Fabrication Basics



Fab Kevin
Fab Kevin

CNC machinery is a way of life in today’s manufacturing world. Anyone can buy parts for their bike that would’ve been cost prohibitive 15 or 20 years ago. When I got my first fabricating job in 1980, there were virtually no CNC machines available, or at least affordable. No plasma cutters, no lasers, no CNC mills. Every single part we made was laid out by hand or traced from a template, then sawn, led, drilled, formed and metal finished. If I were to use those manufacturing practices today, I could never compete.

As a home based fabricator – you can use those old methods for making one-off parts on your own bike. I’m going to prototype a new part and show you how. I will use the simplest of tools: a jig saw, files, belt sander, drill press, and hacksaw. Except for TIG welding it all together at the end, anyone with access to some electricity and a workbench should be able to make this just like me.

This new part is an oil filter mount that attaches to a kicker cover on 4 speed transmissions. I already offer one that recesses inward toward the centerline of the bike. Crime Scene makes a nice one that also puts the filter behind the trans, and inward. The new one I want to make will work with swingarm bikes, or bikes that might have an interference problem with a battery mounted behind the trans, or maybe a fender.

The first thing we need to do is design the part (fig. 1&2). Whether we’re building it by hand or CNC machine, we still have to figure out how to make it. For this part, I’ll draw it out on a piece of posterboard and then transfer the shape to steel. Using an old kicker cover as a reference, I planned the mount to work with an HD-2 Evo oil filter, so I needed to get ahold of one to be sure I design this part correctly. A couple things to keep in mind: the oil enters the filter on the outside perimeter, and returns to the oil tank through the center. All oil fittings on a big twin oil pump are 1/8” NPT (national pipe thread), which translates to about a .22” opening inside the fittings. Some people use larger fittings on the oil tank, but no matter how large you use – all the oil entering or exiting the motor has to pass through a hole smaller than a quarter inch in diameter.

The Evo filter has 3⁄4”-16 threads, so I needed to get a 3⁄4”-16 bolt from the hardware store, and a couple of 1/8” NPT half-couplings. I stole a small piece of 1⁄4” plate from Eric at Voodoo, but you could probably get a piece big enough to make this mount from your hardware store, or Home Depot. While you’re there, don’t forget blades for your saber saw. For cutting steel, I like short blades that have 14 teeth per inch.

After designing the part and cutting it out, I traced the template onto the steel with a sharpie. Normally I would coat the steel with layout ink and scribe the lines, but we’re not building a watch here. I also used a center punch to transfer all of the hole centers (fig. 3&4).

Fab Kevin
Fab Kevin

Clamping the steel to the bench, we’re almost ready to start cutting. 

Reminder: USE GOGGLES!

Charlie Horse
Charlie Horse

A jig saw will send tiny, pupil seeking projectiles everywhere. If you add the cost of a trip to the doctor to drill shavings out of your eyes, you could have paid me to do this for you and had a load of cash left over. You will find that a decent saw will cut through the 1⁄4” plate much easier than you thought. I use a Porter Cable saw that I’ve had for close to 20 years, and I got through this part using one sawblade (fig. 5&6).

Take your time, and saw as accurate to your line as possible. Leaving a little of your line showing will allow you to sand the part to shape afterward. Here is where a belt sander will save a lot of time. If you don’t have one, you can clamp the piece in a vise and file it to shape. It will take a little more time and work, but the end result will be the same. Besides – by the time you finish ling you will convince yourself to go out and buy a nice Kalamazoo belt sander…… (fig.7&8).

The drill press is next. The mounting holes and feed hole are 21/64”, but the hole that could give you some trouble is the 3⁄4” diameter hole for the filter to attach to. Start with smaller drills, and work your way up to the 3⁄4” and you’ll be able to do it even on a cheap (multi- speed) drill press (fig. 9).

The 3⁄4”-16 bolt will get some attention now. We need to drill a hole straight through the center of it. A lathe would be ideal, but it can be done on a drill press if you’re careful. Mark the center of the bolt as accurately as you can, then center punch it (fig. 10). Drill through with a 3/16” bit first, then open up the hole to whatever size you want. I went with a 3/8” (fig. 11). The hex head portion is next to get sawn off with a hacksaw (fig. 12). Clean up the sawcut with a file, and you are ready to start welding (fig. 13).

I chose to weld a half coupling over each oil port, so a barbed fitting could be threaded in. You could just as easily tap the plate as well as the I.D. of the 3⁄4”-16 bolt to accept the barbed fittings. Then, all you need to weld is the bolt to the plate. I used high pressure half couplings, as they are thicker, stronger, and easier to weld than standard fittings.

After a quick test on a spare 4 speed, it looks like the new mount will fill the void between my old mount and Crime Scene’s. It will clear kicker arms with even the slightest amount of offset, and should be high enough to clear the front pipe of most exhaust systems (fig. 14-16).

Fab Kevin
Fab Kevin

From here, I will transfer my data into autocad and write a CNC program allowing me to duplicate this part. Even if you clown around, it shouldn’t take you more than a lazy Saturday afternoon to make one yourself. If nothing else, maybe this exercise will inspire you to get out the mighty jig saw and make some chips. A little determination takes the place of a lot of equipment and technology.