Lathe DRO Accuracy

Yes, on the lathe, sorry thought the thread was about dro on a lathe accuracy. You know I haven't actually compared the dial to measurements .. maybe I do that tonight so I can give very specific numbers.

Dro on the mill is spit on.
 
I have a similar issue as Driveslayer45. I am slowly fixing to instrument the lathe with a .0001 dial indicator and work through the entire scale length comparing DRO with lathe dial with dial indicator movement. I suspect some areas of the magnetic scale have a problem, either more or less transitions than nominal. I will report any interesting results.
I spent many years working on magnetic recording systems, hence I could believe anything.
 
I cannot figure out how to quote while using my phone but the comment about tool height was the answer.
Tonight I took extra care in checking my tool height, it was a little low so I centered it on the work piece using the method where you pinch a machinist rule between the tool and the part. I then took a surface cut to make sure my stock was concentric, mounted a dial indicator on the bed, measuring the tool post, zeroed everything and proceeded to take .040 cuts, three cuts, measured after each cut, and each time and my stock measured where it should be.

I had no idea being off center would cause that.

Thank you very much
 
This hobbyist recently had to make two pins .2035" +0/-.0003 on my lathe. So just how much tighter are "aerospace and electronics" specs? Just curious.
 
wrmiller said:
This hobbyist recently had to make two pins .2035" +0/-.0003 on my lathe. So just how much tighter are "aerospace and electronics" specs? Just curious
Click to expand...
Wow. I would love to hear more about this. What Lathe did you use? How did you measure the pins to know you were in tolerance? What material were the pins made from?
 
Driveslayer45 said:
I cannot figure out how to quote while using my phone but the comment about tool height was the answer.
Tonight I took extra care in checking my tool height, it was a little low so I centered it on the work piece using the method where you pinch a machinist rule between the tool and the part. I then took a surface cut to make sure my stock was concentric, mounted a dial indicator on the bed, measuring the tool post, zeroed everything and proceeded to take .040 cuts, three cuts, measured after each cut, and each time and my stock measured where it should be.

I had no idea being off center would cause that.

Thank you very much
Click to expand...
Let’s make a grossly exaggerated example:
If your tool was .250” low, you would be unable to turn anything smaller than .500” in diameter, as your tool would pass .250” under the centerline of the part. So, if you touched off at 1” diameter, entered that in your DRO, and then proceeded to turn the piece down until your DRO indicated a diameter of zero, the actual diameter of the part would still be .500”.
 
Boswell said:
Wow. I would love to hear more about this. What Lathe did you use? How did you measure the pins to know you were in tolerance? What material were the pins made from?
Click to expand...

I used my 1340GT lathe. Pins were cut from pre-hardened 4140 round stock. As I got close to the proper dimensions the parts were cooled down after each cut and prior to measurement. A digital Starrett mic was used to make the verification measurements of what I was reading on my EL400 (mag scales) DRO. I can take pretty accurate sub-thou skim cuts with those polished, razor-sharp carbide inserts.

Full Disclosure: I did have to make three attempts to end up with two pins. But then I'm just a hobbyist, so that's permitted right? :D
 
Have to make sure that the scale is mounted 'true' to the axis of whatever machine it's mounted on.
I didn't realize it but I had 'bumped' my 'Y' axis mount on the mill after installation and I was off .010" over 6".
 
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