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  #1  
Old 11-11-2015, 12:20 AM
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Bray D Bray D is offline
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Checking Axle Straightness

I have a Samurai axle that's ready to accept some armor, but I'd like to ensure the housing is straight before I start welding on it. I'll check after I'm done as well.

I have some pretty accurate references/tools to work with. It's set up on the fixture table and I have a height gauge with indicators and such.

It's a bare housing right now. Is there an easy way to check it as-is? I'd rather not machine pucks (I just have a mill; no lathe), but if it's necessary, I will.

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Old 11-11-2015, 11:56 AM
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One method is machined inserts that fit in the carrier in place of the bearings, then use a piece of CRS rod to run through the housing and inserts. It then becomes obvious is the tubes are straight.
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Old 11-11-2015, 12:14 PM
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The bar and puck method is by-far the simplest because it checks up/down & Ft./Back at one time and references the differential main bearings...

If you have a CMM, FAR, or L/Scanner but to check with a surface plate and a Height gauge it is going to be a PITA.
First you are going to have to develop external reference points that will repeat can be verified that they do not move and are 90 to each other.
After you have those points you will have to measure the end housing and the Differential bearing bores then do any calculations to get the center-line of the 4 reference points in two planes
Then you will have to your welding and subsequently relocate the original reference points which you likely covered with your truss (etc).

Another possibility would be to simply put a round bar through the housing without the pucks and then measure from the ID of the housing and end to the bar: that may or may not work depending on the various dimensions...

Mill a block square with a hole through the center, make the distance across the points the same size as the bearing bore and use em like round pucks. Wont be perfect maybe, but I could get to 0.001 easy that way.

E

I'll look at this after I find some kaffii
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Last edited by entropy; 11-11-2015 at 02:56 PM. Reason: used a P in the place of a B
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Old 11-11-2015, 02:36 PM
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Sounds like the puck and bar method is definitely the way to go. I thought that might be the case.

I may be able to whip up some round pucks. I have a rotary table and a boring head with right and left hand bars. I can rough it to size with the rotab, then dial in the fit with the boring head.

Is .012" per foot adequate straightness for the reference bar?

http://www.mcmaster.com/#1346k33/=zrliuv
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Old 11-11-2015, 03:25 PM
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Quote:
Originally Posted by Bray D View Post
Sounds like the puck and bar method is definitely the way to go. I thought that might be the case.

I may be able to whip up some round pucks. I have a rotary table and a boring head with right and left hand bars. I can rough it to size with the rotab, then dial in the fit with the boring head.

Is .012" per foot adequate straightness for the reference bar?

http://www.mcmaster.com/#1346k33/=zrliuv
Only if you can live with 0.012 per foot; say that the long side is 2+feet that could be 0.024" or more and while I have seen OEM housings farther out. . . If I was going to do this the low$$$ way; I would get TGP shafting material in 1018 which is generally a bunch tighter like .001 or so /foot and the OD is +0.0/-0.0001. <(off the top of my head)
The last bar I made was TGP&Cr and it was stupid expensive and I should not have sold it but also have not needed it in years.

E
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Old 11-11-2015, 04:18 PM
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Very true. I guess I was considering tape measure accuracy and thought anything under .030" would be doing pretty good. While it would be better than eyeballing with a tape measure, I may as well get some tooling quality material if I'm making a tool.

McMaster has some hardened 1566 shafting that has a 9rms finish, diameter tolerance of .0005", and straightness tolerance of .002"/foot. Not too shabby. Respectable pricing as well.
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Old 11-11-2015, 08:39 PM
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I'm here for the education, not as an expert. However, I'm wondering what a good target for straightness might be? It would be nice if everything is perfect, but that doesn't happen often.

In the case of the axle housing, what is the practical measure of straightness? Is it like a runout case where 0.00X"/ft deviation is acceptable? Or, as implied by one of the posts above, where both a measure of up/down and front/back variation is the real interest?

Also, even if the housing is perfect, what about the axle shafts? To run as true as possible, won't they have to be measured and possibly straightened too?

Cheers,
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Old 11-12-2015, 08:38 AM
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It really depends on the application. Example: a lot of full floating housings have the outer splines crowned to allow for camber/toe misalignment. In that scenario, the tolerances don't have to be super tight because the splines take up small variations, and there are adjustments elsewhere in the suspension to set the wheelbase and axle steer.

That said, I would want to start with the housing as straight as possible, and I like the 0.002"/ft straightness bar much better than 0.012" when you're considering it's being used for a reference. It would really get aggravating to have the "straightness" of the housing change because you turned the test bar 180 degrees.

If I was doing this, I would look at getting an indicator set up so you could sweep the axle bearing surfaces relative to the bar to get a better idea of "where" and "how much" it isn't straight.
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Old 11-12-2015, 09:27 AM
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If you use an indicator attached to the bar and spin the bar, runout of the bar has no effect on measuring TIR.
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Old 11-12-2015, 11:03 AM
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All good points. I ordered the .002"/foot bar last night, as well as some material to machine pucks. I hope to be making chips by the weekend.
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Old 11-12-2015, 03:10 PM
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What are you planning on doing with the axle?
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  #12  
Old 11-12-2015, 03:46 PM
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Regarding the welding, I'm adding the link brackets in the background of the pic in the original post as well as a homebrew truss that'll run a good portion of the long side.

edit - It'll get a weld on diff guard too. Decent amount of welding on a thin housing.

Last edited by Bray D; 11-12-2015 at 03:49 PM.
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Old 11-12-2015, 07:56 PM
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Trust me I know. having built a few of them. Rock Fab had helped me in the past with advice on my Zuk project. I didn't us a bar though to check the straightness of the axle. My method was a little backwards. I used the face of the housing where the diff bolt into and a machined flat plate bolted to it. I fixed the plate square to a jig table and at the ends at the knuckles I used pins attached to the same table square to the plate. a string between them at mid height and a machinist ruler to measure. after finding a square housing I used the housing to make a jig. It wasn't until I was finished with the first few axles that found someone who had a bar and the plugs I could use to double check. I was pretty dang on the money. the axles averages .002-,010 out of being totally straight.
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Old 11-13-2015, 10:47 AM
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Nice. My bar and material are scheduled to arrive today.

I had some smaller stock on hand, so I went ahead and machined a puck for the outer end of the housing.



I don't have a super accurate way to measure ID's that small, so I'm waiting for the bar to come in before I bore the hole in the center.

I'll machine the larger pucks for the carrier tonight or tomorrow morning and I should be in business.
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Old 11-13-2015, 12:07 PM
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Using a Mill for the pucks. Making do with what you have, making a square fit a round, awesome.
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  #16  
Old 11-13-2015, 12:10 PM
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I could definitely use a small lathe from time to time, but it's not in the cards right now. Until then, I'll continue to 'turn' with my boring head, haha.
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Old 11-13-2015, 02:09 PM
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Love the ingenuity... was always told, "It's how the job is set up" great work
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  #18  
Old 11-13-2015, 03:04 PM
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I just picked up an opposite hand bar so I could cut OD's while spinning clockwise. Works pretty well.

The carrier pucks will be the largest OD I've machined yet. I'm excited to see how the machine handles the cut with the boring head being offset so far. I have a 'plan B' if the machine can't handle it. We'll see how it goes.
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Old 11-14-2015, 05:03 PM
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The carrier pucks were right at the limits of my boring head. I need a lathe.

Anyways, all of the machining is complete. I'm running out to install the pig in the housing right now. We'll see how it checks out.



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  #20  
Old 11-14-2015, 08:24 PM
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Fail.

Installed the 3rd in the housing and I couldn't get the bar into the pucks. It would try to start (chamfer on the bar), but the housing was already out so much that I couldn't get it through.

I'm pretty sure the pucks are accurate. I machined both from one piece, then split it to get two. Both the ID and OD were machined in the same setup, so they should be as concentric as my machine is capable.

Just to double check, I installed the knuckles and put it up on the table. Zero'd the angle finder on the table, then checked the angle of the rotor, WMS, and hub. All were within .1 of each other, however they're a ways off from 90.







2 degrees is quite a bit. Would you guys try to pull this one straight or start with another housing?
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