I need a heavy duty worm drive...

[elShoggotho]

...and I want to build it myself. Reduction needs to be high enough to make it essentially self braking, for security reasons. Does anyone know a good tutorial on how to make something like that, or a place to acquire the parts?

[Mr. Boltneck]

Machining even a simple worm drive yourself will, as far as I know, require a hob to form the worm gear on a mill or similar and a lathe to form the worm. More complex forms will take a bit more tooling or tool-making. There are some videos up on YouTube about making and using hobs for spur gears and the like.
As far as finding parts, you could try the usual industrial suppliers on-line, or industrial surplus stores in the area.
Since a number of portable winches use a heavy (and often self-locking) worm drive, you might see if anyone has some scrap or surplus truck/boat/ATV winches available.

[Miles (a sailor)Martin]

how much load is this thing going to carry? that is going to drive the size /weight/cost.
                                                    miles

[bicyclebuilder]

yep, winches are my first guess to Mr. Boltneck.

[elShoggotho]

It's for a friend's BDSM studio. The cross is fixed to a central axle, with means to rotate it. Now they need a worm drive that can rotate the cross safely while a person is tied to it.

[Maets]

You could use a winch.  Replace the cable with a belt or chain to the cross to be turned.  Low speed, powerful and pretty easy to set up.

[elShoggotho]

An ordinary winch offers no reduction though, and reduction is important to move that kind of mass with one hand.

[Maets]

Just trying to understand your usage better. 
You want to hand crank a unit that then turns a large cross? 
Purely hand power or electric ok?

Sketch?

[Mr. Boltneck]

Pretty much every hand-operated winch I know of offers some amount of reduction, ranging from around 4:1 up to 20:1 or more. The BDSM suspension rigs I have seen typically use a medium-duty marine winch with a positive locking mechanism, such as a lockable ratchet, and reversibility, since you need to raise and lower under control, not raise and drop.

[elShoggotho]

Look behind the spoiler, it's a photo of the whole rig.

Warning, photo related to subject matter: ShowHide

[Mr. Boltneck]

Hmm...so if I interpret this correctly, what is wanted is a way to rotate the St. Andrews cross, and lock it in position as needed? Or is there another rotational axis I am not seeing? I've seen invertible St. Andrews crosses at Folsom Street Fair that were just built with a very strong steel stand and pillow-block bearings. If you want to use the worm drive to rotate the cross, then it might be possible to connect the winch drum, or its shaft, to the axis of the cross. I suppose that a reduction drive based on heavy-duty sprockets and drive chain is possible, too, but I might be a bit nervous about such things near limbs, clothes, and hair.

[elShoggotho]

That's exactly the plan right now: get winch parts, build a casing for them, attach them to the rotational axis of that cross. Attach a hand wheel to the worm gear, possibly via two angled gears.

[von Corax]

Something like one of these, then.

(Sorry, wrong side of the Pond, but at least it conveys the idea.)

[elShoggotho]

Something like one of these, then.

(Sorry, wrong side of the Pond, but at least it conveys the idea.)

Nice one, but the stated load capacity of 1,100 lb. lacks in the security margin department. Needs to have a stated load capacity of at least a Metric ton.

[Mr. Boltneck]

Perhaps I am missing part of the design, but it seems to me that if the rotational axis of the cross is at the center, and it is mounted to some sort of bearings, as I have seen done elsewhere, then you don't need the winch to support the load of (cross+human)*(safety factor). It only needs to exert the force required to rotate the whole assembly, which should be fairly low. This might make life much simpler, as well as less costly, since heavy-duty bearings and axles are simpler to find than heavy-load hand-cranked winches.

[elShoggotho]

They've already broken weaker solutions. That's why they're looking for a heavy duty worm drive that can mount a hand crank, to be on the secure side. Worm drives are basically self locking, and they want it to hold up, even when a rather large person is just sitting on one end of the cross.

Oh, and it rotates just fine. It just needs to rotate in a way that auto-locks in any position, to make it possible for a weak person to rotate it safely under load.

[Arceye]

ElShoggotho I would be looking for an old disabled buiggy motor/gearbox, these things are very strong and made to take all kinds of abuse

[von Corax]

You could put a 2:1 or 3:1 gearbox between the cross axle and the worm-drive output shaft. On the 15:1 drive that would be 3300 lb. (I'm guessing that's actually 3300 in-lb. torque, since this type of drive usually isn't side-loaded) and 45:1 speed reduction. (Take a while to spin a person, but not as long as the 100:1 would... )

[architect]

interesting. I have one of those items pictured *reduction gear box* for a very very large machine, so the load rating I believe is something like 2 to 3 thousand pounds. the one major issue it has is that the rod that is a machined part of the worm is broken off so there is only like an inch of steel rod to clamp onto. thus it had to be thrown out. the worm and worm gear are completely fine too so the torque to twist off an inch thick bar of tool steel was not enough force to damage them. quite impressive and I am guessing the reason it was that small was to make sure it was where the unit broke if over loaded rather than the worm snapping or something.

real problem with the unit is that it would cost a fortune to ship it over seas. though the worm and worm gear are not as heavy if removed from their housing. which just needs to be a box with 4 holes in it. 2 sets of 2 holes on opposite sides of the box)

however for load ratings and such I would say you should check out http://www.sdp-si.com/

there are cheaper alternatives once you know what you are looking for, and if you need, this is a good place to show items to them, so they know what they are getting.

[Otto Von Pifka]

something like this for the gearbox if you weld a sproket to the free side of the cable spool.

an alternative you might find as scrap would be the gearbox for an auger on a coal fired furnace
they use a sort of archemedes screw to feed the furnaces.

my dad used a bigger than average one to lift an 8000 pound boat up out of the water to winter over.  the gear box was roughly one foot square with an input and output shaft. I would think a single home sized coal furnace would have a gearbox just right for your needs, and plenty overbuilt for safety.

no idea on what search terms to use.

[Phineas Lamar Alexander]

Have you considered taking the worm and drive gears from a garage door opener and fashioning a reduction drive and crank to the business end of the worm?

Seems the simest way to get your parts together and i suspect that you could probably find one with a bad motor for free by posting an ad on craigslist.

This way you are down to looking for a hand crank assembly similar to those found on small boat trailers complete with locking mechanism.

Just my tupence worth...

Good luck and happy hunting!

[Jedediah Solomon]

Your answer might be found in the automotive arena. For off-road enthusiasts, there is an after-market differential called  "Gleason Torsen" unit.  It uses a very heavy-duty worm wheel and gear and the entire carrier can be taken out and used for another purpose. It usually stays in gear-oil because it myst transmit lots of torque at a vast range of speeds. What are you making?

[Jedediah Solomon]

If you set the bearing carrier into the wood frame and found a way of staying the housing ( bolting through into the uprights or welding steel brackets or rods to the carrier and fastening these to the frame) the unit would not need to be lubricated with the smelly gear oil and it would look very impressive to boot.  If you chose to use a regular, or "open" differential, it could be kept from moving by simply setting a washer between the gears.

[celephicus]

You just need a commercial speed reducing gearbox, like the ones on princessauto. Of course, they will not look as good as something handmade out of iron, crusted with grease and grime. Just go to an industrial supplies shop and tell them what you want (perhaps leave out a few details).

It does not matter what the weight of the load is, the gearbox feels the moment, or torque. The weight is taken by the bearings and supports, which your mate has already. The gearbox supplies a torque to turn the cross assembly and load. You will need a max torque spec, which will be the distance of the load from the axle times the mass of the heavy person on the end. Say 200Kg x 1.5m = 300Kg.m. Mind you, how heavy are the clients?

Do you want to spin the thing a full 360, or just move it from horizontal to vertical? I did work on some physiotherapy tables which were moved by ball screw actuators (this is their name, not another service from your mate's dungeon :}). These are very powerful electrical linear actuators, with a crank they could easily exert a lot of force to turn the cross. Or you could use a pneumatic cylinder.

It all depends if you want the drive hissing, whining or clanking. My assistant Igor, ever a traditionalist in these matters, has a preference for a large rusty squeaky handwheel with a ratchet making a clicking as it was turned.

PM me if you want a bit more help.