Hardinge TM overarm support bearing replacement

leeko · Apr 18, 2018

Hi all,

I'm working on a 1941 hardinge TM, and an getting a lot of chatter with arbor mounted cutters. Looking at the overarm support bracket, the bearing appears to have a little radial play which I'm hoping is the cause and an easy fix. I unscrewed the bearing retainer and knocked out the bearing, which is an MRC 204 SFF. Beyond that step, I'm not sure what to do next. Do the slotted caps on either end of the bearing unscrew? If so, are they right hand? Does the tapered portion slide out of the bearing, or does it need to be pressed out?

Also: is it possible the chatter is due to lack of preload on the spindle bearings? That was the case ony old Gorton 8-1/2, but looking at the parts diagram I don't see any obvious way of adjusting preload on the hardinge?

Any tips would be greatly appreciated, thanks

Lee

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Jim S. · Apr 18, 2018

Lee,
I'm confused by your reference to slotted caps on the end of the bearing. My mill has the bearing mounted directly in the overarm support bracket with a tapered sleeve pressed into the bearing bore. The taper is ground to match the end of the arbor. Perhaps yours has an earlier design or was owner modified.

I looked up my bearing years ago, and IIRC it is a deep groove bearing. There is slight radial play but that is accommodated by "preloading" the arbor with a thick cork pad inside the bracket behind the bearing. In practice, after I've mounted the cutter on the arbor, I slide the overarm support over the taper and soldidly "thunk" the overarm onto the arbor then clamp in place. That compresses the bearing into the cork and axially loads the bearing.

I've occasionally had chatter when using large cutters but I could not attribute it to the bearing.

As for spindle bearing preload, that is not designed to be adjustable. The bearings nearest the nose are a matched high precision angular contact set. The rear bearing is a light slip fit in its bore and designed to move axially with temp changes of the spindle. To achieve its renowned spindle accuracy, Hardinge ground the spindle nose collet surfaces after the spindle was assembled and installed in the machine.

leeko · Apr 18, 2018

Hi Jim,

Here's a picture of my bearing removed from the bracket. There was no cork behind the bearing retainer, just the bearing - maybe that was part of the issue?

The picture shows the slotted end caps on the tapered portion - that whole assembly appears to turn - it actually looks kinda like an extended inner race rather than a separate piece pressed in. I'll take some better pictures when I get back to the shop this evening.

Looking up the bearing number, it does appear to be a deep groove bearing.

Thanks,

Lee

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Jim S. · Apr 18, 2018

Lee,
Here are several photos from a 1955 UM. The tapered sleeve in the bearing is pressed in and retained with a snap ring on the small (outboard) end.
Jim

Jim S. · Apr 18, 2018

one last photo

leeko · Apr 18, 2018

Huh, that looks quite different to mine. I'll get some better pictures this evening.

Most interesting is that your bearing clearly has an inner race visible, while on my bearing the tapered sleeve appears to be the inner race.

Thanks for taking the time to grab those pictures - very helpful!

Lee

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leeko · Apr 18, 2018

Yes, mine appears to be quite different. The bearing housing on my arbor support is threaded for a bearing retainer cap. There's no retaining wire or washer pressed in. I don't have a cork washer or regular washer on the outboard side in mine either (though maybe they should be there).

Lee

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Jim S. · Apr 19, 2018

Lee,
Check to see if the ring with the single split in it turns off the tapered sleeve in the bearing bore (shown in first and third pics above). It looks like it may be a nut that is held on by its own spring pressure, having been made to expand slightly when threaded on. Tap it in a counter-clockwise direction. Looks to be a short sleeve under that nut, then the tapered sleeve would come out of the bearing inner race. TL lathes from the same era had a similar split "spring" nut in the apron.

And in the pic showing the bracket bore, are you sure there is not a large washer with a pad behind it down in the bottom?
Jim

leeko · Apr 19, 2018

Jim,

Correct on both counts, thanks!got the bearing assembly apart, and a new bearing ordered.

The washer and cork were hiding under the grime. The cork disintegrated on removal, so I'll need to order some new cork to make a new one. Looks to be about 1/8” thick.

I don't see any spring wire retaining ring though... Wonder if that's missing, or was never there on mine....

Thanks again,

Lee

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Jim S. · Apr 20, 2018

A retaining wire and phenolic washer replaced the threaded washer on yours. Apparently Hardinge figured out less expensive but equally effective ways to fix the end of the arbor and retain the bearing.
Jim

leeko · Apr 20, 2018

Ah that makes sense. Thanks Jim

Hopefully the new bearing will take care of the chatter issues. There was at least 10-20 thousandths of radial play in the old bearing. Should find out in a couple of days

Lee

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leeko · May 4, 2018

New bearing arrived, and installed. It also had some of the same play, which I'm guessing is normal based on the comments above.

I re-tightened the table, saddle and knee gibs, and had another go. The chatter/vibration is a bit better, but still more than I'd like. Here is my setup - please let me know if there's something glaring that might be the case. Even something basic, as I'm pretty new to horizontal milling!

2-7/8” x 3/8” straight milling cutter
1" arbor
drawbar is tight
Spacers are arranged so that the cutter is within 1" of the outboard support, not in the middle of the arbor
150RPM
Hand feeding (no power feed on this machine). Have tried varying this from very slow to medium
Work is held in 4" vise, and verified not moving after the cut

Depth of cut 0.050" is where vibration starts to get ugly. It'll cut at .100", but the vibration is horrendous. My understanding is that this type of cut should be easily within the capabilities of the TM, so I still have some troubleshooting to do. Any suggestions or tips in the meantime are much appreciated!

Best regards,

Lee

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jim rozen · May 6, 2018

The 3/8 wide cutter is a tad on the wide side but at 50 thou depth of cut you should not be having trouble.

What is the workpiece material?

Jim S. · May 6, 2018

Your mill ought to be handle that size cut if the cutter is sharp and the gibs are tight. I would want the cutter as close to the column as possible and the work as close to the table surface as possible to reduce the moment arm to the extent possible. Here are two cuts I made with my UM showing deep cuts, albeit in cast iron. The T-slot is being made with a standard cutter mounted on the end of a shop made 5C arbor.
Jim

leeko · May 6, 2018

Think I found at least part of the problem. The sample piece I was milling was labelled as mild steel, but after inspection it had clearly work-hardened. I think it's some kind of tool steel or maybe 4140, and didn't like the 100SFM I was using. Rockwell hardness appears to be around 40 on the untouched part. I reduced it to 60sfm and it definitely cut nicer, but at this point the cutter is pretty dull so I think it can get better still with a sharp cutter.

Thanks for the encouragement. Jim - those kind of cuts are what I envisioned the TM as being capable of! I'm curious about the comment above of a 3/8” cutter being a bit too wide though? I was hoping to take light cuts across the whole face of a workpiece with a 4" wide helical slab mill at some point - is that not a reasonable prospect?

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jim rozen · May 6, 2018

With a cutter like that one would want to bury it a bit deeper in the workpiece. I've always found that
just skimming the surface with a plain cutter like that can cause vibration, especially if the cutter is
not real sharp.

If the cutter is not as sharp after the cut, as before, something's amiss.

Jim S. · May 6, 2018

I agree with Jim R that too shallow a cut can be a problem. I would always want more than one tooth in the cut. And stagger tooth and helical teeth cutters are a great advantage. I think a 4" wide cut will be pushing the limits but have personally never tried it. I've got a couple slab mills but have never needed to try them. I think the cutter would need to be scary sharp and the mat'l relatively easy machining. And I'm unsure if the TM-UM has enough power, especially on low speed.

gjrepesh · May 7, 2018

I have two parts lists for the TM-UM. They both show the same series of parts as was previously posted by Car2. What is the serial number of your mill? If its an old machine, Hardinge may have done an upgrade in this area. Or someone modified this area in the shop.

Hardinge TM overarm support bearing replacement

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