Random cut path - what am I doing wrong

[oscarl48]

I have an odd situation. I have looked through the forum but have not found anything that sounded like this but if it exists would be appreciative if you could point me in the right direction.

My apologies for any wrong terms.

Today I was ready to kick my CW. I did a new plaque design for a friend and after 45 minutes it came out better than I had hoped. Carved region was done with the 1/16 carving bit. The plaque design called for a circular plaque so I set up a second cut with the 1/8 cutting bit to cut out the circle. I set the bit for .25 max depth cut with a .75 thick board.

It cut twice the circle with no issues and then on the third pass it decided to travel about 1" perpendicular to the pattern before it started the circular cut again. Since it was no longer in the same track it cut back into the carved region ruining that part of the plaque. I caught it as it had gone about an 1" into the carving when I was able to stop the moving bit.

It almost looked like it thought it was done and was traveling back to center without it lifting the bit up but the pattern was not complete so not sure if that is true. It had completed about 3/4 of the last pass when it decided to do this. I was this close to finishing.

It had done this once before when I was experimenting on cutting gears but it hadn't done it since until today. What am I doing wrong?

Thanks for any assistance. I am using PD 2.0. ;circle tool; select bit 1/8 straight; 0.00 inset; .75 depth; .25 max pass depth.

I cut off the ruined section and will add another design to save the piece so not a complete failure but not happy. Especially after it did such a great job on the carving itself.

[SteveNelson46]

Instead of assigning a bit (in this case the 1/8" straight) use the Cut Path tool.

Also, you probably had a X or Y axis tracking issue. A picture would be good.

[Digitalwoodshop]

Like above, a picture would be great... Tracking is likely the issue with the board loosing contact with the brass roller.... Masking Tape on the bottom of the board helps.... So lets say it was NOT a X Tracking Error and lets say it was NOT a Y Gearbox Issue... One thing your observation told me is that it looked like the Z DID NOT Lift... So lets look at this...

1. The Flex shaft Caught on the under side of the Black cover on the UP STROKE...

2. Dust inside the Z Encoder

3. Clear Plastic Disk on the Z Encoder is LOOSE on the Shaft of the Z Servo. Glue will help.

4. Something in the Z Belt cogs preventing lift.

5. Something on the Z Rails or Roller.... Usually in that "no mans land" between the upper and lower roller.

6. FFC CABLE IS BAD..... It touches then not touch or opens.... This is VERY likey the problem... The Servo Voltage and encoder signals go through that flat copper covered with plastic...

Good Luck,

AL

[oscarl48]

Gents,

Thank you both. I will try the cut path tool and also see how the hardware is looking. It hasn't happened often but it was just aggravating when the carving came out so nice and this supposedly simple thing put a slice through it.

I'll glue up a blank first thing in the morning and see how it goes. The piece that got chopped may still work out thought. It is giving me a place to put some eyelets and put a chain on it to hang. I'll post tomorrow on the finished project section.

[Digitalwoodshop]

And let us see your setup... Remember if you designed the project to let the wood only be held to the table by one roller it can tip up and loose contact with the brass roller... I like to have 4 inches of wood on each side of the length of the cut area to keep both rollers holding the board down along with masking tape on the bottom of the board.

[oscarl48]

Thanks for the advice. Here is a picture of the errant cut. The set up was a 12"x12" board with about a 1" clearance on each side. The part that confused me was it was the third and final pass. The first two passes were perfect. I have not used masking tape yet but I'll start doing that. The machine is still fairly new and I didn't see anything obviously wrong (thanks for the pictures for me to understand what to look at). I don't have a vacuum system set up for it so it could have been some dust getting into the wrong place. I didn't clean out the machine when I switched bits because I didn't want to mess with possibility of changing the board position so it was a little dusty in there.

Though I am intrigued by the mention of the FFC cable. Last time I had an issue (unrelated) it felt like it had come loose. I reseated and error went away so didn't give it much thought and continued cutting. I'll keep an eye on it.

I ran out of time today so didn't have time to do another run so will have to wait for next weekend. Damn the office job. Keeps me from making sawdust.