New Dro issue .... or not ?

sasanifab

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Some of you know that I recently installed a tpac tool 2 axis dro. After I finished i took a Mitutoyo dial indication and checked it against what the dro was telling me. My problem is that when I go to cut say. 1mm it’s generally always larger than that. I usually bring the insert up to the material, touch off then zero out the zero. I take my calipers , measure the workpiece. Say the workpiece measures 22.75mm , I start the lathe move up 0.75 and cut the Material. What I’m finding is that is always greater than what the dro says , even though it dead nuts on the dial indicator. My dro allows a offset from -1.5 to l.5. This doesn’t seem appropriate as my dro is reading correctly. Am I missing something
 

Mitch Alsup

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How are you "touching off".
Touching off requires that you have enough tool-pressure at the point of contact to scratch the material if the cutter (or part) is moved across the face of the tool. This tool-pressure also incorporates all the backlash <removal>and any other gearing tht is positioning the tool at the point of contact.

My guess is that you are touching off with insufficient tool-pressure at the point of contact.
 

sasanifab

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How are you "touching off".
Touching off requires that you have enough tool-pressure at the point of contact to scratch the material if the cutter (or part) is moved across the face of the tool. This tool-pressure also incorporates all the backlash <removal>and any other gearing tht is positioning the tool at the point of contact.

My guess is that you are touching off with insufficient tool-pressure at the point of contact.
I’ve tried moving the carbide up to the material and moving it back slightly so it’s not making contact and also moving it up to scratch the part and zeroing it out. Both situations it usually doubles the Material removed. So if I want 1mm removed I plug in .5
 

jwmelvin

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Doubles as in the DRO reads radius and therefore the diameter changes by double that?
 

Howard E.

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My general experience is that if there's any slop in the system the work will drag to tool into it making deeper cuts than expected. Could be backlash, could be the gibs, loose insert on the cutter or a bit of everything.
 
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macardoso

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So there is a chance that your scales are inaccurate, BUT... that's really unlikely. The cheap China ones are still very good.

More likely is that either your mechanical connection to your DRO scales is wobbly, or there is flexture in your machine and cutting. Try cutting a sample of aluminum with a dead sharp (shave your arm with it) HSS bit. Just skim the surface to true it up. Then dial in a light cut and compare the measurements. If they are way off then something is certainly wrong. If they are dead on then you are seeing machine flex. No DRO is to be trusted without thought. There will always be flexture between the scale and the workpiece/tool.

If HSS isn't your flavor (like me) then some razor edge ground carbide inserts (CCGT or VCGT) give performance similar to HSS with the wear resistance of carbide.
 

sasanifab

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So there is a chance that your scales are inaccurate, BUT... that's really unlikely. The cheap China ones are still very good.

More likely is that either your mechanical connection to your DRO scales is wobbly, or there is flexture in your machine and cutting. Try cutting a sample of aluminum with a dead sharp (shave your arm with it) HSS bit. Just skim the surface to true it up. Then dial in a light cut and compare the measurements. If they are way off then something is certainly wrong. If they are dead on then you are seeing machine flex. No DRO is to be trusted without thought. There will always be flexture between the scale and the workpiece/tool.

If HSS isn't your flavor (like me) then some razor edge ground carbide inserts (CCGT or VCGT) give performance similar to HSS with the wear resistance of carbide.
I’m actually using a cnmg insert on really soft material 12l14, I thought maybe I was pulling more material off ?? Like I said , I measured the dro scales against new Mitutoyo indicators and i measured 0-10 thousands , should I be checking in 10ths?
 

DLF

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I do not know your DRO, but my Ditron D80 has a scale compensation feature where you can dial in an offset for each axis.

This can be used to calibrate the sensors


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