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Bridgeport will not stay square

Craig221

Plastic
Joined
Dec 8, 2020
I recently bought a Bridgeport milling machine. I can tram it and get it square, make a pass and can check the squareness of the head and it will be out. Can anyone tell me what might cause this? Thanks I’m advance.
 
Get specific
Tell us how you trammed it and how you see its out
which direction
what kind of bridgeport

overtightening now or in the past can render them unable to stay straight
 
I recently bought a Bridgeport milling machine. I can tram it and get it square, make a pass and can check the squareness of the head and it will be out. Can anyone tell me what might cause this? Thanks I’m advance.
Maybe tighten the bolts down a little more

Sent from my SM-G973U using Tapatalk
 
Thanks everyone for the replies.

I square the head with a pro tram tool and then double check it with a test gauge setup on the spindle.

By pass I meant I was using a 1/2” end mill taking a .005” deep cut.
 
Also it will be out of square in both directions.

It’s not a round shaft model it’s a series one style.
 
I find that tramming with instruments doesn't do it on my BP. I simply get the widest mill I have and make passes in each direction. Based on the cut pattern leading or dragging, I adjust the head and run the test face cut again. So, I adjust the side tilt by making X axis face cuts until I see leading and trailing cuts on the work. I then make Y axes cuts while setting the nod of the head. So I make 2 Y passes and adjust until I see both leading and trailing cuts on each pass. Once I set the head and lock it down it remains perfect until I crash a large tool into my work (it's a CNC rig). But it will stay inline for months between crashes.

I tried the instrument tramming methods but had zero luck with them.
 
I recently bought a Bridgeport milling machine. I can tram it and get it square, make a pass and can check the squareness of the head and it will be out. Can anyone tell me what might cause this? Thanks I’m advance.

Five thou cut in WHAT? Plastic? 'Loominum? Face-hardened armour steel?

And how much time do you have? It's a notoriously "flexible" mill, so there's a looooong list.

The model you mention hasn't been "new" in a VERY long time, so shall we presume a LOT of wear, everywhere?

Do some reading research. BirdPort's "issues", wear, what breaks, and their fixes are really well-known and well-covered ground.

"Prior over-stress" is high ON such a list.

You may have to do some work on it to put it into better condition before it will stay ANYWHERE you try to put it!

Not a new need. Many have done it. You can do it, too.
 
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Ways of the saddle - table wear in an arc. The top of the saddle ways will be convex and the table ways will have a matching concave shape as a worst case type of wear. Some mills will have a sweet spot in the center and others will cut flat if the table is run to one end and then tram the head. Otherwise use the Y-axis for milling closer to flat.
John
 
For what it's worth, I tried one of those Pro Tram tools to tram my mill and finally gave up in frustration. I just could not get repeatable results with it. Went back to using a single indicator over a wider area and had no problems. I believe the problem lies within having two different inexpensive indicators but I got so frustrated with it I haven't bothered to really track down what the problem was. Not to say that this is your problem but just throwing my experience out there for consideration.

-Ron
 
Someone on here posted a tip that I found to be invaluable. Get a large diameter bearing race, (I had access to used races in the 8" diameter range) place it on the table and run your indicator on that. I'm guessing if you tram it in the center of the table and move it to either end of the table travel and check for any changes that might provide a clue. Most if not all bearings are ground with sides parallel. Being round you not jumping over the tee slots. Anyone have critiques to this method I'm all ears.
 
A free loaded tram is not the same as in use. Why do not so many get this basic point.
Would be nice but not real world cutting metal.
Many cnc owners do the same duh with backlash comp.
A change from cut one to cut two can be cut loading and the fact that all is a spring matters.
 
A free loaded tram is not the same as in use. Why do not so many get this basic point.
Would be nice but not real world cutting metal.
Many cnc owners do the same duh with backlash comp.
A change from cut one to cut two can be cut loading and the fact that all is a spring matters.

How to solve? tram each time the load changes with the load in place?
 
How to solve? tram each time the load changes with the load in place?

Learn your particular mill's "ways", half-a-pun intended.

Compensate for its imperfections.

Don't expect the mill to return the favour.

Most of them just don't give any more of a damn about human psychology than enough to embarrass your ass at odd intervals for the amusement in it.

:(
 
How to solve? tram each time the load changes with the load in place?

Some may change the free load tram or twist for different jobs.
This only works when doing bigger runs. Tram or true under load can be told by cut results and profilometer graph surface finish traces.
I agree fully that this a major pain and just about worthless for few piece jobbers or a home shop which is probably a very large percent of the audience here.

I still do not understand the OP's problem and that bugs me.
Bob
 
I would check your gib adjustments. You're using the table as a reference surface, so make sure it's not moving on you. Just google bridgeport gib adjustments if you aren't familiar, there are tons of resources out there.

Aside from that maybe use a torque wrench to tighten the head bolts, though I do not know to what spec
 
Thanks everyone for the replies.

I square the head with a pro tram tool and then double check it with a test gauge setup on the spindle.

By pass I meant I was using a 1/2” end mill taking a .005” deep cut.

Did you have the spindle running?:)

An .005 doc with a 1//2" em even without the head being super tight should not move anything.

I believe your indicating methods are suspect.
 
Are you locking all axis except the one your checking so sloppy knee gib adjustment tramming should be done over as large an area as possible .
 








 
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