Perplexed - A Little Help Needed

Nyala said:
Pontiac428,

My cuts are no more than .025". It takes me over 50 passes to get to a depth of 1.248". Cuts to widen the slot are done in .020" or less, sometimes half that, so it takes 6-12 passes to remove .126" at about 1/2" deep. Then repeating the process 3 times until I get to the desired width and depth. Then repeat that for the other side. No hogging big amounts here. My machine does NOT like big cuts. I'm going to try reducing the .025" to about .015" to see if that helps.
Click to expand...

Okay. You should be able to take cuts approaching 0.100" deep and half a cutter diameter wide. How are you managing backlash? On a manual machine, you should only turn the lead screw one direction into your dimension. Avoid overshooting and pulling back, unless you back way out and re-approach from the feed direction again. Whatever the DRO reads is where your spindle centerline is, but if you're in the dead band of your lead screw's backlash, the spindle will wander. On some machines a lot! Not trying to insult; gotta cover the basics first.
 
When I had my PM25 3/8" roughers (coarse and fine) were my friends! :)
 
Nyala: do some tests making heavy cuts vs light cuts, I'm sure you will see a difference due to the flex or springiness of the machine
Smaller hobby machines have more flex than big industrial ones
Mark
 
I'm bringing this discussion back up again only to relay some information I found out.

After being unable to resolve the depth of cut problem I contacted Precision Matthews, told them of the problem, and they were as helpful as ever.

I was advised to removed the cover plate from the fine feed digital screen where I would find a small vertical DRO. I was to check the screws on the DRO to insure that they were tight. They were not. I tightened all four screws (all four were loose) and checked the depth of cut against a height gauge that I adapted to check depth. The depth of cut on the height gauge and the fine feed digital screen matched.

Looks like I'm good to go. Other PM-25 users might want to check these screws as preventative maintenance.

Many thanks to PM for their help.
 
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