How can you tell if a Bridgeport or other mill is too "worn out" to be worth buying?

How can you tell if a Bridgeport or other mill is too "worn out" to be worth buying?

I'm looking at picking up a bridgeport at some point in the future. I've used a mill a few times so i'm relatively familiar with them, but I don't know them like the back of my hand. What are the indicators that a mill would be too worn out to be worth purchasing? What kind of places would I look for wear? Are there things I could measure?

Depends how much they want for it and what you plan on doing with it. If everything works, it probably still has merit somewhere in the shop. This topic tends to inspire the "what a real machinist is" debate. Alot of guys won't touch a machine unless there is zero backlash in the ways and screws over the entire travel. Other guys will slap a DRO on a machine and make parts on it no matter how worn it is. Both make parts within spec. They just do it from different angles.

From my experience, wear in the spindle and splines can be more troublesome than wear in the ways because you can't always compensate or work around it.

Ways are everything on a BP. If the ways have scratches or gouges in them, that's not good. That can't be replaced, they have to be scraped. Unless you can do it yourself, that costs money. You can't compensate for worn ways with a DRO.

Run the head. If it's noisey, that's money. If the quill doesn't move up and down smoothly, more money.

Don't look at backlash, that can be very misleading. Look at the X screw in the middle and and one end. Is there noticable wear?

Holes and dings in the table are not good. If the owner doesn't care about that, how else was the machine treated.

When all is said and done, it's your money. Buy what you want.
JR

A brand new acme screw and nut will have about 5-8 thou play in them, most customers get antsy when they have about 80 thou slop over the vice.

@JR nailed it with the ways. Had a customer that swore his machine was in amazing shape, but when you moved the table to one side or the other, the entire knee shifted about 20 thou.

Depending on where you get it from, take into consideration WHY they are selling it. Is the wife making them get rid of it? Or are you about to become Tom Hanks in the Moneypit?

If you are buying it from a reseller, be wary of the terminology that they use to describe it. I know @JR hates when people say rebuilt yet had zero way work done, but you need to think about that. People will say reconditioned or many other fancy terms for clean and fresh paint.

@MBNeagle brought up a great point... What are you gonna do with it? Make money? or just to have it? I think that is important to think about whether it will be an expensive hobby like tattoos and guns, or will you be doing it as a side hustle.

As far as measuring, play in the spindle is I think more important than play in the table. Measure what sort of runout you have in your spindle. You can check screw slop if you want, but even on a sloppy table you can make chips accurately. The ways are huge. Lack of flaking in the middle of the ways can be a great indicator of wear on the ways, however just cause there is flaking doesnt mean the ways are in good shape. I have heard alot of people describe the flaking marks as proof that ways are scraped, which is not at all the case.

Jon
H&W Machine Repair