CNC Router Chatter

[squibble]

Part #1
I recently did a job in a black granite called Oskuromis and found CNC chatter along the edges through out most of the job. Would this be because my machine operator is not putting his pods close enough to the front edge/ close enough together? Am I having a spindle/bearing issue? Is it tis stone more sensitive?

Part #2
I need to polish these out in the home owners house as I am not happy with the finish. There is about 300" of edge. Can this chatter be polished out dry with a rigid backer pad? Does anyone know of a dry rigid turbo I could use? I really do not want to break the seams and remove tops tops for re machining? The 300" length is set up tight between walls on all sides. I may have 1/16" play.

Let me know your thoughts

[Antonio Almonte]

Could you please fill in your signature so that we know who we are talking to. That would be great as it is customary here. Thank you.

1) First let me say that I am a cnc newbie and I do not run the machine. Could the chatter also be that the tooling is not dressed and is glazed? If it is the spindle, is it happening on all the jobs that were processed after that particular job? I cannot see it being the pods being too far out. But, I could very well be wrong on this.

2) Depending on how bad the chatter marks are or if the edge is wavy, it could be a time consuming thing to do on site. I would probably pull it and redo at the shop even though doing that is a pain as well.
If you were to do it on site, I would use a carbide stone (be sure to wear a mask and warn the customers about the dust and try to control the dust. Using the stone WILL make alot of dust) to get it flat and finish with polising pads wet. This is why I would pull out the stone and do it at the shop. I do not know of any dry rigid turbo style pads out there.

Good luck.

[jbergman]

It's difficult to diagnose problems without actually being there, but there are some things to keep in mind. First of all black materials are the most difficult to polish. Slab polishers run at about 30-40% of the speed as compared to just about anything else. It is like a having a black car, everything shows up, especially chatter and waviness. If the spindle bearings are shot, you should be able to hear it - a high pitch whine. How far were the pods from the edge? I would think that if they were within an inch or two, that should be OK. Maybe a little closer for 2 CM material.

What shape are your tools in? Are the diamonds in good condition or a little rough and what are you using for polishing? Vertical edges are far and away the most difficult. How much material are you figuring to remove with each tool and how much is being left for polishing, and are you sure you are actually getting that? There are many CNC's, especially older machines that have no accurate way to compensate for tool wear. It becomes a SWAG, scientific wild ass guess.

Honestly I tell customers that our machines, if properly run with good tooling including polishers, should be able to produce more than acceptable edges in every material except absolute black or similar. For that I suggest a final hand polish or buff. With intricate shapes a lot can be hidden, but not with vertical edges.

Hope this is of some help,

John Bergman
Bergman-Blair Machine Corp
11895 North Lonely Trail
Prescott, AZ 86305
928-443-1100
516-381-6774 cell

[ChrisYaughn]

What edge profile? That is a major variable on a number of fronts.

[clhilde]

could be loose pull studs, y or x axis drives, loose bolt on cones . bearings on the y and x liner rails.

Do a circle and see which side the chatter is on then look at the bearings in that direction.

If it was the spindle you would know it when the finger bit runs hard.


Damn where did I learn all this

[GbD]

My guy says the same as stated above. It can happen on hard granites, and slowing the machine down will help a lot.

Easier to fix it at your shop, then on site. Now that you know about it, check them before they ship.

we go back and forth between doing final polish by hand vs using the cnc to do it all. There is a significant time savings (on the cnc) by doing this. The only thing we run to final polish ios FBN. Everything else we just run the metals.