Tabbing

[simon]

Yesterday I was cutting some small parts out of ABS. The tabbing was on, and the machine was purring away. Suddenly the bit simply took off on a different path, ruining some parts, thankfully not breaking the bit. It swung back to the intended path and continued on its way. I couldnt repeat it, or find anything wrong in the file. I think it must be a tabbing glitch.
Has this happened to anyone else and how did you resolve it? Machine is PRT 96. Software is .14

[btk]

Simon,

Check that your machine is properly grounded (including dust collection and router).
Check for electrical interference (perhaps a USB device).
I had a lose ground a while back and had some very strange sporadic behavior (similiar to what you experienced) with no real rhyme or reason. Grounding everything solved that.

Brian

[simon]

Brian
As it happens the machine is not too well grounded at all. Only the earth wire on the 3-pin plugs you get here in NZ, connected seperately to the router, dust collector and table. I have been meaning to install proper buried "lightning rod dissipator" type of grounding but never got round to it, mostly because I never really had a problem I could trace to this before.
Now I shall do it properly.

Simon.

[gerald_d]

Simon, the earth pin on a 3-pin plug is an adequate earth. That pin, if properly connected by the people who constructed your building, goes to a buried earth. There is no need for a second buried earth - it could actually make more problems with "earth loops".

[simon]

Okay
if it aint the earth, any other suggestions? Does everyone else's tabbing behave itself?
Simon.

[gerald_d]

Here (http://www.mechmate.com/Forum/messages/18/343.html?1134240348) is some of what we mean by "grounding everything". From the yellow lug in the last photo a wire goes to the metal frame of the static table, and from there to the screw on the back of the control box.
In addition to that, we have a ground wire from the nose of the router (alu. casing) to the z-slide.

If your cutter returned to the original path, I don't think it is a grounding issue. Something may have jammed a roller/rail and lifted a carriage without the gear actually losing contact with the rack. That is the only way it can return to a true path by itself.

[srwtlc]

Simon, is the problem repeatable? Is there a "CG" curve in the part file just before the tab? I've had tabbing go awry and the machine start wandering when there were CG's before and after a tab. I stopped using the tab command a long time ago and just draw them in where I want them.

Also, try updating to the latest software.

[gerald_d]

Yes Scott, that also reminds me of the tabs not liking arcs, but I heard that the tab/arc problem was fixed? We also stopped using the SB tabs a long time ago. Simon, I presume you work in metric down there? If so, you must realise that the metric versions of the software are not tested/debugged as well as the inch versions.

[simon]

Yes indeed, Scott and Gerald. The tabs that fail fall on arcs.
I have done a lot of trials in the last day and find sometimes the Z returns only slowly to the bottom after a tab on a curve, and sometimes the xy wanders and then comes back. Again after a curve. Yes I work in metric. Maybe I will have to learn inches for this stuff.
I have downloaded the latest version and this has so far done the Z thing but not the XY thing. I think it is a matter of time though.
I quit using vector a while ago because of other issues I couldnt solve, and dont know how to put in tabs in PW. I dont really need any fancy 3d software, as I keep things simple with Illustrator - PW - SB.
This is a pain because I have a new client that will want lots of small pieces cut out and edge rounded, so tabbing would be ideal for these jobs if I could trust it.

[srwtlc]

Simon, I know that there has been some discussion here on how to do tabs in PW (I don't use PW so I can't help you there), but you could revisit Vector and place the tabs where you want them by cutting and pasting the segment of the toolpath that you want to be the tab to a slightly higher Z position (0.1"/2.54mm maybe) and then connect that segment with "Line/Connect" completing the toolpath. If you want, I could take a look at it for you.

If you want to see something really weird, try using the "TAB" layer to do tabs in Vector when curves/arcs are involed! The machine will get totally lost! I don't wonder if the Vector "Tab" layer problem and the ShopBot tab command problem aren't somewhat related. The Vector related tab is done with this...

SR
M3,0,0,0.1
M3,whatever or CG,whatever (With a CG is when things start to wander)
M3,0,0,-0.1
SA

Maybe somewhere internal, the Shopbot tab does something the same. Maybe someone else can address that.


Scott

[gerald_d]

SheetCAM (http://www.sheetcam.com/) does tabs effortlessly - just point to the spot where you want the tab and give one click. You add tabs at clicking speed!

[evan]

I’ll second the SheetCAM endorsement. It’s a great 2-1/2 D CAM program, especially for the price and Les Newell is constantly updating and improving it (updates are free for a year.) He’s also very helpful and accessible.