PM727M DILEMMA

Yes i do have a lathe also, however, it is apart for repairs. I tried using a piece of drill rod in the spindle about 8" long maybe. Then used a dti to try and center the rod at both ends, then shim the colums for the difference. But my drill rod didnt seem to be straight enough.
 
with issues like this it's worth making a plan and writing everything down.

Square column to table in X and Y. Use a precision square clamped upright to your table. The longer the better - those 123 blocks might not give you enough length to get the column really square. You can always check the column higher up by clamping (some how) the square on top of a 123 block. Make sure you lock the column gib before making a measurement.

Tram head to table, ideally by sweeping directly off the table itself. Make sure your DI/ DTI is repeatable as you'll be going over the table slots. Lock all gibs.

Check quill to table, using the precision square clamped to your table. Lock all gibs and lock quill at top and bottom when you make your measurements.

You can also take unlocked/ locked readings - that will tell you something about your column gibs. You'll get some movement on the DI/ DTI, but it shouldn't be much.

Then report back. Otherwise you'll be chasing your tail and it'll be hard for us to figure out what you've done and what it means.
 
mattthemuppet2 said:
with issues like this it's worth making a plan and writing everything down.

Square column to table in X and Y. Use a precision square clamped upright to your table. The longer the better - those 123 blocks might not give you enough length to get the column really square. You can always check the column higher up by clamping (some how) the square on top of a 123 block. Make sure you lock the column gib before making a measurement.

Tram head to table, ideally by sweeping directly off the table itself. Make sure your DI/ DTI is repeatable as you'll be going over the table slots. Lock all gibs.

Check quill to table, using the precision square clamped to your table. Lock all gibs and lock quill at top and bottom when you make your measurements.

You can also take unlocked/ locked readings - that will tell you something about your column gibs. You'll get some movement on the DI/ DTI, but it shouldn't be much.

Then report back. Otherwise you'll be chasing your tail and it'll be hard for us to figure out what you've done and what it means.
Click to expand...

I have done everything you stated already except for checking the quill since re-shimming. When i lock and unlock the the Dti will move about .025, the bottom clamp always moves the DTI alot when unclamped. Also the gib is adjusted properly. In my earlier post, you will see i use a 8" precision square to square the column. I only use the 123 block to get height off the table. Still when the gib is locked down it should be "0".
 
awesome, can you right all that down in one post? Makes it easier to refer back to.

I'm no expert, but 0.025" movement between locked and unlocked head/ column gib seems to be alot. Yet I think I read that you had it adjusted to the point that it was binding. Have you taken the gib out to check for straightness and twist?
 
Based on your most recent information, the head-to-column interface at the dovetail ways is sloppy and needs to be corrected before any of the other tests and tramming processes are appropriate. Sounds like some combination of gib fit, rough or wavy way surfaces on either the head mounting or the column, or both.

On my Rong Fu 45 (Taiwan manufacture), with a properly fitted and adjusted gib, the head would sag no more than 0.003” when the locking levers were loosened (often less), yet the head would move up/down (with levers unlocked) without excessive force. Loosening the gib would not significantly ease the force required to raise/lower the head, but did induce more head sag, but did not alter the tilt or lateral position. Granted, I hand fitted the gib to the dovetails using Prussian Blue marking and Swiss files/lapping with 500 grit paper on glass. But even before that fitting, the sag was no where near what you are experiencing (0.008” as I recall).

I recommend you get a replacement gib, then re-test and be prepared to tweak the gib fit (common need with entry level Chinese equipment), or exchange the mill for a replacement. A badly fitting gib can be the source of the head wallowing around under pressure or relocation on the column even when it’s clamped down to a point the head won’t move.
 
I watched your video and I stand by my last post.
 
Brad125 said:
Also the gib is adjusted properly.
Click to expand...
Are you positive about this? On my machine, the gib doesn't always sit quite right when being inserted and adjusted. The screws can sort of push it off to one direction so that it will bind long before it is in correctly.

If it isn't sitting quite right, it could be tightened until the axis is binding, then back off a little, and it won't be even close. Then when you tighten the locks, you are actually bending the gib to force the dovetails into the right position which is causing the head to move.
 
You must log in or register to reply here.
Back
Top