Board logo

Pulleys - Need a supplier of some good ones!
dhutch - 18/4/12 at 10:34 PM

Yes, I need some pulleys. Strong and cheap, sized for 6-8mm rope with a diameter around 30-50mm. Any suggestion considered.

I've had a bit of a look and found a few climbing pulleys that are getting there, or industrial blocks and sheaves that would do it if i wanted 100, and sailing kit thats extra ordinarally expensive but nothing quite there yet.

Its for the steering of a narrowboat with wheel steering, where I'm planning to use high 6mm dia performance dyneema rope as a compromise between strength and compactness, as a similar strength steel cable has a much large bend radius and without a lot of work I'm limited to getting it fit in the space of the old system, which used 3mm stainless steel and nylon pulleys, which wasn't up to the job long term.

I need three singles and two doubles (or 7 singles) total budget around £100.

*edit for late night spelling


Daniel

[Edited on 19/4/2012 by dhutch]

James - 18/4/12 at 10:45 PM

Our very own Flak Monkey does pulleys for people. Worth a message to him I'd have thought.

PSpirine - 18/4/12 at 11:18 PM

Don't see why you can't just use normal marine pulleys.. ironically they're even intended for boats!

BRAND NEW Barton size 3 Reverse shackle block / pulley | eBay

7 of those doesn't break your budget? 45mm diameter up to 10mm rope?

dhutch - 19/4/12 at 07:44 AM

quote:
Originally posted by PSpirine
Don't see why you can't just use normal marine pulleys.. ironically they're even intended for boats!

7 of those doesn't break your budget? 45mm diameter up to 10mm rope?

Mainly due to me nervousness of there not being strong enough.

That pulley which is in line with most others with just under 400kg max load and 'breaking load' of only 770kg. The wheel gives a mechanical advantage of around 10:1 and at full lock and full power your just about hanging on as hard as you can which have reckoned at being round 50kg force. That gives 500kgf into the rope, 700kgf into a pulley that's deflecting the rope at 90degrees.

Obviously these peak loading's don't happen that often, maybe once a day (circa 35 times a year) and typically with the wheel held statically, maybe 3-4 occasions per day of applying half that force with movement, normal running forces being a tenth of that. But while I'm open to advice in my book that's still leaving bugger all margin on a critical system that I'm trying to engineer more trust and durability into.#

The pulleys will covered as they are effectively inside, and the boat rarely used on salt water/brackish water so corrosion etc isnt a huge issue.


I'll PM flakmonkey and see what he says.



Daniel

Peteff - 19/4/12 at 08:38 AM

If you have more than one pulley isn't the load shared amongst them ?