Re: [mowbot] Re: Gotta have gas to cut ??

Byron A Jeff (byron nospam at
Sat, 8 Mar 1997 09:58:32 -0500 (EST)

> Ken, there seems to be some problem with your mailer. Your reply came
> back with my remarks unquoted, but your new remarks quoted ???

That's how all of Ken's replies came back to me too.

Well with Ken's encouraging words I decided to try my first experiments
at developing a cutting system. So I set forth with the basic idea of
a DC motor that spins the cutting disk.

The motor was easy. Since it's an experiment and I wanted to be cheap I
stopped at the local Rat Shack and purchased one of their larger 12V DC
motors for $3 US. It's speed rated at 12000 RPM, 1.3A unloaded. Again
since it's just an experiment the power rating isn't important at this point.
The shaft seems to be about 1/8 inch diameter with no attachments.

I then went to the Home Depot hardware superstore in search of a disk. The
saw cutting disks seemed interesting but expensive. Also the prospect of trying
to figure out to map a shaft to a hole many times its size was daunting.

But I finally settled on something a little different: A plastic round
electrical box cover. It's flat, it's round, it's 4 inches in diameter,
it's light, it has to center hole, and it's easy to add new holes too.
And did I mention cheap? $0.50 US each.

Well as expected mounting is the problem. I searched around for some mounting
hardware but I didn't come across anything that exactly fit my needs. The
closest thing was something called a T-nut. I'll talk more about it later.

I drilled a small hole in the center of the plate and pressed it onto the
shaft. The spinning speed was impressive but the disk would move towards
the end of the shaft. As an experiment I placed a nut that was slightly
larger than the shaft on the shaft between the plate and the end. I then
soldered the nut to the shaft. It did the job of keeping the plate in place.

The problems now:

1) The plate really isn't attached to the shaft so while it spins there really
isn't any power to it.

2) The motor speed varies greatly. It goes from moving quite fast to slowing
down. It does it in cycles apparently.

3) A spinning motor is a vibration monster. It's going to take some work
to get it mounted.

4) Heat. Need I say more?

I'm planning on SuperGlueing the plate to the soldered nut but it isn't
an ideal solution.

Anyway back to the T-nut. It's a plate with a threaded hollow shaft mounted
in the center. The plate also has holes near the edge.

It's the right direction in mounting because the shaft of the nut can go over
the shaft of the motor and the holes in the plate of the nut can be used
to mount the plastic plate.

The problem is that the motor shaft isn't threaded.

I think I'll try using a wood block next. If I drill a hole for the motor
shaft and holes to mount a couple of T-nuts on the side of the block, I can
then use a couple of screws through the T-nuts to hold the whole thing
together. Essentially the block would act as a big T-nut with mounting
holes perpendicular to the shaft. I guess it's ASCII art time:



m - Motor and shaft
W - Wood block
T - T-nut
S - Mounting Screw
P - Plastic spinning plate.