Cutting curves... slightly rough cuts

[kenakabrowncom]

I have seen a problem for some time where we notice that along curves the cuts appear to be very slightly rough. Almost what i would call chatter. We are getting tired of sanding so thought it's time I figure this out...

I have a BT48 Alpha Buddy with spindle

For cutting in this example I am using Centurion end mill straight flutes 1/2 x 3

We cut a variety of hardwoods... none seem to be any better than others.

I typically cut 1.5 ips with speed at 14k on my spindle. I have slowed down both of the speeds and saw no change. I also tried speeding up the feed rate and saw no change.

Is what I am seeing considered "normal"?

Again I only see this when the machine is cutting curves... when cutting on X or Y the cut is smooth as glass.

Any thoughts???

Ken

[myxpykalix]

check your postprocessor that you are saving the files with. You need to save your files with the "shopbot_arc_inch" postprocessor.
Just a guess

[gene]

Does the cut on the waste side apear smoother? Maybe try cutting in the other direction and see if it helps.

[kenakabrowncom]

Jack - I failed to mention that I am using PartWorks to create the files.

Gene - Thanks for that suggestion. Actually I did look at the scraps and they look about the same but cutting in the other direction is something that I should try.

[carlcnc]

Ken
I have had the same issue, in my case it was mechanical, when your machine is powered up and at idle try to shake the X or Y axis carriage, you will probably find one of them will "rock" ever so slightly, if yuo can feel it or see the pinion rotate even a tiny amount this can translate to several thousandths of "bounce" when cutting arcs and angles.
see if you can get a bit more pressure on the pinion .
check the set screw on the pinion. even a few thousandths difference in the key and the key"slot" will eventually allow it to get loose,
good luck
Carl

[kenakabrowncom]

Thanks Carl! You may be on to something...

I tried going the other direction with the cut and that did not change.

I also did a first cut like I always do going .20 on each pass then followed that cut with a final cut of 1/32" ... same results. I am still getting a bit of 'chatter' on the edges.

I will look at movement tonight.

Ken

[sailfl]

Ken,

I would suggest creating a diamond that sits on its point. This way you are cutting on the diagonal. If you have some solid surface material it will help show the problem more. Wood is soft and forgiving. Maybe a hard wood would work.

Carl's suggestion about the pinions is an excellent place to start. I think you will find you have a mechanical problem.

[kenakabrowncom]

I am not sure i follow your suggestion Nils...

I did followup on Carls suggestion and I found no movement on X or Y and also found no unusual play with the Z either...

Back to square one...

Ken

[Gary Campbell]

Ken...
Take a look at the chatter along the curved edge. Does it appear slightly scalloped? Does the spacing of those scallops come very close to the spacing of the teeth on your rack gear? IF so this is a pinion, rack adjustment or replacement issue.

Until I replaced my pinions, and even tho I could not find a difference with a mic for wear in the old vs. new, the chatter described above dissappeared after the pinion gear changeout.
Gary

[gerryv]

Gary,

Just out of interest, could it then have been the keyway(s) being a bit worn?

[Gary Campbell]

Gerald...
I suppose that it could have been, but in my case, the key was nice and snug with no indication that there had been movement. And since my problem dissappeared with the pinion replacement, I assumed that they were the problem. My machine was almost 2 years old with a fair amount of cutting on it.
Gary

[kenakabrowncom]

Thanks guys... will take a look later today... Sounds like I may need to talk to tech support on this one as my Buddy is barely a year old ....

[bam_bam]

Ken,
I am fairly new to the forum since it has been several years since we had a shopbot. (sold our old one). But to your problem, I was at a friends shop yesterday and I have partwizard at my shop, but I used to have Artcam pro and I tried it( in Artcam pro) just to see if they had changed it or not, but to the point. Have you tried to have someone create a circle file for you (in say Artcam pro) I looked at my partwizard circles and remembered that they look rough, in Artcam you can create circles with all belizer curves and also smooth the points. But I don't see the ability in partworks or partwizard. It maybe a long shot but worth a try, I know it made a BIG difference in the smoothness of the cut of a circle on our old prt alpha.
Just my 2 cents

[khalid]

I am very less experienced among you all but I will suggest two things :

1- Check the stiffness of your Z-axis, Hold it with hand at bottom side of the spindle and shake it...see if you find any movement....

2- Check your spindle is tightly held in place. If its loose it will create chatters.

3- Check the slides, if you can find any dirt, scratches..see also the roller elements for pitting scratches etc..

4- Check the gears especially the pinion for any backlash..

5- I have had same problem, and i saw some loose bolts, especially on Smaller axis (X or Y whichever is smaller, or on which the Z-rides)...I tightened those bolts and now getting perfect...

6- If you can increase the resolution with the help of microstepping you will get fine results..
AND
AND
from software side:

1- Just check the curves are smooth.. If they are made up of tiny nodes then you will always find the chatters.. You can spline the vectors and shorten the nodes with improving the quality of Vectors...

2- Check the Allowances in toolpath are small..


Do you need more checklist options?

[khalid]

OOoops..the two things become 8..sorry