Drive pulleys

[Frances IoMParticipant @francesiom58905]

I have a need for some 4 or 5 3-step drive pulleys (to take 5mm round belt) some 30mm in length, outer step diameters 50mm, 40mm + 28mm most with a 12mm drive shaft (grubscrew rather than key fixing?) I could use aluminium (I have some 60mm dia stock) or possibly steel – that on one small lathe needing replacement is aluminium.
My initial thoughts are to make a sliding fit 12mm mandrel with 6mm end screw to hold the blank – then to cut, face, drill(say 11mm) then bore or ream? blanks to size before fixing on mandrel for cutting the belt slots. One pair is intended to drive one of Arc -euro’s 12mm shaft mounted ER16 collet to make a small medium speed drill.
Are there any ‘gotcha’s in making these or possibly in expanding drive to 1/2inch post manufacture?

[Frances IoMParticipant @francesiom58905]

[Michael GilliganParticipant @michaelgilligan61133]

Just a thought, Frances …. have you considered using 2-rib J section PolyVee

Example: **LINK**

http://simplybearings.co.uk/shop/Belts-Multi-Ribbed-Poly-V-Belts-J-Section-Poly-V-Belts/c4601_4791_4793/index.html

The transmission characteristics are better than round belt, and the pulleys are easy to make.

MichaelG.

[Frances IoMParticipant @francesiom58905]

I already have the 5mm green belt which I can join to any length – hence my desire to use this – how different are the pulleys as my model is a 4mm flat bottom with steep sloping sides tho one pulley has a deeper 1.5mm centre slot

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Frances IoM on 06/12/2016 17:20:25:
I already have the 5mm green belt which I can join to any length – hence my desire to use this –

.

Fair comment … it was just a thought.

MichaelG.

[Clive FosterParticipant @clivefoster55965]

#2 on Michaels suggestion of switching to PolyVee pulleys. Its trickier than you'd think to make a really good set of step pulleys where all step pairs run at sensibly similar tensions so no adjustment is needed when you change steps. Yet another job where being careful is often not quite good enough so a proper set-up is needed.

When I make step pulleys I do each step as a separate slice and bolt them together afterwards. Most accurate way is to make them on a hollow mandrel bored to fit the shaft they will go on. One end in chuck or collet, one end in tailstock centre works for me. Make the plain blank bored to size with threaded and clearance holes as apprpropiate then thransfer to the mandrel, small step first, for grooving and build up as as you go.

Clive.

[Frances IoMParticipant @francesiom58905]

Thanks Clive
it was the dimensioning ‘problem’ that I hoped to circumvent by copying the existing 3step on my small Perris lathe which has a counterpart on the layshaft driven off the motor – not sure what you mean by hollow mandrel (is this slightly tapered or split with an internal cone drawn in ? – I was going to use a collet chuck and as only 30mm overhang thought the tailstock support not needed hence could use a simple cap head + washer tight arrangement to grip the blank.

How do your join your slices – loctite or a thru pin ?

[Clive FosterParticipant @clivefoster55965]

Frances

The hollow mandrel is cut to length and left inside the pulley when the job is finished. Its turned true to whatever size centre hole you have made in the blanks and bored to fit the shaft that the pulley will go on. When each blank is fitted to mandrel its turned to finished size before putting the groove(s) in. This gives the truest possible running pulley as everything is done in one set up. If you are doing a free running countershaft you get the same accuracy by making the pulley on the shaft itself.

I bolted my slices together with hex socket cap screws. 6 tapped holes in the centre slice. Three tapped and three clearance holes in the end ones. Clearance holes for the cap screws, tapped holes to attach a collar carrying a pair of grub screws at 90° to each other to lock the pulley onto the shaft. If using a hollow mandrel sdrill through after fitting and extend the tapped holes so the screws go right through. With thin slices I'd probably make and fit the collar to the mandrel or shaft you are making it all on first then fix the first blank to that for extra stability. Might be just as easy to make the smallest pulley wider so the "collar" becomes merely a plain extension for the fixing screws. Still need a separate collar at the big end tho.

As ever there are lots of ways of tweaking the concept to suit your job and facilities. I only started out this way because the first step pulley I had to make was a big one, 6" OD I think, and I didn't want to waste a lot of material turning from solid. Especially as I had some plate in stock to make the blanks but would have needed to buy a big lump of bar to go from solid. Having done one and got my eye in I stuck with the method I knew. Overall somewhat more work than chomping direct from solid but its a lot of a small steps and if it goes wrong its easier to recover without scrapping the whole job. With a big one its possible to make the largest step as a ring and use the piece cut out of the middle for the smallest step.

Clive.

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