Flat spots in Circles and Arcs

Greetings all-

First off, thanks to Michael K Jonhson et all for porting us over. I am hoping that people migrate over…

I started to getting flat spots on arcs and circles 90/180 degrees apart. I am baffled as to what might be causing it.

I changed belts, I realigned, loosened, retensionsed, cleaned, snugged all the screws up, realigned again, lathered, rinsed and repeated…

Google Photos

and a scan of that ring, which is 150mm diam, 4mm wide, 0.4mm thick.

It happens basically at the X max & X min positions where the feature of the print goes from tangent=Y direction to a slope. There is a flat spot at the diameter and a kink where it started the curve.

I am pretty sure this is mechanical in nature but I can not put my finger on it.

Anyone dealt with this? What was your outcome?

Thanks in advance

Dennis P.

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What you’re seeing there is either backlash due to binding in the system along bushings, or issues of belt tension, uneven belt tension, or loose grubscrew on a pulley. At the apex of the turn in the y direction you can see that it stops before going in reverses. There’s a slack, or release of tension causing it to not change direction until the backlash has taken out.

I had issues with this, it was basically a problem with the belt tension and also the bushings were loose. Check all of them. I had pressed them into the carriage with acetone but after about a year they started coming loose. Second time around I disassembled everything and epoxied the bushings in place and haven’t had an issue since.

Look as the bushings closely, it wasn’t very obvious they were loose. Good luck!

Also, the porting over was remarkably painless! Thanks Michael!

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Thanks gents. I am still working at it. Been busy and AFK…

I realigned and retensioned everything again. Tip: Buy the 100 pack of M4x4 setscrews from McMaster… you will be glad you did after the 10th setscrew goes to live on the Island of Missing Socks and Things.

I thought about the bushings but did not give them a second look. I think I will next chance I get. I printed my parts in PETG, so I might try using locktite or PVA to ‘cement’ them in place.

Dennis_P, I had a similar problem,and I actually had a problem with the stepper motor, and I ended up replacing it. I thought is was just a belt tension problem,but after a couple weeks of trying to adjust, had a guy look at it, and when we took the belt off the motor and tried to spin it, we could feel the problem in the stepper. Just another thought for you if the other things did not fix it.