Chattering on arcs why?

[Gundawg]

I machine plastic and aluminum why are all the circles arcs etc always chatter looking? The chatter look varies in intensity but they are never smooth. I have had this with 2 different routers. the funny thing is they always seem to happen on external arcs or maybe they are just more obvious the internal arcs seem smooth meaning when I do an inside profile as opposed to an outside profile. I am using a custom PP but I have used other PP with the same result. I am currently running a Shop Sabre with Wincnc but I have ran a ShopBot with the same results.

Mike

[ohiolyons]

Millions of possible issues

1 you are going too fast for the material you are cutting

2 dull bits

3 if it is occurring on arcs and circles only it is the vector and a million nodes. Go into node editing and see if there is a million little black squares. each one is a node, 2 define a line. All depending on how your arc vector was created it could have lots of these little straight lines. Try EDIT, Curve Fit Vectors to clean up your arcs and circles. Select Bezier curves if at all practical.

[IslaWW]

Mike...
Since your brand of machine uses WinCNC control I can offer the following:

Assuming the file was designed with Vectric software and you are using the post I gave you with 6 decimal output there are usually 2 reasons:
Backlash or flex in the machine (use a dial indicator with 30+ pounds of pull to measure)
Machine settings

Dose the machine seem to make velocity changes or variations during the arcs? That would point to settings, if not backlash

[Gundawg]

If backlash or flex was the issue wouldn't it show up in the inside profiles as well?

[Adrian]

All depends on the loading. I had a delay replacing the pinion gears on my ShopBot recently due to thinking I had some in stock. The chattering on the outside curves was really bad due to the play in the gears but barely noticeable on the inside.

[Gundawg]

Millions of possible issues

1 you are going too fast for the material you are cutting No

2 dull bits No

3 if it is occurring on arcs and circles only it is the vector and a million nodes. Go into node editing and see if there is a million little black squares. each one is a node, 2 define a line. All depending on how your arc vector was created it could have lots of these little straight lines. Try EDIT, Curve Fit Vectors to clean up your arcs and circles. Select Bezier curves if at all practical.

No on the multiple nodes. Most of the arcs are either fillets or portions of circles.

Gary

When I was on the phone with Tech support they did adjust the ramp rates and it has gotten a little better.

[Gundawg]

Here is an example I get the same results on many different parts. The inside profile is cleaner than the outside profile both cut with the same bit and same feed and speed. ( I am having problems adding the pictures I will try again in a few minutes)

Knife holder top.crv3d

(28.5 KiB) Downloaded 117 times

[Gundawg]

Here are the pictures I am not sure you can see what I am talking about.

[IslaWW]

Mike..
The inner cuts may be cleaner due to the reduction in hold down as the perimeter is being cut. How are they being held?

[adze_cnc]

The inner cuts may be cleaner due to the bit erasing evidence of chatter as it goes around the corner.

[Gundawg]

All the plastic I cut is held by vacuum on my shop built vacuum system. These parts are rather small but even the larger pieces I cut show this same chatter on corner fillets, I make 40" x 16" fillet tables that show the same chatter on the corner radius fillets and have inside profile pliers slots that look great. I had similar results when cutting with my old Shop Bot. The finish is acceptable but it has always made me wonder why the outside radius cuts were never as nice as the inside cuts?

Mike