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Rope wheel pulley groove form tool

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PekkaNF:
Not sure if this is interesting, but i though of showing how I am using it.

I'll keep the story short. Hope it's clear.

I need to make two different size rope pulleys, only few smaller ones but over 10 bigger ones. Desided to make small ones first and just some big ones and then rest in two batches, just to make sure I don't exceed any dimenssion and tolerances won't accumumulate anywhere. Would be annoying to remake another batch of 10 because one feature would be 0,3mm too small or shave of extra 0,5 mm on everyone.

Aynyway, this is first time I use POM on that size and tolerance. All is made out of 1 metre long 50 mm OD rod.

First near 20 mm "pucks" are cut with band saw. Exact width does not matter as long as there is enough to make the boss (17,5 mm wide).

Then puck is put into aluminium collet that has a recess. The collet face that is towards the three jaw chuck and collet recess indexes the puck in relation of the carriage stop. Carriage stop has two postitions. One that much out that first face/boss is cut on one go.

I made a gang tool that has two 1/8" HSS bits set very carefully to cut boss and side on one stroke.

The puck is removed from the collet, turned and freshly squared side will butt to collet recess. Now I can cut it into exact width: cariage stop advanced and another face is cut + hole drilled. Here I know that the side target measurement is 15,5 mm wide (boss width 17,5 mm) Therefore side feature should protrude 3,5 mm out of the aluminium collet. Fast check.....but temperature, collet pressure, burr + other error sources will crop up here, no point trying to "improve" better than necessary.

This has been repeated until batch of five is ready.

PekkaNF:
Next fixture is a stub mandrell.

Arbor press used to mount the embryo rope wheel into a stub mandrel.

Here I used a gauge to set the wheel face to chuck distance to known distance....that is needed when rope wheel groove is cut as last step. That form tool is not easiest thing to center...but if same carriage stop position is used and a gauge piece is used to set the pulley where I want, that's all I need to know once set.

Then I change normal turning tool return cross slide to "0" and turn piece to 47 mm OD. Nothing to it, least critical operation and easiest nail it with unnecessary accuracy.

Then form tool is changed, carriage is pushed left against the carriage stop and rope groove is formed on one go, only thing was to wch cross slide for "40" when it looked about righ and check that the bottom was near 39,0 mm dia, but not under, then both sides were 1,5 mm wide....about. good enough. Rope is forgiving.

The arbor press is used to press mandrell out an the whole thing is repeated 5 times.

Took some time to "dial" in the tools, but when setup was not disturbed very reasonable time was used for each pulley.

Made two batches on two evenings when I had measuremets dialed in. Only thing is that it's hard to keep very close (just for fun) tolerances with plastic. Temperature, mounting pressure and cutting speed has very pronounced effect on dimenssions.

Pekka

DMIOM:
Ingeniously done and well explained - thanks Pekka.

Dave

PK:
There is skill in making 'one perfect one'.
'QTY 100 in a cost/time effective manner' is next level.  I love this stuff!

Hat's off to you.
PK

PekkaNF:
Thank you very much.

It's all pretty basic and rudimenttary and I was wondering if this interests anybody.

I just needed to find out a way to make 10-20 of these to my friend "for free" and an effective manner.

I put much emphasis to find a method that results could be repeated at later date. There are few of them on the boat and changes are that they need to be refurbished as well.

Thank you,
Pekka

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