PM-25MV Spindle DRO Issues

[devils4ever]

I'm having some issues on the DRO on the spindle of my PM-25MV mill.

First, I'm seeing a backlash issue. When I lower the spindle using either the fine control or the handles, I see the DRO increase as it should. When, I reverse direction and raise the spindle, it takes 4 or more thousandths before the DRO responds. I used a dial indicator to verify this. I thought the DRO had no backlash issues. Any ideas?

Second, I think the DRO is off by 6 or more thousandths when I lower it by 0.375". I'm trying to hit 0.375" DOC for some milling operations and it seems to be off based on my dial indicator and by measuring the depth via a digital caliper. Anyone else seen this?

Thanks!

 

[higgite]

I'm having some issues on the DRO on the spindle of my PM-25MV mill.

First, I'm seeing a backlash issue. When I lower the spindle using either the fine control or the handles, I see the DRO increase as it should. When, I reverse direction and raise the spindle, it takes 4 or more thousandths before the DRO responds. I used a dial indicator to verify this. I thought the DRO had no backlash issues. Any ideas?

Just for clarification, are you measuring .004” of actual spindle movement or handle/knob movement before the DRO responds?

Second, I think the DRO is off by 6 or more thousandths when I lower it by 0.375". I'm trying to hit 0.375" DOC for some milling operations and it seems to be off based on my dial indicator and by measuring the depth via a digital caliper. Anyone else seen this?

Copied from my post in a previous thread on this subject (https://www.hobby-machinist.com/threads/perplexed-a-little-help-needed.79163/#post-677151):
You may be having the same problem that I ran into with my mill before I added a quill stop. Mine isn’t a PM, but I think the same principle may apply. There is backlash in the rack and pinion that drives the quill up and down when you use the handwheel or the fine adjust knob. When I plunge milled with the fine adjust engaged and without a quill stop, I would run the the end mill down to my target depth and stop. The end mill would continue going deeper for a few thousandths until it took up the backlash. It drove me crazy until I noticed the Z-axis DRO changing after I stopped plunging. Before I installed a quill stop, I learned to sneak up on my target depth once I got close. Try plunging to a target depth with your fine adjust and then stop and watch the DRO to see if yours does the same as mine.

Tom

 

[T Bredehoft]

Subsequent to installing my PM25 in the shop I noticed a lag in the DRO on the quill. I fund that the two round head Allen screws just below the head (connected to the spindle) were not absolutely tight. Once they were tightened (I disassembled them and cleanded all mounting surfaces) The DRO no longer lagged behind the movement. Check that before continuing.

 

[Chewy]

I wonder if this is the problem on the PM 30? I mill something and measure it. Say it is .010 short. I down feed .009 and lock the spindle. The DRO goes to .010 by itself. OK I can handle that. In theory you woul think that I hit my mark, In reality I am usally deeper by .001-.003. It varies. I'm having trouble sneaking up on that because it changes. Note: This is on the spindle DRO that comes with the machine. When I use the Installed DRO it hits pretty good with the spindle locked. Never paid attention to backing up the spindle but i will the next time I use the mill. I thought about calling Matt, but I haven't the time to do anything right now.
Charles

 

[devils4ever]

Yes, the dial indicator (and the handle) moves by about 0.004" before the DRO responds when I change direction.

I don't think there is a quill lock for this mill.

So, for me to hit my 0.375" mark, the DRO needs to be about 0.368".

The two Allen screws on the DRO scale were loose and I thought I found my problem. I tightened them, but it does not help at all.

I'm tempted to use the Z-axis on the column instead, but one revolution is 0.083" and the scale is backwards for plunging (scale decreases). I'm sure the 0.083" per revolution is metric, but it doesn't seem to match anything normal since this is equal to 2.1082 mm.

 

[Tmag8500]

the scale is backwards for plunging (scale decreases).

You should be able to switch that in the parameters. They have a manual listed on their website for the DRO. Page 8 starts the parameter section.

 

[devils4ever]

the scale is backwards for plunging (scale decreases).

You should be able to switch that in the parameters. They have a manual listed on their website for the DRO. Page 8 starts the parameter section.

No, the DRO direction is correct. I was talking about the hand wheel for the Z-axis. It is backwards. It decreases as the head drops towards the table.

 

[yendor]

Backlash in the Quill RACK would allow the Quill to continue to drop after you stop moving gthe FINE Feed.
Escentially you are pushing the Quill DOWN via the Rack/Pinion Gears into the the material.
Once you stop gravity allows the Quill RACK to move down the amount of the backlash in the Rack/Pinion Gears before it settles.
So- YEP - you'll need to stop short by what You "KNOW" is your backlash (+ some margin of error) and see where the DRO settles.
When you reverse direction with the fine feed (go up) the backlash is in the gears between the Fine Feed and the Rack. Different Gears for both instances.

 

[higgite]

Subsequent to installing my PM25 in the shop I noticed a lag in the DRO on the quill. I fund that the two round head Allen screws just below the head (connected to the spindle) were not absolutely tight. Once they were tightened (I disassembled them and cleanded all mounting surfaces) The DRO no longer lagged behind the movement. Check that before continuing.

I had forgotten that I had the same issue with the quill DRO lagging due to loose screws. (The DRO’s loose screws, not mine. ) It only lagged when I changed direction of quill travel, independent of backlash. Once I tightened the screws, the DRO lag disappeared, but gear backlash remained a problem for plunge cuts until I installed a quill stop.

Tom

 

[Nyala]

There are actually 4 screws on the spindle DRO not 2. Two are exposed and two are not. You must take off the metal face plate to access the other 2. I was having issues and PM had me remove the face plate and tighten all 4 screws. Problem solved. I then added Locktite to everything secure.