Hardware issue: z axis slippage in horizontal configuration causes progressive z error

Troubleshooting
1

I tried cutting out a job with my Maslow 4 that has edges close to the far edge of the work area (x is about 3cm).

My machine plunged into my floor and wrecked my mill.

After some debug (no mill in the machine and a marker at stock height taped above a z motor) I found the problem, although I don’t know how this one might be fixed.

The machine puts so much tension on the leading belts that the z motor stalls as the machine trys to reduce z depth whilst simultaniously increasing y (basically the y movement prys the sled onto its highest y edge so it would be doing a tiny endo if it were a BMX).

@bar, @dlang this is a tricky one. I think the top right arm having the steepest angle to the floor and the bottom left belt having the shalowest is contributing to this, so I will try to reduce angle of the top left with some stock height shims on the high anchor and re-calibrate. Otherwise, stumped. Video attached. You can hear the z axis groaning and failing. If my job depths were respected, the little stick would not bottom out. The warping in the tape is caused by an artificial offset being added progressively to z due to this problem. After this failure I saw about a 1/8" to 1/4" difference of exposed lead screw, but forgot to take a photo of that.

2

Michael Barr wrote:

I tried cutting out a job with my Maslow 4 that has edges close to the far edge of the work area (x is about 3cm).

My machine plunged into my floor and wrecked my mill.

unfortunantly the video you posted cannot be played on my browsers, so I’m not
sure exactly what the problem you had is.

But as you get close to the edge, you need to have additional material around
the workpiece for the sled to ride on to keep it from tipping off the edge

After some debug (no mill in the machine and a marker at stock height taped
above a z motor) I found the problem, although I don’t know how this one might
be fixed.

The machine puts so much tension on the leading belts that the z motor stalls
as the machine trys to reduce z depth whilst simultaniously increasing y
(basically the y movement prys the sled onto its highest y edge so it would be
doing a tiny endo if it were a BMX).

@bar, @dlang this is a tricky one. I think the top right arm having the
steepest angle to the floor and the bottom left belt having the shalowest is
contributing to this, so I will try to reduce angle of the top left with some
stock height shims on the high anchor and re-calibrate.

add skirting around the workpiece, it doesn’t need to be the full radius of the
sled, but a couple inches will help a lot.

Also, as you increase the Z height of the anchor, make sure there is no flex
being added (you are giving the belt more leverage)

And remember to change the Z offset values for the anchors you are changing.

Otherwise, stumped. Video attached. You can hear the z axis groaning and
failing. If my job depths were respected, the little stick would not bottom
out. The warping in the tape is caused by an artificial offset being added
progressively to z due to this problem. After this failure I saw about a 1/8"
to 1/4" difference of exposed lead screw, but forgot to take a photo of that.

see the thread “one more source of error” from friday, I identified an error in
the math that makes the effective length of the belts a bit shorter than the
should be as the belt angle gets steeper, I expect a fix for that will go out
either this week or next week (changing the math is a dangerous thing to do, so
there may be more testing than is possible before Wednesday). I would not be
surprised if you are running into this as well.

But raising the belts so they are closer to level will help this in any case.

David Lang

3

@dlang, cheers for the fast response. Bummer the video does not play… Not sure what to do about that :confused:

Anyway its not possible to see on the video but I do have support skirts there in case of tipping.

I raised the top left anchor by 2.5" from the ground, approximately its height from the base of the arm assembly, re-calibrated and the issue seems to have gone.

I will mark the problem as resolved in the thread if I am able to complete the job that caused my issue

Another point, I noticed some slight bowing of my support skirt which I clamped down, and added some paste wax to the base of the sled for good measure

boostedanchor
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4

Michael Barrow wrote:

I raised the top left anchor by 2.5" from the ground, approximately its height from the base of the arm assembly, re-calibrated and the issue seems to have gone.

did you change the Z offset to match?

David Lang

5

No, I only raised one anchor point.
I wanted to balance the downward force from the top left and bottom left cables since the uneven down force was causing a tip of the sled and stall of the z axis close to x=0.

I did not see individual offsets per anchor in the yaml, so left z at default. Fitness dropped after recalibration, but the results from the test job seem satisfactory.

6

Michael Barrow wrote:

No, I only raised one anchor point.
I wanted to balance the downward force from the top left and bottom left cables since the uneven down force was causing a tip of the sled and stall of the z axis close to x=0.

I did not see individual offsets per anchor in the yaml, so left z at default. Fitness dropped after recalibration, but the results from the test job seem satisfactory.

They are the Maslow_tlz Maslow_trz Maslow_blz and Maslow_brz variables

it it’s cutting well enough, you can leave it as-is, but if you have any other
issues, I would update the Z offset values and recalibrate (note that when the
math fix goes in, you will need to calibrate again for it)

David Lang

7

Thanks, I should have looked more carefully.

Ill look forward to this maths update as I am hoping for as much accuracy over the full work area as possible