table wear + movement

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liveaboard
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table wear + movement

Post by liveaboard »

I've been measuring, lubricating, and adjusting my "new" 50 year old mill.
I found the screws to tighten the ways, and made them as tight as they could be without creating excessive drag, especially the vertical as when the table is extended it will try to tilt against them.

An indicator on the table shows it's not flat.
Using a good straight edge and feeler gauges, I confirmed that the table is dished, 0.1mm lower in the center.
It seems like a lot, but I don't have a clue. Is this something I can live with, or need to fix?

I worked the surface with a stone a bit, but there are still raised spots and scratches I need to work on.
table error2.jpg
kl7sg
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Re: table wear + movement

Post by kl7sg »

Are you using a straight edge to determine if the table is dished?
Have a nice day,

Mike
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liveaboard
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Re: table wear + movement

Post by liveaboard »

Yes; the indicator says the same thing but that could be due to tilt / wear.

The straight edge + feeler gauges confirm the readings are (probably) mostly due to damage to the table surface.
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Bill Shields
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Re: table wear + movement

Post by Bill Shields »

If most of your work is in a vise then I would live with it.

Getting it flat could require a trip to someone with a large surface grinder...who knows how to use it
Too many things going on to bother listing them.
kl7sg
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Re: table wear + movement

Post by kl7sg »

If it is your table, you can get it surfaced for a reasonable amount of money.

Also, I have never done this myself; but, a longtime machinist friend said that it can be done on the same machine.
Maybe someone can comment on this.
Have a nice day,

Mike
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Bill Shields
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Re: table wear + movement

Post by Bill Shields »

I would be very cautious about attempting to surface the table in situ.
Too many things going on to bother listing them.
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liveaboard
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Re: table wear + movement

Post by liveaboard »

The table is mounted on slots, and can be slide to one side or the other; so the head can actually cover the whole surface, but not without resetting.
Whether it or I would be accurate enough to make it better instead of worse, I don't know.
I'll have a better idea after I've used the machine for a while.

There must be big machines somewhere, I heard there is a shop or two near the port 100 miles north, but I don't have details. At minimum it would require 2 round trips, 400 miles of driving.
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Harold_V
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Re: table wear + movement

Post by Harold_V »

What Bill said. And there's a good reason.
When a machine has experienced years of use, the wear isn't restricted to the table surface. Ways, too, have been worn, and never in a favorable way.

If gibs can be tightened so that there is little slack in the center of their travel, and the ends don't bind, that may not be true, but it would be highly unlikely.

One comment in regards to the condition of the mill. Keep in mind, it's a mill, not a jig borer or precision grinder. It's entirely possible that the error discovered won't be an issue, especially if you are not engaged in high precision work. It is highly unlikely to manifest itself in troublesome errors unless you work on extremely large items that require unreasonable precision.

Keep in mind that a machine tool wears everywhere. The screws are likely to have greater error than the table. The center wears faster than the ends, resulting in loss and gain of travel.

Use the machine within its capability and it most likely will serve you quite well. Don't expect high precision. It wasn't made to do that when it was new.

A stone on the table isn't (in my opinion) a good way to approach the situation. A stone is not selective. It will take material, albeit very little, anywhere it makes contact. What is a better approach (my opinion) is to draw file the table using a single cut file that isn't new. No handle. Place the file on the well wiped table and draw it along with the palms of your hands at an angle. It will readily remove high spots (dings) without removing metal otherwise. Do this until the table feels dead smooth, does not resist the file travel.

Do NOT do this with a new file. If you do, it will cut anywhere it makes contact, and much faster than a stone. That's exactly what you don't want to do.

H
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kl7sg
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Re: table wear + movement

Post by kl7sg »

I haven't tried what I had mentioned about using the machine to correct the problem.
While 0.1mm is a lot, It would depend on what you are making and how you hold the work as to what the final result might be.

I think that surface grinding is the best solution if you need better precision.
Have a nice day,

Mike
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Harold_V
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Re: table wear + movement

Post by Harold_V »

Grinding the table without addressing wear on the ways is a waste of time.

H
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kl7sg
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Re: table wear + movement

Post by kl7sg »

Hi Harold,
Yes I agree.
I have an older machine and it will hold a few thousand's tolerance. For what I am doing, that is good enough.
Have a nice day,

Mike
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Re: table wear + movement

Post by Harold_V »

Hey, kl7sg!
Yep. You have to keep these things in perspective. Putting lipstick on a pig won't make it anything but a pig with lipstick.

I had the good fortune to work where an old milling machine (8-D Gorton) was re-scraped by an individual with skill and talent. The machine went from junk to one of the most precise machines in the general shop, but everything was rebuilt (except for the paint), including new screws and nuts. Anything less would have resulted in a compromise---with little advantage to having done anything.

It's nothing short of amazing how reasonably good work can be accomplished on machines with wear. It requires more attention, maybe even some Kentucky windage---but it can be done.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
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