Home made pulley blocks

[warby1212]

Hi,

Are there any good sources of info on the web (or in the minds of this forum) about making your own pulley blocks? I need some and I thought it would be a great project.

Cheers
Stephen

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[richardandtracy]

Ho Hum. I don't know of any pulley designs on the net, not even via my usually good source 'http://home.clara.net/gmatkin/design.htm', so here goes for a word picture of a design that I've used without too many problems.

How complex & how cheap do you want to get? I'll assume pretty simple and moderately cheap, as thay are much quicker to make. The design below should be OK for up to a 3 wheel block and up to 20mm dia rope. The general design is of a pulley wheel between two cheek plates. There is a hanging bolt at the top, lower down the pivot and at the bottom there is a bottom spacer bolt.

First decide on rope diameter.

Pulley wheel
Diameter should ideally be 10x rope diameter to maximise rope life, though I've seen down to 5x rope diameter sold commercially.
Pulley width = rope diameter + 2mm
Half circle groove in perimiter of pulley = rope diameter. Centralise this to get 1mm land on each side.
Pulley wheel material. This is where it could get difficult. In order of preference: Bronze, aluminium, plastic, hardwood.
Aluminium wheel:
The wheel could be cast from any type of aluminium if you wish - see http://www.backyardmetalcasting.com for ideas on casting aluminium pulleys (admittedly these were for V belts, but the idea is the same). Failing that, they could be turned from solid on a metal lathe using incremental cutting techniques if you haven't got a ball turning attachment (see http://www.geocities.com/mklotz.geo/#top for Marv Klotz's 'ballcut' program which could be adapted). The blank disc could easily be cast - my furnace cost £2 and only took 2 weeks to make from start to finish (total of 5 hours work in that 2 weeks).
Plastic or wood wheel:
Could be turned on a wood (or metal) lathe, failing that a simple fixture to rotate the rough saw cut blank pulley under a router could be knocked up in about 20 minutes.

Pivot:
Stainless (A2-70 or preferably A4-70) bolt + locknut. You will always be safe if you make the bolt diameter the same as the rope diameter, though you could probably go down to 60% of rope diameter - but make 6mm dia bolt the minimum. Make sure that the shank of the bolt goes right through the pulley wheel - this will mean you'll have to saw the end off the bolt after putting the nut on.

Pivot sleeve.
Not really necessary if using metal pulley wheels. If hardwood or plastic, make the sleeve of gunmetal or brass. Inside diameter = bolt dia + 0.25mm (or thereabouts) Make the outer diameter anything convenient above a wall thickness of 2mm. Make as a press fit into the wheel.
Grease heavily!

Cheek plates.
Material: Steel or stainless. Aluminium 2x thickness of steel or hardwood will do if 7-8 times thicker than the steel suggested.
Width = larger of pivot bolt / hanging bolt + 2 x rope diameter minimum (any extra will be decorative & reduce chances of rope jumping out of sheave).
Length = 3x rope diameter + Pulley diameter + Hanging bolt diameter + 12mm
Thickness approx 3mm (though 2mm would be ok for small ropes, say under 10mm dia).
Make sure there is at least 1 rope diameter's width of metal around the pivot bolt and hanging bolt, and the bottom spacer bolt centreline is 9mm from the bottom end of the cheek plate.

Hanging bolt.
If only 1 sheave, make same as pivot bolt. 1.4x pivot bolt diameter for 2 sheaves & 1.7x pivot bolt diameter for 3 sheaves. This hanging bolt could, of course, be the pin of an appropriately sized shackle.
Hanging bolt spacer length = pulley width + 0.5mm
Hanging bolt spacer ID = Hanging bolt OD.
Hanging bolt spacer OD anything convenient that is less than 2x rope diameter.

Bottom spacer bolt M6
Bottom spacer length = pulley width + 0.5mm
Bottom spacer ID = Bottom bolt OD.
Bottom spacer OD anything convenient that is less than 18mm.

Paint.
If you want to.

There you have it. PM me if you'd like a sketch in DXF or DWG format.

Regards

Richard.



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[richardandtracy]

Try Def Stan 02-113 Part 11 Issue 2 at http://www.dstan.mod.uk/data/02/113/11000200.pdf. There's one nice picture in it which could be used to scale from.

Regards

Richard

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[warby1212]

Thank you very much!

Great stuff and those sites you pointed to look fascinating as well.

Boats are such a great excuse to get into other things!

I will PM you for that sketch if you don't mind.

Cheers
Stephen



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[kilocharlie]

Anyone made pulleys with metal strap about a wooden cheek plate? I've machined aluminum sheaves with bronze valve guides as bushings, and I intend for the flange of the sheave to be hidden in a shallow recess inside the cheek plate.