Introducing The Mendel Uni-body

So I´ve been working on redesigning Mendel´s mechanical parts for the past couple of months.
Looking at a few different things but mainly trying to simplify it all by integrate the metal and plastic parts to create a uni-body that´s pretty much all-plastic (except the bearings)
and made from a single casting process. This basically stream-lines the whole production and assembly.
The other main thing was trying to domesticate it a bit, making it more at home
on a desktop, reduce the weight and foot print. Using a polyurethane
plastic has given it a nice finish.
I´ve already done some ¨debugging¨ and It all seems to be functioning fine but i´m in the process of setting up the electronics on the prototype so it´s still partly in the developmental phase.

Here´s some of the specs

weight - 3 kg aprox
Size - same size as the original Mendel (aprox)
Materials - polyurethane, nylon(fasteners), stainless steel(bearings)
Volume of plastic - 2500 ml aprox
Assembly time - 5 to 7 hours aprox

The designs are all open-source, so feel free to use or alter or do what every you want with them. I´ve put one of these up on eBay for anyone that´s interested.












For more images and all the details about this printer please visit the Foton 3d printer wiki page or fotonlabs.com

Edited 7 time(s). Last edit at 07/22/2010 06:41AM by foton.

What happens when it breaks? If it's all plastic it will, due to a phenomenon called stress relaxation, it's just a matter of how long. That unibody is going to make repairs hard, if one part breaks then it's going to hard to replace it.

Looks really nice, foton! Great job! :-)

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Looks like a good starting point to build one out of plywood.

Looks like a lot of good work!

My main concern is, you might be needing some more structural support for the X axis assembly. Right now it looks like it's just supported by the two nylon screws. Are those going to be stiff and robust enough, when the x axis is moving back and forth?

Edited 1 time(s). Last edit at 05/11/2010 01:19AM by jbayless.

Looks impressive.

But I've some serious concerns about the stability and precision of the x-,y- and z-bars. Even standard Mendel with it's 8mm steel bars and 8mm threaded rod could be more stiff.

... i have some really old (>15years) "can-presses" made from white plastic with embedded glass-fibres which i use for pressing connectors with compliant termination(?).

They are really stiff/rigid and don't have any wear or warping over time.

Inserting glass-fibres in plastic moulds could be good candidates for sturdy frame-materials ...

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Viktor
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foton,

I would be lying if I said, "my heart did not skip a beat!"
From an aesthetic viewpoint, it looks beautiful! Excellent work.
I must re-iterate what has been asked already; can you post some videos with a loaded frame? Specifically, that x-axis looks like it might need additional support, in order to minimize deflection.
Love the fold-out tray, btw....

Excellent work, sir.
Marius Botha
Pretoria, South Africa
[mariushermanbotha.wordpress.com]

Hi Gene

For sure there´s failures to this approach to the mechanics, using plastic,
molding and glue definitely lends it´s self to a less flexible system and the kind of problems with repairs and upgrades that you mentioned. But on a particle level glue would seem to be the best solution for repairs along with a supplier
for parts .

Stress relaxation could be a problem, as i´m not an expert on the subject i guess only time will tell, but one of the reasons for using plastic was that from my experience with Mendels mechanics there dose not seem to be a large amount of stress
especially when the frame is stripped down and lighter like this, I´m planning to look
into carbon fiber to reenforce it´s structural strength
but again it´s
a valid point and positive critics are always useful.

regards joss

Edited 3 time(s). Last edit at 05/11/2010 07:48AM by foton.

This is really great work.

I'm interested in how you moulded the parts for this design, were they cold cast?

Plastic failures are not something you should be concerned with as it can all be overcome with careful design.

Nylon glass filled plastic would be an option and has been in the automotive industry for years. You can fill up to around 60% glass. It does become a little brittle though and is difficult to weld, but is dimensionally very stable.

Some of the parts look a little distorted and this may be due to having varying section thicknesses in the material. Something that could be overcome quite easily with reinforcement and or slight redesign of the parts using webs etc.

You could also consider putting something in the mould to increase rigidity. You could use steel, or even bamboo encapsulated in the plasic.

I'm currently the high bidder. Am I worried about the strength? No. I'll add some reinforcement.

My bid won't go too high because I also think it won't be strong enough. Epoxy for broken parts and replace the nylon screw with steel plus adding the z-supports if needed. I think I can add gilesbathgate's z-skates I could be wrong. Won't be the first money I've wasted playing with making my own repstrap.

Hi Freds

I actually first made this out of MDF, plywood would work fine too though, so it works well as a quick and very cheap(about 25 euro for the materials, bearing and all) way to make a repstrap.

Edited 2 time(s). Last edit at 05/11/2010 05:37PM by foton.

Hi markus

The nylon bars are definitely a concern, they are well constrained by the bearings holding them at each end and i am confident about the strength of the thread on them but, the nylon is quite flexible though.
I spent quite a bit of time working
on casting them with stainless steel bars in side them as a reenforcing with good result but in the end
had to give up because i wasn´t sure about the strenght of the thread made form
the polyurethane, I think nylon is the only plastic i know of the i would trust with this job.
The simple and cheap solution would
be to just replace them with steel bars if need be. but again only working experience with it will tell.

regards

Edited 2 time(s). Last edit at 05/11/2010 08:27AM by foton.

Hi martinprince2004

The parts were made from cold casting as you said. Thanks for the tip on the Nylon glass
I wasn´t aware of it, I tried a few fillers
(metal filings and a general filler) both were unsuccessful, so i need to go on
researching.

I think the idea shows a lot of promise and lends itself to injection molding more than the original mendal simply because there's fewer molds to make.(the fact that it's virtually 100% plastic is a huge stepping stone towards the Gada Prize... If it can print the parts to a mother machine(mega-Mendel) and a "Mega-Mendel" can produce it: we have a 2 stage approach to self replication that looks very promising. Combined with molded production: the design could fascillitate large production volumes/market penetration.

Would it be possible for you to provide STL files or drawings?

If I understand the rigidity issue correctly it's mainly due to rapid changes in direction. This can be resolved at cost of speed by modifying the Inverse Kinematics of the machine controller/G&M interpretter to soften rapid accelleration/deceleration.

The moving parts can most likely be skeletonized to resemble "I" or "H" beams, and the frame could be reinforced with panels if it becomes an issue.

Brilliant prototype.

Looking forward to seeing it dressed up in stepper motors and printing.

Please do thoroughly document the build, and flesh out a wiki page seeing as the forum is so volatile.

I see a gada competitor.

How about a unibody-mendel-strap made of wood?

From reprap

This is a Sketchup drawing....it's a work in progress.
unibody-mendel-strap

Hey Foton

Have you proved this frame in a working 3D printer?

I am looking at building a reprap and this could potentially prove to be an affordable repstrap option if, as I assume, you do not price the product in the same range as RP parts are currently going on ebay.

cheers

Hi Arvin

Here´s an image of the first one i made out of fiberboard, and all the parts
involved.

Hi

I think a few people were looking for a video of the frame with the electronics
on it so i rustled one up, this is the one i´ve been experimenting on and am
setting the electronics up on at the moment so it´s a bit rough round the edges
but other wise it´s pretty much exactly the same as the one above, here it is with the motor cogs being turned.

hi Johnycooper

Think you made some good points, as to the STL files unfortunately i don´t have any, what i do have though is images that are plan views of the parts on 1 cm gridded paper and pretty much all the parts are
1.8 cm thick so it gives a good idea of the dimensions and form though obviously not exact, that´s the best i can do for the moment.

Edited 1 time(s). Last edit at 06/21/2010 05:20AM by foton.

Have the parts cut out. Will try to get them put together this afternoon. Will take pictures.

Notes on the Wooden-Foton-Mendel:

The bowden extruder would be ideal.
gilesbathgate's z-skate would add rigidity.
Use steel allthread instead of nylon.
The green is plastic strap from Lowe's lumber
banding. Picked up off the floor.
The shuttle's angle needs 2 oversized screw
holes at each corner for adjustability.
Some more green strap under the moving parts
pressed up under the supports, aka mcwire, may
be needed to hold down the shuttles.

From reprap

and the Sketchup file:
http://adub.webs.com/wooden-foton-mendel.skp

I did a little construction this morning.Here's some pictures.

From reprap

What you can't see is the grin on my face. I didn't know this was going to be cute!
After the parts were cut out it only took an hour to get to this stage. It will slow down a lot now.

Edited 1 time(s). Last edit at 05/16/2010 01:34PM by Arvin.

This design looks like the % of non reprapable parts could be dermaicaly decreased.

Making Adrians dream of a truly self replicating machine even closer to reality.

The design demonstrates the advantage of an adaative build process as well with no waste generated by cutting material out of solid form.

This is an Ideal starting point to look at making mendel with a lot fewer parts.

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I missed out on the plastic one. As usual I didn't bid high enough.

It inspired me to try making one out of wood. Check out [arvinsramblings.blogspot.com]
I hate blogging.

To foton: Awesome! Have you been working on this design, improving it? Would you make another one (or maybe more than one, depending on interest) and put it on ebay?

Is anyone else working on this? It would be great to have a cheap / mass producible structure. It would certainly lower the entry bar for new users.

To the person that won the auction: Did you get it to work, did you have to make some improvements? Share your knowledge!

Hi Carlos
This design is still in the prototyping stage
the current step is getting it up and printing
(there has been some delay due to faulty electronics)
then there will be some
final redesigning.
There are still a few factors that need resolving before thinking about some form of mass production, mainly the weight and quantity of
plastic used are a bit too heigh and assembly time is still too long to make it realy commercially viable, so I´m
working some redesign to this end.

Edited 1 time(s). Last edit at 06/16/2010 07:30AM by foton.

Glad to hear you're still working on this!

You should post your work in progress, to get comments and help, and to get more people into this

I´ve rustled up a little wiki on the subject for any one that is interest you can find it here it´s a work in progress but
hopefully going to be documenting developments there.

Edited 1 time(s). Last edit at 06/21/2010 05:19PM by foton.

It inspired me to try making one out of wood. Check out [arvinsramblings.blogspot.com]
I hate blogging.

Want to wiki it instead?
http://reprap.org/wiki/CrateStrap
(use the code from http://reprap.org/wiki/Example to get started)
Also, I'd suggest doing a single-axis table, double-axis extruder. You get much more print volume.

I´ve rustled up a little wiki on the subject for any one that is interest you can find it here it´s a work in progress but
hopefully going to be documenting developments there.

Ah, you've put your "source code" up. Excellent. You're now in compliance with the GPL. Carry on.

What was your design and drawing process, by the way? Dead-reckoning and laying out mendel parts on wood, tracing, and cutting? Also, why did you go with plastic threaded rod? For the aesthetic?

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-Sebastien, RepRap.org library gnome.

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Hi Sebastien

What was your design and drawing process, by the way? Dead-reckoning and laying out mendel parts on wood, tracing, and cutting? Also, why did you go with plastic threaded rod? For the aesthetic?

My designs developed out of making my first Mendel according to the standard instruction in so doing i notices a few areas where i thought the project needed building upon
most notably, acquiring parts and the assembly, there seems to be a bit of a problem with distribution (largely
surrounding the plastic parts), so i started working on designs that might help to alleviate some of this, focusing on making a frame that was easier to produce and
assemble. There wasn´t any tracing involved i just took measurements and started looking at what parts could be integrated so as to reduce their number and complexity
doing hand drawings on paper and then transposing them on to MDF fiber board, cutting them out, glueing them to gather and finally using them to create a mold.
I used plastic for the threaded bars as i was hoping to be able to cast them which is quicker and cheaper than buying them, also due to its reduce weight.
I´m new to wiki´s and haven´t figured out how to make a link on the Repstrap category page, i think this might be a good idea if someone feels inclined.