Late arrival (as usual) on this revisited and interesting topic:
Where are you using shims @CWret ?
I like using a 15mm shim to reduce the standard amount of sharpening - i use it when the bit is not very dull and only needs a touch-up.
@Susquatch previously answered that question i believe- he also linked my full discussion on the topic in his post #302 above.
Many months ago - i tested (measured) the reduction in total length of the bit when it was sharpened in a VevorA. I did a std sharpening using 6 bits varying from 1/2” to 13/64” diameter and the sharpening shortened them by 0.018 to 0.025” (depending on how consistently you can set the bit in the collet). Then i sharpened 10 other bits (that varied from 1/2” to 1/4” diameter) and used a 0.015”spacer/shim (to hold the bit away from the grinding wheel, as explained in the above mentioned link). Using the spacer, the bit’s length was reduced by 0.003 to 0.011” by sharpening. Depending on the face angle (118 or 135 degrees typically) the amount of material removed from the cutting face is almost as much as the amount of bit shortening (example: shortening a 118 bit by 0.020” would remove 0.017” from the cutting face). Which is a lot to remove from the bit face if only a little touch-up is needed- so I often use the 0.015 shim/spacer. If necessary, the bit can be sharpened again without the shim, easy-peasy & all with the same set-up. Kinda like measure twice and cut once - but in this case it is grind once, assess and grind again if needed.
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Using the Vevor A or B with the optionally sourced larger collet holder (and also with larger collets) as Susq discussed above, they can sharpen up to a 3/4” dia bit. But it leaves a little amount on the outer edge that doesn’t get sharpened. I believe this problem is more pronounced on the B than the A - but i have not seen the difference beside each other so this is IMO.
Here’s a 3/4” bit i sharpened today to show the tiny tip of the outer edge that is not removed.
First the before pic:
and after the sharpening (at a 118 angle):
This small unsharpened tip is easily touched up on a bench grinder.
Then i sharpened the same bit again but to a 135 face angle:
With the 135 angle the uncut tip is almost gone. It is so small that it was easy to remove with a stone.
PS: I just found this YouTube video that explains web thinning vs a split point grind using a 13A and 13B side by side. Like most YouTube it takes 18 minutes to give 9 minutes of info
