Y-axis issues

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caseycrotty
Posts: 2
Joined: Thu Sep 24, 2020 11:19 am

Y-axis issues

Post by caseycrotty »

Hello all, and Happy New Year! I'm new to CNS and bought a Shark SD110. Recently it has been shifting on the Y-axis ever so slightly, but only once it returns to the xyz zero point. If I run a second pass with the same bit, changing nothing at all, the machine will "elongate" the carving to the negative Y-axis. To illustrate what I mean: if you imagine a circle cut on the first pass and then rerun the pass (again, changing nothing at all, not even turning off the router) it will cut inside the circle on the positive aspect of the Y-axis, and outside the circle on the negative aspect. This happens regardless of changing bits (from an end mill to a v-bit, for example) or a simple second pass. I don't think it's a mechanical issue simply because it's consistently on the same axis, and consistently the same error; though on the other hand it's possible because I cut several things (wood) without any issues, and then this started. Thank you for your assistance!
Mr. C
Newbie at large

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Kayvon
Posts: 478
Joined: Tue Oct 21, 2014 11:46 pm

Re: Y-axis issues

Post by Kayvon »

I have the opposite intuition: sounds mechanical.

What happens if you have it draw the same circle three times in a row with a single g-code file, without returning to home? I'll bet you'll find a steady drift over time.

Another test: What happens if you run the single-circle program you've been using several times in a row. You don't need to actually cut anything--cutting air is fine. Make a mark at the precise home position when you start. See if that home position hasn't moved slightly after 10+ runs.

Rando
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Re: Y-axis issues

Post by Rando »

any chance the part moved?
if not, then is the bed and everything mechanically tight?
are the cuts "hard" or "fast" that you might be losing steps?
any chance the head is reaching it's end-of-travel in that axis and is "crashing" and losing steps?
is the first-bit carving perfectly dimensionally correct?
What is the measured offset you're seeing?
Have you ever crashed the machine (hard enough) that you'd have that measured amount of backlash?

Let's start there.... :D

Rando
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Rando
Posts: 650
Joined: Tue Jan 06, 2015 3:24 pm
Location: Hoquiam, WA
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Re: Y-axis issues

Post by Rando »

Kayvon wrote:
Tue Jan 12, 2021 4:02 pm
I have the opposite intuition: sounds mechanical.

What happens if you have it draw the same circle three times in a row with a single g-code file, without returning to home? I'll bet you'll find a steady drift over time.

Another test: What happens if you run the single-circle program you've been using several times in a row. You don't need to actually cut anything--cutting air is fine. Make a mark at the precise home position when you start. See if that home position hasn't moved slightly after 10+ runs.
Good tests to run, Kayvon! when I do those, I go with a teeny-tiny bit, like an 1/8" diameter 60-degree engraving bit, so I can see very small differences. I put down some cardboard (not the corrugated kind, the cereal-box kind) at the home position, and just jog down into it, say 0.005" to make a mark...then do the tests, come back, poke the hole. :)
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ThomR.com Creative tools and photographic art
A proud member of the Pacific Northwest CNC Club (now on Facebook)

caseycrotty
Posts: 2
Joined: Thu Sep 24, 2020 11:19 am

Re: Y-axis issues

Post by caseycrotty »

Hello everyone, and thank you for the responses! Let's see what I can answer here:

1. Is the part moving? The likelihood is pretty remote as I'm generally using 3 - 4 clamps. However, it's certainly not impossible. I can try the 10+ run test and see if I'm getting movement.
2. Is the bit reaching end of travel? No. I've tested in (nearly) the middle of the bed.
3. Are the cuts "hard" or "fast"? I've run them a number of ways: the first run is slower (80%), then the cleanup pass is at 100%; also 100/100%. I'm getting the same error. I'm not sure by what you mean when you say "hard"; the wood is pine, multiple passes so not a tremendous plunge on a first (or subsequent) passes. I hope that's what was being asked.
4. Is the first-bit carving perfectly dimensionally correct? I have not measured this; visually, I would say yes but empirically I don't know. Another good test.
5. Have you ever crashed the machine hard enough...? I've not crashed the machine. (yet).
6. What is the measured offset you're seeing? Unfortunately I used the boards again for other tests before measuring (where's the face palm emoji when you need it) so I need to run more test boards to get the measurements. However, I can then also check to see if the first carving is dimensionally correct at the same time.

Looks like I've got some testing to do! Unfortunately I won't be able to mess with it for a while due to travel. Thanks again for the ideas/feedback!
Mr. C
Newbie at large

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