Loading
Hey! This thing is still a Work in Progress. Files, instructions, and other stuff might change!

Akimbo - A redesign of the Mendel Frame

by raldrich, published

Akimbo - A redesign of the Mendel Frame by raldrich Aug 13, 2012

Description

Version 0.5

Akimbo is a redesigned Mendel frame, designed with increased build area, dual extrusion, easier assembly and increased rigidity in mind.

The top of the frame is tilted outward, to increase the frame's rigidity, and to keep carriage and extruder parts from banging into the frame at the top of the build area.

The space between the top horizontal bars is increased to 100mm, to allow clearance for placing the motors on top, and to keep the belt on a horizontal X carriage from rubbing against the frame at the top of the build area.

The frame is designed to be squared entirely with simple jigs, and uses parts that enforce frame geometry whenever possible.

All axis use a hybrid design for their movement - LM8UU (or equivalent) on one smooth rod, to provide maximum constraint, and a pair of 683 (3mm x 7mm x 3mm) roller bearings on the other smooth rod, to prevent binding.

The design supports 2 separate tool carriages, which allows 2 extruders with different hot-end lengths to be used on the same printer, and allows one extruder to be parked offsides while the other is in use.

Recent Comments

view all
For a single extruder (where I can center the motor on Y, and raise the extruder), I expect I can add 30 to 40mm of build height (the amount depends on the length of the hot-end).

With dual extruders there are more trade-offs - extra Z may end up costing X or Y travel.
Ok, cool! That additional triangle stiffening it up makes sense. I hadn't considered the z smooth rods part of the frame.

I can't decide if I want to do this or a Mendel90. I think the Mendel90 will let me print a lot faster, but it's more work. Any idea what kind of z travel you can get with this design? it looks like it should be able to go all the way to the top, so maybe 150-200mm would be possible? Either way, n
ice work! :) I'll be watching this design develop.
Yeah - I found that after several hours of printing - for now, I'm simply going to bolt motor down with two screws.

by the way, there's a worse bug in the bottom z mount - not enough space for all of the nuts and bolts.

hopefully I'll manage an update for it tonight - I've got the geometry fixed, but I'm not happy with how much plastic it's using.

More from 3D Printers

view more

Liked By

view all

License

GNU - GPL
Akimbo - A redesign of the Mendel Frame by raldrich is licensed under the GNU - GPL license.

Give a Shout Out

If you print this Thing and display it in public proudly give attribution by printing and displaying this tag. Print Thing Tag

Instructions

Sources are available at https://github.com/Lodran/Akimbo

Threaded and Smooth rod lengths are compatible with either Sells or Prusa (i1 or i2) designs, except for the Z axis screws, which are M5 threaded rod, 260mm in length.

Jig lengths are identical to Sells design, with a new jig added:     J1 - 290mm - length of triangle sides, measured between the inner sides of the vertex brackets.     J2 - 234mm - length of bottom horizontal rods, measured between the inner sides of the vertex brackets.     J2b - 304mm - length of top horizontal rods, measured between the inner sides of the motor mounts.

Version 0.2 put the parts on a diet, fixed a couple of bugs, and added Z axis smooth rod clamps.

Version 0.3 tweaks the parts for easier printing, strengthens the Z linear rod clamps, and makes measuring distances along the x axis a bit easier.

Version 0.4 adds X axis, Extruders, Carriages, and some of the Y axis parts.

Version 0.5 finishes the Y axis.

Note: The endstops I've currently designed for are non-standard - see http://www.thingiverse.com/derivative:38617

iam missing some screw holes for the Z motor mount, only 2 of them are useable :D

time to drill
Yeah - I found that after several hours of printing - for now, I'm simply going to bolt motor down with two screws.

by the way, there's a worse bug in the bottom z mount - not enough space for all of the nuts and bolts.

hopefully I'll manage an update for it tonight - I've got the geometry fixed, but I'm not happy with how much plastic it's using.
For me, the main problem of the Prusa is the location of the Z motors; moving them at the bottom would be a major improvement (no more problem with sliding coupling, less shaking because of a lower gravity center...)
My first parallelogram frame actually did just that, without widening the top. It had a few disadvantages.

1) With a standard Prusa 1 or 2 X axis, build height was not improved, because the belts still run outside the frame, and still interfere at the top of the build height.

2) Having the Z screws be under compression instead of under tension may be a disadvantage when using more flexible (i.e. M5) Z
screws.

3) Moving the motors to the bottom requires the use of longer Z screws, which reduces the number of Prusa frame parts that can be reused.
You could still have the Z screws under tention if you suspend the screws on bearings mounted at the top, and decouple the motors at the bottom. This way the load still hangs from the frame, while driven from below.
Are you sure the parallelogram frame does increase the stiffness? Intuitively, it seems like that would just add a rotational component to the resonance induced by the x axis vibrations. Could an engineer chime in and give their opinion?
fma - in reply to nopoe
I think it does (theorically), because they are not aligned anymore with Z axis rods, and they all makes a triangle.

But is it enough? I don't know...
It's not just the parallelogram that's formed by the frame that improves stiffness. It's also the additional triangulation that occurs where the Z smooth rods meet the bottom frame.

Handling the Akimbo frame, it feels far more rigid than the Sells or Prusa frame, but it's still possible to push the top out of line with the bottom.

Still, increased frame rigidity was not my primary goal. I'm after increased build area, particularly when running two extruders.
Ok, cool! That additional triangle stiffening it up makes sense. I hadn't considered the z smooth rods part of the frame.

I can't decide if I want to do this or a Mendel90. I think the Mendel90 will let me print a lot faster, but it's more work. Any idea what kind of z travel you can get with this design? it looks like it should be able to go all the way to the top, so maybe 150-200mm would be possible? Either way, n
ice work! :) I'll be watching this design develop.
For a single extruder (where I can center the motor on Y, and raise the extruder), I expect I can add 30 to 40mm of build height (the amount depends on the length of the hot-end).

With dual extruders there are more trade-offs - extra Z may end up costing X or Y travel.
Sounds like a good idea.

Now, how to get this commited into the Reprap trunk to become part of the next generation?
Good question. Once I've made it quicker to print, It should be fairly easy to get it linked to reprap.org's front page, but the politics involved in actually trying to replace an older design are not a battle that I'm willing to invest my time in.
Top