Hopefully someone has run into this problem befor. Machine is a generic 3018 with mod's. Material is 6mm cast acrylic, parameters are; feed rate of 300mm/m, plunge rate of 200mm/m, depth per cut is .5mm, RPM is 12K, bit is a 3mm, 2 flute , end mill brand new. On the 12th of 13 passes, after it has been working perfectly, as you can see from the photo it suddenly runs amok. It does not occur near a tab or when plunging to the next level. It is totally random. Happens with both "easel" software and Vectric 2D. Machine has a 500w spindle and NEMA 23 steppers so it should not be underpowered. Any info appreciated. I aborted th
Take the picture without flash. It's hard to see the edges. I'm seeing shadows and glare. It could be melting. It could be shatter. Are the tabs recessed, or are they full height? For acrylic, I would use an O-flute on a lower end machine. It provides better chip evacuation, which means less heat.
It is definitely shattering. Upper cutout was done 2 months ago with the same parameters and working correctly, chips and no melting. Checked every nut and bolt on the machine, nothing is lose. Z axis support is rigid as is the table. Plastic was securely screwed to the waste board. Depth of cut is set to ramp in Vectric. As stated, it will do 90% of the cut perfectly. Very frustrating.
Questions. You indicate it was a new bit so was the cut from two months ago with different bit? Was the bit specifically designed for acrylic? Have you inspected the bit to verify no micro bits of plastic have melted to it?
Setup was same as 2 months ago. When the first piece started to go belly up we thought " dull bit" and changed it. It's not an "O" flute but i've never had trouble befor. Bit is clean and sharp. It acts like the spindle is told to move the bit closer to the piece and not follow the same path though the G-code is identical to all the other passes. Instead of cutting a 3mm wide by .5mm deep axial cut it acts like it was told to make a 6mm deep radial cut, pushes into the piece and freaks out. It happens too fast and too randomly to really observe. Thanks for responding.
Truly hard to say what exactly is happening but the problem appears to be somewhat directional. I would check for play on the axis perpendicular to the direction it is heading at that point. Another suggestion would be to do the same cut in a 6mm thick piece of soft fine grained wood (basswood, poplar, etc.). You'll be be able to see better what is happening as it won't be exploding like acrylic. Finally, I would suggest trying another bit. Find something specifically designed for acrylic. Acrylic is one of the most difficult materials to machine between the melting and the fracturing.
This has been a joint project with my 21 year old grandson. After looking at the cut plastic he thought the edge was slightly beveled. Quick check with a straight edge and sure enough something went wrong in the Z axis support. Looks like a tear down is in order. I've never been happy with the amount of length and therefore leverage there is between the bit tip and the spindle motor.\, especially with long bits. Something else to look into. Thanks again for your assistance.
So a good news, bad news, afternoon. Per the photo's, the spindle support itself is perpendicular to the table. Good part. Bad part, the spindle is off vertical by 30 thou in the X direction and 50thou in the Y. Major work needed.
Another thing you want to tackle while you do the rebuilt is to have the spindle clamp on the bottom of the spindle and not on the top. Think about the fulcrum arm.
