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Hotend sag solution

Posted by dmould 
Hotend sag solution
January 04, 2014 10:34AM
To get printing quickly, I originally temporarily taped a strip of cardboard along the X axis for the 9mm bearing to run on. However this has compressed over the past few days of printing, and the sag is again a problem. Probably the best permanent solution will be to replace the 9mm bearing with a 10mm part, but I have a few prints I want to do over this weekend and cannot get hold of a bearing quickly. So I am just about to print a simple strip to use instead of the cardboard, which I will attach with double-sided tape. By rotating it diagonally in Slicer, I can get 230mm, which is long enough to support the bearing over the printing area. Here's the STL in case anyone else wants a quick fix.
open | download - Xrunner.stl (684 bytes)
Re: Hotend sag solution
January 04, 2014 12:12PM
Try this solution - it worked for me.

• Remove the x-carriage M3 screw, 9.0mm bearing and washer.
• Check the x-carriage slot is clear and allows the M3 screw to slide freely. If not clean out with a 3.0mm drill bit.
• Replace the M3 x 12mm screw with a M3 x 16mm screw - this is important.
• Re-install the 9mm bearing with 5 washers under the bearing.
• As you tighten up the screw pinch the bearing and hot end fan with your fingers and thumb ensuring the bearing is pushing up against the black x-axis - don't press too hard as the acrylic is quite brittle.

You should now be able to get the head assembly level.



RS Ormerod No 192
Re: Hotend sag solution
January 04, 2014 01:08PM
That's a solution very much in the spirit of Reprap!

I found there were 2 causes of hotend sag:

1. Initial sag was caused by too much play between the x-runner bearing and the x-plate. Fixed by fettling out the slot and nut trap, and then installing a 10mm bearing. I bought a cheap pack of ten 623zz bearings via eBay UK for £2.98 inc carriage and the bearing is working fine so far.

2. Later on the head sagged due to the screws that attach the hot end to the nozzle mount becoming loose, presumably due to heat from the hot end. I tightened up the screws. Someone (sorry, I forget who) has posted a revised nozzle mount design on this forum.

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].
Re: Hotend sag solution
January 04, 2014 03:48PM
I used an old hacksaw blade.
Ground the tooth off, sanded it and stuck it to the side of the X axis with Kapton tape

Hardened and ground bearing surface :-)

Seems to be working well so far.

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