Bit is trying to step over while cutting, help

[willmorgan]

I have been cutting acrylic letters for a while now but yesterday while trying to cut the machine started acting weird. While cutting different passes on a profile tool path in V-Carve pro v8 the bit is trying to cut like a slope, but it's not consistent in where or how it does it. I have attached some pictures. I have tried using different bits and different shanks. I did put in a 1/2 x 1/2 bit and cut it just to see what it would do and it worked. Of course this is too big of a bit to use. I have tried 1/4, 1/8 and 1/16 bits all with the same results.
I have changed feed rates, number of passes and RPM's and nothing works. It seemed like it did get a little better with a feed rate of 3 and rpm of 19,000 but the number of passes didn't really matter. The material is .375 acrylic.
Any help would be appreciated.

[scottp55]

Will,
Might help the guys to know what year and model of machine and what maintenance it's had if bought used. Also Version of SB3.
Good luck.

[willmorgan]

Hey Scott,
Thanks for the suggestion.

It's a 2006 PRT 4x5 with a router. I just put the newest controller on it and new motors with the latest download for SB. It has cut the same letters fine up to yesterday. I have also cleaned out the collette.

Could it be a collette issue?

[Brady Watson]

With the control box on and the machine at rest, grab the gantry and wiggle it front and back (X). Then proceed to the Y and wiggle it front and back. Grab the router and wiggle it up and down, front and back. You should not feel any appreciable movement in any of them. If you do, some adjustment is in order. You want to make sure that each axis is able to hold its position without moving under light hand resistance.

One of the pinion grub screws could be loose. One of the X motor drivers could be flaking out or wiring pinched not allowing full motor power.

-B

[willmorgan]

Thanks Brady,
I will try this today.

[RossMosh]

Machines jump like that under two scenarios.

1. Mechanical issues like Brady mentioned.
2. Pushing the router too hard.

[MogulTx]

Could be a bit that is inappropriate for acrylic getting loaded up with semi-molten acrylic, and pushing away from your cut. It looks like you did level cuts at about .1" depth each pass. I have never used 19K RPM on acrylic. I use bits specifically for acrylic, and try to watch my cut to see if the material is fusing back to itself or if it is cutting and sending off loose chips. Brady is starting you off at the first thing you should check. Then I would look into the type acrylic you are cutting ( cast and extruded DO cut differently). Look at bit type. Look at rotational speed (and chip size) and recommended feed rates. ( I will go to my machine and look at what I do when I am cutting some acrylic and what exact bit I am using... but you may solve your trouble with the checks that you have already received!)

OH: AND you need to look at the drawing file and see if you have smooth arcs or what.... That cut is jagged. Should not be like that at all. If Brady's suggestion on loose pinions in the gear track is not the issue- then I would be checking my file from which I set up my cut. Blow it up and see how smooth your curves are.

[steve_g]

What I’m seeing…
In your first photo, all the issues seem to be in one axis… (all the paths seem to line up on the left ok) This would seem to point to something mechanical, such as grub screws or other adjustments already mentioned…
SG

[willmorgan]

I changed the router motor, didn't help. I changed the stepper motor and that seemed to fix the issue. Thanks for all of the help, you guys are great!