Cutting smooth curves

[johnny_s]

Okay, I have been cutting curves and radiuses for a while now. I notice problems when I cut plastics, but usually follow up with a clean up cut at very slow IPS. This is getting old.

I was cutting a rectangular table top with 3" radiused corners in solid surface material. First of all, PW is really, really bad for this, it broke up the corners and cut them first at 8 passes each, inluding the retracts


Then it did each edge, in the same dumb manner - I should have just made my own path.

Back to my problem. The curves where cut very jagged at 1.5 ips, and 3.5 ips - at both .01 and .3 circle resolution. Does the cicle resolution make any difference? Is there a secret, or do I just have to suffer with clean up passes at .5 or.2 or some other turtle pace?

Might be that I have a PRT 120, and it bounces some, but it's only amplifying the movements that the bot is producing. How to get rid of the jumpy stepping?

Thanks.

[Brady Watson]

John,
You should not be cutting at 3.5IPS on your PRT. That's part of the problem, although several things could be the culprit.

1st of all, definately slow down the speed of your X&Y. Make 1.5 IPS your upper speed limit and adjust RPM accordingly. I often cut plex at 10000 and 1.5 to 1.9 IPS with the Colombo. I toolpath in PW, and never have any problems with my edges not being perfect. If you are running a PRT at 3.5IPS I'd put money on it that you are losing steps. This is particularly critical when cutting arcs. Solid surface cuts like butter. I have cut it between 1.5 and 2 IPS with no problems in a single pass on my PRT. You should be able to do the same. I tend to run things slow...and as a result have a low mortality rate.

I wouldn't be so quick to fault PartWizard. One area you want to check is the tolerance value on the toolpath page. Set it to follow the vectors at the finest amount possible, .0001". I have had issues with this setting doing things like you are experiencing. When you say, "Circle resolution" in your post, what are your referring to exactly? What program & where ?

Another issue may be the vectors themselves. If they were generated strictly in PW, then you should be fine. If you imported a DXF, AI or EPS, then you may have some nodes out of place, causing the jaggedness...

Hope that helps,
-Brady

[gerald_d]

Does PW2 still break up circles into separate segments?

[johnny_s]

Brady-
You cut plex with curves and no problem with edge quality?

I don't fault PW for quality, but for it choosing to create 4 or 8 times the retracts or move/jog routines than it needs to on a simple reqtangle with radiused corners - LOL!

Regarding the "circle resolution", I am going off memory, as I type this stuff from home and don't have the control software in front of me. I will make note of that or post that information when I get to the shop - but it is in the control software, not PW.

It is a DXF import. But you should be able to see the nodes in PW, yes? On the radiused corners, it has only the end and middle node, which I think is what PW would create itself. I see the tolerance option now, I am sure that will help as it is set to .01 by default.

I ended up cutting at .8 ips, but I bet adjusting the tolerance would have allowed me to cut faster.

Thanks

[johnny_s]

I don't think I would upgrade to PW2 since I use Rhino.

[Brady Watson]

John,
Reset the control software back to the default settings for arc tolerance. I have never had a problem with the standard settings. Also, do your outside profile passes in Conventional, and inside ones in Climb.

When you import your DXF, a message box pops up asking you if you want it centered in the page, and what the tolerance should be. Make sure that is also set that the default .0004" in both boxes. Yes, you can see the nodes in PW when you select an imported DXF.

Another tip...the output files are harder to read than the standard ShopBot_Inch post procesor, but you can download the ArtCAM arcs_Inch postp (on the SB downloads page) and put it in the PartWizard PostP folder. You will then be able to select this post when saving your toolpath in PW. I noticed less glitches and smoother circle cutting than with the standard post because it uses arcs to move around a circle instead of small straight lines.

Hope this helps,
-Brady

[richards]

Brady,

I'm curious about your recommendation to cut outside profiles using conventional mode and inside ones using climb mode.

If I've watched my Shopbot correctly, it seems that using conventional mode moves counter-clockwise on an outside profile and clockwise on an inside profile, or in other words, it cuts the same way most cuts using a handheld router are made, while the climb cut is just the opposite. Normally I route most cuts using the conventional mode, reserving the climb cut mode for extremely light finishing type passes or as a last resort when cutting lumber that has excessive tear-out. Am I missing something that would improve the quality of the pieces that I cut?

Mike

[Brady Watson]

Yes...Using that formula will definately smooth out the cuts. It's sometimes hard to get your brain around which way to go. Doing Conventional on the outside and Climb on the inside, the remaining stock has the toolmarks on it and the finished pieces are nice and smooth, in my experience. A fellow botter told me to do this from day 1, and it has worked well for me.

Don't take my word on it. Try that method out in a few srcap pieces. I'm sure you will see a difference. Try both wood and plastic.

-Brady