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Bed high and low issues

Posted by Mils24 
Bed high and low issues
February 10, 2016 06:03PM
Hey guys

I am trying to help a fellow Kickstarter delta kit backer to get his machine up and running. I have suggested everything that I can think of and we're still stuck so need your help.

The issue is that he is getting two low spots (0.8mm) between towers opposite towers X and Y towards the edge of the bed but a high spot (0.5mm) in front of X at the edge of the bed. (Pic below)

The issue I had with mine was low spots between all three towers out towards the edge of the bed - this was resolved by a combination of changing the rod length to the actual length (Originally I was using the Kickstarter kit designers length which was 0.3mm out) editing the delta radius and replacing the rod end bearings which were crap.

What we know and have checked on his printer is the following:
- The frame is all square, true and solid.
- All towers are square to top and bottom base
- Gaps between all towers are the same
- Bed is flat and perpendicular to towers.
- Rods have been measured with callipers and rod length adjusted to suit in EEPROM - 280.5mm
- steps per mm is tested and correct = 320 steps/mm (0.9deg steppers with 32bit microsteping / GT2 belts and 20 teeth pulleys)
- Delta_Radius has been set to give all 4 points (each tower and 0,0) to be within 0.04 of each other

One thing we have found is that there are half of the bearings on the rods have a little slop in them, ranging from 0.09mm-0.13mm linear play. Note each rod has a perfect bearing with no slop and one bad one. Would this be enough to cause the issues described above. To me (and I still count myself as a novice) I think there must be something else contributing to it. Would the 'slop' stated above not just limit the ability to print at any great speed?

Below is a graph showing the issue more clearly and a bed map the owner created using a DTI clock mounted to the end effector.

Any and all help greatly appreciated guys as I really am out of ideas.


Edited 2 time(s). Last edit at 02/11/2016 02:39AM by Mils24.
Re: Bed levelling strange behaviour
February 11, 2016 02:50AM
Two suggestions:

1. You said you have low spots opposite two of the towers. Do you also have a high spot opposite the third tower? If so, you need to make tower position corrections. Either use firmware with full auto calibration built in, or use my delta calibration calculator at escher3d.com.

2. If you waggle the Bowden tube from side to side or front to back, does this cause the effector to tilt a little because of play in the joints? If so, that will be causing part of the problem, because the direction of the force exerted by the Bowden tube varies with effector XY position. To solve or reduce this effect you can eliminate play in the joints and or use springs or elastic between the rods to take up the play and or support the Bowden tube using pieces of elastic from the too of the frame.

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
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