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View Full Version : A question about worm and wheel reduction boxes ...any engineers here ?



PeterSibley
10-16-2010, 01:06 AM
I'm about to build a light duty crane for my ute ,quite similar to the one in the picture below .It will have around 350 kg (770 pound ) capacity and a worm and wheel slew mechanism .

http://pic40.picturetrail.com/VOL282/9443996/17245530/392660673.jpg

I could use a braked boat winch as the main lift mechanism ,like the one pictured , but thought I might use my battery drill as the power and build one based on worm and wheel box driving a wire drum .The ''braked ''boat winch I have runs out under load and I don't trust it .

I scrounged around in my shed and came up with 2 worm and wheel boxes , one 15 to 1 ,the other 30 to 1 .The 15 to 1 unit can be turned by the wheel to turn the worm .The 30 to 1 unit cannot ...the worm (thread) remains stationary under load .

My idea is to use the 30 to 1 unit as essentially a braked winch .Is this OK ? Will it remain locked under a heavy load ? The lift would be around 120'' per minute .

What reduction ratio gives this ''locked''effect ? I was surprised that the 15 to 1 unit could be turned but assume this is a function of the wheel tooth angles ?

P.I. Stazzer-Newt
10-16-2010, 02:11 AM
It's not the reduction ratio which gives the lock - it's the efficiency, whenever the efficiency is below 50% you get no run-back.

PeterSibley
10-16-2010, 02:37 AM
Is the efficiency is in in the wheel tooth shape ?

I'd rather use the 15 to 1 box , is there any way I can easily brake this mechanism ?

Syed
10-16-2010, 03:07 AM
A small brake mechanism on high speed side should suffice to hold the crane at desired position. It should be normally brake applied mechanism and released only when intended. For safety reasons one must not depend on 'auto stop' due to friction. Movement can start after some delay.

G'luck

PeterSibley
10-16-2010, 03:12 AM
Thanks Syed , it looks as if you gentlemen might be saving me from a dangerous mistake ...which is why I asked !

Perhaps I should just buy a braked winch instead ?

Something like this ? http://cgi.ebay.com.au/Atlantic-Brake-Winch-10-1-7-5m-x-6mm-Cable-/200520694361?pt=AU_Boat_Parts_Accessories&hash=item2eaff6fa59

PeterSibley
10-16-2010, 07:02 AM
I have no experience of a ''braked winch '' ,how does it work ? Does it just stiffen up the lowering under load ?

Syed
10-16-2010, 09:04 AM
Peter,
I think your original idea of using a suitable reduction drive should be workable if you mount a ratchet on the handle shaft to not let the drive turn in reverse unless you lift the ratchet finger.

PeterSibley
10-16-2010, 05:48 PM
Thanks Syed ...I'm having another good look at it ,I'll look at the rachet idea to see how I can do it .

gibetheridge
10-16-2010, 06:59 PM
It's possible that there will be sufficient additional drag on the high speed end from the drill itself, and it should be pretty easy to build a temporary setup to test it. I would test the 30:1 with more weight than the boom can handle.