zixxerboy said:
I'm curious to know how the rear brake works with the short arm...
It won't....i've put some time into this and the leverance required was to much and would have been to sensitive
. so i've gone back to the drawing board and started again, this time it will be more conventional, but still using 1960-70's parts. My biggest headache at the moment is i can't finish anything as I'm still waiting for parts
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The good news is i share my work space with a research company and they have just brought a small powder coat unit to test the feasibility of powder coating composites, and, well as we are all good friends and a couple of them ride, i've been able to "help" setup and "test" there unit with them ;D. I've brought some gloss black to start with and hopefully will be able to produce a finish worthy of the "dotheton" oracle's.
Tim said:
That's pretty sweet. How do you bond the titanium to the carbon (not that I have either in my garage at the moment)? Pretty trick setup - would look great swiss-cheesed. Put some big holes down the centre - maybe you can get it down to 1.5 oz!
Tim
The material i work with is aerospace grade and this makes it quite easy for me to manufacture parts out of leftovers and "scrap". the principal is the same no matter what material you use. I used carbon 220 weight bi-directional pre-preg as this is readily available and relatively cheep. I cut a template to the shape i wanted and them laid up the fibre making sure that the orientation of the outer ply's were in the longitudinal direction, ie, length ways, and the centre two ply's were laid so as the fibre orientation were at + 45. This gave me a laminate that exceptional strength and stiffness.
As high end composites have excellent tensional strength, this is perfect for torque arms as they have no lateral loads and are only under load when the brake is applied, the amount of load is quite low comparative to the slip load of the tyre, ie the tyre will skid before the arm reaches it tensional load threshold. (+ 6000 lb)
After lay-up i cut two payers of film adhesive and applied them to the 0.020" titanium outer skins and laid the whole lot up to be cured in one go on a core plate with a .0.100" alloy plate over the top to ensure even load distribution, cured in an over under vacuum for several hours.
Job done, you can do the same with dry cloth and epoxy resin.
1. make your template and cut your outer skins. You could use alloy, if you do, use aircraft grade alloy, 2000 series is the best as it's a copper alloy and will withstand corrosion better than most, but can't be welded successfully, or, 5000 series as this can be welded and has good corrosion resistance. This alloy MUST be tempered, it will have a designation like T3, T851 etc do not use material designated "0" as this is very soft and has little internal strength. Or use aircraft grade stainless steel 1/4 hard or less.
2. Get you're self some carbon or "s" (structural) rated glass bidirectional woven cloth around 200-300 weight, remember that you will need to cut two ply's at +45 deg to the length of the fibre so make sure that you have enough cloth for this.
3. Ok, resin, go to your local supplier and get some room temperature cure structural epoxy resin. tell them what you are doing and they should be able to guide you. but it must be structural resin, Hysol, 3M are two good brands. You will only need a small amount, say 250 - 500 ml or 1/4 -1/2 quart.
4. befor you start make sure that you have everything that you need
scissors
permanent marker "medium"
1" paintbrush
enought clear plastic to create an envelope
beer
a squeegee, spatular, or something soft that you can push the resin around with
stapler
a clean work space
beer
a small amount of clear plastic to lay your job on
gloves!!!!! they are cheap and you can get a box from the chemist of rubber/latex gloves for nix ;D
A roller
more cold beer
5. Ok still with me
you should now have your, outer skins cut and trimmed, enough cloth for the job, good quality epoxy resin and consumables.
6. Plastic.....you should be able to get clear plastic off the roll from a large hardware store, try to get plastic that comes as a tube...around 4 foot wide and when cut along one side can be opened out to create an envelope.
7. right ;D ;D ;D where to start
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place enough cloth inside the plastic envelope to do the job and then staple it in along the seam, this will stop it moving around and keep it secure whilst you work.
8. using your template draw your ply's on the plastic remember to make sure that the fibre is orientated along the length of the job and that you have two that are at +45 deg to the length of the fiber as it came off the roll.
The number of ply's must be even. so think of the center point and work out. the center is between the 45 deg ply's and their must be the same number each side of them.
9. take you outer skins and clean them using acetone. Scrub them with scotch-brite until they are a uniform mat finish -very important- then wipe them down with CLEAN tissues soaked in acetone until there is no visible crud on the tissue, this step is very important as the adhesive won't bond to the skin otherwise. put them aside on a clean surface brown paper plastic etc...
10. Mix your resin and then open the plastic envelope and pour in enough resin to wet out the cloth, close the envelope, if you have done this right you should have an envelope with your cloth and some resin inside.
11. Ok this is the important bit. work the resin from the OUTSIDE of the plastic using the plastic spatular, making sure that the cloth is completely wet through, turn the job over and make sure that it's completely wet. do not force he resin as it may move the fabric. Now move the excessive resin using the plastic spatular to the the folded and stapled side.
12. You should now have a plastic envelope with your ply's drawn on one side and the cloth inside wet with just enough resin inside and if done right the resin is trapped inside the envelope and not on you or the bench.
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Got to go gents 8) so the next installment will follow hopefully tomorrow
Rod