Guest JAMIE T Posted June 12, 2001 Share Posted June 12, 2001 I had some machined from 6061 T6 billet using the drawings that have been floating around. Does anyone see a problem with that? Jamie Deathstar 250GTO Quote Link to comment Share on other sites More sharing options...
DavyZ Posted June 12, 2001 Share Posted June 12, 2001 Jamie, I'm not saying I know for sure--most parts of a brake system like brackets tend to made from steel, which is stronger than aluminum and has less of a tendency to crack. However, T6 aluminum is pretty strong stuff, and if no one else see a problem with it...go for it! I think the gurus should weigh in though... David Quote Link to comment Share on other sites More sharing options...
pparaska Posted June 12, 2001 Share Posted June 12, 2001 FWIW, the brackets on my rear Arizona Z car sourced Wilwood setup are Aluminum. They are just flat brackets. I'd use 6061 T6 stock as well. Build it beefy enough and the finite fatigue limit of the Aluminum should be many cycles away? But as I remember, that bracket is stepped, so there's you stress concentration. Quote Link to comment Share on other sites More sharing options...
Guest scca Posted June 12, 2001 Share Posted June 12, 2001 i dont think i would use alum for the maxima style . where the step is isnt that thick. the weight savings your talking about is less than a pound. also making this bracket out of alum will cost more than steel. so for more cost less strength and harder to work with i cant see the benefit. for the later style (ala Pete's) with a flat bracket and the outlaw/wilwood alum would be fine- or for the 81 style rear caliper its flat as well.. but for the 83 calipers iwould use steel- as Ross and I are in the brackets we will have made up soon... Quote Link to comment Share on other sites More sharing options...
pparaska Posted June 12, 2001 Share Posted June 12, 2001 Agreed. With the Maxima bracket, I wouldn't want to see that thin step in AL. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted June 12, 2001 Share Posted June 12, 2001 Yikes! Loads that go into that bracket are quite huge. Aluminum is weaker and more prone to fatigue than steel. Not a good idea. Quote Link to comment Share on other sites More sharing options...
jeromio Posted June 13, 2001 Share Posted June 13, 2001 Having made a set of these in Steel, I can tell you that 1/2 plate is really hard to work with. Although I'm certainly not an engineer, but I do know that 1/2 inch Al would definately be much easier to work with. You could probably use thinner steel stock - I don't know. Avoid the half inch steel though. That was a chore that I would not inflict on anyone. What about the Ross C group purchase thing? I'd wait for that. Bound to be cheaper. Quote Link to comment Share on other sites More sharing options...
DavyZ Posted June 13, 2001 Share Posted June 13, 2001 Whoa! 1/2" plate? Is that how thick they are??? Quote Link to comment Share on other sites More sharing options...
Modern Motorsports Ltd Posted June 13, 2001 Share Posted June 13, 2001 quote: Originally posted by DavyZ: Whoa! 1/2" plate? Is that how thick they are??? Yeah/stock is eXtremely stout IMO. 13.5mm thick on the hub end and 15.2mm thick on the caliper end. Not sure what Dan means by 'huge' loads, compared to what? I haven't got my steel design books back from a 'borrower' so can't do a check on it. But I am debating having a P.Engg structural go thru it to see if in fact it could be substantially thinner (not sure this cost is justified/longterm likely but shorterm unlikely). I have a hard time not believing 1/4" plate is adequate. The material thickness doesn't affect cost as the overall piece thickness is a function of the actual offset so only area for mods is the actual thickness of each end 'flange'. For an update...I have a version of it drawn up and am presently getting design feedback on it before having the first prototype made. I agree on the aluminum aspect. These are not very heavy pieces where substantial gains are to be had. If I was to go aluminum it'd most likely be aircraft grade (ie. $$) and at the least it would be engineered for my piece of mind. Wheel spacers etc where they're all in compression are simple/brackets like this with torque/torsion and potential pullout are quite different in complexity if one wants to make a 'minimal' weight/material bracket. As for looks steel can be machined for as fine a finish and then cad plated or painted or ceramic coated etc....not as easy to polish as aluminum but the material savings are justified IMO. Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted June 13, 2001 Share Posted June 13, 2001 I have the brackets already. They didn't cost me anything since I had the the 1 1/4 6061 plate, and my uncle is a machinist(sp?) The bracket does get thin in the step. I was thinking of adding some weld in the steps on both sides to make a large fillet(I weld Alum. everyday) I can go either way on the brackets, steel or alum., I can chaulk the alum. ones up as experimental use only(do not try this at home). The steel is just so damn hard on the tooling, But the program is in the mill and it don't care if its alum. or steel, just slow the feed. Thanks guys for the input. Jamie Deathstar 250GTO Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted June 13, 2001 Share Posted June 13, 2001 Hrm, yes this is a stress area but it seems to me that the loads aren't in a flex sort of direction but more a compression load. Is that clear as mud? In other words the loads will be trying to rotate the bracket not flex it where it's thin. Yes? Wouldn't that allow it to be thinner and still be strong? Quote Link to comment Share on other sites More sharing options...
73BOTIZ Posted June 13, 2001 Share Posted June 13, 2001 I have machined 2 pair out of 1-1/4" thick 4140 steel plate. The extra time it took for machining is worth it for peace of mind. Mike in San Leandro Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted June 13, 2001 Share Posted June 13, 2001 Despite 6061-T6 being referred to as "strong", its Ftu is 42ksi, compared to 55ksi for mild steel (7075-T6 is up around 75 ksi.) Filling in radii with weld returns the material to the T0 state, so post-welding T6 heat treat would be required, or you've substantially reduced the material's strength right where the stresses are highest. The load from the caliper is primarily transferred through shear in the bracket lugs, with tension in the top of the lugs and compression in the bottom, as viewed when mounted. My fear is that repeated tensile loading at the top of the lower lug, where it is very thin, will lead a crack initiating there, followed very quickly by failure of the part. This is NOT the place to try to save less than a pound per side. Machining out of 125ksi steel with as generous radii as are allowed would be the minimum I'd go with if stock parts can't be found (I've got mine right here, tee hee). Loads for 1-g braking assuming a 70/30 distribution under braking, 2800 lb car, brake force at one rear tire = 420 lb. Assuming a 12" tire radius, the load into the bracket (at a radius of 4.25") is 1185#. The fabbed brackets out of 1.25" 4140 Mike mentioned are the only ones I feel remotely OK about so far, for the offset bracket. I would do an FEA of the aluminum one before I let it get near the back end of my car. Dan Baldwin M.S., B.S., Aerospace Engineering Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.