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homemade saddle

Discussion on bikes, and whatever...

homemade saddle

Postby Jeffr » Wed Jun 20, 2012 5:07 am

I recently tried a Sella SMP Composite which I liked pretty well but had a few complaints with. Although mostly I just wanted a project. Here's the original saddle:

http://www.smpselle.com/smp4bike/images/stories/demo//composit/01.jpg

And here's mine, which still needs some final sanding and clearcoat:

http://people.freebsd.org/~jeff/bikes/saddle8.jpg

I have a spray gun on order to apply clear but I also ordered some kangaroo leather and may wrap this one. The goal wasn't light weight but it is presently 92g. This is lighter than the full carbon sella smp! The shape changes include a shorter and slimmer nose, a wider center channel, and a filled in back. I don't put my bits on the nose or very back of the saddle and filling it in made a simpler shape to mold with better mechanical properties. The sella design results in an overly stiff and unforgiving saddle when fabricated out of carbon.

I took some pictures of the process. Here's the mold I took off of the smp and a plaster copy:
http://people.freebsd.org/~jeff/bikes/saddle1.jpg

The first mold I made before changing the shape further:
http://people.freebsd.org/~jeff/bikes/saddle2.jpg

The first test shell of the right shape. It's only two layers of carbon to experiment:
http://people.freebsd.org/~jeff/bikes/saddle4.jpg

I ended up trying 2, 3 and 4 layers. I stuck with 3. It's all 3k weave as that's what the supply store had. The final shell was 30g after being cut to size. Here it is as it came out of the mold:
http://people.freebsd.org/~jeff/bikes/saddle6.jpg

I weigh the epoxy and lay it up only slightly too wet and then vacuum bag it. At 3 layers it had a comfortable and slight springiness to it. The rails added some excessive stiffness. Here's how I bonded the back of the rails:
http://people.freebsd.org/~jeff/bikes/saddle7.jpg

And one more bike shot:
http://people.freebsd.org/~jeff/bikes/saddle9.jpg

There are cosmetic defects but I consider this a prototype. it is very strong. I have ridden it over the local 'cobblestones' and purposefully jumped up and down on it as hard as I could stand. I am currently making carbon fiber rails. I will probably cover this one and make another with an improved surface finish now that I have learned better techniques. I also ordered some nicer fabrics online. I suspect with carbon rails it will only be ~70g.

I have to thank carbonfiberone from weightweenies who gave me a lot of advice through this project and has gotten me addicted to epoxy fumes.
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Re: homemade saddle

Postby pritchet74 » Wed Jun 20, 2012 5:30 am

WOW. Nice Jeff! I am diving into working with carbon soon as I am going to repair my frame myself next week. I love the idea of making a saddle, so fair warning that I will hit you up for tips!
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Re: homemade saddle

Postby j0m » Wed Jun 20, 2012 9:24 pm

Very cool Jeff. Thanks for sharing. I might need to try this as I have some nitpicks with all my saddles. Actually it pretty much sounds like your saddle would be my dream saddle if only it was a bit flatter :-)
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Re: homemade saddle

Postby Fibre-Lyte » Fri Jun 22, 2012 11:41 pm

That's a good effort Jeff. If you give that mould a really good polish you should get a better finish for your saddle.
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Re: homemade saddle

Postby Deluz » Mon Jun 25, 2012 10:07 pm

Did you mold it to your butt?
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Re: homemade saddle

Postby Jeffr » Tue Jun 26, 2012 8:54 pm

Any polishing tips? I used 2,000 grit sandpaper. That's all I could get here. I think my PVA application is not smooth enough. Is it safe to just use wax if I use many coats? I will have a HPLV gun soon for spraying clear but it seems like a lot of hassle to set that all up just to spray PVA.

The guy at the local glass store suggested I do one light coat of epoxy inside the mold and let it slightly set before I lay the carbon in. That would give it a smooth finish free of pinholes. I'm going to try that next. I'm waiting for my vacuum pump to arrive. I used an old vacuum cleaner to get the one nice part out. :-)

I did not mold my butt. I like the sitbone area of this saddle. Just the nose was too long and slightly too wide and the channel wasn't big enough. So I changed the shape of the front.

I'm now trying to mold rails. I got some reasonable test rails out but I need to refine my mold for that. It's quite difficult dealing with such an odd shape. I tried just using clay but it didn't come out very nice.
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Re: homemade saddle

Postby Jeffr » Fri Jun 29, 2012 4:32 am

http://people.freebsd.org/~jeff/bikes/saddleleather2.jpg
http://people.freebsd.org/~jeff/bikes/saddleleather3.jpg

I decided to put leather on this one since it didn't come out of the mold perfectly. I now have a proper vacuum pump. I cut the leather to size, soaked it in a hot 3 part water 1 part alcohol solution. Then vacuum bagged it into the saddle with no glue to stretch it. I then put a light coat of epoxy on the shell and wrapped the leather around, clipping it in place with binder clips. It's setting up now. In a couple of hours it should be dry enough to see if it worked.
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Re: homemade saddle

Postby Jeffr » Fri Jun 29, 2012 5:10 am

http://people.freebsd.org/~jeff/bikes/saddleleather4.jpg

Complete. 115g with leather. I'll ride ti tomorrow. Should've put something between the clips and leather but it looks pretty good.
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Re: homemade saddle

Postby Fibre-Lyte » Sat Jun 30, 2012 11:58 pm

Haven't been on the forum much and missed the thread, sorry Jeff. Do you have 'wet and dry' in your part of the world. Basically a very find grade sandpaper that you can used with water. That can bring the mould up to a nice sheen. Even better once the mould is smooth, is to just use a polishing compound, then before moulding use a release agent such as Freekote. To get the best finish you could try using a gel coat first before applying the fibre, in the same way that the glass store is recommending the epoxy. I didn't realise that you weren't using a vac pump but now that you've got one at least you can eliminate many of the voids.
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Re: homemade saddle

Postby pritchet74 » Sun Jul 01, 2012 2:18 am

Jeff - this looks amazing. Where did you get the leather? Was it a specific type?
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Re: homemade saddle

Postby Jeffr » Wed Jul 04, 2012 4:15 am

I have been wet sanding up to 2,000 grit. I guess I will get a polishing wheel for my dremel and some polishing compound. I've been using wax and PVA as the release agent. Although the PVA doesn't go nicely over wax so I may try only wax.

The leather is kangaroo leather from tandyleatherfactory.com. In most cases you can only buy leather by the pelt. So you have to get a whole animal. The kangaroo is light and durable and also a smaller animal than a cow. :-)
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