Movie About the Z-axis Skipping

[Chazz]

I dabbled over the last few weeks to no real effect. However, today when I went to check it out, I managed to get the problem occurring on video. Towards the end of the video, you can even hear the stepper skipping.

Any thought please?

Chazz

PS,
I had to send it to YouTube as it is too large for here even though it is only 31 seconds... It is unlisted so here is the link:

https://youtu.be/uLLdmX5ZCSA

Thoughts?

[Chazz]

Here is the toolpath file up to (and slightly past) the point that it skips.


TestFinish_025bn_ZB_Diag.txt

[gc3]

I would rethink hold down method and use a shorter bit, reduce vector boundary to stop unwanted z retract. Reply may not be related to z problem.

[Chazz]

I would rethink hold down method and use a shorter bit, reduce vector boundary to stop unwanted z retract. Reply may not be related to z problem.

In general, I would agree. This started out as a test cut of a part of the pattern which had steep (sheer) drop-offs.

In this particular case, it skipped while it was not even over the test material. In the end, that was material it was removing to help make sure the collet didn't smack into the material. That is why it ramps up towards that end of the run. However, in this case, I caught it being unable to lift the router. I just re-checked and the spring is attached and free from binding.

This all started after installing my 5.5 upgrade. I am fairly sure that must have something to do with it; but I am at a loss as to what. I ran a toolpath file to run it up and down over and over for about 20 minutes and no skipping. In this case, it was while it was moving with an increasing X. I don't know what that might have to do with it; but I am thinking of a test to try to see if I can do it reliably in air (without cutting material).

Thank you for your thoughts though,
Chazz

[srwtlc]

Chazz, try dropping the Z axis feed rate from 2 to 1.8 and try again. If it still does it, drop it a bit more and try again. You could also try adjusting the ramp values (VR) to soften 3D ramping a bit with the 3D ramp threshold (try something above 100. 150 is good for the larger Bots). Lowering the slow corner speed can help too. A high 3D ramp threshold can make the Z axis ramping be harsh and could cause loss of steps with 3D files. Just a few thoughts.

[Chazz]

So check me on these modifications please.

For the z-axis feed rate, I could change the:

MS,2.0,2.0

into

MS,2.0,1.8 (or less, I would be OK with 1.0 for now)

After that, either try it first alone or group the cures together, try to add in:

VR,,,,,,,,,,,150,,,,,

or

VR,0.4,0.4,0.4,0.4,0.4,0.4,0.4,0.4,0.2,0.2,150,0.1 5,65,,,0.2

(Not sure if I can just skip the values to leave them unchanged or reset to defaults.)

As for cornering speed, while perhaps a generally good idea, does it apply in this case? It was skipping while not changing Y at all. Does the cornering speed also effect X-Z plane corners?

[srwtlc]

Yup, change the MS in your file and it's easier/better to do the VR right in the fill-in sheet that comes up with the VR keystroke combination (blank values, when placed in a file, does leave the parameter unchanged). Cornering speed can add a little cushion to the change in direction at the end of raster moves and if the Z happens to be in motion at the same time as a raster change (like a steep relief wall), it might affect the Z, not sure, but it does soften XY direction changes which if too abrupt, can cause loss of steps.

I wouldn't go lower than 2,1 on the MS as the XY axis will be forced to slow down while the Z axis is trying to catch up. I'd start with a 3D threshold of 150 and run it. If that doesn't stop it, drop the speed to 1.8 and then 1.6..... Also, try setting the minimum distance to check to 0.08. Too soften the raster direction changes try around 40%.

A desktop unit is going to behave differently than a full size machine and a standard differently than an Alpha, so settings will vary. Once you find some that work for you, you can save those settings out to a custom file (US) and load them when needed. Just remember to also save your preferred default values so you can return to them with out having to write them down or do a full reset. I have saved, a set of values for default, 3D, and v-carving and just set them up as custom cut #'s to load at will.

If anyone wants to read up on VR settings and what they apply to, Brady's 'excellent adventure' is here. This should really be a 'Sticky'! Admin, we should have a few 'Sticky' threads/posts for such things as it's a little hard to find these in the blog part of the website.