Mitsui 250 MH installing the ball ways

[dsatchell]

Hi, been working on the Mitsui 250MG. The grind of was generally visually flat, except for a repeating dimple at about the distance between balls, you couldn't see it visually unless you used a flat stone on the surface, then it would be obvious. The dimple measured about 0.2 thou. I'm guessing that at some point it was shipped without proper securing of the table (when we got it, it was correctly supported, but who knows). Along with the other elements on the machine, we're now fixing this one. I've not replaced this type of way before, though 'I think' I'm thankful that the ways can be removed and replaced. Removal of the ways was straight forward, I did take torque measurements for the bolts, but they were generally pretty random so I doubt it mattered. I think firmly snug with a 5" Allen key is appropriate. The flat support for the ways are scraped, but the interface on the ways themselves are only ground and there is no key in the base or table for the ways, so there is a slight amount of possible movement as you're reinstalling them.

My question is, for aligning the ways, would it make sense to have them slightly loose, then run the bearings and table for a bit to help get them aligned? And then tighten the way bolts to snug?

As always, any other insights would be helpful.

 

[michiganbuck]

One abrasive grit along the ball way can do that, or perhaps it was damaged(?).
I would likely indicate straightness if there is any side wiggle in the assembly, not travel loose..
Hard hone With a good/new hone the set position just to see if any high spots or bugs, tighten from the in/center and work outward.
Getting back together place a strip of 1" masking tape along the parting line between the long table and the base to keep future grits out on the back/far side.
We used to send out ball racks for grinding and then shim them back to their original height. usually one Can grind off.020 and still be hard (Cincinnati said we could safely grind 035"). You trig out the amount to take because the V and flat get a different amount.
If using old balls, I like to put them back in the same order. (egg cartons are good for keeping order.)

likely you will re-grind the chuck(wet). doing that I like to check that the chuck hold downs are not overtightened, 20 lbs is plenty tight.
If never grinding a chuck be sure to research how to do that.

 

[dsatchell]

Hi, thanks for the note. We did several rounds of cleaning out the oil and using a precision ground flat to check the way surfaces. Sure enough, found two clean ding's at the center and then off center on the ways closest to the operator. A similar ding was also indicated on the flat way in the rear. Unfortunately with a ding, there was not ability to burnish it out. we did smooth it out some with the flat stone, but that was when we 'achieved' the 0.2 thou bump on the parts. It was worse initially.

 

[michiganbuck]

Hi, thanks for the note. We did several rounds of cleaning out the oil and using a precision ground flat to check the way surfaces. Sure enough, found two clean ding's at the center and then off center on the ways closest to the operator. A similar ding was also indicated on the flat way in the rear. Unfortunately with a ding, there was not ability to burnish it out. we did smooth it out some with the flat stone, but that was when we 'achieved' the 0.2 thou bump on the parts. It was worse initially.

0.2 thou bump on the parts? I can't imagine a grinder having that.

 

[dsatchell]

Hi, we were surprised at the bump as well. Once we pulled the ways, you can see the dimple on the way surface.

What we've done up to this point is replace the spindle cartridge, balls and ball ways. With the new ways, we did install the bottom set semi-snug and then ran the bed a few times (10), I did this because I was concerned about the lateral play on the ways before you tighten them down and getting the ways aligned so that as the bed traverses, its orientation is parallel to the travel (I don't know how much that matters, I didn't take that measurement before we pulled the ways). We did use white grease #2, with oil it would keep dripping and running down the side of the machine (there is no oil drain below the bed). Once we got the ways in, we lifted the table and tightened the bed to a firm snug, there was no spring in the ways as you snug them down, just flat on flat. So far, our initial full surfaces measurements show <0.2 thou across the fully surfaced bed in all four corners. (~8x18" bed). now when we run a precision ground flat across the surface, there are no high spots. Quite a relief.

I don't have a specification for this unit, does anyone know what we should be seeing wRT the table flatness?

 

[michiganbuck]

QT Less that .2 throw is misleading meaning two-tenths of a thousandths perhaps.?
A sudden 2 tenths would show up in the view but likely would be difficult to measure.

(there is no oil drain below the bed).Sometimes careful not to overfill, and a drip catch can be used.

 

[sfriedberg]

(there is no oil drain below the bed).

Really? Mine drains from the ends of the ways. There's a small hose that leads to the sump in the rear part of the base (which can be surprisingly full after years of operation).
I am not in the shop right now to look, but ISTR there's an oil catch at or very near the wipers.
Or maybe we are talking about something different?

 

[dsatchell]

Hi, for measurement 0.2 thou == 0.0002 inch (bad shorthand?). I'm looking for a drain, didn't see any tubing to that location in the space under the table. There are drain tubes to other locations but not there. When we tried oil, it just dripped off the end onto the lower (outer) dust guards and got slopped around by the rubber skirts. Please let me know about the shorthand, I don't want to be whipping a deadhorse if we're already achieving good cuts.

Does your oiler put oil into the ways?, there is definitely no oiler connection to them on your machine.