Why does my shopbot do this?

[gdub]

On circular figures, rounded corners and circles it makes a lopsided "corner". Attached is an example of something I just routed, and look at the "O" the center and the outside, the bottom left is far worse than the top right of each letter. HELP!!!

http://s31.photobucket.com/albums/c395/geedub123/Work/?action=view&current=weston.jpg

[paco]

What is the material used?

What machining spec. did you used?

Can we see the toolpath start point and order of cut?

What is the hold down method?

What if you just cut out a hole or a disk?

My first guess would be toolpaths order of cut and/or start point of individual toolpath...

[dray]

I was wondering if you zoomed in on the font in what ever program you used it also had flaws in the font?

I had a similar situation in a sign I made and finally I zoomed in on the font and the flaw was in the font I used..

[wcsg]

All your characters have unique errors to them. Maybe check your gantry bearing seatings. I bet you have a lot of movement in there

[gdub]

well if i cut a circle it is very lopsided looking, very uncirclish. and rounded corner rectangles look very bad ass well, very unrounded looking. It is not the file, or the path, I have zoomed in and double triple checked the path and the toolpath. The router was in the shop when the shop was purchased, set up but never used. So when my boss purchased the shop he started using it and it has always had this problem. I will cut out a circle and post my results.

[hindocarina]

Before I bought a cnc router, I read that this problem is a characteristic of the backlash in rack and pinion systems. Ballscrews supposedly help to eliminate the problem. I would be interested in comparing your circles to those cut by other shopbot owners to see if your gearing has some slop or if it is a pervasive problem.

[gdub]

update

here are the pics I said I was going to post:

http://s31.photobucket.com/albums/c395/geedub123/Work/?action=view&current=router_test2.jpg

that is the actual cut out of PVC (sorry camera is about to be nonuseable, makes weird pictures)

and here is the artwork I used (turned .gif afterwards):

http://s31.photobucket.com/albums/c395/geedub123/Work/?action=view&current=Cut-File.gif

And here are the settings I used in the software, I made 2 different files, one for the interior cut and one for the circle, both set up the same minus cut inside vs cut outside.

Inside Shape
------------
Profile Side
Inside
Start Depth: 0
Finish Depth: .35
Allowance: 0
Tolerance: .001

Machine Safe Z
Safe Z: 2
Home Position
X:0
Y:0
Z:2

Profiling Tool
End Mill 1/4"
Stepover: .25
Stepdown: .35
Feed Rate: 30
Plunge Rate: 30
Spindle: 21000
Tool #1

Cut Direction
Climb Mill

I zoomed in on all lines after creating the cut path and everything looked fine.

[harryball]

Power up the bot and have it sit idle. Try moving the gantry, Z axis, Y car etc... you're probably going to find some slop in there. With it powered on it should not move in any direction, it should be rock solid. Even if it *seems* solid check your pinions closely make sure they are not loose. From your description the pinions should be new so they shouldn't be worn. Still, you might want to check them in case "never used" really means "I never used it usefully, just cut a few things while never greasing anything"

Robert

[gdub]

so try moving it with my hands while it's powered up? and if it moves it needs to be tightened?

[gdub]

well I shook it a bit, it's definately not very sturdy. I pushed the carriage positive on the y axis and accidentally moved it from home, didn't mean to do that, now I need to know how to reset home. Ugh. The carriage moving on the Y has quite a bit of movement, not solid at all, so there is obviously "slop" in there. How do I go about fixing this?

[Brady Watson]

Drop the Y motor and remove the grub screws that hold the pinion to the motor shaft. Put some loctite on the grub screws (don't forget this step) and tighten them down until you bend the allen wrench. Put it back on & enjoy perfect cutting.

While your at it inspect the pinions. If they are more than 6 months old, order new ones. Grease them! Pinions are cheap & affect cut quality more than anything else. You should not feel any slop in the gantry. Also check that your v-roller bearings (the ones that go sideways) are tight against the rails.

-B

[jay_p]

Gary,

If I were you, I would go here:
http://www.shopbottools.com/documentation.htm
Find the appropriate manual and at least read through the machine set up protocols. If you didn't set it up initially, you owe it to yourself to find out how it all works. Brady's advice is great, but I would even go back a few steps, check to make sure that everything is square and so on.

Jay

[harryball]

Yeah, what Jay said. I'd pretend you just got everything bolted together to the "finger tight" stage and use the manual to check everything. If it is not setup right it will be miserable to try and troubleshoot.

Robert