Saturday, August 31, 2013

How to build a Cafe Racer Seat

Ok, everyone wants it, here it is.  Here's how you do it, the definitive guide on making your "cafe racer" seat.  If you really actually truly follow these steps, and really actually listen to what I'm saying, don't skip steps, don't half-ass bits of the process because it was cheaper or you didn't have that tool, etc etc, you'll wind up with a nice seat that doesn't use 4 cans of Bondo.

Invariably, yes, it is cheaper and easier to buy a ready made seat, and frankly, the only reason you should do it this way is if you want your own style, or are a serious massochist.  

tools to build a cafe seat

The first thing you need is tools, shown here are a can of spray adhesive, a flexible tape measure (used more as a contour gauge than a ruler), coping saw, small drywall saw, rasp, contouring sanding block, ruler, xacto, tape measure and some pens.  

laying out a seat design

And the first step is DRAW THE DAMNED THING!  If you're one of those youtube generation kids, you've stopped reading by now and are just scrolling through the pics, so have fun with that.  If you're still tuned in though, drawing the thing is the first step to a good design, sit on it for a day or two as well, you'll be amazed how many changes you make because of things you didn't consider, and how many changes you'll wish you made if you just start slogging fiberglass at something without thinking.  

cafe seat patternmaking

When you're really happy with the design, print it full scale, or if you drew it full scale, use it to trace out negative templates, these will guide you and help keep your part symmetrical.  I like to use melamine from the hardware store, but chipboard or scrap boxes work too, just a bit flimsier.  

seat templates

As far as materials, I use urethane foam from the hardware store (it's the yellow stuff, not the pink or blue).  The reason for this is that it's easy to carve and doesn't dissolve in contact with fiberglass.  Most of the videos you see on how to do this tell you to cover your foam in plastic and mold release it.  This is absolutely the worst thing to do, you want your fiberglass to stick to and follow the shape of your foam, not lay on top and slide down the sides because of the plastic and release agent.  When you're done with the seat, you don't pop it off your foam anyway, you tear the foam out with the back of a claw hammer, you're done with it, there's no point in trying to save it.  

laying out patterns

carving foam for the seat

building the seat shape

adding material to the seat

forming the shape of the cowl

Here's where your guides come in, you can use them to rough in the shape as you stack up the foam layers, then use them to guide your rasping and sanding to finish the shape.  

cafe seat final shape

Final carving has to be done carefully, because the final foam form is what determines your end shape, if the foam isn't straight, or smooth, then you're boned.  The only way you'll recover from that is by grinding massive high spots down through the foam, reglassing, grinding again, and adding massive amounts of bondo to the low spots and adding a ton of weight and time in sanding.  99% of the fiberglass seat diy builds I see skip the step of getting the foam really smooth and straight, and go straight to slogging fiberglass.  Then with the magic of editing, they turn 28 hours of sanding, grinding, rebondoing and swearing into a minute's worth of "finish work".  Balls I say... this is how you really do it.  

glassing the seat

The next step, once you're absolutely positively sure your foam is good, is to begin glassing.  You don't start glassing with mat, or cloth, or whatever, you start with surfacing veil, the really fine thin stuff that barely adds any thickness to the part.  The reason is because you first want to create a nice shell surface to add thicker stuff to, a shell that will help thicker stuff stick and keep you from distorting the foam underneath as you apply the main glass layers.  

wetting out the fiberglass

first round of fiberglass

once you've got a layer on, there are usually a few spots that don't stick all the way, so sand down the whole part to knock those off, and apply a second layer of veil, the second layer will lay down perfectly now.  

adding more glass to the seat

laying out cloth for the seat

And now onto a tacky but hard second layer of veil, you start applying your cloth.  I don't like building one-off's with mat because it really doesn't lay down in a consistent thickness, doing it with cloth will save you hours in finishing time.  A critical step is to really carefully plan how you trim your cloth, make sure it doesn't fold over anywhere, and where you overlap pieces, make sure the next layer skips the overlap, that way you're not creating any high spots that you'll have to grind off later.  

shaping the fiberglass

If there are any areas that don't want to lay down, use some tin foil to hold them to the part, it peels off easily once the glass is cured and will keep you from having to spend more time grinding out bubbles and reglassing. 

filling the fiberglass

now that you've got a glassed part, hit it with the sander to knock down any high spots or burrs, and apply a SKIN coat of bondo, a skin coat is basically running the squeegee across the surface so the filler only fills the low spots, there should still be spots of fiberglass visible, and that's okay because your glass conforms properly to the foam model.  

smoothing the seat shape

Once the bondo is cured, hit it with the sander again, you'll see a mix of glass and bondo on the surface, and that's fine, then apply another skin coat, this time use the curve of the squeegee to match the surface of the part, and do your best to make a consistent thickness layer of filler over the whole part (like, 1/32", not 1/4").  Hit the second layer with the sander again and if you've done things right, you'll wind up with a straight smooth part, strong and light.  

adding primer to the cafe seat

I personally use Duratec surfacing primer next, it's essentially a gelcoat but has better sanding properties, spray the whole part evenly, you can use a cheapo HF spray gun to do it.  The part should have a very light ripple, the stuff never lays completely smooth, but the ripple can then be sanded out with a sanding block and some 220 paper.  

final sanding of the seat

Any spots that are still low after the sanding can be skinned with filler, as they're probably only a hair's width below regular surface.  Now you're ready to remove the foam, mount up the seat and prime&paint.  

Thursday, August 29, 2013

DIY Cables

Every now and again I take in service work, often it's fixing "cafe racer" builds which were put together with little consideration or craftsmanship and promptly sold.  One of the most common and annoying things I see on these is dropped handlebars with stock length cables, usually by the time they end up in my shop, the cables have either broken or are sticking because they're kinked at some ridiculous angle and have worn through the sheathing.

cutting the cafe racer cable to length

With just a little patience and a few dollars in parts, any garage builder can make or modify an existing cable to the proper length, preventing the problems that come with poorly routed cables and too much or too little slack.  I usually use a special tool I made for crimping the cable housing ends, but in this demo, I'm going to use a really simple tool I made when I very first started fixing bikes.  

adding ends to the shortened cable

Nothing in this post is especially expensive, and the only thing that really can't be found locally are the cable parts themselves, however, the cable ends, sheathing, sheathing ends and cable itself can be purchased online through motion pro's website.  If you're shortening an existing cable, you really only need purchase the housing end, and the cable end.  

crimping the end on the motorcycle cable

The first step is to establish the length of the housing, then cut it to length and clean up the ends, I like to use a drill bit to pick out the scraps of the nylon sheath that like to get stuck inside when you cut it.  Then pop on the ends, and using a really simple tool, you can stake the end to the housing so it'll never come off.  

crimped end cap on the cable

Then establish the length of the cable itself, if there are any adjusters in the line, I like to move those to fully tight and make the cable a touch on the long side.  The ends for the cable can be purchased online, or can be made with a drill press and file, I make mine from brass on the lathe, but if I did a lot of cables I'd certainly buy a cable end assortment.  

cable housing finished

I keep some silver solder in my solder pot, which is just a scrap stainless part with a cap welded to the end, I find that if you don't have any tools to make something like this, a stainless measuring cup works just fine!  Some plumbing flux and a blowtorch are the only other tools you'll need.  Just put the ends on the cable, flux it, smoosh the end of the wire so it frays and won't easily slip back through, and dip in the hot solder pot.  The flux, if done right, wicks the solder all the way through and around the cable end, ensuring a really good solid bond.

soldering the ferrules

After some cleanup on the grinder, or with a hand file, the cable is ready to go, no more shotty cables on your cafe racer!

grinding the extra solder off the new motorcycle control cable

a finished cable for your cafe racer

Wednesday, August 28, 2013

Sand Bending a CB750 Exhaust

Today I started reviving an old technique lots of folks like to talk about but hardly anyone can actually do!  This technique, known as sand bending, has been around as long as the need to bend pipe (basically since steam power started!).  It used to be pretty common practice among hot rodders back in "the day" but has been mostly forgotten since mandrel bending machines and prefab aftermarket exhausts became very common.  There was a time when a garage builder had no other option to make the smokestacks for his souped up roadster, and since sand bending isn't especially expensive, it certainly fit the bill.

In my case, sand bending wasn't preferable due to cost, frankly, buying pre-bent stainless sections and welding them together isn't all that pricey and is a hell of a lot easier!  I chose to use sand bending for the project of the day because it lets me build a seamless pipe (better for performance) and the quality is simply far better than what's available from mandrel bending shops now - the last time I ordered mandrel bends, they came scarred from the machine's clamps and I was told that's basically par for the course and if I got better, I was lucky.  That just wont do!

Since I have used this before on other cafe racers (the cb350 spitfire, a few cb400f exhausts), I knew what I liked, and what I had trouble with.  What I liked was the way I could create any radius bend and make the pipes fit like a factory setup.  What I didn't was that it's damned hard to freeform 4 pipes and get everything to match up.  Something had to be done before my next attempt.

Since I am building a 4-1 pipe for a cb750, I know I'll have to make the turns from the exhaust port all line up especially well because that's a really visible area that would just look bad if it wasn't tip top.  I also know that the pipes won't be a simple plane, there will be bends coming off in different angles if it's to work right, so I decided to devise a good form and clamp jig to keep my bends consistent as well as to let me twist the tube where necessary.

I tossed up a chunk of aluminum on the good ol' bridgeport machine and turned it into a softjaw clamp that matches my 1.5 OD stainless tube just perfect, clamp down the 4 10mm screws and the tube can really be bent to hell and back without slipping in the clamp and especially without scarring the tube by using a simple vise clamp.

The radius form comes from a piece of 5" pipe I sawed up and welded together, when all's said and done, this jig lets me form a whole 90 degree bend the same way every time, then reclamp the part to form the second turn where the pipe goes into the collector, any intermediate twists and bends are also possible by either holding the clamp in the vise and freeforming, or reclamping on the exhaust pipe in a different area and using the jig again.  It was at least 3 hours work to build, but it's a tool worth its weight in gold for making custom pipes.