Hello,
I’m trying to drill a 20mm diameter hole in mdf. The final hole is ending up about 0.4 mm too small in both x and y dimensions. Using helical drilling option in estlcam. I tried drilling near x0 as well as out in the middle with the same result. I’m wondering if my belts are too loose, some other potential thing, or if the machine shouldn’t be expected to be that accurate. The holes are all consistently the same size though. Any thoughts?
0.4mm could mean that it’s not a 1/8 flute but a 3mm. Try to measure your endmill, it seems to be a common problem with cheaper endmills.
I think they have 1/8 shank and are ground smaller 
Does estcam have an allowance? In vcarve I leave a allowance to adjust for this now and also deflection and my last batch of pegs were oversize by .2mm so there is someone else adding a fudge factor.
Or measure the hole! .4 is not alot. Maybe you have a small run out problem! Many recommend to measure cut not tool. Just in case tool or machine or both have runout, etc!
I think Phillip is right and it is mostly the bit. I don’t have metric calipers, and it’s difficult to exactly measure the end of the bit, but it seems much closer to 3mm than 1/8”. I recut the hole with my cutter diameter as 3mm, and now a 20mm benchdog will fit (albeit very snug!). I think I’ll add a some allowance to the 20mm holes to get it closer, but this result is more what I was expecting.
Thank you!
Noah
FWIW, all of my supposed 1/8" endmills cut a 3mm kerf. I had a bunch of tab and slot box joints that just did not fit together, and needed a lot of “sand to.fit” adjustments. I found that holes were too.small.and tabs were too big when I put my calipers on them.
0.4mm isnt much, but 0.8 (combination of tab +0.4 plus slot -0.4) means stuff doesnt fit. (0.36, I suppose, technically.)
Defining the bit as 3.00mm to Estlcam fixed the problem perfectly. Both exterior and interior dimensions matched expectations and tab and slot joints work perfectly.
