Can't Get My Circles Round

[toddalin]

I have a ShopMaster Tri-Power with CNC and am having a problem getting my circles round. I've been through the Mach3 stepper controls to calibrate the distance using my DRO and I think the problem is mechanical or data related.

Sometime the table will stiffen up (slight almost grinding noise) along the Y-axis as the collar moves along the screw. I've tried to adjust the table tightness, and when I run it though by hand crank, I don't feel this stiffness. Maybe an adjustment of the collar tightness, or lubrication of the screw? What sort of lubricant should be used for the table/screws?

I've also noted that sometimes the Gekko board will "chirp" when asked to make a movement, or change direction, possibly creating a "hiccup?"

I've also noted that sometimes my uninterruptable power supply will beep during the run and maybe this creates an interruption in the data stream?

Finally, I noted that the Y-stepper motor became quite warm during operation.

Any suggestions?

Thanks

[hammermill]

binding up seems a likely suspect if you are running with out encoders so the system knows how much it moved. not just how much you told it to move

put a volt and amp meter on the supply as see what s being drawn for current. may be as simple as bearings or debris

[Rick]

I with Hammermill I would check out what he said first, especially if the circle is out in the y axis direction and you are not using feedback. Another issue I have seen cause not round circles is backlash compensation not set correctly. If there is backlash in the table drive system then that will show up on circular cuts if its not compensated as both axis change directions during the cut. Which axis is the circle not to size or is it not to size at a 45 angle? One other issue I can think of, and this one is a bit harder to figure out, is if your stepper system is hitting harmonics during the circular path this would be less of a problem the smaller the circle is and is due to your system(stepper with no feed back I am assuming here) not be set up as good as it could be (mainly the accel and decel not high enough).

[toddalin]

Gotta be something binding or slipping or...

Initially I was getting good circles and with calibration, I would get a near perfect circle. Then the other day they were not so good and the stepper motor would heat up. The last one was more of a half round, and yes, it seems to be the Y-axis.

There is no feedback loop, so the Mach3 software doesn't know anything is wrong.

I've tried adjusting the shim strip along the table (the retention lock bolts were loose) and maybe that freed it up a bit. How tight should this be? This is why I was asking about lubrication.

Thanks

[hammermill]

try this put a stethscope on the stepper and listen as it runs thru a cycle, may be suprised what you hear??

[laurent_parti]

Hello,

Maybe an idea that can help. If stepper begin to be too hot, they will loose steps. So then you have the wrong displacement.

I had experienced some trouble with my machine and as I use a water cool spindle, I derivated the cooling circuit on coils that I put on my steppers body. Since I did that, I would never had any concern.

Here it is a short video that show how my cooling circuit goes with the stepper and the spindle too:

https://www.youtube.com/watch?v=VLdV0sb3UNw

To create the coils, I only bought small copper pipe and rolled them around body stepper then just make the cooling liquid take the hot !
Hope it can help.

Laurent

[Rick]

I've tried adjusting the shim strip along the table (the retention lock bolts were loose) and maybe that freed it up a bit. How tight should this be?

I believe you are talking about the y axis gib.
Its not a matter of tightness more so just adjust to remove as much clearance in the slide as possible without causing the table to be hard to move. Its a important adjustment to have correct for your machine to preform properly.

Let us know what type of gib system your machine has and we can help with how to adjust it.
Are the adjustments screws from the side and there are a few of them that run the length? or is the a screw at each end of the gib inline with the gib?

[toddalin]

I've tried adjusting the shim strip along the table (the retention lock bolts were loose) and maybe that freed it up a bit. How tight should this be?

I believe you are talking about the y axis gib.
Its not a matter of tightness more so just adjust to remove as much clearance in the slide as possible without causing the table to be hard to move. Its a important adjustment to have correct for your machine to preform properly.

Let us know what type of gib system your machine has and we can help with how to adjust it.
Are the adjustments screws from the side and there are a few of them that run the length? or is the a screw at each end of the gib inline with the gib?

Thanks,

One side of the table has a strap metal "spacer" that the table slides along. There are four Allen screws spaced along the "spacer" that can push it tight against the table to lock the Y-axis. Each Allen screw has a lock nut to hold it once adjusted.

I last loosened all the lock nuts, ran the 4 Allen screws down to where they would no longer turn freely, then backed each out 1/2 turn and locked the nuts. This seems smoother than it was, but I've not had the time to retest it yet.



Here you can see two of the Allen screws/lock nuts.

[img]