PM727M DILEMMA

How tight was your Z-axis gib in that video? When you tighten the handles, how far do you have to turn them from the first point of resistance until they are snug enough that it's hard to move the head?

Just checked the PM-727V in my garage - if I rotate the handle so that it flops down to 3:00 when looking at it from the left side of the mill, I can turn it to about 5:00 before it gets pretty snug. If you can tighten yours much further than that your gib is too loose...
 
I also have a 727m that is well out of warranty. Now that you mention your issue I have a thought. I just went out to the shop and tried mine. the head does move similar to yours when tightening the locks. And also I know for a fact if I adjust the gib at the center of travel on the column it does bind at the top and bottom. I have noticed this since the machine was new. I remember measuring the column dovetail with pins at the top and bottom and that the center area measured narrower but don't remember the numbers. when my mill arrived the Z axis locks were very tight and the quill was setting on a wood block on the table. Now that you bring up your issue I wonder if the column was distorted by the locks being so tight during shipping. This is probably an issue I should have addressed under warranty. My theory is that the dovetails are closer together in the middle then at the top or bottom.
 
Thats how mine is, loose in the middle and really tight on top and bottom. The z-axis gibs are tight enough that the the travel of the head will stop 3" before the top of the head abd about 2 inches on the bottom
 
I think you should measure the dovetails with pins and see if its narrower in the middle. I generally don't do high precision projects but now that I see I'm not alone with the loose tight issue I think I may investigate a solution for my machine. I wonder if the column flexes enough in the middle to allow the dovetails to actually bow together when tightening the locks. It will be interesting to see what others have to say. And by the way QMT has been an awesome company to work with for me. I had motor troubles early on and they handled it very well. I knew when buying my 727 that it would probably have some Chinese idiosyncrasies but I have not been upset by them. the machine as is a good value in my eyes.
 
tweinke said:
I think you should measure the dovetails with pins and see if its narrower in the middle. I generally don't do high precision projects but now that I see I'm not alone with the loose tight issue I think I may investigate a solution for my machine. I wonder if the column flexes enough in the middle to allow the dovetails to actually bow together when tightening the locks. It will be interesting to see what others have to say. And by the way QMT has been an awesome company to work with for me. I had motor troubles early on and they handled it very well. I knew when buying my 727 that it would probably have some Chinese idiosyncrasies but I have not been upset by them. the machine as is a good value in my eyes.
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I agree, the machine is a good value. I just want to find a solutuon for mine. I am going to upload another video for everyone to view and see what they think, or if there is something else i can try. My lower reciever will be here monday, and machining starts in 2 weeks. I cross my fingers that this will be resolved before then.
 
PM just got back to me today, he said to try and shim the gib to see if it helps and also to try and isolate where the problem is. How in the heck do you do about shimming the gib? I heard of shimming straight gibs, but not on a tapered gib like these colums have.
 
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They also said that they will keep working with me until we figure out what it going on, and do whatever they have to to make it right. Atleast i can rest alittle easier if shimming the gib doesnt work.
 
Brad125 said:
PM just got back to me today, he said to try and shim the gib to see if it helps and also to try and isolate where the problem is. How in the heck do you do about shimming the gib? I heard of shimming straight gibs, but not on a tapered gib like these colums have.
Click to expand...
 
Awsome video, my next question is how thick of shim would i need? If the head moves .025 thousands when clamped. Should i use half that at .012ish?
 
You said that when the head is at the top or bottom of the column it binds up and won’t move. When it’s bound up, does loosening or tightening the clamp screws move the indicator?
 
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