Best method for straightening arbor shaft?

I have a Hardinge TM milling machine with a 1" diameter
arbor which I believe is slightly bent. I have a decent
surface plate and spotting dye so I should be able to
determine where exactly the bend is. I'm guessing that
the arbor shaft is at least case hardened.
What do you suppose is the best method of straightening
this shaft without marring it or making things worse?
Thanks
Reply to
Artemia Salina
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How slightly, is slightly bent? A few tenths? Ten thou?
Likely the shaft is hardened and ground to finish size.
I'd look at a pair of rough use V blocks, a dial indicator on a magnetic base, and a hand pumped hydraulic press to tweak it back into line. Brass or aluminum pads to prevent marking the surface, and a small diamond file to knock down any pimples on the surface.
Worst case is it can be ground to a 7/8 arbor on a cylindrical grinder.
Or it breaks, I suppose.
Cheers Trevor Jones
Reply to
Trevor Jones
By slightly do you mean, a thousanth or so?
Plain milling cutters should be taking big bites, if you are worried that not every tooth is taking a cut at one or two thousanth depth passes, don't be.
Jim
Reply to
jim rozen
I used to straighten lots of heat treated shafts. The easiest way I found follows. First, you will need two good vee blocks to set the shaft in and turn it while measuring runout with an indicator. If you can't get good vee blocks then drill two holes in a block of steel and glue a ball bearing in each hole. Lap the blocks with sandpaper placed on your surface plate so they won't rock when placed on the plate. Next, saw two more blocks out of aluminum and place these on the press. Mount an indicator on the press so it contacts the shaft when placed in the aluminum vee blocks. Use another piece of aluminum between the shaft and the press ram to prevent marring the shaft. The soft aluminum vee blocks will take an impression of the shaft so there will be a lot of movement at first. Using the press mounted indicator as a guide bend the shaft a little, remove, and check in the setup on the surface plate. Keep applying more bending until the shaft starts to move and become straighter. When this happens bend the shaft in the press in small increments because once it starts to bend it is easy to over bend it. Then you will need to bend it in the other direction and it will move real easy that way too. ERS
Reply to
Eric R Snow
On Wed, 18 Aug 2004 07:30:26 -0700, Eric R Snow vaguely proposed a theory ......and in reply I say!:
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I am but an egg, but from my extensive mucking about with beams etc, doesn't what you say below mean that you have actually damaged the steel of the shaft? If it gets to a stage where it bends easily, you have weakened it considerably.
***************************************************** Marriage. Where two people decide to get together so that neither of them can do what they want to because of the other one.
Reply to
Old Nick
Well I just got back from running a dial indicator on the arbor and I can find no more than .002 TIR, and that's at the pointy (outboard) end of the arbor, so I'm stumped as to why the cutters (all of them) make that rhythmic "GRUNT, GRUNT, GRUNT" sound as I'm taking a cut. Chip loading on the teeth of the cutters also indicates that only about half of the teeth are doing work (very rough estimate).
As for the depth of cuts I'm taking, with a 3" x 3/8" staggered tooth cutter, for example, I routinely take .050 cuts. With that cutter I just made a 3/8" x 3/8" x 4" slot in mild steel in 4 passes (3 @ .100 and 1 @ .075).
The cutters I have I bought as a used lot from a machine shop that had closed down. Some of the cutters have "sharpening notes" for lack of a better term, attached to them. It seems like a long shot, but I'm beginning to wonder if the cutters could've been sharpened out of round... I doubt it.
Reply to
Artemia Salina
All cutters do the thump, thump.
None of them is sharpened perfectly round. You can minimize this by increasing depth of cut (a horiz mill is a two cut machine. Rough to within .030 and finish) Also keep the feed up so that more than one tooth is cutting simultaneously.
Eventually the tooth that does most of the cutting wears down and the next one starts.
When I am only doing light cuts, I run my mill without a key. It lets the tooth/arbor eccentricity change and lets a new tooth do the cutting.
Staggered and spiral cutters are excellent choices for these small mills, you should feel the thump,thump with a wide straight tooth cutter.
Paul K. Dickman
Reply to
Paul K. Dickman
Not really. You have to get the shaft to the yield point by slowly increasing the hydrualic pressure. Once you get it to that point, each stroke on the handle moves it that much. This movement does indeed work harden the shaft but you need to move things on the order of 10% to see significant changes in soft steel, perhaps 2%-3% on a hardened shaft. .002" in 12" is not even worth discussing as far as material changes.
I've talked to the local heat treater. They straighten all the 4140 heat treated shafts unless you ask them to skip that.
Old Nick wrote:
Reply to
RoyJ
You might try increasing the feed rate on this, I tend to use teenuts rule of thumb that I start feeding by hand until the machine starts to complain, then I back off a bit and set the power feed to that rate.
My UM also gives the grunt-grunt-grunt noise - if I'm feeding too lightly. If I pick up the rate on the handwheel it becomes a steadier note.
I've never put an indicator on my arbor, but I likewise suspect mine may have a teeny bit of tweak on it. The mounting system into the 5C socket is a bit whacky, honestly, so I could imagine it being a few thou different each time it gets re-installed.
I take it you *are* using the overarm support for your work, yes?
Jim
Reply to
jim rozen
What I mean by easily is that after a certain amount of displacement the metal is beyond the elastic limit and instead of returning to the original state it starts to take a set. So the first .100 thousandts of bending may not make any change in the bent shaft but the next .010 after that may result in a .005 change. When bending the other way the material usually doesn't need to be displaced as far before it starts to take a set. ERS
Reply to
Eric R Snow
On Thu, 19 Aug 2004 00:26:18 GMT, RoyJ vaguely proposed a theory ......and in reply I say!:
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Thanks Roy and Eric.
So the steel is "soft" (by makeup and treatment) enough that passing the yield point by this small amount does not do _significant_ damage? I was not _thinking_ pf work hardening. I was worrying about actually weakening ghe shaft, by passing the YP.
I assumed the shaft would be pretty hard and probably brittle.
Is it's 4140, and tempered/annealed, then I can see the situation.
Thanks for that.
***************************************************** Marriage. Where two people decide to get together so that neither of them can do what they want to because of the other one.
Reply to
Old Nick
The shafts I did mostly were hollow, about 2 inches OD, .187 wall, and about 2 1/2 feet long. With flanges each end. 4340 alloy. They were adapter shafts that allowed a turbine engine to be used in place of a piston engine on light aircraft. Apparently, these aircraft were used in parts of the world where the price of jet fuel was so much less than av gas and where the availability was so much better that it made economic sense to swap a turbine engine for the piston engine. These shafts never failed. I made lots of them. ERS
Reply to
Eric R Snow
A well heat treated shaft has all the characteristics of mild steel, just in a different spectrum. Tensile and yield are much higher, the % elongation in 2" is usully much lower. If tensile and yield are close together it usually means a part with a low % of elogation before snapping. ie a brittle part. If you push a lower alloy part to the limit with the heat treat, you get something that probably could not take the straightening. Go up to a fancy alloy, the tenisle and yield can be moved apart, and the part will be much more reliable. ie get the good stuff and it works better. :)
We do 4140 1-1/4" solid bar up to 145kpsi, 4130 tubing assemblies up past 200kpsi tensile. One of the tubing assemblies got run over my an 18 wheeler, bent 90 degrees. Completely deformed, no fracture. I would NOT want to try straightening that piece however!
Old Nick wrote:
Reply to
RoyJ
On Thu, 19 Aug 2004 16:14:41 GMT, RoyJ vaguely proposed a theory ......and in reply I say!:
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snip of stuff for retention....
That's "malleable"!
Wooss!
***************************************************** Marriage. Where two people decide to get together so that neither of them can do what they want to because of the other one.
Reply to
Old Nick

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