wobble while drilling

I’m pretty sure I know what’s happening here, but in case there is a simple fix I haven’t thought of, I thought I should post it here.

I’m cutting 1/4" MDF, 1/8" downcut bit, and I have the old version of the MPCNC. When drilling the holes, 1/25 or so has gone crazy, after cutting most of the way through, and ends up wobbling and making a big hole. I’m using EstlCAM, and it’s cutting 1mm deep, then backing all the way up, until it reaches the full 6mm depth.

So my thoughts were:

  • Downcut bit for drilling is not great. I have an upcut bit, but I really like the contours the downcut bit makes. So maybe a bit change?
  • I thought it was maybe a dull bit, but I switched to a brand new one, and it failed on about the 6th hole. Then finished another 20 with no issues.
  • The 525 version is more rigid, so maybe I should just bite the bullet and update my MPCNC, maybe take the chance to switch to stainless 1" tubes while I’m at it. I’m trying to hold off until I finish this MP3DP.
  • The bit isn’t perfectly perpendicular to the board, so as it goes deeper, it’s getting slightly jammed against the side. The DW660 mount is another thing that I’m trying to just kick the can a little further until I update to 525.

So my conclusion is, this MDF is cheap, just cut it again, and if I really want to ensure success, either do a tool change, or just do 2mm deep drill holes, and finish with the drill press. Anyone have any other thoughts on what I could be doing wrong?

Downcut bits should never be used to drill holes. You can actually start a fire doing that. Think about it. They push the cut chips down through what you’re cutting. If you’re cutting a slot, it’s not a big deal as the chips get thrown out the slot. If you’re just drilling a hole they get compressed into the bottom of the hole. You’d get the same result by chucking a wooden dowel into your router. You can use them if you do a spiral hole cut, but the bit needs to be smaller than the hole.

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Hmm, I get the same problem right now.

I´m cutting coated plywood 12mm with a 3mm normal 2 flute. I milled a hole set of plates and all went well but recently I got the same problem as Jeffeb3.

On the 3rd or 5th hole the flute starts vibrating into a circle. I made a complete check of the MPCNC and it helped to reduce the diamter of the vibrated hole but it still happens after 4 drill operations. Trid different bits and settings, moved my buildplate up but no success.

Does anyone have an idea?

I have better luck with larger holes. Anything in the 1/8" size, I just drill too 2mm and then I use my drill press to finish.

If you wanted to drill 1/8" holes, you could do it with a 1/16" bit. Hopefully, someone else can come in with more help.

The problem is the router isn’t perfectly perpendicular to the work. As you get deeper more of the bit touches the sides. Eventually you end up with more force than the mount can handle and the whole assembly moves, which makes it worse.

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Yeah, that’s a good point. Print one of these and see if you can fix it:

My MPCNC was pre-525, and it wasn’t perpendicular when I cut my MP3DP, which is where this thread started.


[blockquote]Yeah, that’s a good point. Print one of these and see if you can fix it:[/blockquote]

Will try that.

The strange thing is that I succcesfully drilled around 50 holes with the same setup and material.

Investigating :slight_smile:

Ok, I think I found it. Perpendicular was the magic word. I added a stabilization ring on the spindle during some milling and the screws underneath it that hold the tool mount against the conduit introduces some offset in my axis. The ring from my mpounting set is ok but I should have payed attention to the screws offsetting it.

Thanks! I hope that does the trick.

Finally solved that problem.

It was the classic chips get compressed in the borehole problem. Works well well with a additional ,5mm helical movement for clearance. :slight_smile: