Lets put things in perspective here .003 is about what a human hair measures ... Are you sure that bar is "tool steel"? ... That would be HUGE money! You guys that doubt ... Take your bar ... Clamp it in a lathe or vice with 2 feet hanging out.... Put a .0005 indicator on the end... Now push gently with your hand... How much movement you see just from that? Anything I have seen with a tolerance like that .... It gets welded than machined ... Now if the tolerance is .050 that seems possible ...
That's no shit about cost, I picked up a 16" long 1" diameter of 01 ground drill rod and it was over 30 bucks.
thirtytwo, you added an extra zero, its .005, not .0005 but yes, its a little more than a human hair. I'm assuming the .0005 is a typo. Look at what OJ is doing. Thats how its done. If your track testing regime is tight, and you correct accurately for weather, a housing that is .015 out will actually show a couple hundredths on a time slip. The bar is probably not tool steel, but it will be centerless ground. I could mic my bar and check the fixtures, but its bedtime. I would guess the clearance between the bar and the bore in the fixtures is probably .001, its a tight slip fit. I worked as a machinist in my twenties and I know you do as well, so yes, I do know what sort of tolerances I am talking about here, thats the point. This is why I said earlier on, the right way to do it is the way OJ is showing, you do all the brackets and spring pads first, then use the mandrel (not mandril, right oj?) and weld the ends on last. Yes, this is precision work. Thats why I was kinda disturbed when I saw what he did. If he is even CLOSE its a total fluke.
The "tool steel" callout didn't really catch my attention because to most people that's just a catch-all name for any material with a grade higher than mild steel. What did stand out is the dimension OJ stated for his alignment bar. I could understand saying 1&1/2" or 1.500 but 1.450 doesn't equate to any standard material diameter.
Just a guess, they probably started with 1.5 and ground .050 off when it was centerless ground? Mine is the old Alston kit and it was BIG money, like $600 back around '81 or '82. That was a shitload of money just for a jig back then. Theres a guy that sells the ends and the mandrels for the housing ends on ebay right now for $100 per rear-end, but you have to provide your own bar. I would have to look at his ad to see what size bar you need for his jig. The Alston jig came with mandrels for Chevy, Mopar and small and big bearing ford, and early Olds. Hotrod428's post caught my attention, never thought of that, but its probably true.
Just looked it up on the Alston site, the jig still costs about the same as it did when I bought it! $493 + $50 for the pinion centerline gauge. When you figure it in CDN dollars and shipping, its only gone up about $75-$100 in 30 years!
George I really doubt the .050 under deal, I think OJ just stumbled on his keypad when he typed 1.450. I built mine in the late 80's myself, just used 1&1/2" TG&P (turned, ground, polished). @ 1.4995, machined the end spud bores to 1.501, eazy peazy. Guess what mine cost......zip, notta, zilch. Shop time and materials. I had built a shotgun mole trap (damn dangerous and illegal) for the shop foreman, he said we were even. Government jobs for the boss are the best, they turn their head when they see a part on your machine when it doesn't look like a shop part. Those were the days.
No George you got it right ...on semi-precision stuff we use an .0005 indicator... that's what we use to tram in vices and bridgeport heads and dial fussy parts on the lathe, so not only am I a hack fabricator but also I have done fairly precision machine work .... Lots of Low run stuff to .0005 ... but thats it ...I have friends who have done some real precision stuff though Anyway what I am trying to say is .... a 2 foot of bar will flex a measureable amount with some pressure my guess is atleast .001 probably more ( use a .0005 indicator to see movement clearly), now you have the bushing that goes into the bearing end, it's a slip fit , my best guess is its .002 under... Probably more... Now it has to slide on that bar also... I will give you credit for super smooth finishes but still going to need another .001 atleast to make it slide on that shaft but I bet it's more ... Now you subject it to a heat cycle on top of all that ... I just can't comprehend that Lets say somehow it IS .005 when done .. It's still .005 with a couple clutch drops? I'm not going to say anything is impossible but that sure seems like a real small tolerance on a piece 5 foot long that sees a huge amount of abuse How are you measuring this spec? This is a whole new world to me ...now I am really curious of how to make an ultra precision rear... And no I'm not busting your balls , but I am baffled I believe average human hair is between .0025 -.005 , mine is .0035 with a iso 9001 calibrated micrometer ;-)
Oh , ok whenever I hear tool steel I think HSS lathe bits I have to sharpen ...or material for molds and dies ...big $$$ 1.450 Could be 1.437with a harbor frieght caliper
It is H11 tool steel, I bought it in 1985 and cost over 1K, it is very precise. And, .050 is a hole not a tolerance.
When its done I am putting a dial indicator on the end of the bar and measuring the concentricy of the bearing bore relative to the bar. The .005 max runout isnt something I came up with myself, it was the way I was taught 40 years ago by Bob Crosbie, and I know other racers who routinely do this. Without a doubt, I would be willing to bet that the housing deflects CONSIDERABLY more than .005 on launch, although I cant imagine how you could measure such a thing. But it doesnt stay there down track.
No doubt about this, I have done it myself many times, it takes very little pressure to deflect a 2' bar MORE than a thou as indicated by a dial indicator. Take the pressure off, and it goes back to zero, or very close to it. When you said .0005, I thought that was a typo in reference to the rear-end tolerance.
I was just thinking about this and a light went on. My guess is, when I bought my jig in the early eighties, the components were probably made by an actual living breathing machinist in Sacramento, the components in the current kit are probably made by a CNC machine in Mumbai...
An update... Well I now have a 9 inch alignment tool. Here is where it was at after using the jog to setup the rear end . Both ends , the one I messed with and the other were off . Ironically about the same amount. I was able to get the rearend into alignment by heating the tube and allowing it too cool. Amazing the amount of movement you could get in a short amount of time.
Fyi, what I learned ... Any amount of heat will move the tube's on the rearend , the more heat the more it moves. I cannot image these things could withstand any welding and stay straight .. The alignment tool has play.. tool steel polished bar ordered a 1.250 measures is 1.245 , alignment components are 1.254-2.256
Who's alignment tool is that? I have been messing with mine, and I think my 1.5 shaft has a swag in it from laying on the floor. Dad always said to not lay a crankshaft horizontal on the floor, it would misshape it over time. I am going to look for a new alignment bar for my fixture.
I've had my alignment tool for 30 + years, always stored the bar on end, seems to have stayed straight although it is looking a little worn after many 100's of rears. I use it now mostly to check the housings as the brackets are welded on.
The weld is done with a machine that either rotates around the tube or the housing will rotate in a positioner similar to a lathe and welded automatically.
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