Multipass Cut Through - Not Retracing in the same spot.

[TNWALKINGHORSE]

Hello, I am a new owner of a used PRT 32x24 ShopBot running version 1 of PartWorks. I am still learning the machine and it is quite fun and quite a challenge at the same time. Today I was playing around with cutouts and was using a 1/8" upspiral to cut though a piece of 3/4 select pine. I set it up to cut .20" inches per pass. It did cut though...(I also used 4 tabs). However, the second, third and final pass did not retrace over the 1st pass. It shifted slightly. I was using a small 9" x 9" piece of scrap screwed to the table with 4 screws. The letter "M" seen in the pic below is only about 2.25" tall. Anyone no what is causing this? If you need more info, please let me know. -Matt


0330152336.jpg

[scottp55]

Almost looks like "Lost Steps" in 1 axis?
Just out of curiosity can you post pics of the complete letter And rotate 1 pic 90 degrees?
Also maybe try one with a .06" Pass Depth and show comparison pic?
Sure others will chime in shortly with better opinions.
scott

[bleeth]

Looks to me like one or more of a couple things:
Loose or worn pinion gears or the tension not correct on the motor mount springs.
Also tram your router to ensure it is truly perpendicular to the table.

[harryball]

A 1/8" bit is kind of small for that so I thought it might be bit deflection at first, but what you have going on is a lot more than that. On the inside of the M, the cuts opposite the top, did the bit correctly trace the path or did it cut into the entire block? If it is only off in one direction it rules out lost steps as once you loose a step it will look like your entire cut file moved over on the material. For lost steps to happen, the insides of the M would be cut for the entire depth when the bit was running inside. I don't know if a 1/8 bit would take the pressure if that happened.

Check your pinions, make sure one is not loose. With the Buddy it would mean in one direction you could be dead on but in the other you could be off as the shaft turned in the pinion to bind before beginning to turn in the other direction.

/RB

[TNWALKINGHORSE]

I am going to try the same cut file with the same bit on HDU to see if the softer material makes a difference (less deflection.) If it cuts fine there, is it safe to assume that the z-axis is square and all pinions, etc are OK?

[bleeth]

Go ahead-and when you're done and see the same thing read the suggestions and follow through.
(you can lead a TWH to water but you..........) LOL

[MogulTx]

I think Dave is trying to tell you that you asked for, and got, good tips from some experienced people. If you want to go off and do something different, then do it... but you are ignoring the logical path toward tracking down this cut issue. And sooner or later you need to check out the things that the people with experience - from whom you solicited input- have told you that you should check out.

If that were deflection: The amount of "deflection" you are seeing would have snapped that bit. THAT is not deflection. You may very well have had some deflection due to depth of cut ( max depth of cut should be about the diameter of the bit unless the material is exceedingly soft- like foam). But you can clearly see the second pass is a rougher cut and does not follow the pattern of the first cut. That indicates something is loose or worn (or both) . Check your Pinions. Check Spring tension.(Springs holding drive motors to the rack) Check your Router-to-mount is secure and the mount to Z Axis is secure. Tramming can't hurt. (Do a search on "Tramming" the router.) Checking for "play" in your axes is probably going to fix 90% of what you have going on there.

Best of luck. And with that new Basketball coach, too. I understand UT (Tenn) just got Rick Barnes. Good coach. Stupid move on UT(Tex) 's part.

[steve_g]

FWIW… If your issue involves missing steps, cutting in foam likely won’t replicate that part of the problem, sending you down the wrong rabbit hole!
SG

[TNWALKINGHORSE]

Thanks Mogul and thanks Dave and everyone else who responded. I really do appreciate all your help. I am now going to take a drink of water...lol. I will go ahead and check pinions, spring tension etc. I just need to find a few hours and sit down and do it. I really need to cut wood, so HDU won't solve anything anyway. Thanks again and I will report my findings. :-)

[TNWALKINGHORSE]

Ok, I took off the 20 tooth pinion on the "X" Axis to inspect further. By the looks of these pictures can you tell if this is a good or bad pinion. Not sure what to look for. Thanks again!