Hole diameter issues

Hey everyone I am having some issues with holes coming out too small, specifically in aluminum but I will be trying them to plastic today as well.

For example if I model a 8.1mm diameter hole, the hole comes out to 7.8mm. If I model a 13.1mm hole the hole comes out to 13.7. I am measuring with a caliper so not the most accurate measurement in the world but more importantly the rod I want to put in the hole does not fit.

I am generating the g-code from Fusion 360 and I have tried a variety speeds and feeds as well as tool paths and they all result in the same deviation.

The machine is accurate in all the other operations I have tried (slots are the correct length, machining a 6" long stock to 5.9" comes out 5.905" etc)

Any ideas of other settings I could try?


Did you measure your tool diameter? Lower priced tools will never be the size stated on the package. Whiteside is notorious for this. Harvey is better but still measure.

1 Like

What feeds & speeds are you using? Helical boring requires much lower feeds, possibly down to 10 ipm. This is because the outer edge travels much faster than the path of the bit’s center.

Beyond that, cut a few holes and see which one fits.


That is true in metal. I see that all the time with woodies getting in trouble using metal rules and then blaming the max acceleration for their bad results.

In wood, the helical and ramps should all the the same feed rate as the cut.

:rofl: At least that works on my magical machine!

I am an old metal guy. I am new(ish) to wood. Wood is all about keeping the feed constant. Especially in our lovely monster sized machines with aluminum extrusion frames.

The less feed changes the more consistent the surface quality.

If you spiral real slow into the wood and then start yanking around, that isn’t max acceleration. Your lead in and out are too slow.

Remember, Fusion is by default thinking metal. Never worked with that vcarve thing…


Holey Moley - I’ve had the same problem using VCarve Pro in wood. I measured tool diameter, checked feeds + speeds (including trying a very conservative 10 ipm feed rate for the helix), re-leveled and re-trammed, all to no avail. The X and Y dimensions of the holes were always equal, just slightly too small. Ended up scaling the holes in VCarve to make up for it, and have done this on several projects. Never got to the bottom of the issue, so if you do, please post what you learned. The fact that you’re using F360 whereas I am using Vectric suggests the problem is not in the CAD program – perhaps in the GCode generation.

Wow you guys/gals are legends!!!

The winner is @subnoize :laughing: :wave:

I was using a Kyocera 1/8" single flute to cut my smaller holes and given that is was Kyocera from Japan I found it odd the it was measured in imperial. I measured the tool and yep really 2.7mm or .106299" not the .125 speced on the Kyocera website. Plugged in the correct number and boom, perfect circles to spec (give or take .001") and the pins slide right in. I did 2 different sizes 6.7mm and 13.4mm

To double check I just got a 3mm Kyocera end mill, it measured to 2.99 so I left it at 3mm given I have a no name caliper and yep, perfect circles both small and larger diameter.

So @robs6 measure the diameter of your tool and see if that is the issue, it seems to have been my issue.

1 Like

If you don’t mind, @Bill mark mine as the solution above so I can get some brownie points :wink:


Hi, Bill - the endmill is a Whiteside .5" diam. compression spiral (UD5152). I just measured its diam. with my Mitsutoyo 500-196-30 AOS digital caliper, which is spec’d to be accurate to within +/-.001". It measured .5010", though admittedly, such measurements are really tricky to get right. However, the holes I was milling were more than .01" too small to accommodate any of my 3/4" brass and plastic dogs - so while those dogs could have been overfed, so to speak, the endmill seems unlikely to be the problem. When I milled the holes to .76", the dogs could be pressed in, but it was still a very tight fit. So maybe the undersized endmill theory is barking up the wrong tree.

I use a drill press to measure the diameter of the cutter. Just chuck up the endmill, lock the quill or raise the table. Place a caliper on the table rotate the cutter and that’s all there is to it. I typically do this 3 times per cutter and have had reliable measurements. Sure beats trying to hold the cutter and caliper at the same time :wink:

After struggling for 30 minutes I finally slid mine into a collet and measured it that way. By hand was driving me nuts!!! :laughing:

1 Like

Done brownie point for you!

Thanks, Bill. Great idea - I’ll give that a try!

Thanks, John, always good to learn from someone else’s experience. I’m cutting pretty much only wood, so this is helpful.


This sounds like maybe it’s a simple tolerances issue. For joinery, I’ve used wear offsets to get a good fit, though I haven’t done that with holes.