Precision Issue

[Pete Cyr]

The pictures of your ruler and the resultant cuts would seem to indicate to need to re-perform this viewtopic.php?f=105&t=3528...................but that may not be the issue

The reason I asked you to cut a square/rectangle was to determine the parallelism of the bearing rails and the perpendicularity of the gantry to the bearing rails

bearing rail alignment.png

..........in your case I don't really have enough understanding with what may be the issue without the large square being cut and measurements of each axis corner to corner as well as the diagonal corner to corner.

[Jeffrey Aley]

The "ruler" test is interesting. What are your speed and acceleration settings? Try repeating the test (or my dot mode variant below) several times to see if the laser is consistently off, and if it's always off at the same places. I'd add more lines / spots (0.25" would be good).

You could try to eliminate the Y axis ENTIRELY by just making a row of spots. The simplest way would probably be to use "dot mode".

With the power off, can you move the X axis smoothly by hand? Or does it bind at some spots? Are there any interesting mechanical sounds, especially when rastering?

Do you have the software set up to use Inches or millimeters? If the former, perhaps there's some precision lost when the software does the conversion (that's a stretch, but I don't use SAE on the laser).

Is the bed of the laser loose? Does it jiggle much when the laser is moving back and forth?

As I recall, the quality of your lines is good (please confirm). I am wondering if the laser head or lens is loose and therefore wobbling in the Z axis (I'd call this "theta Z"). If this were happening, your lines would be "wavy" instead of straight / smooth.

[Jason Chancellor]

..........in your case I don't really have enough understanding with what may be the issue without the large square being cut and measurements of each axis corner to corner as well as the diagonal corner to corner.

Ok, took a bunch of measurements and pics. Let me know what else would provide some clues. Anything else I can measure?

First, did the 100mm square cut at top/left and re-calibrated the machine using a digital caliber - this was a close as I could get it. I did the same square cut on the other 3 corners as well and only with the X axis starting on the left can I get consistent results.

x-measurements.jpg

y-measurements.jpg

all-four-corners.jpg

Next, I did a large square cut (26x 18). The top and bottom measured at exactly 26". The left and right both measured at exactly 18 1/16 inches". I also checked for square. The machine is square.

top_left_square.jpg

bottom_right_square.jpg

bottom_right.jpg

bottom_left_square.jpg

[Pete Cyr]

Your testing would seem to indicate rails are parallel and the gantry is perpendicular to the rails.
The smaller squares shows good resolution.
Take a look at the belt tension of X and Y. They should be similar in tension.

[Doug Fisher]

I would be very interested to read advice and tips on how a user checks their belt's tension! How do you do accurate measurements with and without specialized equipment?

[Pete Cyr]

The professionals I am told use a meter to measure resonance(the noise the belt make when plucked) to get tensions even between the x and the y

I am not an expert - but what I have read -Belts should be taut and the spring/deflection should be aprox equal in both x and y. Appearance and deflection for a given finger pressure is all I have to recommend. Not very technical.

[Jason Chancellor]

The "ruler" test is interesting. What are your speed and acceleration settings? Try repeating the test (or my dot mode variant below) several times to see if the laser is consistently off, and if it's always off at the same places. I'd add more lines / spots (0.25" would be good).

You could try to eliminate the Y axis ENTIRELY by just making a row of spots. The simplest way would probably be to use "dot mode".

With the power off, can you move the X axis smoothly by hand? Or does it bind at some spots? Are there any interesting mechanical sounds, especially when rastering?

Do you have the software set up to use Inches or millimeters? If the former, perhaps there's some precision lost when the software does the conversion (that's a stretch, but I don't use SAE on the laser).

Is the bed of the laser loose? Does it jiggle much when the laser is moving back and forth?

As I recall, the quality of your lines is good (please confirm). I am wondering if the laser head or lens is loose and therefore wobbling in the Z axis (I'd call this "theta Z"). If this were happening, your lines would be "wavy" instead of straight / smooth.

Couldn't figure out how to do just dots, but redid the ruler test using 1/4" spacing as you suggested.

- What it shows is what all my other tests show, that there is inconsistency across the X axis. It seemed to be precise inches 0-6, then 12-26. There is a gap in there where it seems to get off.

- I have the speed set to very slow settings. In User->Key Setting = "Slow Cutting".

- I attempted to tighten and loosen the belts and that affected nothing.

- The X/Y can slide smoothly. Hard to tell with the belt on, but nothing noticable.

- Mechanically, the machine seems great. No slop / wiggle in the X. Bed seems nice and tight. The rails seem clean, scratch free, nothing visible. I'm actually really impressed with the machine.

Things I'm considering as next steps:
1) Do some rastering to see if higher speeds shows any problems...
2) Is it possible the stepper is simply not accurate enough for my needs. Maybe move to a servo?
3) I'm planning on removing the belt so I can slide the head easier to see if there is any binding.
4) Maybe re-oil the rails with machine oil - looks like its silicone or something now?
5) Deep examination of the gantry. Is there something wrong with a pully, is the belt rubbing somewhere I haven't seen?

Anything else I should check for?

wide-line-test.jpg

[Pete Cyr]

Best Grease Mobilux EP 1, EP Grease, NLGI 1,

https://www.amazon.com/Mobilux-EP-Greas ... B009OXHTGC

Lithium NOT silicone

Slacking belts and moving by hand will give a good indication of drag - but if you grease first and re-perform the test you may be better off

[Jeffrey Aley]

Couldn't figure out how to do just dots, but redid the ruler test using 1/4" spacing as you suggested.

- What it shows is what all my other tests show, that there is inconsistency across the X axis. It seemed to be precise inches 0-6, then 12-26. There is a gap in there where it seems to get off.

- I have the speed set to very slow settings. In User->Key Setting = "Slow Cutting".

- I attempted to tighten and loosen the belts and that affected nothing.

- The X/Y can slide smoothly. Hard to tell with the belt on, but nothing noticable.

- Mechanically, the machine seems great. No slop / wiggle in the X. Bed seems nice and tight. The rails seem clean, scratch free, nothing visible. I'm actually really impressed with the machine.

Things I'm considering as next steps:
1) Do some rastering to see if higher speeds shows any problems...
2) Is it possible the stepper is simply not accurate enough for my needs. Maybe move to a servo?
3) I'm planning on removing the belt so I can slide the head easier to see if there is any binding.
4) Maybe re-oil the rails with machine oil - looks like its silicone or something now?
5) Deep examination of the gantry. Is there something wrong with a pully, is the belt rubbing somewhere I haven't seen?

Anything else I should check for?

Dot Mode: I can't tell from your profile which sub-version of RDWorks you're using. For 8.01.24, the options for Processing Mode are "Scan", "Cut", "Dot", and "Pen". (I assume you know how to switch from Scan to Cut; Dot is another option in the same menu).
Set a dot interval of .249" and a dot length of 0.001". Then draw a horizontal line (hold down CTRL to force the line to be orthogonal). Check the Preview to be sure you're going to get what you want.

Check the grub screws (set screws) on the X-axis drive pulley. It is not uncommon for them to be missing (!) .

Check your acceleration settings. Record their values and then try lowering them by half as an experiment. Note that there are (IIRC) two different acceleration settings: Idle (when the laser is moving between objects with the laser off), and Cutting (laser on). These are under User -> Cut Parameters.

Stepper resolution - it should be fine, assuming you have microstepping enabled. Find the little black boxes that are the stepper motor controllers. Observe (photograph) the DIP switch settings. If you're lucky, a table of DIP switch settings is printed on the top of the stepper controller. If not, you'll have to Google the model # to find the info.

There was somebody on this forum who ended up w/ a bad stepper or stepper controller. Since your Y-axis seems perfect, you could try swapping stepper controllers to see if the problem follows the controller. You could also swap the stepper motors to see if the problem follows the motor.

Good luck!

[Jason Chancellor]

Quick recap of issue as thread is getting long (thanks for everyones help): I cut a 100mm square on the left side of the bed, it measures accurately, but the same square on the right side of the bed is under sized by about ~0.4mm on the X axis only. The Y axis is perfectly accurate when I cut the same square on each of the corners of the bed. The X axis issue is consistently inaccurate. Its always off by around .4mm which is very confusing to me.

Machine dimensions are 700x500.

Check the grub screws (set screws) on the X-axis drive pulley. It is not uncommon for them to be missing (!) .

Check your acceleration settings. Record their values and then try lowering them by half as an experiment. Note that there are (IIRC) two different acceleration settings: Idle (when the laser is moving between objects with the laser off), and Cutting (laser on). These are under User -> Cut Parameters.

Stepper resolution - it should be fine, assuming you have microstepping enabled. Find the little black boxes that are the stepper motor controllers. Observe (photograph) the DIP switch settings. If you're lucky, a table of DIP switch settings is printed on the top of the stepper controller. If not, you'll have to Google the model # to find the info.

There was somebody on this forum who ended up w/ a bad stepper or stepper controller. Since your Y-axis seems perfect, you could try swapping stepper controllers to see if the problem follows the controller. You could also swap the stepper motors to see if the problem follows the motor.

Good luck!

I removed the belt to check the x-axis rail. It was fine - I was actually pretty impressed with how tight yet free flowing the rail was for a cheap rail system. The belt itself seemed fine as well.

There doesn't appear to be a set screw, the pulley must be somehow permanently attached to the motor.

This is the stepper driver in my machine: https://www.ebay.com/itm/New-Driver-ACT ... .l4275.c10
It is already a "micro-stepper" so there were no toggles to switch. I did verify that the switches were the same between the two steppers. I tried your suggestion of swapping the two drivers and it didn't change anything.

Next Steps I'm thinking:
1) Swap the x-axis stepper. If I do this, I was also thinking I might upgrade to a 3 phase or maybe even a closed loop stepper motor and driver. Cost is not really a driver at this point, getting it accurate is. Any recommendations on brands, where to buy, etc???
2) Replace the belt and idler pulley while I'm at it. It looks fine, but what the hell...

Anything else I should try here? On a positive note, I'm learning a lot about this machine right now!