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R W
03-28-2011, 07:04 PM
Am about to start making a set of swivel wheels for a gantry, could anyone
tell me what the correct offset should be to allow the wheels to swivel in regard to the direction of travel.

Roy Andrews
03-28-2011, 07:09 PM
any offset will make them swivel. the longer the offset the easier they turn but makes the handling poor.

metalmagpie
03-28-2011, 07:15 PM
I put locking casters on my gantry. Not the kind that locks the wheel from turning, the kind that locks the caster from rotating. That way you can lock two of them straight and leave the other two rotating and "drive" the thing much more easily. Also, you can lock wheels offset by 90 degrees so the gantry cannot move.

The biggest problem I have with my rolling gantry is my uneven driveway. It looks flat, but it isn't. I wish I had some kind of slick adjustment to make one side of the beam adjust vertically by an inch or so to level the beam after moving it. Right now I have to roll it up onto boards, which is irritating.

I made mine height-adjustable so it can lower down far enough to roll into my shop, or high enough so I can lift a Bridgeport onto a low trailer. Suits my needs very well.

I used a commercial beam clamping product to bolt the beam to the legs, so the whole thing can knock down and be transported in a 5x10' trailer.

metalmagpie

R W
03-29-2011, 04:02 AM
May try it with two fixed and two swivel similar to my engine hoist, the fixed
could be made to be rotated 90 degrees and pinned.
How does between 1/3 & 1/2 the diameter of the wheels sound for the offset. Wheels have been fabricated from heavy pipe 6.5" in dia,2.5" wide, 5/8" plate centres with I.5" bosses drilled to 7/8". Swivel pins will be 1"dia.

hardtail
03-29-2011, 07:22 AM
Heres the ones I bought.....the offest isn't very much, it would be nice if they had a better side view......

http://www.princessauto.com/all-seasons/farm/casters/heavy-duty-500+/2040291-8-poly/steel-swivel-caster-with-brake

MM I would be interested in seeing that beam clamp.

justanengineer
03-29-2011, 08:12 AM
If by swivel wheels you mean casters do yourself a favor and dont unless the casters retract and there are solid pads/feet in use for actual lifting. If you want a safe and dependable system otherwise use lockable rollers that have a good crown to them.

SVS
03-29-2011, 08:36 AM
1/3 sounds good to me. I'm sure there is a magic formula "somewhere".

metalmagpie
03-29-2011, 07:21 PM
MM I would be interested in seeing that beam clamp.

I ordered them from beamclamp.com and I got part number BT1G12, not that I can find them on their current Web site .. but poke around there, you will get the idea.

Incidentally, if you want to see my working sketches click here: http://www.tinyisland.com/images/temp/gantry.pdf

metalmagpie

HAP
03-29-2011, 08:57 PM
How about some crank down leveling jacks. Levels and secures at the same time...

metalmagpie
03-30-2011, 11:20 AM
How about some crank down leveling jacks. Levels and secures at the same time...

I like the idea, HAP, but I'd have to spoil the clean lines of my gantry to do it. Still, it's worth thinking about ..

metalmagpie

Doozer
03-30-2011, 12:32 PM
FWIW-
The offset in casters is properly called "trail".
I think someone along the line some time ago thought the offset was actually caster, and the name stuck.
Another odd thing, the industry calls them "swivel casters" and "straight casters", and I would say a straight caster has no caster, or more properly, no trail. Odd how language evolves.

Lets see some pics of this gantry. He He He...

-Doozer