[Newbie] Dro Error

[turbotoys]

hey everyone. I just picked up a new PM-1440GT and just installed an Easson 12B dro. I'm having an issue with the accuracy of the glass scale on the Y Axis. I have checked the mounting - the scale is within .0001. Everything is new, tight. square. parallel.

Yesterday i was taking some test cuts and I cut the workpiece down to 1.011" - measured with two different calipers and set the dro to that measurement - i took two more cuts down to 1.00" then took a measurement and got .989. Every piece I cut is undersized so I have to keep measuring and resetting the dro - its actually just easier to not use it but didn't pay all that money for it to collect dust.

Do i have a defective scale? I haven't even checked the other axis yet, as this one is frustrating me enough.

Any ideas??

 

[T Bredehoft]

Does your scale measure the movement of the tool or the diameter of the work? You moved the tool form 1.011 to 1.000, you got .022 movement.

 

[whitmore]

hey everyone. I just picked up a new PM-1440GT ...
Yesterday i was taking some test cuts and I cut the workpiece down to 1.011" - measured with two different calipers and set the dro to that measurement - i took two more cuts down to 1.00" then took a measurement and got .989

If you start with 1.011 diameter, take off '0.011', and end up with 0.989, did you take
that cut off the diameter? Or, the radius?

 

[magicniner]

When I install DROs I always check the DRO indicated move against actual using a dial gauge.

 

[turbotoys]

It measures movement of tool. I took it off diameter, I assume that's the problem...

 

[RJSakowski]

I think Whitmore hit it. DRO's designed specifically for lathe use usually have the option of setting the x axis readout to read either diameter or radius. If set for radius, and the diameter is set for 1.011" and the cross slide moved to the reading of 1.000", you will have removed .022" of stock which would measure .989".

 

[higgite]

It measures movement of tool. I took it off diameter, I assume that's the problem...

You don't have to assume... that IS the problem. When you take an .011 depth of cut on a rotating piece of work, it takes .011 off all the way around, not just on one side. Some DROs will work in diameter or radius, operator's choice. Don't know if yours has that feature or not.

Tom

 

[Bob Korves]

A new scale installation will also require calibration of the scales. As installed, DO NOT accept the numbers shown on the DRO as being correct until you have tested them, calibrated them, and tested them again to be correct. There are at least a handful or more issues that can cause the DRO reading to not match the actual travel, even if the scales themselves are perfect. The good news is that they are relatively easy to correct. I would not use calipers or a dial indicator to prove the scales. I would use gage blocks, to multiple distances. You want the scales to be more accurate than calipers or dial indicators which can have various problems, not the least of which is cosine error.

 

[turbotoys]

So after some research I downloaded the manual and found a lathe supplement that my manual didn't have. I am supposed to take the diameter / 2 and then hit the % sign and that will give me the actual amount.

I'm going to try that tomorrow. I'm sure it will fix all my problems.

Thanks for all the comments.

 

[4ssss]

You may just want to check to see if the DRO is set to the machine you're using. Some can be used on different machines and need to be switched over just by hitting a key.