Pics of a Duetto racer buildup - Page 37 - Alfa Romeo Bulletin Board & Forums
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post #541 of 764 (permalink) Old 01-19-2015, 07:34 PM Thread Starter
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Once the differential caught wind of what I had in store for it, he got all excited and popped this giant boner (can I say that?):
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post #542 of 764 (permalink) Old 01-19-2015, 08:09 PM Thread Starter
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The rectangular slots in the metal plate are there to accommodate the aluminum casting blocks on the differential. It helps lock down the plate while it's girdling the sliding block's peg. Getting that peg hole drilled in the precise position with minimal clearance around the peg was no small feat. The diff looks just about ready for the sliding block.

Question is, why is he so mad?
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post #543 of 764 (permalink) Old 01-19-2015, 08:41 PM Thread Starter
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I think I know why he's mad.

I made that peg out of 1144 steel. It has about twice the tensile and yield strength of mild steel. It's relatively easy to machine; it prefers HSS over carbide cutting bits on the lathe for a smoother finish, and sends off a shower of tiny flaky chips when machined.

But Grade 5 titanium is still better. It's almost always better. Its tensile and yield strengths are higher than 1144 steel, it's way lighter, and will never rust. I happen to have have a thick rod of the stuff, so I remade the peg. Smaller, too, which allows for more meat on the Delrin sliding block so it won't fail.

It resulted in another small cloud of precious titanium shavings. Yes, I'm still saving this stuff.
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post #544 of 764 (permalink) Old 01-19-2015, 08:53 PM Thread Starter
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Post-rhinoplasty in titanium. All better. Now that's one happy diff!
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post #545 of 764 (permalink) Old 01-19-2015, 08:57 PM
Nice work but don't expect Pixar to come calling anytime soon..

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post #546 of 764 (permalink) Old 01-20-2015, 08:53 AM
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The Autodelta sliding block system used a special diff casting that was substantially reinforced, and mounted the sliding block on a plate that bolted to the diff with six bolts.

I'll add a pic if I can find it.

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post #547 of 764 (permalink) Old 01-20-2015, 11:09 AM Thread Starter
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Thanks, Robert, but I already have those pictures on file. I do a lot of research before I embark on a new project. I know that you can buy AD reproduction diff cases in Al or Mg from Alfaholics. I also thought about welding threaded Al lugs directly onto the case. Back when they were still around, Vintage Prep used to supply a sliding block setup with a bolt-on diff bracket and delrin block/plates. There are a number of options, mine is a hybrid.

I cut and drilled a block of Delrin. The Autodelta pin is about 22 mm diameter, but my Ti version is 19 mm. That allows a little more thickness for the Delrin block, and still allows it to fit in an Autodelta repro yoke. I figure the 19 mm pin is adequate since most Alfa panhard linkages seem to use 12 mm bolts in the spherical bearings, and race mustangs with Watts linkages use a 5/8" (15.8 mm) differential pivot pin.

Since the differential filler hole will remain functional, I need to be able to torque the Ti peg on and off, so I milled some flats on the end to fit a 14 mm wrench. Once I get the yoke mounted and figures for final clearances, I'll use washers to shim the block into position on the peg.
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post #548 of 764 (permalink) Old 01-20-2015, 12:30 PM
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Every time I read an update I want to go out and get a mill and a lathe....

One of these years...
/Neil

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post #549 of 764 (permalink) Old 01-21-2015, 10:21 PM Thread Starter
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Neil, I know what you mean. When I first started fabricating things, it was with handtools. I used an angle grinder and a cordless drill to fabricate rearset brackets for my vintage race bikes. I'd also make spacers and bushings by eyeballing where the holes should go, then drilled them by hand. Incredibly sloppy. When I got a drillpress, it was like a revelation, being able to drill holes exactly where you want them. Same goes for a welder; being able to fuse metal took fabrication to another level. Currently, I'm eyeballing plasma cutters. It's the only reasonable way to cut titanium plate.

Back to the project: understanding that the Delrin sliding block is a consumable item, I went ahead and made up several more to have on hand. Swapping them out is a matter of undoing a snap ring. If they fail, I have a back up plan involving a big hunk of titanium.
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post #550 of 764 (permalink) Old 01-22-2015, 06:53 AM
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Steel plate "girdle"

Quote:
So I fabbed up that steel plate to girdle the pin for additional support.
Why steel ? And so much excess metal!

Now that you have a pattern why not Titanium?

Richard Jemison
RJR Racing

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post #551 of 764 (permalink) Old 01-22-2015, 03:23 PM Thread Starter
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You're reading my mind about Swiss-cheesing that plate, Richard. As for making it out of titanium, see my comment above about getting a plasma cutter. I need to save my pennies to get a decent American-made one (I'm dreaming of a Hypertherm 45).

I have now turned my attention to the yoke. I had it and the diagonal struts heat treated to T6 at a Seattle foundry. I like how this race car project exposes me to these industrial processes: waterjet cutting, ceramic coating, foundry...

This yoke piece is currently under the knife to shave off some rough casting excesses. It'll need some drilling as well.
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post #552 of 764 (permalink) Old 01-22-2015, 05:20 PM
Richard Jemison
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Cutting Ti

Plasma cutter for Ti?
Have you watched Titanium burn? While cutting down some 5/16 (SBC)valve heads to Alfa sizes I had the material burning comming off the insert!

I`d suggest a water jet!

Richard Jemison
RJR Racing

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post #553 of 764 (permalink) Old 02-05-2015, 05:44 PM Thread Starter
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The sliding block components, made from original Autodelta parts, required a fair bit of machining. These are about the biggest things my little machines can work.

I think I can, I think I can...
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post #554 of 764 (permalink) Old 02-05-2015, 06:01 PM Thread Starter
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Makin' holes

Fenestrated the girdle plate. In Switzerland, they call it "cheesing." (I made that up.)

It was a lot of work to make the plate in the first place, so I was anxious about drilling it full-o-holes. That's where the cheap cab comes into play. Liquid courage. (Shouldn't be doing that when dealing with sharp power tools.)
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post #555 of 764 (permalink) Old 02-05-2015, 06:14 PM Thread Starter
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I thought the passenger side bracket for the SBPGP (sliding block peg's girdle plate) could use some bolstering against the differential fins. So I machined up some 7075-T6 lugs to shoulder the weight.
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