DRO for PM-25MV

[GA Gyro]

With my new PM935TS mill (BP clone), I ordered an Easson '12' DRO... pricy.
This DRO came with glass scales mounted, Matt and his crew did a good job of mounting the DRO.

The mill is set up and running, and the DRO reads in 'tenths'... however getting the mill at a specific 'tenth' location with the table and knee cranks would be an exercise in minute movement... doable... yet something one would have to 'creep up on'... CAREFULLY... :shush:

What WRMiller mentioned in a post earlier... about robust roughing cuts and then fine finishing cuts... remembering machine, tool, tool holder, spindle, and even work will flex under the load of the cut... is reality.
Knowing how to 'creep up to' what you intend to end with... is different than just setting the dials and let it cut. This takes practice... and experience...

If it were me... I would get something a bit better than what you can envision today... as IMO when one learns more (and gets more practice and experience)... their expectations of what they want to do (and can do) will expand. Getting something 'economical' (read that cheap) now... then having to replace it later... well how much $$$ has one spent cumulatively?

 

[jimcisme]

I have done half thou and less work on my PM25, which is more than I typically need as a hobbyist.

The trick with the PM25 or any of the smaller bench mills is to remember that these things are not very rigid and WILL flex as a function of how much load/cutting forces are placed upon them. When roughing in, you don't pay that much attention to part/machine flex other than to note how much in preparation for dialing in the next cut.

When you start getting close to your final dimensions, taking smaller cuts will reduce the machine/tool deflection (cutters flex too) and permit you to achieve your final dimensions without too much drama. To hold to a thou dimensional variance seems to be everyone's goal, but remember that even on a Bridgeport an experienced machinist doesn't try to hold any better than that (so I'm told). That's what surface grinders are for.

In my personal experience, I DO like to see those tenths on the readout (.0002) as that helps me 'fudge factor' for part/tool deflection as I'm sneaking up on final dimensions.

I totaly agree. Very well put.

 

[jbolt]

Another example: When I bought my first mini-mill 12 years ago I bought a small 3-axis DRO from a Canadian company that used toothed rods and gears for scales (sorry, can't remember the name off-hand but they still exist) and while I thought it was kinda funky from a design perspective the little stinkers actually worked quite well!

That would be the Shooting Star CBX DRO. I had one on my Smithy Granite 1324. That was the affordable system at the time in 2001.

The rack and pinion system works very well. The read head is an optical encoder driven by precision gears. The split wire loom covers for the rack gear work fine for general use but would not work with heavy coolant use. Mine was powered on 24/7 for 14 years and the only issue was a failed wall wart transformer at 11 years. The owner helped me troubleshoot the problem on a weekend and helped me find a suitable local replacement. Excellent customer service. At their price point there are better offerings now.

We have had two SINO glass scales fail on our PM-1127 in less than two years. Fortunately they were replaced under warranty but it makes me wonder about the longevity of the low cost import glass scales.