DC Motor question

[GlennR]

I'm building a centrifugal glass casting machine. It spins like a pottery wheel, and has an open face mold on top that you pour molten glass into. After pouring you turn the speed up and spin the glass to form a concave bowl shape, that is smooth on the interior.

Anyway, I'm using a 90V DC gear motor and the controller has a potentiometer mounted on the circuit board that varies the volts from 90 to 120. My motor is a 90V, but will run faster when I adjust the pot. I installed a separate potentiometer that controls the speed from 0-170 rpm. I'm curious if I run the motor on 120 volts if it will damage it. Does anybody here know?

The reason I ask is I don't really know how fast I will need to spin the mold, and 170 rpm may not be quite fast enough. I just ordered a digital tachometer, so I'll know how fast it's turning. 120 volts may be handy, rather than having to order a different drive pulley to increase the speed. But, is it safe for my 90V motor?

[kbalch]

Hi Glenn,

I'm sure that the proper speed will be directly related to the viscosity of your molten glass. Here's one site suggesting that up to 3,000 RPM may be required:

Glass casting info

[safety nag mode]Good luck with this and be safe![/safety nag mode]

Ken

[GlennR]

Thanks for the link. The type of pieces I'll be making won't require speeds anywhere near 3000 rpm. That would be for very small, thin, or low viscosity glass. I'll be making large thick bowls, that will be drilled to become sinks. The glass will be about 2100f and weigh 25-30+ lbs, so it will have a lot of thermal mass and not require high speeds to flow & fill the mold.

I got the drive shaft keyways cut today, and was able to partially assemble the machine & test run it. I'm using the lower portion of a 55 gallon drum as the mold containment shell, that will hold the foundry sand mold. I'm mounting the drum on a plywood disc as a stiffener between it & the hub flange. I used the machine as a lathe to turn the wood disc to size, which fits snugly into the recess on the bottom of the drum. I got the disc pretty round, but the flange isn't as precise as I'd like, and it has a bit of wobble. I am planning to fill the drum will plaster and spin it slowly while it sets, hoping that it will spin balance.

The disc is 22.25" in diameter. It "looked" quite fast at top speed (approximately 190 rpm). Here's a link to a glass spinning machine that I'm basing my ideas on. It's a sturdier design than mine, and also has a push-up lift to raise the finished bowl. I decided to use materials on hand, and see if it works. If not, I will make a better one.

Hot Glass Spinout – Richard Morrell Glass

[DIYer]

I'm getting intrigued by your build, GlennR. Looking forward to seeing pictures of that!

[GlennR]

Right now it's not much to look at. Just imagine a shipping crate with a short shaft sticking out the top about 4".

I had to take the flange hub to the machine shop and get it trued. (I don't have a lathe) It wobbled about 1/4", measured at the edge of the 22.25" disc. The hub is one I picked up from Northern Tool, it's for go-carts or ATVs. It has 4 wheel studs tack welded on, but I grind those off. It fits on a 1" shaft. I have used one before for making a 24" flat lap grinder, which has a 3/4" think steel plate for the wheel. I'd forgotten that they need to be flattened.

I'm heading out of town tomorrow, so won't be back in the shop for about a week.