Frame Detailing

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Basic Frame Detailing

  Some builders like to do frame prep last, after the bike has been mocked up several times and every possible tab, bracket or lug has been welded into place.

Working on the bike doing mock-ups while frame is still grungy or rusty is perfectly normal for some people. Just sand down any places where you'll be doing welding to bare metal.

I personally prefer to do most of the frame prep first. It’s pretty easy to add tabs and brackets by sanding away primer where you need to do some welding. I suppose it’s six one way and a half-dozen the other.

Regardless of the sequence of work you prefer once you're completely ready, it's finally time to sandblast the frame, even if it doesn't show any signs of rust. If it looks relatively 'clean' it's still a good idea to swab the whole thing down with a chemical rust remover. Blasting or a chemical wash not only gets rid of rust but also provides a little 'tooth' on the metal for the primer to adhere to when you get to that stage. Keep in mind that even 'new' DOM tubing has a 'mill scale' on it but it looks nice and shiny. It still needs to come off for a good job to be done. Be sure to plug any threaded holes and the neck stem before you etch or blast.

While the frame is bare metal you need to closely inspect every inch of tubing and each weld to be sure there aren't any 'cracks' appearing anywhere. Sand, file or chisel away any weld splatter.

In general, what you end up seeing after the frame has been cleaned up will be what you’ll see after it’s painted so I aim to make the raw steel, welds and all, as visually appealing as possible without sacrificing structural integrity.

You can see some of the ‘dingleberries’ left over from weld-splatter in the snapshot above. Don’t bother trying to ‘sand’ these away as they are very hard steel. The best way to get rid of splatter is to just lightly tap the blob using a small hammer and dull chisel. That seat mount by the way will be replaced by one much nicer that we’re working on right now.

Watch out for small 'spurs' created by bits of wire left over from wire-welded frames as seen below, this is just one of eight we found the hard way.

You can safely grind or sand down any small spots in a weld run that are obviously much 'higher' than the adjoining sections of bead but do not grind or sand down any welds in an attempt to make them look smooth. There are often 'high spots' in a bead where the weld starts, stops or changes direction and these spots can safely be blended in with the main run of the weld.

The ‘blob’ seen below on top of the bead is typical and can be ground without any problems.

With respect to grinding or sanding weld beads there are two general rules to follow. The first is that you never sand or grid down what are typically called ‘concave’ beads like that shown below.

This bead shape is usually seen on Tig welds which are easily blended into the adjoining tubes or flat work with body filler. There is absolutely no reason to mess with weld beads having this characteristic.

The second rule of thumb is that it is generally okay to slightly grind or sand down the ‘crown’ on a weld like the one shown below but extreme care must be taken not to remove too much material.

In dressing such as weld you never grind below an imaginary line on a 45-degree angle extended between the opposite edges of the bead. You absolutely never grind such welds into a concave cross-sectional shape.

I’m personally ultra conservative when it comes to welding and in general only grind or sand down a weld bead where parts of the bead are visually disproportionate with the main run of the line. If I think a factory weld looks sketchy, I’ll grind it out and re-weld it.

On any parts of the frame made from 'flat' pieces of steel like axle blocks, motor and tranny mounts, wishbone reinforcement plate, neck gussets, fifth mount, upper motor mount or control mounts look for 'sharp' edges and sand these edges to a small radius, just barely knocking down the edges to prevent paint from building up a ridge or cracking at the sharp transition point in the future.

A typical example of a sharp edges can be seen on the axle plate in the snapshot below.

All coatings including powder-coat, primer and paint will tend to build up a ridge, called a ‘fat edge’ on one surface adjacent to a sharp edge and then a ‘thin edge’ of coating immediately opposite the ridge. The phenomena are illustrated below.

The ‘ridge’ or ‘fat edge’ in paint will also be seen around bolt holes unless the holes are well beveled with a countersink.

To avoid paint chipping and flaking at such sharp edges or bolt holes it’s desirable to put a smooth radius along the edges of all flatworks on the bike. Your painter will thank you for the work.

Most frames, both old and new will have poorly tapped or rusty bolt holes in the various mounting lugs. Take a tap and run it down or through any and all tapped holes in the frame. You'll probably need both regular and 'bottoming' taps. Make sure to use a cutting lubricant.

As you’re inspecting the frame and doing prep work use your bare hands to feel the metal as you’re working on it. The touch of your fingers will always reveal countless imperfections your eyes will overlook.

This particular frame needs a lot of cosmetic work but it’s fairly typical of mass-produced frames and nothing out of the ordinary. It’s much straighter than a lot we’ve worked on in the past so I’m confident it’ll make a good ride.

Initial Cleanup

I didn’t think sandblasting the frame at this stage of the work was worth the expense since I’ve had good luck in the past with using chemical de-rusting solutions, so I used ‘Krud-Kutter’ to give the frame an initial de-rusting. This is one of the best acids wash I’ve found that is available almost anywhere. This frame was heavily rusted as you can see in the detail snapshots above and in less than 30-minutes 95% of that rust was completely dissolved, even some heavily corroded spots on the castings.

That greenish-yellow color on the castings and flat-work is the zinc-chromate coating left behind by the solution. The tubing which is much harder steel hardly absorbed any at all but are protected enough to give me a few months before I need to worry about rust again.

I’ll give this frame another wash tomorrow after I work on some areas that had pretty sever rusting but overall, I’m very happy with the results. I’ll still blast it with fine abrasive prior to molding and primer later on down the road.

How far a person goes into what is basically an exercise in ‘cosmetics’ is up to the bike's owner. Some people will be happy with just tapping the bolt holes and removing weld splatter and then they’re ready to primer and paint. Other people might like to do a little more and lightly bend in some of the tube junctions with body filler. Even other people will do full blown detailing with more extensive blending and molding. Sometimes this even involves grinding out ‘questionable’ welds and re-doing them.

Regardless of where you stand on this point a certain amount of frame detailing is worthwhile. A well prepped and detailed frame is not only a sign of good craftsmanship it also helps with the resale value of a bike.

I’ve already heard the argument that “I’m building a Rat bike, so I don’t need to do any fancy crap”. If you look closely at some of the best ‘Rat’ bikes however you’ll see that they generally are just as well detailed as a show bike.

Tools and Supplies

Tools of the trade for frame prep and metal work in general are pretty basic and most of the readers probably have most stuff they'll need already but for those just starting out this section of the article may be helpful.

For de-burring, blending and grinding nothing beats a small variable speed rotary grinder like a heavy duty Dremel or Foredom tool and a supply of variously sized collets to hold mini-flapper discs and tapered sandpaper spirals.

Small pneumatic die grinders also work great if you can throttle down the air supply to keep the tool running at about half speed.

The key, whether electric or pneumatic, is to find tools that are as small as possible so it's easy to get them into tight places.

The snapshot below gives a sampling of typical tools that I use most often for deburring and general frame cleanup work.

From left to right we have a flexible shaft Foredom tool. A variable speed Dremel works okay but you’re somewhat limited as to the shank sizes they accept, and you’ll probably burn it out before you’re finished.

Above the handpiece of the Foredom are a few tapered spiral sandpaper rolls. Next is an ancient Black and Decker mini belt sander. This one is about 40-years old and will be upgraded by a new Makita someday. Next in line is a cheap Harbor Freight pneumatic mini belt unit. It’ll get into some really tight spots. The heads on these sanders will rotate as required. Next to that is a typical pneumatic die grinder. This one has a flapper wheel mounted. Next in line is small pneumatic angle die grinder, a regular old hand file, a typical abrasive fiber disc and then the ever popular 3.5” angle grinder. The red and black thing is one of those small orbital sanders with the ‘shaped’ sandpaper. Usually called ‘detail’ sanders, several makers offer a variety of models.

Absolutely never use a ‘flat’ sander on tubing as you’ll inadvertently create small but long flat spots in the surface that go unnoticed when the frame is in primer but jump out at you once the frame is painted.

Abrasives

The flexible abrasive discs are great for rapidly getting rid of old paint and rust from tubing. They also perform very well when getting rid of the mill-scale on tubing prior to building frames or forks.

These pads come in numerous diameters and thicknesses as well as several ‘grits’ much like sandpaper. You can also buy them already mounted to a somewhat flexible backing plate, but I much prefer the unmounted pads, stacked together to the thickness needed for a specific purpose. If the pads seem too ‘flexible’ for your liking, you can stiffen them up by using flexible plastic ‘flanges’ sold at places that provide polishing accessories and supplies.

Flapper wheels are the greatest invention since sliced bread. The come in diameters that range from 3/16” up to around 6” and ‘lengths’ from an eighth to several inches. You can buy them ‘mounted’ in which case they are permanently bonded to a steel shank or mounted to a threaded shank to be screwed into a tool adapter.

I never throw away a wheel unless it’s worn all the way down to the shank. You’ll find that old wheels are useful for fitting into ‘weird’ spaces or deburring odd-sized holes.

Flexible discs and flapper wheels should never be used until they have had the ‘edges broken’ slightly by running them against the edge of a sharp piece of metal or a carbide file.

The picture below shows a wheel with the edge broken. This prevents the new raw edge from deeply scoring a line into parts you’re only trying to blend into one another.

Of course, you'll need sheets of sandpaper and those nice little flexible foam backed abrasive 'pads'. It should go without saying that you should use good quality wet-dry autobody sandpapers since the backing is flexible. One-inch-wide roll-stock paper can come in handy as well.

The second greatest thing ever invented was the ‘Flapper Adapter’ as seen below.

This handy little ‘tool’ is available from flapperadapter.com and it’s not cheap but it’s well worth every penny you’ll pay for it. Beware that there are imitations out there, but none compared to the original. This adapter allows you to turn a small 3.5-inch angle grinder into a tool fitted with an arbor like a die grinder. You can order the adapter to fit a wide variety of angle grinder shank threads and with various collet sizes. I used to have five of these but four have mysteriously disappeared over time.

Paste Abrasives

Semi-Liquid or paste abrasives as they’re commonly called predate all others and have been used for millennia to ‘blend, smooth and polish’ objects such as sculptures, jewelry, cabinet parts and even glass. Regular old sand mixed with animal and vegetable oils was the first ‘sandpaper’ early man ever used and ‘paste’ is still the choice abrasive for a variety of trades today.

Most readers are probably familiar with the various grades of ‘cake’ or ‘stick’ compounds like Jewelers Rouge and Emery sold at hardware stores but there is an entire range of compounds ranging from vary aggressive course cutting grades to mirror polish abrasives sold by several dozen compound manufacturers. The consistency or viscosity of the compounds range from almost liquid or semi-paste like valve lapping compound to solid sticks. Most of the material that applies to what bike builders use are compounds that have the consistency of a thick pliable clay. It usually comes in a cardboard tube or cylindrical plastic bag.

In practice you apply the compound, usually 80 to 100-grit for framework, to shaped felt ‘bobs’ or ‘wheels’ attached to your die grinder and then go to town smoothing down imperfections in much the same manner that you’d use a flapper wheel. The difference however is that the flexible felt material conforms better to transition points between the frame components and creates a smoother ‘blend’.

It’s seldom that a frame needs this extreme of blending and smoothing but it’s good to know that there are other ways of doing this type of work other than in using flapper wheels alone.

Keep in mind that these paste abrasives in the course grits can take away a lot of metal, more in fact than flapper wheels so be careful you don’t overdo it if you decide to try them out.

Plugs, Caps and Chemicals

You'll often need to plug holes to keep acids and/or finishes from getting inside and 'masking plugs' are readily available from a variety of sources. I buy from McMaster-Carr. Plugs made from EDPM are acid resistant but paint sticks to them, so you'll also need plugs made from silicone for use in painting as they're reusable. It’s also handy to have various sized ‘thread protectors’ or ‘caps’ around the shop.

Chemicals include Lacquer thinner, Metal-Prep and Acetone and of course filler putty and catalyst. A good rust remover is also handy to have around. I’ve already recommended ‘Krud-Kutter’. It comes in a handy spray bottle.

The reason I make a distinction between a rust remover and 'Metalprep' is because the two products are actually very different. 'Metalprep' is a brand name for a phosphoric acid formulated for cleaning and slightly etching metal prior to primer application. Most rust removers have a wide variety of other chemicals included in their composition, most of which you don't want on your frame or sheet metal prior to primer application. The rust removers have to be 'neutralized' and then thoroughly removed before anything else can be done. Metal prep on the other hand is applied and then washed off with water after about a two-minute etching time.

Eastwood makes a product called ‘Pre-Painting Prep’ that comes in spray cans that is excellent to use immediately prior to primer application. It can be applied to etch the metal and then just wiped off. It doesn’t need to be ‘neutralized’ or washed off with lacquer thinner or water.

Frame Detailing

As I mentioned before, what you see with your eyes when the frame is raw steel will be exactly what you see when the frame is painted. Any deficiencies, blemishes, dents, scratches or other defects in the raw steel will look even more obvious under gloss paint.

For this reason, it really pays in the long run to spend a significant amount of time in detailing the raw frame to make it as attractive as possible, without grinding down the welds, and loosing structural integrity.

I make a distinction between frame prep and frame detailing; Prep should always be done as it takes very little time to clean up weld splatter and run a tap into the threaded holes and lugs. Detailing on the other hand goes beyond this basic level of attention and can take a considerable amount of time.

In detailing we’ll go over every square inch of the frame and remove any and all blemishes in the tubing and flat work like axle plates, top motor mount, tabs, brackets and castings. We’ll carefully smooth away any obvious blemishes in the welds that do not contribute to structural integrity and then we’ll blend all the multiple transitions and intersections of the various parts with molding until we have what looks like a more or less monolithic fabrication.

I absolutely hate sharp corners and edges on flat pieces of metal like axle plates, tabs and brackets so we’ll spend a fair amount of time putting some nice radiused edges where we can and while we’re doing this, I’ll be making a list of new tabs and brackets we’ll be needing. On this frame we’re chopping off the tank and seat mounts that it came with, so we’ll need to make some new ones.

Here’s a shot of the axle plates in the process of being detailed. Note that we’re putting a nice radius along what used to be sharp edges and we’ve touched up a few of the weld beads where we could without weakening the primary body of the weld.

So far, my list of things that we’ll have to add to the frame include:

A horn of some kind, remote oil filter mount, chain guard tabs, exhaust pipe supports, seat mounts, tank mounts, oil tank rear mounts, fender mounts, floorboard mounts (maybe) and side car hoops just for looks.

While we’re on this subject it’s really a good idea to keep long term repair in mind as you’re mounting various bits and pieces. For instance, you don’t want to mount your rear fender in such a manner that you can’t remove it easily without dropping the rear wheel or getting a wrench in behind the oil tank. In a similar vein you want plug connectors in wiring that leads to the taillight so the fender can be removed without messing up your wiring. Every fastener on the bike should be easily accessible once the bike is completely assembled. Nothing should be left to chance because once you’re on the road your tool kit will be minimal. Something easy to do in the shop with a full complement of tools might become a nightmare on the highway.

Once all the detailing is finished it’s time to do a little molding.