rotational molders

[charper]

anyone building any machines? I would like to build one at home and make my own aluminum casts for them. Applications for rotational molding any one has? Check out my old school machine and small molds that my students are making. Let's talk rotational molding.

[greencoulee]

charper-
very nice. Reminds me of a prototype machine we built out of an Oldsmobile wagon rearend and an electric motor. I used to work at a large rotational mold builder. (large company and large molds). Is that an old electric stove element used to heat? Much safer than LP!

[drcrash]

Here's the "NEW!" IASCO mini rotomolder.

This is clearly a common-or-garden rotisserie oven, like you can find at the thrift store for a few bucks, plus a few bucks worth of other parts. (A bearing, a C clamp, a couple of plates, a few bolts.)



It looks like it would be really, really easy to make one of these for $20-40 if you can figure out how the 2nd axis rotation works.

It doesn't look like it uses any gears to drive the 2nd axis rotation---just a bearing added to one of the rotisserie crossmembers. I'm guess it uses some simple weighting trick so that the mold flops around on that axis as the whole thing rotates on the rotisserie axis.

I don't know if that works well. If not, it shouldn't be difficult to come up with something simple and cheap that works better. (Such as pendulum mounted in the rotisserie that flips and flops at each rotation, with a ratchet to drive the other axis in one direction at each flip or flop.)

[drcrash]

Here's a no-heat rotomolder for hollowcasting resins, from the projects page at solsylva.com (http://solsylva.com/cnc/projects.html).



I don't think there's anything special about this particular design, except as an exercise in CNC-routing gears, but it got me thinking. If you scrounged some reasonable-sized gears (not outsize like this, relative to the frame sizes) and used a drive shaft or two, you cold make something like this that folds flat---the two oncentric frames would just fold together, and you could detach the base, fold it up, and store it in the middle. That way, you could make a big roto-caster and store it reasonably compactly. (Like maybe a human-sized one that you store in the garage, pull out and set up in the back yard to use it. Then you could make some big full-3D objects now and then.)

[drcrash]

I'm wondering whether CAFE molds would be easy to make and work well for a little rotomolder like this, or even a big one.

(CAFE being Composite Aluminum Filled Epoxy, discussed in the "Aluminum molds for thermoforming" thread: http://www.cnczone.com/forums/showthread.php?t=28086.)

I'm thinking the lower thermal conductivity might be less of an issue for rotomolding than other kinds of molding, because the cycle times are already pretty high. As long as the aluminum-filled epoxy is conductive enough to keep the mold surface at the right temperature, the increased heat-up and cool-down times would be negligible compared to the time taken to actually rotomold something.

[monkeyracing]

im going to be building up a rotomolder, to make fuel tanks and water bottles for motorbikes and cars, but due to the size will also need to build a larger oven to have it in to melt the plastic down,

was wondering if anyone knew of a plastic which comes as two liquids that when mix cure at room tempeture or a very low heat, i know epoxy resin would do the job but this is just to brittle for tanks that will endure alot of vibration,

any help anyone could provide would be great,
cheers

[crashmann]

It looks like there has been an update to the design of the wooden roto-molder. No more wooden gears, now there are belts and pulleys:
http://solsylva.com/cnc/rotomold.html



Regarding a two part liquid plastic for fuel tanks - I'm not sure what to recommend for that. I suspect the fuel would have a detrimental effect on the cured plastic. I purchase my stuff from http://www.smoothon.com You might contact them and see what they would recommend (however, they are located in the US, and I suspect your in the UK...)

Good luck!

Charlie

[kayaker43]

Roto molding looks fun, as usual, the oven is the tricky part but should be less fussy than thermoforming?

Polytek makes a resin that gives the look and feel of polyethlyene, but I doubt its as fuel proof.

Larger roto molds are often made from sheet metal, great for making fuel tanks and other boxy shapes. Epoxies should work with a longer cycle time?

Might be tough to find small quantities of powdered resin, and some need to be pre-dried too.

[Khalid]

good job

[planebuilder]

No posts for a while?
Is anyone making any progress on a machine build?
I built a 5' x 5' x 7' oven for powder coating and plexiglas molding, am now building a 24'x8'x8' oven. It could easily be adapted to also rotomold. I am hunting for pics and drawings of rotomolders. I have been to look at a few in operation and they are not very complicated. With a little thought I think a very simple one could be made.