Gallery, Projects and General > How do I??

DRO calibration

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I recently installed a DRO (thread elsewhere) on my round column mill. To calibrate it, the best I have for equipment is a 6" micrometer (.0001") and its 5" standard. I also have a cheap 8" digital caliper, some 123 blocks, and some old gage blocks won in an auction

The DRO resolution is approximately 2560 lines per inch, which I'd like to refine as close as I can.

What I've done so far is grip a ~6" piece of aluminum in the mill vise, dust cut one end with a new 3/8" carbide end mill, then traverse to the other end 6.375" with the DRO and make a second cut. Then measure between cuts with the 6" micrometer. That reading should be correct at 6.000" in an ideal world. Presently it's 6.008" with the DRO calibrated at 2560. I'm thinking I should reduce to 2557 or so.

So here's the question folks, is there a better way to do this with the tools I've got? I can imagine that if the mill is not exactly .375" (or properly its cut isn't .375) or the spindle wobbling, etc that measuring between cuts might not be ideal.

What do you think?

Classic way is to mount a DTI as a zero indicator against a stop block, then insert a stack of Jo Blocks of known total length and bring DTI up to zero and compare DRO to know Jo Block length.

Thanks, Andrew.  :beer: The gage blocks I have are rather small, and frankly, old and unknown. Stacking them might not be any better.

But the 5" micrometer standard is new, and I could probably use that the same way.

Since the standard is a rod, it's a little tricky to position, but I think I'll set it in ground Vee blocks and check orientation with the indicator first

Also I think I'll reverse the usual procedure and set it against the stop, first for zero set, then remove it and traverse to the stop for the second measurement. That makes positioning a lot easier.

Actually, I could just mill myself a squared off standard block and check its length with the micrometer. Doesn't have to be any particular length except between 5-6". Then mark it for future use.

Then it will be easier to position.


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