X-axis travel dip

[redvan22]

Hi,
When I try to tram in my mill vise, that I always center on my table, I seem to have a curve in the table or a dip. What I mean is as I traverse the vise from one end to the other with an indicator, there's a dip in the middle. I set the indicator to zero at one end and as I move towards the other end, the needle goes negative by a few thousands but then comes back to zero at the other end.
The vise jaws appear to be parallel. I used a 1-2-3 block (vise is only a 3") and looked for light but it was tight.
All I can think of is a dovetail issue.
The gibs are snug and travel of the table from one end to the other is smooth except for the very ends where it gets a little tight but still moves.
Thought about dismantling the machine and checking the table dovetails but would rather hear from experts before I take that on.

Any ideas or suggestions?

Michael.

 

[pontiac428]

Sounds like vise jaws to me. They are bolted on, which can cause a flex, for example- there are other plausible causes, the vise jaws are several degrees of freedom from the ways. Clamp a block to the table and try tramming that, it will probably not show the same curve that you are seeing on the vise.

 

[sdelivery]

Have you trammed the table less vise?
Do you have the same result?
Many people over tighten the clamping system to the table tee slots, whether you believe it or not can distort the table.
If you are seeing the same dip or hole with nothing mounted to the table you might have way wear.

 

[redvan22]

I LOVE this site. Quick responses and very helpful.
So glad I posted before the dismantling the machine!!!
When installing my vise for tramming, I snug up one bolt and tighten the other to be the pivot point but after I'm happy, I securely tighten both.
As for the vise jaws themselves, never thought about them being distorted.
I have some work to do to test these ideas.

Thank you.

 

[RJSakowski]

It sounds like you are sweeping the vise jaws in the vertical plane. Rather than sweep the jaws, I will mount a parallel in the vise and sweep the parallel. If your mill is a used mill, it is possible that you have wear in the central portion of the ways. You could try moving the vise to either end of the table and repeat your tram. If you get the same result, then you can zero in on the vise. If your dip now moves to the end of the vise, then you should be looking at wear in the ways.

I would also check the table itself for alignment, as mentioned above. If you perform these tests, you should be able to determine the root cause of the problem.

Note: To me, tram means setting the head of the mill so the spindle is perpendicular to the plane defined by the mill ways. I sweep the vise or work to set them parallel to the either the x or y travel.

 

[pontiac428]

It's best when making micro measurements to assume that nothing is straight until you prove it is. You'll see...

 

[redvan22]

Sounds like vise jaws to me. They are bolted on, which can cause a flex, for example- there are other plausible causes, the vise jaws are several degrees of freedom from the ways. Clamp a block to the table and try tramming that, it will probably not show the same curve that you are seeing on the vise.

Well, took the vise jaw off with an allen key and piece of pipe. Wow, was it tight. One bolt was so tight that it had deformed and I had to replace it. Also, dirt and other stuff were under and behind the jaw. Proves to me that nothing, absolutely nothing can be used right out of the box, even an expensive vise.
Next sweeping operation (R J) was much better after cleaning and reassembly - no dip.

Thank you everyone.
Michael.