How do you offset a straight V style holder? (2024)

VMG 35 deg diamond bit in a straight holder. Normal procedure on my Prototrak is to set the X and Z by taking cuts and measuring the diameter and face (all tools are offset to reference tool). This works fine for X but I can't think of a way to measure Z. You can't face with the diamond bit in a straight holder. I could try guestimating the point position with a magnifier and then offset the radius and maybe get close.

Some way I haven't thought of to do this?

I've wondered the same thing, and look forward to seeing what others do for this case. I've done a test cut in a setup piece and measured as best I could but would be nice to have a more definitive process.

Regards.

Mike

On my threading tool holder (laydown inserts) I offset to the edge of the insert because in most threading jobs it doesn't really matter where the thread starts, only that the tool doesn't hit a shoulder. But I am trying to contour with the diamond insert, comp offsets by the radius but expects to know where the (virtual) left edge is. Without that the contour will be offset relative to features cut by other tools. An optical comparator held over the tool is about the only way I can think of.

I guess one could program say a 45 degree taper with a left hand reference tool, then chase it with the V tool and adjust Z offset to match. One peculiarity of the Prototrak control is, cutter comp is only applied during a running program so it would be a little tedious.

jhearons said:

Touch the shank of the tool to the face of the work and set Z. Shift Z by 1/2 the width of the shank. If for some reason the tool has a jogged head, refer to the manufacturers catalog (or measure ahead of time ) to find the amount to shift.

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Good idea, I'll try that and see how close I get. There would be a build up of tolerance: measure width, measure edge, divide, subtract the tool radius. But at the least a quick way to get a starting point.

Maybe a block with a sharp V cut-out matching the tool angles made with its centre line a known diatance from the side would be more accurate and worth the extra trouble. Think I'd arrange things so the block could be strapped to the tool shank with the V wrapped snugly around the tip then bring the whole kit and caboodle up close to the end of the workpiece or other suitable calibration point and measure the gap. Measuring is likely more repeatable than simple touch off. I guess a loose part carrying the V fixing to a shank with appropriate clamping arrangements would be easiest to handle. Single screw through clearance hole large enough for sufficient fine adjustment ought to work. Sounds a ton of trouble to do but if it just works may be worth it over cut'n try.

Only times I've ever done anything like this touching the shank worked fine. But good enough was within 20 thou or so.

Clive

Actually, since this tool is no good for anything other than finishing a profile that needs it, I'd say that picking it up very accurately in Z is essential.

There are 2 ways that I can think of.

First the easy one: If you have an optical comparator, just create the face with your known tool, and then use the VNMG to plunge a shallow groove
into the OD somewhere. Record the Z position. Take the part to the shadowgraph, measure the distance from the face to the groove center, add the value to the offset
register. Simple

Without a shadowgraph:
Create a known groove with a grooving tool, say .100 wide and center being @ .100 from the face.
Then take the VNMG, position it somewhere inside the groove, and then move backwards until the tool touches the back edge.
Zero your operator Z position, then move forward until you touch the front.
Read position screen, move back 1/2 the amount and bang, now you're .100 behind the face.

I'm never more than .002 off with either of these methods, and I do set up quite regularly with this tool.