The M2 Platform Rocks!

[pyronaught]

And that's a GOOD thing.

I used to think it was a bad thing until this recent project I'm working on. I'm making parts that involve a domed screen nested inside of an outer solid dome. The domes are large, so printing them with support is just not worth the extra cost and time. So I just print them without support and then go clean up the mess on the dome ceilings with a ball sander afterwards. However, quite a mountain range of globs build up when closing the top of the screen domes. This is because the slots in the walls prevent the walls from being made using concentric circles, so it gets very messy as the thin fingers curl up on the ends and scrape filament onto the print head which builds up and then gets dropped off elsewhere. It's very unsightly to watch, but amazingly the printer gets through it despite having to drag over such a rough surface. As bad as that picture looks below, it manages to self heal itself and you would never know it was there.

Now, if this were one of those printers with the rigid, fixed platforms where the print head moves on the Z axis instead this would never work. Those blobs are rock solid and not going anywhere, so something else would have to give. The model would get knocked off, motor steps would be lost, the print head might get knocked out of alignment... something would have to give. But on the M2, the platform flexes instead and deflects this load in a non-destructive way. Without that flex, these vacu-form screens I'm selling would not be a viable product due to the increased time and cost of printing with loads of support material.

So M2 designers, if anyone ever complains about the platform flexing PLEASE DON'T CHANGE IT! That flex makes it very blob tolerant, and sometimes there is just going to be blobs.

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[ednisley]

a domed screen nested inside of an outer solid dome

Man, that design just cries out to be printed in sections and glued together.

Do the inner & outer domes as shown, up to just below the level where the inner dome fingers begin. Print the "top" section of the inner and outer domes separately, inverted with the closed end down, adding those triangular supports under every finger. The top sections of the domes look like they'd fit side-by-side on the platform.

I'd be tempted to split the top of the solid outer dome into two sections that would print standing upright, nested like spoons, to eliminate any support. You can't do that with the whole dome, but it'd probably work with the upper section.

Put alignment pin holes on all the mating surfaces, add filament snippets, glue 'em together, and it'd be perfect.

The total plastic volume would be about the same, so it wouldn't take any longer to print, modulo a bit of setup / takedown time. I think gluing would take less time than sanding, it'd be much less hassle, and a whole bunch cleaner, too.

Whaddaya think?

[pyronaught]

It actually works well as a one piece mold though, and the sanding is very fast. A sanding ball on a drill press makes short work of cleaning up the inside dome-- faster than gluing pieces would be. The outside is already smooth and requires no sanding, and the outside of the inner dome along with the inside of the outer dome are hidden from view so their condition doesn't matter. There can be stringers and blobs all over the inner surfaces and nobody will ever see them.

There's also a piece of stretchy fabric that goes over the mold face so even the sanded surface is not visible to the end user. These are plugged into a shop vac and used to suck paper mulch from a vat in order to produce paper hemispheres which are then used to make spherical firework shells.

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hemi_3_drying.jpg (407.96 KiB) Viewed 11370 times

[Mark the Greater]

I just figured out what your name means...

[pyronaught]

I just figured out what your name means...

Ha, yeah it's what I do. www.passfire.com

[ednisley]

faster than gluing pieces

Ah! So that's what the whole thing looks like: clamping would be a challenge. Definitely a good use of 3D printing!

Years ago, our lass collected charred scraps of spent fireworks during a show where the wind directed a bit more energy toward the crowd than predicted. We wondered how they made the shells and now I know...

[Mark the Greater]

The really cool thing here is the versatility. Like, you could totally make mini Death Stars, or cruddy fake oranges, or...mannequin...parts...

[pyronaught]

This particular method of making hemispheres is actually not the same as the commercial process used to make real firework hemis, but it allows anyone to make their own hemis with only a shop vac and the mold. The Chinese use a big press that stamps them out from layered stacks of flower shaped disks, with the gaps between the petals closing into a seam once formed into a hemisphere. That method is faster and the hemis aren't as fragile coming out of the mold, but the hobbyist can't do this very easily. The vacu-form method uses the same technique used to make the paper drink holders you get from McDonalds, and you could of course make a wide range of shapes as long as the form will release from the mold easily. The DIY method requires that you first find some recycled kraft paper, get it wet and then chew it up in a blender bit by bit until you can fill a trashcan full of pulverized paper slurry. You can also use the shredded newspaper insulation that comes in bales at home improvement stores to skip the blending step, but it is not as strong as kraft paper.

The molds must have a layer of spandex or similar flexible fabric attached over the opening, which acts like a fine screen to let the water through but not the pulp. It also helps release the mold afterwards too. Then you just plug the mod into a shop vac hose and dip it in to the vat for a few seconds to charge it with pulp. I apply some diluted wood glue on the pulp while the vac is still running to increase the strength of the finished hemis, then I have some printed plugs I push into the cavities to compress the paper down for a denser hemi wall. Then you just hold the end over a screen and shut the vac off and the hemi set pops out. I can dry them in an oven set to 325 in just 20 minutes, but for large production batches I have a big drying rack that air dries them in a day or so.

And yes it is an ideal application for 3D printing. Prior to owning a 3D printer I had to try and make these molds out of fiberglass, which was a major pain and required drilling hundreds of tiny holes to produce the screen. I also had to find appropriate size molds to use for both the inner and outer shells, which was not always possible. Firework hemis have to be an exact size, and the mulch actually shrinks a little on drying so you can't even use existing firework hemis for laying up the fiberglass mold or the hemis would be under sized. If you can't find the exact right size sphere then you just can't make one out of fiberglass. With 3D printing of course this limitation goes away and you can make any size sphere you want without any drilling at all, and the resulting one piece mold is a lot more sturdy and you don't have the problem of glue joints cracking. The ability to put a ridge around the edge for tying on the spandex cover solves another big problem too.

So yaay 3D printing! I now have vacuum molds for the full range of firework shell sizes from 1" all the way to 6".

[pyronaught]

Here is some being used to make 4" shells. I have another machine I built that puts the finish layer of paper over top of these. Mulched paper is not strong enough to use for the final shell casing.

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[youtube]https://www.youtube.com/watch?v=q278kMpBnHA[/youtube]

Youtube embedding does not appear to be setup for this BB and I don't see a way to edit html directly in a post either. I guess you just can't embed youtube videos here?