What Resolution On Dro Scales For A Pm-932?

Jim Wilson

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I'm looking into putting a DRO on my PM-932. The vendor I'm talking to ( looking at a Fagor DRO) - has different options available for the scales.

I'm wondering if it's worth the money to put a higher resolution scale on the PM-932 - or is the mill just not capable of taking advantage of it?

Here's what the have for options:
- resolution .00005”/.0001”
- resolution .0002”/.0005”
 
.0002 is almost meaningless as far as a milling machine is concerned, IMHO any more is money spent without return.
 
resolutions, is only part of the picture, you also need to consider accuracy, repeatability, & Hysteresis.

This image below (from dropros) & webpage are good starting points.
Scale%20tech%20specs.jpg


http://www.yuriystoys.com/2013/12/selecting-scales-for-a-hobby-dro.html

Scale%20tech%20specs.jpg


Scale%20tech%20specs.jpg


Scale%20tech%20specs.jpg


Scale%20tech%20specs.jpg


Scale%20tech%20specs.jpg
 
Dan,
You beat me to it, by seconds.
 
I have the "factory" one installed--It is great. It reads to "tenths"----HOWEVER, & this is a big "HOWEVER"--after getting everything set, and then tightening the assorted locking devices, it usually changes anywhere from 2-4 tenths on mine. It is relatively easy to hold to less than a thousandth, though.

Jerry in Delaware.
 
Thanks for all the info everybody - I'm going to have to sit down and do a little reading tonite and educate myself.
 
I was recently talking to the folks at DroPros about the EL700 DRO for my new mill, and they said that typically you don't see resolution below 5 micron on mills, but it is not uncommon to put 1 micron scales on lathe cross slides. Which is what I did. I'm putting the 5 micron scales on my new 935. FYI the 1 micron reader heads are a $100/ea. upcharge IIRC. Ouch...
 
I'm looking into putting a DRO on my PM-932. The vendor I'm talking to ( looking at a Fagor DRO) - has different options available for the scales.

I'm wondering if it's worth the money to put a higher resolution scale on the PM-932 - or is the mill just not capable of taking advantage of it?

Here's what the have for options:
- resolution .00005”/.0001”
- resolution .0002”/.0005”

Jim,
For lathe's cross slide I can [marginally] justify a 1 micron scale if the lathe is of "tool room" quality. I used on my Jen 1024 and it's a grotesque overkill. I got mine very cheaply, so it didn't matter than much, but I would not pay extra for one.
Here is some food for thought: cast iron has coefficient of expansion of 0.0000058 in/(in*degree F). Aluminum is double that, almost exactly. Glass can be between 0.0000022 and .0000050 (pyrex vs. plate glass).
Let's say your scale is 30" and temperature in the shop fluctuates between 65F in the winter (in my case) and 80 in the summer. That's 15F over 30 inches. Cast iron will have delta of 0.00261, glass - 0.00099. That is 0.00162" difference between how much scale and the bed expand (best case scenario). This basically means that in order to take advantage of the regular 5 micron scales the shop needs to be climate-controlled, etc.

Hope this makes sense

Regards
Yuriy
 
This basically means that in order to take advantage of the regular 5 micron scales the shop needs to be climate-controlled, etc.

Regards
Yuriy

No, you don't need a temp controlled shop. My lathe or material is not going to see that much temperature swing during operation regardless of what temp it starts at (winter or summer). The DRO measures distance traveled from a point you select, for example the point at which you just contact a round bar with your cutter, and from there only reports how far you have traveled from that point. There is no fixed point reference from which all measurements are taken.

I can hold tenths tolerance on a part regardless of how chilly or warm my machine is. :)
 
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