Delta printer nose dives

Hi all

I recently designed and built my own delta 3d printer based on the kossel 2020 frame work and running marlin firmware.

The problem i have is when the print gets to a certain height, between 2 and 4 mm, the hot end crashes into the print. It looks like the hot end is trying to go through the glass bed. That only happens when im trying to print a slightly large object. I printed king marvin from thingiverse without a problem, but i cant get the delta calibration ring printed without the printer going into self destruct mode.

I am at the point where im going to scrap the delta design and rather build a cartisian box styl printer.

If there is anyone that has an idea of what could be the problem, please help me. I realy want to get it going.

Thanx in advanced

Have you calibrated:

1) Steps per mm
2) Arm length
3) Delta radius

?

Inspect the gCode for errors as well.

I have setup the steps p/mm and used a vernier to make sure that it is accurate.
I have measured the arm lengths about 7 times to mlae sure that i dont have an issue on that in the firmware.
I manually set the delta radius so that i dont have any dome or concave movememt, i also have a z probe which is supposed to help with the flatness of the bed.

According to me, if it was a problem in the g-code, the problem would happen at the same place in the print everytime but it doesnt.

I thought that it might be the electronics thats going into thermal shut down so i added a fan thats blowing over the heatsinks on the ramps board, they now stay ice cold and the problem still happens.
Swoped out the PSU = no change
With and without heatbed = no change
Heatbed on different psu = no change
Belt tention less/more = no change
Printer frimness (mechanical changes) = no change

This printer has so far taken a year just to not work

This isn't a calibration problem, its basic electrical, mechanical or software, and Id also be inclined to discount the GCODE, it would be a pretty crappy slicer that added a random -Z pitch

When the printer does the nosedive what move does the printer think its making, ie does the Z current position change

Are your timing pulleys lose on the stepper shafts? check that the grub screw is central to the flat on the stepper shaft... but unless you are using large pulleys this wont give 2-3mm of offset.

Could be that one of the driven axes is loosing steps from catching on something, or from a move too rapid for the stepper driver or motors to actually achieve, if this happened you would get an XY shift as well as a Z shift

---

RepRapPro Mendel 3 Tricolour
RepRapPro Fisher
-Carbon Arms
-Easy adjust Carriage+effector
-axis stiffness mods
HE3D -600 delta
-Duet 0.8.5
-PanelDue
-DC42 Height probe
-RobotDigg metal components
Simplyfy3D
RS Design Spark CAD

I went trough every possible cause for this, electrical, mechanical and gcode.

The only thing i didnt check was the firmware ( marlin rc).

So yesterday before i scraped this project, i loaded repetier and did all the calibrations again and i got a full 3d printed part without nose diving into the bed. I think there might be a bug in the version of marlin that i have.

Im now just going to fine tune every thing to get the best possible print quality out of this printer, save the firmware in a well guarded place and then get a fresh copy of marlin again. It would be intresting to see if the bug pops up again and if it is just the copy that i have