tuz

I'd like to make some fenders for 20x2.0'' wheels. I have some oak veneer, a West epoxy slow-cure kit and a Wald fender as a mold. The plan is to laminate the veneer strips on the mold with the epoxy. Sounds simple but I'd like some advice before starting.

Namely:

• How to prevent the work from bonding on the mold? Wrap an inner tube around it? Use resin only for the first coat?
• I'm not not sure how to clamp the strips on the mold, if needed;
• Not sure how thick the fender needs to be;
• Should I worry about mixing the grain direction

MassiveD

• How to prevent the work from bonding on the mold? Wrap an inner tube around it? Use resin only for the first coat?

Just about anything will stop it from bonding to the mold. Packing tape with some light wax. Plastic wrap.

I would saw a mold out of plywood and make holes for clamps. I made a set of fenders about 10 years ago, and they came out fine, but the deal way that they spring back form the mold, so you get a larger radius than you want. I was making them for 700c tires, and used a 26" rim for a mold. That worked out OK but the ends were straighter than the middle. So the next time I do the same thing I will make the ends a compound curve so they get tighter radius. I am sure there is some perfect formula, but it worked out pretty well regardless. Often it takes two shots to get stuff perfect.

Epoxy will bond to rubber.

Not sure what you mean by first coat only. I used epoxy for glue, and for the final finish. WEST is the best, but it is not UV proof. You need to top coat with UV varnish, but in my case I didn't bother. On a boat I would have, but for this I figured it wouldn't see enough sun. If you park it outside, or live in Florida, don't count on that.

• I'm not not sure how to clamp the strips on the mold, if needed;

Veneer is very light, so you need a lot of clamps, and a backing strip. The basic rule is that the pressure spreads out in a V of 90 degrees so if your object was 1" thick the clamps would apply 1.44" pressure. What this means on thin veneer is that you are getting virtually nothing more than the contact patch. You can use backing strips to spread the pressure. Or a lot of stapples (not so good on the top sheet). WEST needs very little pressure, but you need to get it tight enough to close the glue lines for the best look.

The executive set-up is a fire hose filled compressed air. I have that for building bows.

The ghetto method is using string and wedges You wrap with string and insert multiple wedges. Where there is a will there is a way.

You veneer is an advantage because it bends easily, but that gives you problems with clamping.

There is a picture here of a non-standard wedges approach:

https://leatherwall.bowsite.com/TF/lw...s=5&CATEGORY=3

https://leatherwall.bowsite.com/tf/lw...=19&CATEGORY=3

• Not sure how thick the fender needs to be;

I would guess 3-4 mm A wood or bamboo fender needs a little beef to survive I amde mine too thick. Just play it by ear. You know how rough you are on stuff, and as you add layers it will become strong enough. Remember the hardware ads structure. Also. I added a light layer of glass to the inside, so as to protect it from mud and water. If you do that, you need to assume that will add some structure, so you want to quit with the wood layers while it is still a little flimsy. If you glass only one side, you need to epoxy the rest. And you need to be aware that you might get a little sectional change if you freeze just one side.

The good thing about glass is that it allows you to see how much spring you get from the lams, and then correct a little before you glass.

• Should I worry about mixing the grain direction

It is positive, but not necessary.

fietsbob

[*]How to prevent the work from bonding on the mold?

>>mold release , essentially wax ..[*]I'm not not sure how to clamp the strips on the mold, if needed;

>>build a jig to make an inside curved space and inflate an Innertube bladder,within
to push each ply into the other .. and press out excess epoxy/glue.
then hold it there till it cures

or go top shelf .. build a Vacuum Bagging rig ..
suck the air out of the bag surrounding your mold with a vacuum pump.

[*]Not sure how thick the fender needs to be;

>>you figure it out **

[*]Should I worry about mixing the grain direction

Worry , it's a choice .. do it If you want to ...

how about bias ply 2 middle layers? .. **4 layers in total..



or study how they strip build canoes, it involves Steaming the wood to make it flexible.
and cooling it in shape ..

they make Guitar sides like that too.

hot wet wood put into the mold, held there, and cooled and dried .

hueyhoolihan

i had a roommate at one time that made classical guitars by hand. i remember him boiling one thin wooden side (it was of course straight at the time) of the guitar body on the stove for several hours in a handmade and soldered trough. he had also made a wooden frame/mold with a profile in the shape of the side.

he took the hot/boiled side off the stove and out of the trough and laid it on top of the wooden mold and stretched 30 or 40 big rubber bands one at a time over the top of the boiled side while gently forcing it to conform to the mold. each band was anchored on a partially screwed in screw in either side of the top of the mold. he left it like that for a day or two. when removed, the side was pretty close in shape to the form. it sprung back a little, but was easily persuaded to conform.

the wood was Indian Rosewood and about 3-4mm thick.

Mark Kelly 

The Wald fenders are round rather than flat, yes?

It is difficult to get veneer to follow a compound curve: you will need to think carefully about the translation from three dimensions into two.

unterhausen

from my guitarmaking experience, rubber bands make pretty good clamps. I've always wanted to do this, but I think that wood simply doesn't bend in a way that makes this possible. I think most wood fenders the shape of a wald are laminated in both directions and then carved into the desired shapes. As far as release, just wrap the wald fender in plastic wrap

tuz

Thanks for the suggestions. Yes the Wald mold (say that 5 times) has a compound curve. And playing with the veneer it looks likely that it will crack on me. It's about 1 mm thick.

How about this. Soak a veneer strip in boiling water, clamp with rubber bands to the mold, let dry, release a band, apply epoxy, reclamp, move to the next one, etc. And repeat for a few layers.

North Coast Joe

I did make some for my FG, but my methods were different from your plan. I'm sure yours will work, but here's what I did FWIW:

I used poplar slats, planed to a narrow edged profile, soaked in a tank for a few days, then wrapped around a wheel of the bike's diameter and dried for a week. The fender did relax slightly when unstrapped, but it turned out to be just the right amount.

Fitted to the frame, drilled, then finished with polyurethane, finally paste wax & fitted to the frame with stainless hardware.

Here's how they came out, although I've made some mods since this pic was taken. It's no longer an IGH, the bag's off now, rear fender is bobbed, front shortened slightly and a Brooks mudflap somehow found it's way to the front. Musta been the mudflap fairy!

North Coast Joe

Forgot to mention one important design feature!!

Consider making a quick release for the front fender brace. I made one that snaps free if road debris becomes lodged between the tire and fender. The original edition didn't have that, got a stick in there that compressed the fender....splintered it, and sent schrapnel into my leg. There's a thread in the over 50 section showing the damage to fender and leg. Consider a release of some sort for that brace. It also may save you from going out the front window should the same event occur.

Booger1

If I were to try this,I would make a steam/soak box.Then clamp it to a wooden mold or a 26 inch rim if it was for a 27/700 wheel.Sounds alot easier than trying to laminate it into shape.

I don't think you'll be able to make a compound curve.....At least not real easy.I think you would have to glue them into the rough compound shape,then finish them.

unterhausen

for something the thickness of veneer, you really don't need to steam. In fact, all but the most traditionalist guitar builders nowadays just get enough water on the slats to make them wet on the surface and then heat them. That is enough to make a 1/16" side bend perfectly, so thinner veneer will certainly bend fine. The problem with something with the shape of the wald is that you are asking some of the fibers to stretch quite a bit. Not going to happen. You can try it and see, but I'm pretty sure it isn't going to work. You can cut the veneer into strips, but I'm not sure if it will even want to conform to the sides without being really narrow.

I think bending wood is a hoot, it's worth messing around with it.

There are chemical treatments that help bending. Fabric softener used to work, but they have changed the formulation and I don't know if the new formulations work as well with wood.

tuz

Yeah I gave it a try and indeed the compound shape is too much to ask. I'll try to lay a base of narrow strips 90 deg to the wheel axis followed by narrow strips parallel to the axis...

Canaboo

I would highly recommend using Elm if you can get your hands on some. Elm is unigue in that it has very tangled fibers so it is not nearly as prone to cracking if you bend it from side to side.
It used to be used for forming cheese boxes in a wheel shape and the actual wooden rim for wagon wheels.
It also has fantastic heat bending capabilities.

tuz

Here is a pic. It's cracked and far from flat, but it's not that bad given my meager means (water and rubber bands). There are a few things I can try next.

fietsbob

Vacuum bagging the mold, makes a Carbon fiber mudguard possible too ..

tuz

Yeah I'm thinking fibreglass or carbon fibre will conform to the shape naturally. Simply rolling the fibres + epoxy should leave a decent finish?

fietsbob

once it cures you apply more , generally the smooth finish is a clear coat applied to the inside of a negative mold

Using the outside of say a wald mudguard the inside would the surface its wrapped over ,

the outside would be the extra layer of applied Resin ..

to be sanded smooth and maybe lacqured a few coats..

Canaboo

You can just lay carbon or any other fabric over a mold covered with clear tape and stretch an inner tube strip around it to smooth it. Tape one end of the tube down and stretch it around the circumference of the mold and tape down the other end.
The rubber will peel off cleanly and the finished fender will pop off the clear tape surface.

MassiveD

The nice thing about the bamboo fenders was that they come curved to start with, and when bent they did not flatten out. I cut the inside to match the outside. And I laminated glass in there. Worked very well, the only thing I noticed was that I could have made them lighter, but It didn't really mater, they were heavy compared to light plastic ones, but not unreasonable.

What I learned, or thought I was learning was that:

1) Flat does not impede effectiveness. This is partly a mater of containing the water, and keeping me dry which they did though a lot less contoured than regular models. Another part of effectiveness is drag, and as far a that is concerned flat fenders ought to have less drag. It isn't all that wet during our nicer months, so low drag is a good thing.

2) I made the fenders wider than the tires, but almost all the wet marking, and dirt marking were up a 1/2" or less line in the middle. I am tempted to make my next touring fenders about an inch wide.

Boiling sides for guitars is not the best way to go. Water has little use in bending wood. It is often used as a means of getting heat to the fibers. Steam is more effective at doing that, and wets the wood less. The failure mode is normally tensile failure on the outside of the bend, so getting the wood wet weakens the fibers significantly. With thin wood like guitars, using a hot pipe, with little or no water, is a great method.

unterhausen

I would love to see a picture down the centerline, it looks better than I figured.

While it's common to see wood fail in tension, it's a lot easier to stretch it than to compress it. I think most guitar builders have more problem with compression than actually breaking due to too much tension

tuz

Here it is.

I think that superposing a series of narrow strips oriented along the two curves would work. But that seems like a lot of work, I can't figure out a way to do that efficiently. I might try fibreglass cloth instead...

Canaboo

You have that backwards. Bent wood compresses on the inside of the curve, it doesn't stretch on the outside. That's why support straps of metal are used in most steam bending applications. That forces all the deformation to happen on the compression side. Wood on the outside can only stretch about 1% before it fails.

unterhausen

you're right, of course. I use steel slats so that the wood doesn't break if I get the process down right. I have had trouble with the compression side folding funny though, there is only so much you can convince the wood to do

Canaboo

For sure. You're trying to convince all the cells to squeeze uniformly and many woods want to "crimp" in a couple of spots instead.
Much of that has to do with wood type selection as well.
I only bend woods that are proven to behave reliably.

MassiveD

Most woods can be bent, if guitars are anything to go by. They used to say that kiln dried woods couldn't be bent, or were a lot harder to bend, but it sounds a little far fetched if industrial production is anything to go by.