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Topic: Worm Gear
Message: Posted by: Bryan Gilles (Dec 30, 2006 03:01PM)
I'm looking for a large worm gear much like one used in Steimeyer's Pole Levitation. It would need to support my weight (175 lbs.)

Any ideas?

Message: Posted by: makeupguy (Dec 30, 2006 08:42PM)
I think that you can adapt one from a garage door opener... but... I think you might be better off making it from scratch from parts at GRAINGER.

I'm actally looking to do the same thing for a levitation I want to build.. there are a number of mechanical FX guys in LA that could tackle it.. but those guys charge about 50 an hour just to have lunch.
Message: Posted by: Bryan Gilles (Dec 31, 2006 12:42AM)
I toyed with the idea of using a large threaded rod (like a super-long bolt) and hooking the base of it to a chain and gear system to hook it up...

not sure if that made much sense.
Message: Posted by: RiserMagic (Dec 31, 2006 01:44AM)
Acme screw threaded rod - not worm gear. The threaded rod and matching nuts may be obtained from MSC or the like. There is more to building a safe lift than the threaded rod and nuts. Safety must be the prime concern on such items.
Message: Posted by: raywitko (Dec 31, 2006 09:17AM)
I get all my linear actuators and other lifts from Duff-Norton. They only sell to distributors but if you contact them they will tell you who distributes near you. They have all kinds of lifts etc. I don't have a web site for them but if you do a search you can locate them.
Message: Posted by: Bryan Gilles (Dec 31, 2006 12:08PM)
Thanks guys...
Message: Posted by: makeupguy (Dec 31, 2006 10:28PM)
A linear actuar is a VERY diffent thing than worm gear.. and just as diffrent from Threaded Rod..

A worm gear rod is hardend steel.. threaded rod is soft.. and the threads are WAY too close together..

I've seen a real licensed Three Pole Levi and the threads were pretty wide.. and it had a "dimmer" to control the speed of the motor... which is GREAT.. a little faster at teh bottom.. and then it just slows to a stop.. the way someone would really probably levitate..
Message: Posted by: RiserMagic (Jan 1, 2007 12:16AM)
One of the big problems with the Magic Café is the amount of misinformation given out by those who really do not know what they are talking about.

Most linear actuators consist of a gear motor (to slow down the motor rpms and increase M.A.) sitting at the end of a cylinder. Inside of this cylinder is an ACME threaded rod coupled to the output shaft of the motor. The tpi varies with the requirements of the job at hand. I currently have three linear actuators sitting in my shop being modified for lifts. All three have different tpis. One is 4 tpi, one is 8 tpi, and the third is 5 tpi. 10 tpi is also a common thread. The tpi is selected to give a certain mechanical advantage and a selected rise/fall per rpm of the motor. BTW - tpi is threads per inch. The builder selects the tpi for the shafting - none of the tpis listed above are "too fine".

ACME threads are SQUARE threads which are ideal for the task and ARE what is used/desired. Usually a steel shaft with the ACME threads is used in conjunction with a softer brass or bronze nut. This allows the nut to act as a simple bearing (the bearing needs to be softer than the threaded shafting). Lube must be applied to the threaded rod. More expensive ball screws could be used; but most often are not.

I have also made lifts utilizing cables (wire rope) with pulleys and a winch. In addition, lifts have been made using chain/sprocket drives.

Threaded rod is the cheapest and most reliable method for making such lifts.

BTW - The guys charge $50 and way up per hour because they know what they are doing and ARE worth it. It's difficult to put a price on safety. I certainly would not want an amateur building a lift for me. Bryan, do not mess around with safety.
Message: Posted by: silverking (Jan 1, 2007 12:01PM)
Just look at your bench vise screw or lathe screw to see an ACME thread.

The reference a few posts above to a "dimmer" could be a bit misleading.
You could use a "motor controller" on a DC motor, which would maintain full torque throughout the RPM range. DC motors (with the appropriate controller) can maintain full torque at all RPM.

Using a "dimmer" on an AC motor would REDUCE the torque as you slowed down the motor, usually rendering the motor useless at around 50% of its rated voltage.
AC motors develop less torque as you reduce voltage.
You can slow down a ceiling fan AC motor because there's very little load on it, as soon as you apply any load you require full voltage in order to get full torque.

As I work with performer safety each and every working day of my life, I'd have to say that if you're engineering and building effects in which, or on which other people float, levitate, hang, or fall you really should know the difference between a 29 degree Acme thread and a 60 degree V-Thread.

Calling technical advice from Jim Riser into question is beyond my ability to understand.
Message: Posted by: Tom Bartlett (Jan 1, 2007 08:07PM)
Jim Riser is on the money. He does know what he is talking about and not just from reading but from applying it, check out his web site. It would be in your best interest to play close attention to any help this man offers.

As for linear actuators, I have had great luck buying from online auctions for pennies on the dollar. A lot of them are salvaged off of high-end tread mills and sold on ebay.