Major problems with endmill chatter and vibration

Mostly Printed CNC - MPCNC Troubleshooting
1

Hey guys!

My MPCNC is unfortunately suffering some major endmill chatter. The endmill chatters hard during cuts, is clearly bouncing around, and I am pretty sure it is due to an excess of machine flex. Here are my specs:

Build Size: 460mm X, 980 Y.
Conduit Size: 3/4 ID (0.922 OD) Conduit.
Spindle: DWP611

I have tried the following:

  1. Belts are tight
  2. All bearings are making good contact with their tubes
  3. Noticed some cracks in the Top_Corner pieces, so I printed new ones and made sure they were snugged down
  4. No obvious jiggling or looseness in any of the parts contacting the metal.
  5. Motor mount has no looseness, seems to be held sturdily in place.

Alas, I am getting some major chatter. The chatter seems to vibrate through the mount and throughout the X and Y gantry tubes. On further inspection, I seem to be getting quite a bit of flex in my Y axis center tube (960mm length). It is fairly easy to flex and I believe this may be causing the chattering, or at least allowing it to happen.

I am in Canada and am using Columbia EMT, I believe its one of the only brands that are sold (every major chain does just that kind.) Does EMT vary from bar to bar in terms of stiffness or rigidity? Am I screwed? Is there anything else I can look for to solve this problem?

Thanks

Paul

2

Is that build volume or footprint, and z length? Either way the y axis is pretty long, you would benefit from some mid span supports.

Speed you are using and depth of cut, bit type, material you are cutting.

3

That is footprint, so the dimensions of the y tubes are 980mm long, and x tubes are 460mm.

I’m using a 700mm speed with a 2.5mm depth cutting simple plywood. I’ve tried various spindle speeds and feedrates lower than that, and still get the vibration.

My next step I think is to shorten the thing into a square and see how that works.

Paul

4

Smaller is better. but mid span supports might fix the issue. Plywood is about the worst material to test with it is all over the place because of the glue layers. Try pine its cheap and soft.

How long is the z axis and what kind of bit?

5

Ok, I tried some makeshift supports on the longer y axis… although it made it noticeably stiffer, I’m still getting no improvement.

I have tried MDF, and it seems to fit fine, until it gets too deep in the cut, and then chatters.

I’m going to try shortening it into a box shape today, let’s see if that yields any improvement.

Is stainless steel rod much stiffer?

6

Stainless is stiff but also a different size.

What bit are you using?

7

Hey Paul, did you ever get this fixed. I am having the same problem.

Stuart

8

He upgraded to 1" stainless and brought the size of his mpcnc down to the recommended size.

9

Thanks Barry