[VESG_Dave]

Anyone else with this Issue? I've recently noticed that the machine was not cutting straight on one of the axis, but strangely enough it only happens on the pass cutting the bottom of the shape cutting from left to right. Allow me to give a bit more detail, the shape is a rectangle (cutting out on 1/8" acrylic plastic sheet) and is positioned with its long sides horizontally when looking at the board, the initial cut starts at the top right corner then cuts the top of the shape moving to the left, as it starts to cut the bottom line of the rectangle moving right thats when i noticed that particular line is bowed inward and not straight, keep in mind the corner dimensions of the rectangle are spot on after the cut and i've tried this several times with other shapes that have straight lines and it does the same thing ... but only the bottom portion..
My initial troubleshoot was check:
1) Waste Board - no visible obstruction, although the there are some grooves from previous cuts, overall plastic sheet lays relatively flat
2) material sheet is secured to the wasteboard, i don't notice the spindle jogging irregularly at any particular point along the trouble axis described (trying to rule out material moving or spindle somehow moving)

Anyone reading this seen anything similar? or know what might be wrong?
thanks

 

[difalkner]

Welcome to the forum, Dave! My first thought would be flex in the machine. Are your cuts too aggressive for your machine? What feeds/speeds are you running? Is this a climb cut or conventional? What bit are you using? Is that side of the rectangle straight in your CAD program?

Oh, and we do like photos! They always seem to help in diagnosing an issue.

 

[VESG_Dave]

Hey thanks for the reply, not sure its flex in the machine since it doesn't happen to any of the other sides when cutting. I'm using a 1/16th bit and haven't seen this kind of issue in the past when cutting this material. Some of the feed settings are posted in image below, nothing new I haven't used before. If you look at the image the slim rectangle piece with the blue arrows indicates the problem edge. You'll see that the opposite side looks fine when held against a straight edge.
Now after cutting a few of these to try and troubleshoot I can say that they all exhibit that same issue. Now if it is hardware issue what could it be? stepper motor? or is it software? but I can't think of any probable cause for it to bow inward like that. Oh yes I did double triple check that my pieces actually have straight edges in the CAD file.

 

[difalkner]

Rotate your piece 90° and cut it again. If the edge that was bowed is now straight then there's an issue with your machine.

 

[old55]

Welcome to the forum.

 

[jw2170]

G'day Dave, welcome to the forum..

 

[TimPa]

O flute is best bit for acrylics.

i hope i have the axis correct: try to watch the "Y axis drive" (motor, screw , rack, etc?) during the bad cut, that is, as the router is going across the table in the X axis. the y axis drive motor should remain still during the cut. if the motor is moving, the controller is likely telling it to move. if it is not moving, then the problem is machine flex or material movement.

does the problem reproduce itself anywhere on the table? is it the same with wood?

 

[gwilki]

+1 to the other comments. I cut quite a bit of acrylic, from 1/8" to 1/2" thick, using a 1/8" o-flute bit. I realize that you are using a 1/16" bit. I run my 1/8" with a 30" per min feed and the lowest speed on my makita router, which I believe is 10000rpm. I would not push a 1/16" as fast as you are. You may want to slow down your feed rate on that bit. Is it an o-flute or a standard 2-flute bit? If you are getting any heat, the acrylic will melt and pull the bit off the line.

Of course, if you have had good results with your process in the past and if this problem is recent, just disregard all of this.

 

[VESG_Dave]

Rotate your piece 90° and cut it again. If the edge that was bowed is now straight then there's an issue with your machine.

Yeh same issue, still can't quite explain how it would only affect that bottom cut

 

[VESG_Dave]

+1 to the other comments. I cut quite a bit of acrylic, from 1/8" to 1/2" thick, using a 1/8" o-flute bit. I realize that you are using a 1/16" bit. I run my 1/8" with a 30" per min feed and the lowest speed on my makita router, which I believe is 10000rpm. I would not push a 1/16" as fast as you are. You may want to slow down your feed rate on that bit. Is it an o-flute or a standard 2-flute bit? If you are getting any heat, the acrylic will melt and pull the bit off the line.

Of course, if you have had good results with your process in the past and if this problem is recent, just disregard all of this.

my spindle is max 12,000 rpm I tried slowing it down spindle speed and feed rate to 30 but same result. I understand the acrylic melting and sticking to the bit. But I haven't seen this inconsistency of cut on the other sides.. which leads me to believe its not only the bit. I am using a bit that is 2 flutes i believe and is an upcut type (not entirely familiar with all the different types) So I've noticed this same defect on my other cuts so it leads me to believe that there is some kind of hardware/controller issue... I've reached out to the manufacturer... hopefully they can help. I've worked with this machine for 2 months so still working out the kinks, I've used the CARVEY machine before this with much better results. Thanks for all the thoughts

 

[difalkner]

Just out of curiosity, if you switch bits to a 1/8" or 1/4" do you get the same results? How about in a piece of ply or MDF?

 

[wyzarddoc]

Could you be near the bottom limits of the Z axis on the last cut and if so possibly be racking the Z axis ?

 

[VESG_Dave]

Just out of curiosity, if you switch bits to a 1/8" or 1/4" do you get the same results? How about in a piece of ply or MDF?

Hey David, yes I tried 1/8" bit with same result. Even slowed down the feed rate to 20 in/min. I don't have a 1/4" handy and we are mainly cutting acrylic or HDPE. I'll have to see if its same result with wood.

 

[VESG_Dave]

Could you be near the bottom limits of the Z axis on the last cut and if so possibly be racking the Z axis ?

no doesn't look like we are at the Z limits, plus i have limit switches setup.

 

[wyzarddoc]

If your software supports setting the cutting direction I would try cutting in the opposite direction. Climb cut vs conventional cut. In wood I have had problems with direction on my table router but not my CNC machine but maybe plastic is different with the melting. Good luck and please post your findings when you solve the problem it will be good info if I am ever tempted to cut plastic.