Problem with tabs

[awalt1250]

I am having problems with anomalies being introduced near my tabs. I'm not sure what to call them...maybe divots? This problem only happens near a tab. The problem area is the same general diameter as the bit.

See the attached pictures. I'm running a shopbot desktop with vcarve pro, cutting 1/2" baltic birch using a 1/4" upcut spiral. This is the first time I've seen this happen. Total time on the machine is maybe 10 running hours.

Any help or suggestions would be appreciated.

[Bob Eustace]

Andy I dont think its anything to do with tabs. Try converting your part to "bezier" and you should get a smooth job.

[myxpykalix]

go into node editing, click on your vectors and then see if they are smooth or come to sharp points. If so do like Bob says and turn them into bezier curves.

[awalt1250]

The shapes are bezier curves already..not seeing any sharp points that large on them. Would small points get magnified?

I'm going to try 3d tabs, increase the number of passes from two to three, and slow down the feed rate to reduce the load on the mill.

[Bob Eustace]

Try a downcut Andy as your problem could be the job moving slightly. You could post a pic of your hold down set up and tell us the feed rate and depth of cut. 3D tabs are generally the norm as they don't slow the machine down. The Desktop is the most accurate machine in the range according to the experts here.

[srwtlc]

Bit deflection/recovery as the machine slows to make the tab and then takes off again. Try the 3d tabs and see if it's better. Stop the cut after the first pass, before it makes the tab pass and see if it's present then.

[myxpykalix]

you might also get some scrap material and redo your toolpaths and eliminate the tabs and rerun the toolpaths in scrap to see if you get the same results. If you do then you know the tabs are not the problem.

Or you could relocate your tabs and rerun the file on scrap to see if it does it also in the same location relative to the tabs to confirm it.

[steve_g]

I agree with Scott... what speed and DOC are you using?

SG

[myxpykalix]

I respectfully disagree with Scott. I can't imagine that the bit deflects to that degree, that would make the same issues at each slowdown/speedup location.
Plus i can't imagine that the machine can speed up and have to slow down in such a small space.

I still think it is a vector issue. Have you checked to see if you have any duplicate vectors hiding anywhere?

One way to check this is to do like i suggested about redoing the file and changing tab location and seeing if that problem follows to the new location.

This isn't the first time i've been right (OR WRONG!)

[steve_g]

Jack...
It’s all just speculation! Here’s how I see it happening:
Spiral tool path at a high chipload factor. Bit is deflecting and any machine slop is all preloaded in one direction. Machine stops to negotiate first tab and all preload and deflection is relaxed. Continuing on after first tab and does not develop chipload of pre tab cutting because remaining cut is shallow and likely does not reestablish full speed due to ramping at remaining tabs...

Now, I could just as easily make a case for another point of view! I went with this one because I ASSUMED that this was a vector that had been cut previously successfully without tabs.

SG