Opinions on Condition of Bridgeport Ways

Is it possible to visually determine the wear on the Y axis ways of a Bridgeport mill, or can you only tell by running the table in and out and looking for loose or tight spots?

If only I had the power ...

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mrplasma said:

Is it possible to visually determine the wear on the Y axis ways of a Bridgeport mill, or can you only tell by running the table in and out and looking for loose or tight spots?

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You can look at the scraping on top of the knee, if it’s in good shape, it’s just one of several indicators of the condition of a Bridgeport......doesn’t mean the X axis is not wore out?

You really need to put your hands on and run the machine to get a better idea!

That’s just a starting point.......

Kevin

mrplasma said:

Is it possible to visually determine the wear on the Y axis ways of a Bridgeport mill, or can you only tell by running the table in and out and looking for loose or tight spots?

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Why would you be LIMITED to "bare eyeballs" only... if you were close enough to see it at all?

Are you not allowed to carry-with some form of straight edge and a DI? Move it? Apply any side or twisting forces?

In addition to just "running it in and out."

Which.. by itself.. sounds like the usual way to get f****d, choice of orifice optional?

Speaking of which.. is this a "look but do not TOUCH" cordoned-off type of auction or the like?

Not sure I'd class that as "getting a good feeling here."

The first and worst wear point is going to be the right hand side about a third of the way back. You can get a general idea how worn it is by how much of the original scraping is visible and/or whether there is any significant scoring of the way has occurred. Run the saddle all the way back and have a peek. Of course this doesn't mean that there aren't plenty of other potential issues, but two good indicators of general condition on knee mills are the surface condition of the ways, and how much backlash is in X and Y screws.

thermite said:

Why would you be LIMITED to "bare eyeballs" only... if you were close enough to see it at all?

Are you not allowed to carry-with some form of straight edge and a DI? Move it? Apply any side or twisting forces?

In addition to just "running it in and out."

Which.. by itself.. sounds like the usual way to get f****d, choice of orifice optional?

Speaking of which.. is this a "look but do not TOUCH" cordoned-off type of auction or the like?

Not sure I'd class that as "getting a good feeling here."

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I am 500 miles away from the machine, and not in a position to travel to see it. I must rely on close-up photos and a video.

swarfmeister said:

The first and worst wear point is going to be the right hand side about a third of the way back. You can get a general idea how worn it is by how much of the original scraping is visible and/or whether there is any significant scoring of the way has occurred. Run the saddle all the way back and have a peek. Of course this doesn't mean that there aren't plenty of other potential issues, but two good indicators of general condition on knee mills are the surface condition of the ways, and how much backlash is in X and Y screws.

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There is .028" backlash in the X axis and .010" backlash in the Y axis.

mrplasma said:

There is .028" backlash in the X axis and .010" backlash in the Y axis.

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OH F**K.

So it isn't brand-new, then?

Go figure.

All the OTHER BirdPorts are, aren't they?

JFDWT.

Or use your magic wand.

What TF did you think they GAVE you a magic wand FOR?

mrplasma said:

There is .028" backlash in the X axis and .010" backlash in the Y axis.

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I don’t think backlash is a good indicator of wear on the ways. It indicates screw/nut wear and can often be adjusted out.

I would go with flaking evidence. If the knee ways were worn smooth, that doesn't mean the mill is shot by a long stretch. If you can still see flake marks and the price is right, buy it.

Straight edge may be a way to check machine ways. I don’t think a DTI is all t hat helpful. The trick to the DTI is working from a known reference to something,

Inspecting a mill for wear and understanding how measured wear translates to a mill’s precision or tolerance holding is nothing to sneeze at. Many discussions and dare I say arguments about this subject here.

Can you post the pics here? Are you already sold on wanting the machine and asking us to back up your want to buy it? To be upfront, I am always hesitant when people ask what a machine is worth or what the condition is if I cant see it. Because everyone I have ever heard of that got screwed over by a seller is told "the machine is in excellent condition." So I always am cautious when guys call asking us for advice.

Sight unseen, not having run the machine or able to see what sort of rock and slop the machine has, that is a huge gamble.

I concur with the others, if there is flaking at the ends of travel and no flaking at the center of travel on the knee, that is the best indication of wear without having the machine in front of you.

Jon

True, backlash can often be adjusted out. The fact that it hasn't, somewhat indicates the level of maintenance the machine has seen in the past. FWIW, I have seen plenty of bridgeports where the split nuts were worn beyond their range of adjustability. Still no big deal as the screws and nuts aren't that hard to replace.

Another indication of condition would be to use a mag base dial indicator, and check for how much the table shucks back and forth as measure from the saddle, and how much the saddle shucks back and forth as measure from the knee. Again, this can usually be adjusted out, but if it hasn't it's an indication of the level of maintenance the machine has seen.

AdamC said:

I don’t think backlash is a good indicator of wear on the ways. It indicates screw/nut wear and can often be adjusted out.

I would go with flaking evidence. If the knee ways were worn smooth, that doesn't mean the mill is shot by a long stretch. If you can still see flake marks and the price is right, buy it.

Straight edge may be a way to check machine ways. I don’t think a DTI is all t hat helpful. The trick to the DTI is working from a known reference to something,

Inspecting a mill for wear and understanding how measured wear translates to a mill’s precision or tolerance holding is nothing to sneeze at. Many discussions and dare I say arguments about this subject here.

Click to expand...

swarfmeister said:

True, backlash can often be adjusted out. The fact that it hasn't, somewhat indicates the level of maintenance the machine has seen in the past.

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Agree, but would like to respectfully quibble a tiny bit. The nuts may not be split. Mine were not. That change occurred at some point in time after 1967 when my mill was made. So adjusting out screw slop wasn't so easy (possible) before the nuts were split. Secondly, we can't assume all machinists really know their equipment. Good machinists do. Guys here are Bridgeport Enthusiasts, not typical machinists. The shop I bought my mill from knew very little about what was wrong with the mill they sold me. They were not curious enough to pull the Y-axis and see that the nut had come loose due to a broken $8 retaining screw head. This was easily identified and sourced from H&W. They sold me the "broken" mill to get it out of their way for $500.

If I were looking for evidence of abuse, I'd look first for grease in the oil zerks, holes of shame or chips in the table, and overall cleanliness of the mill. I don't think flaking or backlash are the first or best predictors of the mill's future capability.

In person, I'd run the table to the extremes of its motion, tighten the gibs, then run it back to center and see if there is noticeable looseness in the screws. This could indicate wear on the ways. Noting changes in backlash should provide clues about screw wear.

For a point of reference: My 1967 mill exhibits almost no difference in drag/friction through its table range in both axes. I split the nuts with a hack saw and adjusted them to about .005" of backlash, again with no or little change throughout the travel. This despite obvious wear on the knee and saddle. See attached picture. Note evidence of flaking throughout. I think flaking is around .003" deep. So, I would imagine the amount of wear on this mill is slightly less than that. But that would mean there is no wear on the ends of the knee, which is not likely. So its possible the knee is out of flat up to .003 or possibly less than that, which would explain the mill's performance today.

Based on my experience with my mill alone, I no longer feel condemning every old Bridgeport as worthless unless its been re-scraped has been an accurate or responsible response to so many threads here. Bridgeports are designed to accept a possibly undefinable amount of wear and still function acceptably. Identifying and quantifying that wear has eluded me and others here, despite the confidence in the replies.

So fundamentally, the questions: "How to quantify wear on a BP mill?" and "How much wear is too much?" have not been answered here to my satisfaction. I don't know the answer (as I just stated) but I THINK if the ways are worn smooth, then you really have no idea how much wear there is. Could be .005" or 1/8". I think that would give me pause.

swarfmeister said:

True, backlash can often be adjusted out. The fact that it hasn't, somewhat indicates the level of maintenance the machine has seen in the past. FWIW, I have seen plenty of bridgeports where the split nuts were worn beyond their range of adjustability. Still no big deal as the screws and nuts aren't that hard to replace.

Another indication of condition would be to use a mag base dial indicator, and check for how much the table shucks back and forth as measure from the saddle, and how much the saddle shucks back and forth as measure from the knee. Again, this can usually be adjusted out, but if it hasn't it's an indication of the level of maintenance the machine has seen.

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I have to disagree with the expectation of adjusting backlash and gibs as part of
the maintenance of a machine. Not all BP axis nuts are split. Yes you can cut them
in half and split them. But no one with any sense would do this. Only those with OCD.
Splitting the axis nut takes away HALF of the thread surface area, and therefor it
wears twice as fast. If you are trying to climb cut and hog at the same time,
you might better re-evaluate your methods on a manual mill.
Same goes for adjusting the gibs tight when they wear. Not a maintenance item,
in the large sense. Tight gibs wear more. Fact. When Bridgeports wear, the
experienced machinist just uses the machine with looser gibs for run-of-the-mill
jobs, and will tighten the gibs only when necessary for a fussy job, like pocket
milling or the like. Then slack them off again half a screw turn again, as not
to fight a tight table all the time. No machine is new forever, and keeping
everything tight just leads to excessive wear and binding. It is not a ball
screw and ball way machine. Things are not simple, if it wears, adjust it,
and there are no side effects. On a older slideway machine, there is a little
bit of wisdom and workaround involved. Unless a machine is a commodity and the
boss buys a new one every 5 years. But if I own the machine, I try to make it
last many years, and try to be pragmatic about way and screw adjustments.
Just my way of thinking. In your environment, things might fall in to play
exactly as you point out. But as I say, a lot has to do with environment and
expectations.

---Doozer