Fastest928

Here are some pics of our (marc and tom) dry sump project pan roughed out...a bit more machining on the pickups and then some finishing touches and ready for install. But still a ton more work!

It is designed to allow individuals to mount different baffle configurations by welding.

The plate started "solid" and is now mostly chips!

We are making 4 more after this one.

Timing...soon

Marc

atb

Codename: Machupichu

Looks killer.

Peter F

Looks interesting,

any pictures from other angles to share?
What will the cost be?

/Peter

SharkSkin

It's not clear why you would choose such an expensive method to make this part -- why not weld it up out of plate?

JEC_31

CNC rules. You design it, then you cut it to tolerances that welders cannot fanthom.

Lizard928

this falls under one of those, "if you have to ask" catagories.

Fastest928

Cost will be about $1500 per pan. Once we test the first one, the remaining set will go really fast!!

Welding is not precise enough and the pan will end up warped and is suspect to cracking. The cost to machine, cut and weld up a pan is not much different in cost. Also, the oil pickup needs to be very precise and our method will ensure a leak free system, just like stock!!

Cheers,
Marc

SharkSkin

Sorry, I don't buy that. When you cut that much material off of a block of aluminum, it moves all over the place as you relieve stress in the metal. I would be very surprised if the gasket surface on that part is any less warped than it would be if you welded it. In either case, if the warpage is beyond what you can take up by tightening the pan bolts, a cleanup pass will have to be made to flatten the gasket surface.

Fabio421

JEC_31

You should check out a machining shop sometime to get up to speed on how it's done. Aluminum is soft stuff that does not have hardly any stress cast into it in billet form. When cutting it, a continous stream of coolant (which cools and lubricates) is sprayed directly at the cutting tool as it smoothly converts block to chips. These chips actually take the brunt of the heat and they are flung away at high speeds, usually landing on coworker's nearby toolboxes if the CNC machine lacks an enclosed shroud. At the correct cutter RPM and CNC feedrate, the heat soak to the workpiece is minimal and warpage non-existent.

I used to do this 8 to 14 hours a day, making checking fixtures within .050mm (0.002 inches) - with a cheap little off-brand CNC. When the program was done, I picked up the blocks with bare hands - warm but not hot. The only time I warped something was when I was cutting a thin plate and my coolant flow got choked by chips in the resevoir tank while I was eating lunch.

I'm 110% sure that Marc's beautiful dry sump is not warped even on a molecular level.

Mike Simard

Yes, a machined block of aluminum is the best way to make the pan. The pan on a 928 is very shallow and not much more than a flat plate is required for a dry sump. If it were very deep than it would be impractical to machine a massive block and then welding sheets would be practical. Aluminum is very stable after being machined and will be far flatter than a weldment. I'm planning on doing the same thing in my shop, one of the things I look forward to with the method is knowing that the mounting surface will be the flattest possible.

SharkSkin

Well, it wouldn't be the first time I was wrong. But, during the 1986-1995 part of my career where I was responsible for having many different tooling plates and fixtures made up for various purposes, this issue had been raised over and over again by machinists. One specific example I recall was a 1/2" cast aluminum plate, ~12" x ~20" had to be taken down to 10mm thickness. I was told by the machinist (later confirmed by our in-house mechanical engineer) that the plate had to be flipped repeatedly and light cuts made to keep the flatness within the .002" spec. Were these guys full of it or has machining technology/metallurgy changed that much in 10 years?

Mike Simard

If that plate were stainless steel you would have significant warping from the machining forces and taking material away in steps like that would be helpful, I do that all the time with stainless steels. Most aluminum used today is extruded bar, usually 6061 alloy. I find it the most stable metal I work with as far as changing shape from machining, other aluminum alloys like high strength 7075 seem to be very stable as well. There must have been something funky with that cast plate in your experience and the whole idea that a particular peice of material can be funky is one of those things that keep us machinists from getting bored ;-)

Edit: more machining trivia: hmm. .002 over 12x20 10mm thick is tricky. The hardest part is holding on to the part without the clamping warping things. Two sided tape can come in handy for that and it can also be ground on a surface grinder for the last passes, a corse open wheel with some tap magic for aluminum will keep the wheel from loading up and the part will look nice.

JEC_31

Interesting experience! 0.002" flatness over a 10mm thin 12" x 20" plate is actually pretty tight tolerances. The 1/2" cast stock was probably not anywhere NEAR .002" flat from the vendor, doubly so if the flatness has to be on both sides. So that's why they had to flip it and make light cuts. Perhaps they didn't have very cutting-edge cutting tools either, modern coatings have made a world of difference.

svp928

Mike and JEC are right, most aluminum can be relied upon to stay flat IF you cut it right... we make a lot of large flat plates, like bulkheads, with many pockets in them, and floor thickness as little as .030". and they stay flat within a .002- .005". As long as the cutter is very sharp, little stress is left behind. But, a slightly dull cutter rubbing across the surface will turn the part into a potato chip...
Marc's pan has relatively large section thickness, so warpage should not be a problem.