"SteveB" wrote in message
...
I have a large commercial sewing machine, a Singer 111W155. It has a base
with the treadle, and a large motor. I would guess it weighs about 130#.
The legs come down straight to big grommets that sit on the floor.

I want to put two pieces of half inch thick by three inch wide flat bar
across the bases front to back, mount them to the bolts holding the
grommets on, and have them extend out so I can put swivel casters on it to
move the machine around better. This is going to improve the width so as
to make it more stable, but not the length.

How much flex would be in the flat bar? The flat bar would extend past
the current edges of the feet by about four inches. I think the flex
would be minimal, and that it would hold, but wonder if I should weld on
some diagonal brackets made out of simple rods. I could weld them on, but
then it would be difficult if I ever want to remove the wheels. I could
make them to bolt on, but that requires more work.

How much flex?

Steve

Here's a nifty calculator. Knock yerself out:

http://www.efunda.com/formulae/solid...imple_2symload

I'd do it for you but I'm lazy and busy today.

Oh, all right...

"L" is the total length of your bar. The legs apply force at points "P". The
distance from the points where you'll mount the casters to the points where
the legs are bolted on is distance "a". Young's modulus is around 30,000 ksi
(for almost any steel), which is already set as the default in the
calculator. Moment of inertia for a bar 0.5" x 3 " is 0.031 in.^4. "c" is
0.25".

I made some rough guesses about other dimensions and I come up with a
deflection of around 0.001" at the casters. If you lean on the thing with
most of your weight, maybe it's 0.002".

The deflection itself is not enough to worry about. However, 0.002"
leveraged up through the legs might result in some noticeable vibration if
the thing shakes at all.

Flat bars are not very efficient for loading like this. Someone suggested
L-channel. That would be much better.

--
Ed Huntress