[niner_zero]

The good news is I finished my machine and it is operational. I am fairly new to CNC and machining so i did my best squaring the machine. I have yet to get a dial gauge. I made few square and circular cuts on 1/4 ply and it worked well. Then i started cutting a dust hood parts on cast acrylic started noticing the machine slipping on the profile cuts. I used a single flute 1/4 acrylic bit at 10000rpm and 30 ipm. First i thought the work piece was moving, so i secured a second piece and repeated the test. no luck. Any thoughts or suggestions?


Jacob

[niner_zero]

Then i did another test by cutting .05in deep profile cuts of 16 x 5 holes matrix. I marked the home with a marker and executed the cuts. By the 11the hole the bit was barely touching the bed and by second row it was mostly air cutting. At the 3rd row i cancelled the operation and issued "go to Z" the new home position was at least .125 in high for Z and off for x and y as well. See the picture attached. I looking forward to hear from some you experienced folks.

Jacob

[IN-WondeR]

Have you surfaced your table before doing those test cuts??

A tabletop made from plywood or MDF, will never be perfectly flat from the beginning.
I surfaced my table to get it flat and true to the machine. I believe that's the way things are done in the industry also.

[niner_zero]

No, i have not used a tool to surface it, but checked the surface using a level. I can understand the change in depth of cut due to surface imperfections, but my cuts are shifting forward. Also that does not explain the home shifting after cuts.

[ger21]

Reduce your acceleration settings by 50% and see if it still loses position.

Where you show the cuts drifting inwards, are they moving the same amount at both ends? If not, it sounds like it may be mechanical. Check that all your pinions are tight.

[niner_zero]

The machine is drifting on both ends. I haven't accurately measured the drift on both ends but looks the same. Major drift is along x axis and there is a minor drift in y axis (left to right) too. I will run a 50% feed rate this evening and let you know.

[nlancaster]

One thing that is a repeated issue with the CNCRouterParts machines, and it isn't a design flaw. Are the timing pulleys secure on the stepper shafts? And did you loctite them, they seem to like unscrewing themselves causing this kind of behavior.

And Gerry is reffering to acceleration rate in motor tuning, not the feedrate. If anything you are running very slow feedrate for that machine, I cut acrylic on my CRP4848 at 100-200ipm without issues.

[ger21]

I will run a 50% feed rate this evening and let you know.

No, use 50% ACCELERATION.

[alexhawker]

Then i did another test by cutting .05in deep profile cuts of 16 x 5 holes matrix. I marked the home with a marker and executed the cuts. By the 11the hole the bit was barely touching the bed and by second row it was mostly air cutting. At the 3rd row i cancelled the operation and issued "go to Z" the new home position was at least .125 in high for Z and off for x and y as well. See the picture attached. I looking forward to hear from some you experienced folks.

Jacob

Could it be that the tool is being pushed up further into the tool holder?


Sent from my iPad using Tapatalk

[FoxCNC1]

One thing that is a repeated issue with the CNCRouterParts machines, and it isn't a design flaw. Are the timing pulleys secure on the stepper shafts? And did you loctite them, they seem to like unscrewing themselves causing this kind of behavior.

And Gerry is reffering to acceleration rate in motor tuning, not the feedrate. If anything you are running very slow feedrate for that machine, I cut acrylic on my CRP4848 at 100-200ipm without issues.

Not only that, (I never had a problem there) but I did have to shim the metal rails on the gantry and make sure my Z axis was tight. I was seeing some wondering of the tool as a result of slight bowing of the rails.

I was very frustrated being relatively new to CNC but Ahren and Corry where there all the way helping me. I have nothing for good things to say about them and my machine.

[niner_zero]

Just want to give you all a quick update. I took the advice and removed the motor drive units and tread locked the pulleys and tried 50% less acceleration. I was still getting some minor missed steps. I then talked to Cory and Arhen from CNC router parts and they were very helpful as usual. They thought the problem was missing steps due to software/computer. So i checked the version of mach 3 and found it to be the old version.
I updated Mach 3 to the latest version and change the kernel speed to 35K Hz. Looks like that solved the problem. I have put the acceleration back to the original setting and made few cuts. Now the "go to zero" is taking the bit to home correctly and the cuts are straight.
Attachment 255928

[foam27]

Run the drivertest program in the MACH3 directory, make sure you have a reasonably smooth line, and do what Gerry said...