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StephenK
11-12-2004, 12:14 PM
A person that I do machining work for asked me if I would look at a Bridgeport that's available. With all of the knowledge on this forum I would appreciate some suggestions on what to look for in evaluating a mill. I would certainly check out the table and ways.Also ask to have it run if possible. Are there other items to check for?
Thanks to all.

ERBenoit
11-12-2004, 12:45 PM
In addition to that check the following:

1)Determine what is acceptable to the buyer.
2)Spindle runout.
3)Condition of spindle taper.
4)Fit of the quill.
5)Backlash on table screws.
6)Tooling (or lack thereof) and condition.

The following will be easier to check if the mill is connected to a power supply.

1)If it is an older J-head, check clutch mesh.
2)Hi-Lo Range is operable.
3)If the quill is power feed, check to see that it operates.

The overall condition of the machine should give you some idea of how "used" it is.

I'm would think others will chime in with other ideas, this is what I can think of without really thinking.

Be careful evaluting a machine for someone other than yourself. What is at stake? If you say the machine is o.k., they buy on YOUR advice, and the machine, yet within the parameters they gave you, turns out to be something other then what the buyer expected..... Then what?


[This message has been edited by ERBenoit (edited 11-12-2004).]

gundog
11-12-2004, 01:12 PM
what would be exceptable runout or backlash what is good and what is whipped out?
Mike

SGW
11-12-2004, 04:03 PM
"Acceptable" backlash is what you're willing to live with. As you probably know, every regular screw has some amount of backlash. Since you always have to allow for it anyway by taking up the play in the same direction, by itself it's probably not a reliable measure of accuracy. At some point though, backing up the screw past the backlash and then feeding forward to where you want to be gets annoying.

Personally, I think I'd find that anything over about 30 thou would get annoying, but that's just me. Machines with a lot more backlash than that get used every day with great success. 10-15 thou would probably be reckoned pretty good.

Is the nut adjustable to take up the backlash? Trouble is, because of uneven wear that can go only so far. Adjust for minimum backlash in the center of travel, and it will probably bind at the ends.

jburstein
11-12-2004, 04:58 PM
http://www.mermac.com/freemill2.html

There's some good stuff in there.

J Tiers
11-13-2004, 01:51 AM
Man, that mermac info is right on.

I have bought a machine that some knucklehead was looking at just before me. They were diddling this and wabbling that, measuring and fussing. Finally they left.

I ran it, looked at the machine, turned a few cranks, and wiggled a couple things, and in 5 min I was loading it up. Its about the best machine I have.

I dunno what the other guy's problem was.

Stuff that moves, should. Stuff that doesn't, shouldn't. That is about as complex as I get, aside from having a sort of mental scoring scale of "how much" things move vs what they sould or shouldn't.

I have only got screwed on one machine.
Even that is misleading, I knew about the problem, but was wrong about the cause, and I did squeeze out a substantial discount on account of it.
(I thought the die filer plunger bearing was worn. Instead, the hardened plunger is scored and needs to be built up and ground, which would be too expensive to bother with, and I don't know how to disassemble the plunger parts anyway)

One thing I REALLY have a problem with is evaluating for someone else. If I screw up my own purchase, I eat it, done.

But if I screw up someone else's purchase, or even if I don't but some buried problem comes up, that's an issue. I don't like that, and so I try to avoid that sort of deal.

sandman2234
11-13-2004, 09:51 PM
I am surprised Dave's website is still up, since he closed down his machinery dealings. Real loss for us, no doubt.
David from jax

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Have gun, will travel.