Holes?

[IDBD]

Hi all,

I need help please.
I'm trying to cut a hole for a bearing to go in wood.
The bearing is 55/64
I'm using a 1/16 tapered ball nose bit.
The problem is hole is still being cut too big even when I tell it to cut on the inside.
What am I doing wrong?

[Gary Campbell]

Why are you using a tapered bit? Tapered bits cut larger, the deeper they go
You would get a more accurate hole with a straight 1/4" bit

[sharkcutup]

If the bearing you are trying to install into wood has tapered walls yes a tapered ball nose bit would work provided the taper is close or the same as the bearings taper otherwise you would want to use a straight bit (end mill).

You must be that guy who is still trying to figure out how to fit square pegs into round holes!

Have a GREAT DAY!!!

Be SAFE around those AWESOME machines!!!

Sharkcutup

[cjablonski]

Potentially another work around I use frequently is to "spot" the holes using the cnc ( drilling in a small area centered where you want it) and drilling the correct hole size using a drill press. I haven't had much luck using my CNC to drill holes that are actually circular due to flex in the gantry and play in the lead screws, so I tend to default to the method mentioned here. Good luck with whatever way you choose to tackle it

[Kayvon]

Cjablonski uses the drill press method because he's a clockmaker. On clocks, those holes often need to be extremely precise, which is when I use that method as well. Other times, the precision of the CNC machine is sufficient.

[Rando]

I work more in Aluminum than wood these days, on the Shark. Which means I tap the holes. The nice thing about the CNC is that it's possible to get a hole 0.220" or 0.223" if that's how much thread-engagement I want. If it's a truly critical hole diameter, I'll leave a margin of 0.005" or so and add a finishing pass to take off that last little bit. That may help with the out-of-round issues, at least somewhat. I'll admit it's a challenge getting accurate **small** hole sizes. Another way to get dimensionally accurate hole cuts is to do some tests, and figure out exactly how "wrong" the results are from what's programmed, then offset the wall by that margin in both the rough and finish cuts. That way the results match the design, and only the toolpath knows for sure.

That, and yes, using a normal (non-tapered) endmill for bearing pockets.

I prefer radiused endmills for my work, since the rounded tips are much stronger and don't break nearly as often. Useful for working in metal; not so much in woods. Typical sizes are 1/4"D with an 0.030" tip radius, or an 1/8"D with an 0.015" or 0.020" radius. The other thing it does it make nice smooth transitions at the bottoms of pockets, but I digress...

Regards,

Thom

[IDBD]

Thank you everyone.
It was a bit issue.
Used a 1/4" ball nose bit and sent the correct decimal for the mm size and it cut great.
I also order me a forester drill bit at the correct mm.

Thank you all again.