) and secondarily to align the rear wheel in the chassis.
Well, this is true up to a point but if we align the rear wheel in the chassis with the axle adjusters, we have also in all likelihood misaligned the rear drive sprocket with the transmission sprocket unless we also realign the motor and transmission in the frame.
In reality nobody does this so as a result we have constant premature wear on all of the drive components even though the bike goes straight down the road. Ironically the bike goes straight even though the tire is wobbling about the hub axis because the adjusters only work in a horizontal direction and vertical alignment is totally ignored in almost all designs.
At one time chain tensioning was taken care of by frame mounted 'chain tensioners' which do a superb job and do it correctly without changing the alignment of the wheel and transmission sprockets. Of course, these devices were used when frames were built straight to begin with, and the rear axles holes were properly aligned from the factory and there was no need to 'adjust' the axle to achieve proper alignment.
As mass production processes demanded cheaper manufacturing methods the so-called axle adjusters in the axle plates came into being. With the slotted axle holes, you could build a little less than perfect frame and then monkey around with the wheel's axle to make the frame roll straight and halleluiah, you could also tension the chain at the same time saving about twenty bucks on every frame you built.
So, there we have it. Axle adjusters are used to 'adjust' an axle that isn't square with the frame or the transmission sprocket to begin with. The fact that you can also tension the final drive chain is just a freebie.
In the real world 'axle adjusters' are totally unnecessary if you're using a frame mounted chain tensioner to keep the chain 'slack' properly adjusted as it stretches.
Our original frame designs all used a simple piece of 1.25" DOM tube with a 3/4" I.D. as the axle 'plate' but we found that even the large shops which spent thousands of dollars on their jigs could not produce frames that were straight enough to use this particular configuration. Small independent builders however, who can spend the time, have successfully adopted this style of axle collar and in fact I think that a few 'notable' builders have built some production frames on a limited basis using the 'old' style non-adjustable axle collars but that's another story.
To get back on track we're going to make and install axle plates for the Old School frame in this article that incorporate conventional axle adjuster slots only because this type of plate is widely known and understood. These plates are made from 3/8" thick cold rolled steel plate but there are literally hundreds of more inventive and creative ways to fabricate adjusters.
Several builders and manufacturers have made their axle plates/adjusters a trademark or hallmark for their shops and it’s pretty easy to spot a frame’s origins by looking at the adjuster design. Paughco for instance uses an old-school type of plate on most of their frames where the plate actually extends completely through the rear tubes by about three eights of an inch on the top and the bottom. Santee uses a distinctive 'boxed' adjuster housing with cover plates.
Figure 6.59
Figure 6.59 illustrates a stock WL axle plate casting, and you'll notice that it's designed like a bicycle axle adjuster where the tire could be removed from the rear without pulling the axle.
Figure 6.60
Figure 6.60 shows an oval tubing type of adjuster housing.
Figure 6.61
Figure 6.61 depicts a plate type adjuster and note that the frame rails have been bent parallel with the top and bottom of this simple rectangular design.
Figure 6.62
Figure 6.62 illustrates what is becoming a very popular style of adjuster. This particular example is a 'boxed' design but the way the tube rails are extended to the rear until they join in an apex is easy to build and adds a custom touch to the frame.
Figure 6.63
Figure 6.63 is another simple plate design but uses two plates between the top and bottom rails.
Figure 6.64
Figure 6.64 is a very fancy 'boxed' design with a little 'decorative’ web reinforcement added. Adjuster blocks like these sure do look great but they also add about six pounds of weight to a typical frame.
From a philosophical standpoint such massive ‘decorations’ actually are contrary to the primary objective of building a chopper in the first place, which is to reduce weight.
Figure 6.65
Figure 6.65 is another 'boxed' style adjuster providing a better shot of the adjuster bolt. I’m not sure why there isn’t a jam nut installed on this particular adjuster to keep it from vibrating loose.
Figure 6.66
Figure 6.66 is something different and original on an old-school custom chopper. Note the mechanical brake linkage.
Figure 6.67
Figure 6.67 is a non-adjustable axle housing which is the style I personally prefer. It's clean and simple, lightweight; trouble free and very easy to build. This particular one is on a Sporty if you haven't noticed.
These snapshots only show a very few of the design possibilities for adjusters, plates and housings and are included here only to give you some food for thought.
Figure 6.68 shows a drawing for a 'round' three-dimensional type of adjuster housing that we've used on several scores of bikes. It gives a 'fixed' axle look but still provides adjustment. The axle nuts can be hidden with a cover if so desired. This particular piece is to be machined from solid stock, but it can just as easily be made from tubing with a 3/8" plate welded into the inner side. The overall diameter and length of the slot is up to the builder. Even with as much as one inch of adjustment these can be made with 2.5” tubing.
Figure 6.69
Figure 6.69 shows this type of axle housing being used on one of John Stewart’s frames.
Regardless of the style or type of adjusters, plates or housings you finally decide to build it is imperative that they are installed in near perfect alignment with the motor, transmission and front wheel axle axis. You'll no doubt realize that I deliberately didn't say that they need to be installed in alignment with the frame itself because they don't, and in some cases shouldn't be.
It is almost impossible to build a 'perfectly' aligned frame with zero tolerances even if you're using a fairly accurate welding jig. Accumulated errors and welding distortion will inevitably creep in to the design. Consider yourself either very good or very lucky if your frame is within one-eighth of an inch square and plumb measured in every conceivable direction when its finally welded up prior to installation of the steering neck and axle plates which brings us to a problem of sequencing the fabrication.
There are two schools of thought about necks and axle adjusters. One school holds that it's better to weld in the axle plates before you weld on the steering neck and the other holds that it's better to weld in the neck and fit the adjusters secondarily.
I've done it both ways and haven't personally found one method superior to the other, so I'll leave it up to you to decide which method produces better results on your own projects.
For the purposes of this article, we'll be installing the axle plates first.
The axle plates, or adjuster boxes, if that's what you're building, have to be installed so that the rear axle holes or slots are situated in such a manner so that the axle itself, when it is 'adjusted' stays in the same plane and remains 'square' and 'plumb' with the front axle axis and the transmission output shaft sprocket.
Figure 6.70
Figure 6.70 illustrates a typical 'alignment' problem where one plate, shown by the light gray line in the picture above, has the adjuster slot 'canted' in relation to the opposite adjuster plate. If the axle is centered in this particular example everything is great but as the axle is adjusted to the rear or to the front it will become 'canted' relative to the tranny drive sprocket and the front wheel axle.
Figure 6.71
In Figure 6.71 we see another common alignment problem where one of the adjuster plates has been welded into the frame without being perfectly square and plumb with its opposite counterpart. In this case the rear axle will always be crooked no matter how it's 'adjusted'.
Ninety percent of all mass-produced frames we've worked on over the past couple of years have had the plates installed with a combination of these two common adjuster alignment problems which is why we want to point this problem out at the onset of this article. It also is the reason that we don't provide 'standard' templates for axle plates.
If you're having a problem on a stock or aftermarket bike with the chain or belt not tracking properly the first place to look is at the alignment of the adjuster plates relative to the transmission sprocket or pulley and the location of the adjuster slots relative to one another.
I strongly suggest that you not cut your plates or adjuster boxes until your frame is almost completely tacked together and you can use your tubes, as they are, to make a template from. You will do doubt find that one side of the frame tubing is ever so slightly different than the opposite side and for this reason you'll probably have to make two different templates (or one oversized) to make your plates exactly match the angles that your rear tubes ended up being bent. The objective of course is to keep the axle hole or slot exactly the same even if the two plates themselves are slightly different in dimensions and angles.
In addition to aligning the adjuster slots as seen in a 'profile' view it's also vitally important that the plates be perfectly parallel when viewed form the top or bottom or from the front or rear and not only should they be parallel to one another but also aligned in the same plane as the chain or belt as it leaves the transmission drive sprocket or pulley and it goes without saying that the rear and front axles should be aligned as well.
How accurately these components are aligned is subject to debate but in general most builders agree that if the front and rear wheel are within an eighth to a quarter of an inch the bike will track properly. The drive sprockets or pulley's however require much more precision and if you're off by more than a twentieth of an inch (0.05") you'll probably have some long-term problems.
To make the template for the axle plate I'll usually just use a piece of cardboard and 'scribe' around the frame tubes freehand as shown in figure 6.72 below.
Figure 6.72
At this point all you need is a very rough idea of the shape and general dimensions so that the plate matches the physical dimensions and angles at the rear of the frame tubes. Once you have this rough template you can keep refining it down until you get something elegant. Quite often I'll go from the cardboard template to a wooden mockup from cheap 3/4" pine and I'll refine this pattern until I'm satisfied with the shape and proportions and then I'll use that as a template for cutting the 3/8" steel stock for the real axle plate.
The frame tubes in the picture above have not been trimmed to their final lengths, which we'll get to later.
In figure 6.73 below we've made a nice clean illustration board pattern for the final plate design we're going to use on this particular frame.
Figure 6.73
Once the pattern is cut it can be used as a template to scribe around on the 3/8" cold-rolled stock used to fabricate the adjuster plates or it can be used to make a wooden 'follow' block if you're going to plasma or flame cut the material. We prefer doing this type of work on a Band saw so we simply transferred the pattern directly to the steel.
Figure 6.74
The rough-cut plates are shown in Figure 6.74. The slots for the axle tube were cut on a milling machine but they could have been done with a drill press using multiple passes cleaned up with a little grinding. As you can see we deviated from the patterns inside cut on the final product and made a nice large radius that matched one of the ideas we sketched out on the original cardboard pattern shown in Figure 6.72 only because it ended up being easier to make on the band saw.
For this project we're using a 3/4" axle and the slot is configured for a 2" range of total adjustment.
The plates ideally should be installed in such a manner so that the axle is positioned closer to the front of the slot when the chain or belt is initially installed so you have plenty of room for rearward adjustment as time goes by. I try to mount then so that there is about 3/4" of forward adjustment and 1.25" of rearward adjustment. This gives you enough room to bring the axle all the way to the front to install a chain. Of course if you're installing a belt you have to pull the axle anyway but once it's on the pulley you'll still need some wiggle room on the front side, which brings us to another matter.
As we've mentioned before there is no 'standard' measurement between the tranny and wheel sprocket or pulley on a chopper, so this dimension is usually set during the frame mockup stage to match the chain link or belt nib count you're planning on using. For those interested we've measured several types of frames and this dimension ranges from as short as 19 inches to as long as 23 inches. On our rigid frames this distance is usually 21.625 inches. For those of you wanting to run belts I strongly suggest that you use a 136- nib belt as they're now the defacto standard on most factory bikes. The original 4-speed drive belts used 125 nibs, being about 1.375" shorter (installed) than the newer five speed setups. For those of you wanting to do this without the benefit of a real mockup you can figure that one link or nib equals roughly .2" of horizontal axle movement using average sized sprockets.
Part 9
Here are the axle plates finally cut from the template we made in Part 8. I've slid them on the dummy axle shaft just to check that they line up with the angles of the tubes.
Figure 6.75
You'll no doubt realize that we haven't installed the rear transmission mount cross member yet and we need to do so just before we do the actual installation of the axle plates, but we've left this pretty critical part of the frame fabrication until this late point in the build-up, so we have a final chance to do some frame straightening before we button it up at the rear.
Chances are that unless you have a pretty good tubing bender and an accurate jig that the ends of the lower rails and the ends of the upper wishbones don't exactly line up vertically if you're looking at the frame from the rear as seen in figure 6.76.
Figure 6.76
Actually, this photo was taken after we straightened the lower right tube that was about 1/4" off center and had already tacked the transmission cross member in place. The short focal length camera lens and our poor setup for a vantage point in this shot makes the frame look pretty out of whack but it isn't. We haven’t straightened the lower left side tube yet to pull it up about three quarters of an inch.
The easiest way to straighten or align long sections of tubing is to insert a piece of 1" thick-wall tube or solid bar as an extension handle deep inside the rail and apply a little manual pressure in short 'bursts' using the leverage of the 'extension' handle. Hopefully you won't have to do this but if you do be very careful, as it's easy to over bend tubing using this rather primitive technique.
Once you're satisfied that everything lines up install the cross member and I suggest that you complete any welds that remain to be fully finished at every point on the frame except for the axle plates and steering neck. Do a final check for alignment afterwards and then we're ready to install the plates.
The back half of the frame should now resemble what is shown in figure 6.77 below.
Figure 6.77
We're now ready to trim the rear tube ends to their final, length so that the axle plates will mate up properly. If I'm using a jig, the plates are just slid onto the dummy axle and a mark is made on the tube ends that will give us about 2" of the axle plate 'leg' embedded into the tubing.
Figure 6.78
Actually, the plates will be embedded into a 2" deep slot we'll cut in the tube end once they're trimmed to length. If you're not using a jig the plates can be held tightly against the tubing by running some all-thread rod completely through both halves to hold them in place as you're measuring and marking.
I usually trim off the excess tubing with either a saws-all or one of the small mini-grinders fitted with a very narrow abrasive blade.
I prefer to have the plates centered along the longitudinal axis of the upper and lower tubes but some builders prefer to have the face of the plates flush with the inside edge of the tube rails. Again, the matter of personal preferences dictates many facets of custom chopper construction.
Part 10
In part 9 we finished up the fabrication of the axle plates and cut the ends of the wishbone and lower rail tubes to their final length and now we're ready to install the plates and button up the major portion of the work on the rear end of the frame.
Since we're going to install the plates on the centerline of the tubes for this project start by marking out the location of the 'slots' that the 'legs' of the plates will slip into as shown in Figure 6.79 below.
Figure 6.79
You can cut these slots with a reciprocal saw, a saber saw, a hack saw or with a small grinder fitted with a very narrow abrasive disc but the objective is to make the cuts very straight and just ever so slightly to narrow for the plates to slip into without doing some fine-tuning and touchup grinding or filing. To start with, deliberately cut the slots a little to short and as you're fitting the plates into their final position deepen the cuts as necessary to insure a good tight fit while keeping the plates plumb and square to the frame and the axle axis.
Figure 6.80
Figure 6.80 is a snapshot of a plate slot in progress that was cut with a abrasive disc on a small grinder. It's pretty rough at this stage but we'll dress it up as it's deepened to fit the axle plate. The only really critical thing at this point is to keep the centerline of the notch parallel to the frame rails in the longitudinal direction and square and plumb with the frame centerline in the transverse or horizontal direction.
Fitting the axle plates is one of the most laborious steps you'll probably ever undertake when building a cycle frame and I cannot over emphasize how important it is to take great care in setting up the alignment of the plates since in effect they determine to a great extent the overall handling characteristics that your frame will inherit. Axle plate alignment is so important in fact that many shops build their entire jig around the plates and work forward with the rest of the framework.
If you're building a frame without the benefit of a jig I strongly suggest that you at least build some kind of fixture that insures both plates are installed in exactly the same manner with the axle slots perfectly parallel and square to one another even if they are not perfectly in alignment with the main frame rails.
If the slots (or holes) in the plates are not identical from side to side your bike will experience rear wheel wobble, which not only causes premature drive train wear but gives the cycle pretty horrible handling characteristics.
Like everything else in life there are certain acceptable 'tolerances' as to how far you can be off and still be within reason so it might be of interest to learn that on about fifty or so factory frames we've measured over the years the plates were 'misaligned' on average by just under a tenth of an inch from front to back at the plate slots and about a sixteenth of an inch top to bottom of the plates themselves.
When you're lucky enough to have accidentally bought one of the few bikes where everything is spot-on you'll have a ride that you can steer just by just breathing hard in one direction or the other.
To get off track for a moment I'd just like to say that most of us have probably never ridden a perfectly aligned bike so we have nothing to compare our riding experience against. The very first motorcycle I ever owned vibrated and wobbled so badly that I thought all bikes behaved the same way so I was utterly amazed when I had an opportunity to ride a properly built bike years later and discovered that the ride I owned at that time was a piece of crap and should have been in the junk yard. When you buy a frame via mail-order and sometimes even if you go to the shop in person you won't be able to put the frame up against a 'square' and do a rudimentary check on alignment so you have to take the builders 'word' for the quality you're going to be getting and unfortunately this 'quality' is sometimes pretty awful.
Figure 6.81
Figure 6.81 is a snapshot of a 'name brand' swing arm cage made for a very popular wide tire conversion kit provided by a so-called 'top quality' manufacturer that sells thousands of these units every year. A very quick rudimentary check on alignment shows that the axle plates are almost .25 inch out of whack relative to the vertical plane and even though we couldn't get a picture since we didn't have the entire frame we found later that the longitudinal alignment was even worse once we started to put this assembly together. Unfortunately there are hundreds of riders out there running this piece of shit and not knowing how horrible their bikes are handling due to rear wheel misalignment problems.
Getting back on track again and working on a frame you have complete control over, once you've cut in the notches in the rear tube ends you'll have to fit and fine-tune the axle plate fit until they're as perfect as you can possibly get them.
Figure 6.82
In Figure 6.82 we've tacked the plates into position and we'll show how to make some nice 'end-pieces' that dress-up the transition from the tubes to the plates themselves a little later on.
Once you're satisfied with the fit of the plates it's time to mount a 'dummy' wheel on an axle and check for final alignment before doing the final plate welding. If you want perfection you can mount a dial-indicator on the frame rail and measure the run-out on the wheel.
The easiest way of visually checking to see that everything is properly installed is to mount the wheel and pick the frame up by the front end and 'drive' it down the driveway like you were pushing a wheelbarrow. If you can see any wheel wobble whatsoever you have to break the tacks and try to re-align the plates.
When you've done everything that you can possibly do to get the rear end aligned you should have a frame that resembles that shown in Figure 6.83 below.
Figure 6.83
To dress-up the raw ends of the tubing at the juncture of the axle plates many builders resort to just welding on regular old tube ‘caps’ prior to cutting the notches for the plates but I’ve always thought that this method didn’t show much imagination and made the frame look like a ‘production’ model.
To give this termination a little more ‘professional’ touch it’s very easy to fabricate some small ‘bullets’ by cutting pie shaped segments from the same size tubing used to build the rails.
Figure 6.84
Figure 6.84 illustrates what I’m talking about. These segments can be cut short and stubby of extremely long and tapered depending upon the look that you’re after but even if they’re cut very short, like the lower one in the picture above, they look 100% better than a plain tube cap.
Figure 6.85
Figure 6.85 illustrates some bullets on Jim Sawyer’s build.
Remember that the welds on these fittings are non-structural so they can be ground down and polished to become completely invisible and totally blended into the axle plates with long smooth transitions creating a perfectly seamless look as seen in the following snapshot.
Figure 6.86
Now that the plates are installed we can do the first 75% mockup of the frame and see for the first time the real shape of what we've spent all this time creating which is shown in Figure 6.87 below.
Figure 6.87
In this picture we've mounted a 150 rear tire and blocked the frame up to ride height. As you can see even with the radical chopper profile of the stretched straight backbone line this is very low frame. The steering neck will be just slightly higher than our workbench, at 32-inches, when it's finished and the seat height is less than 18-inches. This basic frame design is much smaller, tighter, lighter and lower than the typical boulevard sled frames that many companies are pushing.
So far we've only spent $490.00 on this project, which includes the wheels and tires so we're well under budget.
The next step is to install the steering neck itself.
Part 11
In Part 10 we mounted the rear axle plates and now we're ready to install the steering neck, which is actually quite easy but requires a great amount of care to insure that the neck is straight relative to the centerline of the frame. In addition this step of the buildup also requires some very good welding since we'll be joining a very thick piece of tube stock to the relatively thin material of the backbone. It is essential to get deep penetration into the neck without burning away the edges of the top tube.
There are several different methods of cutting the notch in the backbone that will accept the steering neck. In the production shop environment this notch would have been cut very early on in the fabrication process but for the garage-based builder or those doing one-offs it's better to cut the notch last as we'll be doing here.
To start with, mark a centerline running down the top of the backbone and then using the neck-piece as a guide, mark out the location of the upper portion of the miter cut, the heavy black line in this snapshot. If possible leave this initial cut-mark a little on the long side so you'll have some 'fudge' room for fine tuning and fitting as we progress.
Figure 6.88
To actually make the notch you can do one of several things.
First of all you can have a friend help you hold the whole frame up on a tilting drill press table and use a mounted hole saw to make the cut at the desired rake angle. I usually work alone so for me I've found that it's easier to just use a hole saw mounted with a long pilot drill. I'll center-punch the top tube where I want to center the pilot drill and then standing over the frame I'll drill down at an angle I think is close to the neck rake angle I want. I usually make this initial cut about one quarter of an inch further forward on the top tube than I really want to install the neck so I'm sure I've got room to do some fine tuning later. If possible try to use a hole saw that's just a little smaller in diameter than the outside diameter of the neck-piece you're planning on using. Someday I'll get around to making some kind of fixture to make this all a little easier.
Remember that if the frame's sitting in the jig or on the ground that the top tube is already sloped at a 24 degree angle so for a 40 degree neck angle for instance the drill only has to be sloped rearward sixteen degrees from perpendicular with the tube. If the angle of your initial notch is little off it can be corrected very easily with a grinder when you dress up the cut.
Figure 6.89
Clean the notch up slightly and make a trial fit of the neck piece and check the rake with an angle finder. To decrease the rake grind away on the lower edge of the notch and to increase the rake grind away on the upper portion of the notch.
If you feel uncomfortable with cutting this notch more or less freehand as I’ve shown you can buy or build a simple adjustable drilling fixture as shown below.
Figure 6.90
This particular frame is a single down-tube version but the principal is the same. Note the end of the pilot drill is being guided at the correct neck angle down into the curved down-tube. You could perform this in one operation if your pilot drill is long enough to leave room for the hole-saw bit.
If you're installing one of the so-called 'hourglass' shaped necks you'll usually have to do some fine grinding on the shape of the upper notch to get it to perfectly match the tapered segment of the neck-piece. The lower portion of the notch will almost always be a perfect semicircle. We use several different styles of necks as seen in Figure 6.91 but for this low-cost bike we're just going to use a piece of .156 wall DOM tubing. If you're interested in looking at other possibilities check out the section on steering necks.
Figure 6.91
Once you get the rake angle roughly set it's time to check that the neck notch is properly aligned with the centerline of the frame and not twisted to one side or the other. This is very easy to do if you're using a jig with a neck fixture but for this segment we'll work without the benefit of the welding jig in true old-school fashion.
First of all we need to find someplace in our shop or garage that is absolutely flat both longitudinally and transversely where we can set the frame. If this is a problem you can set the frame on cribbing and shim it level with some wedges but it's fairly important that the frame be stable enough to work on without moving it around.
Using a very long straightedge (or piece of steel or a chalk line) scribe a perfectly straight line on the floor that will extend well past the limits of the frame and the 'projected' intersection of the steering neck angle and the ground as shown in Figure 6.92 below.