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This thread is for those interested in a modular chassis design of the Shellmo that will allow for reduced time/part printing and target Replicator 2 class machines with resolution of .2mm or greater without support.

I spent about 12 hours yesterday in sketch up reworking parts so they have at least one flat side, combining components into solid structures and dividing the chassis into modules.

My progress.
could you make the stls available when you are finished?
Hello James,

the modular chassis will be the key to a successive design. With this one can modify functions and parts without redesigning and reprinting everything of Shellmo new.

For my opinion we should first build a crude chassis with the focus on easy printing and save durable function. If we have reached this, we could fine tune it and make it nice looking.

Rainer
I finished the first test prints of the modular chassis. Everything was printed at .2mm 2 shells 55mm/sec on a raft without supports.

As you can see in the pictures the parts fit very well together. Besides the front and back all pieces fit very tightly. I used a very small mallet to tap each part together.

The bad news is simply tearing apart Sho's chassis into pieces isn't going to work. The pictures show obvious warpage along the length. Way beyond what would be tolerable. The modular parts are going to have to be further modified to optimize printing using PLA.

More pictures.
Hello,
Your concepts & results looks nice !
In my Replicator2, I can reduce warpage with printing temperature about 250C' for PLA.
(04-20-2014 06:29 PM)sho Wrote: [ -> ]printing temperature about 250C' for PLA.
PLA with 250°C sounds way to high for me. Is this a recommendation of Replicator?
The solution (hack) would be a heated bed, though I think this would be unsatisfactory since we can't expect people printing with PLA to have one as its not a common setup. The parts just need tweaked to compensate for the tendency to warp on long slender parts.

While I was laying in bed last night I realized that this could be fixed as simply as changing print orientation. I am going to print them flat (originally I printed vertically because I am lazy and hate removing raft from flat faces). The cross members should then force any warpage true. I'll start some flat frame pieces right now and update in a couple hours.

(I just figured out yesterday that if you use a glass scraper which is just a razor blade with a handle you can easily remove the most difficult rafts but wear a think leather glove on the hand thats holding the part so you don't cut yourself if you slip)

(04-20-2014 06:29 PM)sho Wrote: [ -> ]Hello,
Your concepts & results looks nice !
In my Replicator2, I can reduce warpage with printing temperature about 250C' for PLA.

Yeah, not sure. That could be your PLA more than anything else. I have really good results with 215-220 using Makerbot filament. 230 default of the Replicator 2 seems a tad too high. If you notice the parts I am printing without support require the PLA to be slightly cooler I think just because of the way some of the angles are designed and to bridge 3mm+- 90 degree angles I would think hotter PLA would droop down so I always run cooler.
(04-20-2014 09:48 PM)jmccartney Wrote: [ -> ]so I always run cooler.
Cooler printing = less warp.
Latest version of the frame module for the chassis. This is still a work in progress. Will still be printed vertical, but with all the horizontal reinforcement I added and tying both frames sides together I think the warpage won't be a problem. I added a bunch of edges to make construction easier and help with the front and back modules to connect to the two frame modules (right and left).
[attachment=56]
I thing one has to play with design and printing a while till you get good results.

3D printing is a little like working with cast iron - part of my professional work - this parts are still alive after pouring/printing. The tensions in the surfaces and in it's inner material will do their job

Soft shaped and symmetric parts are best. Also try to avoid big bunches of material at one location. Make all walls with equal thickness. All this are good design guidelines for cast iron and so will be for 3D printing too! - my personal opinion...
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