Simon's hex coupler

by Wired1, published

Simon's hex coupler by Wired1 Aug 25, 2012


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Few more mods to Eric's awesome coupler idea. Made it hex shape so you can get a shifter (adjustable spanner) onto it - and yes it can take the torque, also added three grub screws at the top. This prints side-ways without the need for supports and came out really well.


Just print it.
3 perimeters, 3 layers, 0.35 nozzle, 0.25mm layer height, 25% infill at 90 degrees fill angle.
Motor end is printed at 5mm so clean it out with a 5mm drill.
Threaded rod end is printed at 9mm so should be a comfortable fit as it comes off the printer.
M8 nut fits inside the open end of the hex coupler.
Run another M8 nut up from below with a washer and tighten it as much as you dare.

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This worked great! Minus the whole standard nut being too big to fit, nothing a little grinding couldn't fix.

Nice to see this design still being popular. I'm beginning on an i3 for .35/.25mm printing. I believe these will work, but the i3 uses thinner X threaded rods so I'll be making an adjustment to these. :-) Keep up the good work.

Hey Wired1,

just printed your coupler but I can't get a standard M8 nut into the opening. What type of nut are you using for this?

Thanks in Advance

I used a standard M8 nut as well and it is a snug fit. Might be a variation in nut sizes around the globe or might be tweakable in Slic3r with the extrusion multiplier figure. I guess you measured your filament with a vernier? How far off fitting is it?

yes I measured the filament with a vernier. My nut is 6.4mm high, but the opening in the coupler only 4.7mm, so i doubt it is an issue with the filament diameter. Slic3r does not complain about anything also so I don't know what seems to be the problem.
What height do your nuts have?

Ah yes my bad. I used some M8 nuts that came from the States with my first printer, a Mendel Prusa kit, and it came with these 'thin' M8 nuts.

Nice Upgrades. I am raising an 8mo old now so My design time has been limited. I like the 3 grubs, my single kept tearing out. I also wanted to get rid of the support. The next version I was thinking would use a slot through the motor side and two long screws/nuts to squeeze the slot to clamp down on the motor shaft. should handle massive torque that way. Anyhow. Good job on this!

Version c has built-in flex - not sure how well this will last but it prints out nicely.