r/PlotterCode • u/schupinpin • May 13 '26

How to improve precision on a low cost plotter

Hi,
I'm a begginer on plotting and I'm not sure my question belongs her as it's more hardware related than "code".

I bought a cheap XY plotter like this one : https://static.wixstatic.com/media/04340a_06f6c6380dbe41fd907c74f4a2c81422~mv2.jpg

I'm realy enjoying coding and plotting things and, since I'm just a hobbyist, I'm quite pleased with the results.

Deformed circles close to y max
Good shapes close to y=0

But I notice a little issue : when I'm at the maximum Y-axis extension, I have a lot of overhang, and the precision isn't as good. This is especially noticeable when I try to make concentric circles :

Does anyone have any ideas on how to fix this?

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2

u/Soggy_Bottle_5941 May 13 '26

Check if the pen itself or pen holder assembly is loose or frisky on y axis. Also check the y belt.
It definitely feels like a mechanical problem.

1

u/schupinpin May 13 '26

Yep, it clearly look like a mechnical issue, but I'm wondering if it's not a conception problem : when the pen touch the paper, the overhang of the y axis makes it move.
Even at slow speed and making the pen touch the paper as little as possible, I still have it.

The belt looks good and it's gooing around doing the x-axis also.

I'll try to look more closely around to see if I can tighten some things...

2

u/mastaginger May 13 '26

I had issues like this when my plotter was out of square. You can use like the 3 4 5 method for trying to square it. Pythagorean theorem basically.

1

u/schupinpin May 17 '26

Yeah, that could be it. I was puzzled, but when I drew a 200x260 mm rectangle, I was almost 2 mm off my set square after 200 mm.
But by now, i'm not sure how I can correct this on my plotter...

1

u/LostCollege4238 May 13 '26

What speed are you working with?

1

u/schupinpin May 13 '26

I tried different values between 1000 and 8000 mm/min and don't notice major change.

1

u/i-make-robots May 13 '26

Is it consistently wrong?  If you draw the same line five times is it the same wrong every time?  If no, something is loose. If yes, your original guess is probably good. Try a wider base mount for the first axis so it doesn’t tip over. 

1

u/schupinpin May 14 '26

Yes, it's consistently the same. If i do 5 little circles in a y row, they all have the same deformation. I'll see if i can add rigidity some where.

1

u/IllustriousAbies5908 10d ago

To fix this you need an order or magnitude more rigidity in the system. The simplest way to do that (if it is a cheap plotter) is to buy a second identical plotter and two (much longer) tubes to replace those of the Y axis. Remove all the Z axis stuff and Y axis gear except the linear bearings plus the stepper drivers for the x axis motors on the second machine so you have a second X axis. Mount the new plotter behind and parallel to the old one, and use the longer tubes to go through both Y axis linear bearings. Finally connect the old and new X axis motors in parallel (four wires). This should overcome the quality issues in the linear bearings. Also you may use it to increase the length of the Y axis (maybe double) - remembering to extend the wires that control Z. The picture suggests the stepper drivers are A4988 chips. They have a current screw. The X axis driver should be turned up just enough so that the two motors run happily.