Sunday, September 29, 2013

building an alloy cafe racer fender

I took some time to document building an aluminum fender for a bike I'm working on.  I make quite a few of these parts but usually don't have time to record the process.  I start with a piece of 14ga 3003 aluminum, cut to about 20" and 4-5" wide, depending on the style I'm going for.

The fender is a combination of two curves, the main curve to match the diameter of the wheel, and a tighter curve to match the profile of the tire.  To get this shape the center of the fender needs to be stretched and the sides shrunk.  Since the shrinking is minor, I'll use a dolly and soft slapper to do it, rather than a tuck shrinker which is for more dramatic shrinking.

I start by drawing a center line and two other lines each about 3/4" from the edges, the center line is for reference and the two other lines are so I have a guide to where shrinking and stretching part ways, I could do this by eye now, but doing the lines is habit and probably not bad practice.  In theory, the lines off the edge mark metal which isn't either stretched or shrunk, so technically it's not moved.  That's a good way of thinking about it.

I start off by hammering the center portion into a shot bag, and then going right to the dolly to bring the sides in with the soft slapper.  Right away the fender starts to take shape, it's a pretty basic form so the only challenge really is to keep things even.  I use the wheel to smooth out the hammer and shrink areas, then do a check on the tire.  One more round of hammering the center and lightly shrinking the edges gets the curves where they should be.  Another go in the wheel, and a second pass with a large radius anvil from side to side smooths the fender out.  I use a ruler to make sure the edges are spaced evenly, some light working against the dolly brings them in where needed.  The final check is done against the tire and the fender is ready for sanding and polishing.

Where to get this part

building an alloy cafe racer tank part 3

I put together the finishing up video of the aluminum tank I'm building for a customer's XS-650, this part includes turning an aluminum bung to match up with the filler cap threaded ring, and welding the bung into the tank.  I don't weld the filler on the outside of the tank, even though that is the easier way, I weld on the inside so the cap can sit closer to the surface of the tank, it also keeps distortion down, welding on the outside can wind up wrinkling the top of the tank due to weld shrink.  I didn't get much of the bottom of the tank construction or sanding before polishing, mostly because my priority is finishing the tank properly, so sometimes I use all my concentration on the tank and forget to record parts.  Stay tuned though, I'll be making more videos, so any parts left out will probably find their way into future vids.

RCC's parts store (where you can get a tank like this)

Wednesday, September 18, 2013

Handmade alloy cafe racer tank

I got a lot of questions about the basics of metal forming in regards to the manx tank build I'm illustrating.  Unfortunately I didn't take that many pictures of the actual forming processes while building that tank, so I took and edited some video of the actual forming basics for another bullet cafe racer tank I'm working on.  The shape is different, but the same methods apply.

I use something called a tuck shrinker to shrink edges, some people like to use an an edge shrinker, but hammering a tuck more effectively shrinks than a mechanical shrinker.  Stretching the center is done with a hammer and shotbag.  Lots of people new to metalworking are under the impression that the english wheel is the workhorse of the shop, but most of the shaping is actually done with the first two tools.  The wheel is really a finishing and fine shaping tool.

I'm using a wooden buck I made years ago for this tank, since then I usually make a foam buck because it's not really necessary to have something as sturdy as wood when you're just using it as a shape reference.  Wood is certainly nice when you need to clamp panels in really complex shapes or where really critical accuracy is required, but for most alloy tanks, getting things within half an inch or so is perfectly fine.

Monday, September 9, 2013

Building an alloy Manx tank

Going to do a little writeup on building an aluminum tank, recently I took some in process photos as I built a manx tank for a customer's cx500 cafe racer.

manx tank for a honda cx500

First I like to start with a pattern, foam is fine to use as a template, especially when it doesn't require an exact copy, but you're just working out a shape.  It helps to figure out mounting and clearance issues with the bike before banging out any metal too.

manx alloy tank

Depending on your style, you can start forming any part of the tank first, I usually like to start the sides on manx types first, because the top is mostly flat and a lot simpler.  I like to be able to put each side next to each other to guarantee symmetry. 

Since the pics were just in progress pics, I'll detail more of the actual forming process in the next few days' posts. 

Friday, September 6, 2013

How to do quality cafe racer seat upholstery (Part 2)

 When the pan is all padded, I use it as a guide to cut the vinyl covering, I could just make patterns and stitch each cover the same exact shape and size, but if the trimming on the foam or fiberglass is off just a little bit, the cover won't ever look right.  It takes more time this way, but it guarantees a top notch result.

Since I use a flat fell type of seam for durability, I need to create a trim line offset from the edge of the foam by a little more than usual, I like to use about 1/2".  This is where the vinyl will be trimmed and where I'll line up the edge of the skirt piece.

To stitch the skirting to the main seat piece, I use transfer tape to stick the pieces together before actual stitching, this keeps things from moving around and ruining the straightness of the seam.  The first stitch is done on the backsides of the vinyl, then it's folded over and the next stitch is done about 1/4" from the first seam.  This makes the skirting hang perpendicular to the main seat piece without any bunching.

Next, the back piece gets stitched to the main seat piece, I use transfer tape again to lock it in place so nothing bunches up while stitching.  This piece can be cut extra large because it's trimmed to match the back piece of foam.  

Once the back piece is stitched, the whole cover is temporarily put on the foam and the back piece is pinned to the back foam, this gives it the shape it will take on when the pad is done.

To make the back skirt piece, I use two pieces of transfer tape, one to fold the first 1/2" of vinyl over on itself, and the next piece on top of that fold.  

The rear skirt is then stretched over the back piece of vinyl and pressed so the transfer tape holds it in place, then the pins are removed and the piece is unfolded and stitched. 

The piece is then folded over and the second stitch is done, extra care has to be taken here because any mistakes will cause the back of the seat to be uneven. 

The cover is then checked against the foam, when pulled tight it should be even and have no bunching anywhere. 

The cover is then riveted to the base and pulled taught as it's riveted.  Any excess material is trimmed off and hot melt adhesive can be used to flatten the creases against the fiberglass base.  

All ready for installation!

Tuesday, September 3, 2013

How to do quality cafe racer seat upholstery

I've been upholstering my own seats for a few years now, and when looking back at the first ones, I'm a bit impressed at how they look now.  Not blown away mind you, I'm a novice at best, but I think I can share some techniques with beginners that may help them along the way.

The style of pad I like to do is a separate upholstery unit, in my mind, it makes for a much cleaner look on the bike and is a lot easier to remove for underseat access than the snap cover type.  This type is shown on my personal bike, yeah, I actually ride on the parts I make!

The first step in my process is to make a fiberglass base pan for the pad, I use an original seat for the mold, and wax it so the glass doesn't stick to it, a couple layers of chopped mat is stiff enough for this purpose.  When it's all cured, I remove it and trim to the shape I want, I use templates for the seats I make all the time, it saves some measuring and marking time and ensures everyone's getting exactly what's in the picture.

Next I drill out holes for 1/8" rivets along the edge of the pan, I find rivets work best to hold down the material without starting tears in it.

Depending on the firmness desired, I make a base layer of at least 1/2" of high density closed cell foam, similar to yoga mats, or those floor covers for work areas.  Spray adhesive or contact cement work well to hold the foam to the fiberglass base.  The next layer(s) of foam should be a lower density type that adds a bit of cushion and lets the sewn material move a bit, it looks better than using only high density foam throughout.

With the foam layers adhered to the fiberglass base, I use a bandsaw, or a hand razor saw would work as well, to cut the foam using the edge of the fiberglass as a guide.  This makes sure the foam is straight along the sides and won't make the covering look lumpy.

Next, and this is a very important step, (I've had people tell me some of the "really famous" builders don't do this and have problems with the covers tearing!), I cover the fiberglass edge in either a few layers of masking tape or gaffer tape.  This keeps the abrasive fibers from rubbing holes in the vinyl covering... surprised that some people never think that far ahead.

tomorrow - sewing the cover