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Mendel + Lego = MendeLego

Posted by rob.m.clarke 
Mendel + Lego = MendeLego
January 31, 2011 02:16PM
I've been working on this off and on for a while now but I thought it was time to share where I'd got to and see what the rest of the community thought of this idea for repstrapping a Mendel type 3d Printer.

All the vertices are made from Lego bricks.

I'm going to go document where i've got to on my posterous blog.

All opinions gratefully received.

Edited 1 time(s). Last edit at 01/31/2011 03:29PM by rob.m.clarke.
Re: Mendel + Lego = MendeLego
January 31, 2011 02:43PM
Nice one Rob

It looks great, have you needed to mod any of the Lego?

Are they M3 bolts holding it all together, any bits just using Lego-stick

You may need a bit of glue in the end to stop it breaking up?

Good luck, i'll keep an eye on the blog

Re: Mendel + Lego = MendeLego
January 31, 2011 03:05PM
Thanks for the post.

I've only had to "modify" a couple of Lego bricks so far and that was a conscious decision on my part.
The holes in the bricks are 0.2mm off taking an M5 bolt and those are M5 threaded rods I'm using too.

Take a look at that image, you can see the thread that is cut in the ABS when an M5 bolt is wound into the piece.

The only real pieces I've modified are the white ones in the pic below.

Thanks again.

Edited 1 time(s). Last edit at 01/31/2011 03:07PM by rob.m.clarke.
Re: Mendel + Lego = MendeLego
February 08, 2011 03:58AM

Just wanted to follow up on the whole glue/no glue aspect.

One of the things I wanted to do with MendeLego was to try and make it so that once you'd finished with your RepStrap, you could disassemble it and put the Lego bricks back into the pot for the next model you want to build.

You can't really do that if you've used an ABS glue to stick the pieces together.

What I have found is that by bolting the pieces together you remove a teeny gap that is built into the Lego brick. Let me illustrate.

Holding up those normal Lego bricks to the light, you can see that light leaks through a gap between the bricks.

This is part of the normal Lego tolerance, which allows young fingers to get the bricks apart without ripping into their hands.

By screwing the Lego bricks onto an M5 threaded rod or bolt, you can force out this gap. The upshot of this is that the nubs on the top of the brick get ever so slightly closer, as do the receptors in the bottom of the brick. When you join this at 90 degrees to another Lego brick you can "feel" the fit is a lot tighter than you'd get with a normal connection. If you join it to another "bolted" pair of Lego bricks, the join feels even tighter still.

I'm hopeful that this extra grip in these joins should make it easier to build a structure like this that doesn't need to be glued.

I've added a lot more pictures to my blog and I'm slowly working on a dedicated page that hosts more build instructions

Re: Mendel + Lego = MendeLego
February 09, 2011 06:35PM
Hi Rob

Still sounds like a good project and I like the tapped silver steel rods, my only worry would be the flex you get in the M5 rods, but you may just get away with it.
Huxley uses M6 so with a little more support it may not cause too many issues for you.

Is it going to be full size? And are you going for a prusa style design with bushings or lots of Bearings like Mendel?


Re: Mendel + Lego = MendeLego
February 11, 2011 12:03PM

I know what you mean about flex. That is my biggest concern at the moment.

I have a mk4 makerbot plastruder here, which I think is going to test the design to its limits.
I just need to find time it put it together.

It'll be resting on those 5mm silver steel rods though, so I don't think there'll be too much flex in those.

As for the rest of it, I'm current playing with the idea that Lego bricks can also be re-purposed as bushings.
Hopefully this will keep the weight down and prevent flexing too.

Size? I'm hoping to have room for a 200mm bed but the z-axis may suffer if I go that large.
Re: Mendel + Lego = MendeLego
February 21, 2011 02:13PM
How ridig is the frame turning out to be?

With all those hinge points in each vertex, and large levers connecting into them, I'm curious if the whole structure is rigid enough not to rack under load.
Re: Mendel + Lego = MendeLego
February 22, 2011 07:05AM
Short answer... I don't know.

If I lean on things they bend, so I try not to lean on them. I've not got my z-axis sorted out yet but the x and y axis run on 5mm silver steel rods.
I can flex those rods with my hands but that takes a fair bit of effort to do so.

As for the joints. Yes, I can see that these could be a point of failure if the frame is put under stress. I just don't have the time at the moment to spend on this. Perhaps after Easter I'll be able to give this the time it deserves.

I am still optimistic at this point that the whole frame, axis and drive mechanisms (excluding the extruder) can be built using Lego Bricks.
Re: Mendel + Lego = MendeLego
February 22, 2011 03:56PM
Thanks. I think you've answered my question -- it sounds like the joints themselves are rigid enough to work.

If the design I've been working on doesn't work out, I was planning something similar to what you're doing.

rob.m.clarke Wrote:
> If I lean on things they bend, so I try not to
> lean on them.
> I can flex those rods with my hands but that takes
> a fair bit of effort to do so.

Hey, great work on the MendeLego! Have you thought about going with the Prusa instead? I think that's my inclination.

It would be great if your MendeLego page had a "what's next" kind of roadmap. I'm sure you know what needs to happen next, but I'm not sure what I'd do if I were to build what you have and try to extend it to the next logical step.

There's a standard LEGO piece that I think would work instead of the modified white flat pieces you're using.
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