LocostUSA.com

Does anyone know the grade of aluminum the Miata power plant frame is constructed from? I am about to weld up a shortened PPF. I could probably get by with about any aluminum filler metal but if I knew the grade aluminum it would be good. Or maybe someone that has already done this can give me some pointers.

I do not know the alloy -- I had the welding on mine done by Lucas Restoration here in Houston. You can give Gregg a call andhe can tell you the filler rod he used. No very many folks keep the PPF (you would be the third i know of)

_________________
William Keeling
Houston Texas
Spec Miata Racer

Why can't you use one side of the transmission tunnel as the PPF? I don't mean use the Miata PPF, I mean making one side of the transmission tunnel extra strong and bolt the diff to it.

Regarding the aluminum PPF, welding it softens the material to "dead-soft", so the alloy isn't going to matter much if it's been welded to.

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

Is that a property of the PPF or supposedly Aluminum itself?

_________________
mobilito ergo sum
I drive therefore I am

I can explain it to you,
but I can't understand it for you.

mine is working fine -- keeping the PPF puts less drive line load thru the frame and using the trans tunnel does not isolate the drivetrain from the frame

_________________
William Keeling
Houston Texas
Spec Miata Racer

Strictly speaking, if you separate the diff from the trans by removing the PPF and mount the nose of the diff to the tunnel or frame, there is no PPF. There is no reason you can't do this. Millions of cars have been built in this manner. Just keep in mind leverage and the stresses involved. Design the nose mount accordingly. Or keep the PPF and keep any welding as far forward as possible.

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

I don't know much about the treatments for aluminum, but alloys like 6061-T6 are heat treated. I think it also involves some type of liquid solutions, but again don't really know.

Here's some info that's useful on welding aluminum and some of the issues with different alloys. Google popped up plenty of stuff on "aluminum heat treating" so take a look, it's interesting.

Note the comment on the difference between designing for strength and flexibility...

http://www.lincolnelectric.com/knowledge/articles/content/comistakes.asp

_________________
Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

That is assuming it has been heat treated, is a heat treatable alloy, and is a weldable alloy.

If it is heat treatable alloy then it will be on the -O state following welding. You could pay someone to reheat treat it and restore the strength if you were worried.

If it is not a heat treatable alloy but it is a weldable alloy, then its strength will not be compromised.

If it is not a weldable alloy (5xxx and 6xxx alloys and a few other odd balls), then its going to crack very soon.

If you were careful and did the cutting and welding as close to the transmission as possible then you will be in the lowest stress area.

_________________
-Andrew
Build Log
Youtube

The reason I was wondering was I grew up in an aluminum fabrication shop my dad owned and we welded all manner of aluminum pieces all the time with no apparent detriment so I was thinking that maybe there was a special alloy here we were working with.

If any of you are trying to say that welding aluminum somehow destroys it's integrity unless it's heat treated afterward then someone has some bad information.

_________________
mobilito ergo sum
I drive therefore I am

I can explain it to you,
but I can't understand it for you.

Annealing (by heating) aluminum absolutely makes it dead soft. It's a very common technique to resoften aluminum after it's work-hardened during forming, case in point: http://www.tinmantech.com/html/aluminum_alloys_continued.php

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

Well dang it then I guess every weld I ever made failed. All those purty light fixtures and bike frames probably killed someone later.

_________________
mobilito ergo sum
I drive therefore I am

I can explain it to you,
but I can't understand it for you.

That's sort of a silly response, why pick a fight. Obviously people weld aluminum. For instance the space shuttle fuel tanks are welded. At the same time Boeings, in general are not. The link I posted explains these things pretty quickly. It also mentions bike frames.

If you weld a heat treated aluminum alloy, it will no longer be heat treated. Seems simple enough. The pictures of the PPF do not look like a part made from a heat treated alloy which are typically extrusions, plate or sheet. It may have been work hardened during manufacture. I've never looked at one. Welding at the far end from the load should be OK though.

When I see pictures of these parts in Locosts, they look like a truss installed inside another truss - the driveshaft tunnel. Just seems extra...

_________________
Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

I cut and tig welded my OEM PPF today... worked just fine. The plasma cutter cut it like butter the Tig setting wet set to 6160 (set to high cycle frequency AC), used a pin-point (pen) torch, no need to pre or post heat.

The trickier part (for me) was attaching the PPF to the RX-7 transmission! I ended up using two grade 10 (8mm x 1.25) bolts on the side and two (same) bolts to the top so the up / down forces are fixed and the lower part of the "C" box is secured against the transmission. The welds are for bolt spacer tubes to snug it all tight in both axis’s with redundant bolts .

The Plasma cutter just melted away the shifter area cleanly, and with no excessive heat.

As in all aluminum (and tig welds in general) the area MUST be clean, lots of inert gas, (large nozzle) and very fine torch tip. As for the cracking statement I read earlier, well anything can crack of it was not properly welded. But if it is FUSED as it should be, it is every bit as strong and the material it is fused to. That said, it is a tricky bit of tig welding but any experienced TIG welder knows all the settings for his equipment. I put more emphases on the talent of the welder than the nature of the metal / alloy. Since I have a live drive shaft a few inches away from me… I am “walking the talk”.

_________________
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well-preserved body, but rather to skid in broadside, totally worn out and proclaiming, 'WOW, WHAT A RIDE!!!'"

~Bill McKenna

this worked for me and is still working (only 300 miles so far). I took about a foot out of the middle.

_________________
William Keeling
Houston Texas
Spec Miata Racer

Thanks for posting your pictures, guys. The PFF doesn't look quite like what I remembered. It appears to be stamped from either an extrusion or made from plate. So it might well be a 6061 type material. The non-weldable materials are the very high strength ones like 2024 and 7075. The higher strength ones are less corrosion resistant so wouldn't really be a good choice for a car. Considering that it's unlikely it would have trouble with welding, which is your experience.

From the link I posted:


Since you folks have chosen to use the PFF, you should take advantage of this to use softer mounts then most to reduce vibration/harshness. That's a nice feature... I think that's your plan anyway!

_________________
Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.