Small Circles Not Round

[Paint Chip]

I'm having trouble getting small circular cuts (<3-4 inches dia. ) to come out round. Larger circular cuts (>6 inches dia.) and square parts (even small ones) all look fine. I've tried slowing down the speed while cutting circles to 60% using a cut path rule but it doesn't seem to help. The shapes I get are repeatable, i.e., If I have duplicate parts, they all have the same irregular shape. Do I have my acceleration set too high in my motor calibrations? Is this something that comes from Sheetcam? The shapes look fine during creation of the cut file. Or is there something else I'm missing?

[tnbndr]

Have you already read through this:
http://plasmaspider.com/viewtopic.php?f=89&t=11768

[urbnsr]

How thick of material are you cutting when this occurs?

[Paint Chip]

I did see the Jim Colt write up previously. I checked all the set screws, did not find any loose. I also confirmed I am hitting the pierce and cut heights. I'm cutting 1/8" with a 45 amp nozzle at 190 in/min with a cut height of 0.06 in. I used a 60% speed cut path rule on the circle cuts and I am running with the DTHC off. I think I am satisfying pretty much everything on his list. My issue is small circular cuts are way out of round - but in a repeatable way. If it was loose components I wouldn't think multiple parts would be exactly the same. I'll try and post a picture this afternoon of a couple pieces I cut.

[Paint Chip]

Here is a picture of two parts (one is a sheetcam duplicate of the other).



You can see how out of round the circles are - they are 2.125" dia. The lead ins were on the straight part. If you lay one piece over the other they are identical.

[RAD]

I had similar problems, the cause was a loose set screw that was causing massive backlash. 90% of the time its mechanical related when circles are not round, do a thorough check on your mechanics!.

Also make sure your x axis is squared to the y axis, that also helped me. Another thing is larger holes may seem more round than small holes but they are still out of round just harder to see.

[Paint Chip]

Ok, thanks. I'll give it a thorough go over again. I guess now is a good time to loctite all the set screws.

[RAD]

do a research and be sure to use the right locktight tho otherwise you'll have to apply alot of heat to remove it if ever you need to.

[Paint Chip]

Green loctite was recommended by Ron at PPLLC so that is what I'm using.

[acourtjester]

Loctite is not the only answer I always make a flat place on any shaft for the setscrew to land. The motor shafts are hard and setscrews seem to slip more often, a flat give you an extra advantage.

[steel 35]

I would try the 10G settings that are 95-100 IPM, Fine cut is also 95?

[Paint Chip]

Well, I guess I need to find a crow.dxf so I can cut it and eat it. A couple of the set screws on the drives had come loose. I just checked these last week too. I loktited them this time. If that doesn't hold then I guess I'm going to have to try to get some flats ground on them or maybe drill some dents and use pointed set screws. Thanks for the input folks.

[BAR M]

Two more cents. Instead of Locktite, I use 2 set screws, one atop the other,

[Paint Chip]

Good idea. I've done that with nuts on bolts but never thought of doing it with set screws.

[ovrrdrive]

When I bought my kit from PPLLC they sent red locktite and instructed to put it on the shafts and the screws.

I haven't had any slippage yet. Is a little bit of a pain if you need to adjust a pulley though.

[Paint Chip]

I think if I see slippage again I'm going to try and drill dimples into the shafts through the set screw holes so the set screws have something to bite into and use either green or blue locktite on the set screws. This seems like the best option for tight holding and ability to take it apart later if needed.

[tcaudle]

Drilling into a hardened shaft may prove to be challenging. Loctite makes a product (600 series) expecailly for cylindrical bonding. Its not designed to break loose under torque. Once the gear/pulley/coupler is on the shaft its there until you apply heat to break the bond. It WILL stop rotary slippage.

[Paint Chip]

Did not know the shafts were made of hardened steel. I guess the loctite compound makes more sense now. Thanks for the tip. Not looking forward disassembling the pulleys though - looks like a pain.

[Bigtakeover]

I have the same problem. Anyone find a fix?

[adbuch]

I have the same problem. Anyone find a fix?

Welcome to the forum Big! Specifically which part are you having problems with? More details and perhaps some photos would be helpful.

You might also consider creating a separate post under the heading "Introduce Yourself" and let us know a little bit more about yourself. What table/cutter are you using, what software do you like for your design work, and what particular projects are you working on?

Here is the link:
viewforum.php?f=147

Thanks,
David