DIY glass fibre pulley?

[RemanParticipant @reman]

Just sort of thinking allowed here,

I need to have a 3 step flat belt pulley at some point in the future. The dimensions I need are a bit odd (1" wide steps, with diameters of.4.25", 3.25" and 2.25", Plus it needs to be bored for a 3/4" shaft) so eBay hasn't popped anything near the right sizes in all the time I've been looking,

I'm resigned to the fact that I'm most likely going to have to make it myself, and I'm gonna need a pretty big/expensive slug of steel or aluminum to do it……… But am I?

I played with the idea of laminating several ply discs together and turning them to the right size steps, But making a part to use with a metal lathe out of wood just feels all kinds of wrong to me, So I started thinking about what other materials I could use.

Due to me wildly overestimating quantities needed for a little project last year, I've still got one and a half large (2kg?) tins of Isopon P40 glass fiber filler doing nothing in the garage.

I'm thinking I could make a slightly oversized mold that would also hold a thick walled 3/4"id steel pipe squarely down the center, pack around it with glass fiber filler, then turned it to size (While wearing every item of PPE I own to keep glass strands out of my eye's, lungs and skin. ). Balancing it up shouldn't be too difficult, But I'm wondering what the chances are of it surviving the 400 or so RPM it would see in use when running flat out?

I'm pretty sure it would hold together for the long term (Despite all the vibration and shock loading when I do something stupid with the cutting depth), and if it would work it would pretty much cost nothing to make because if not used, in several years time the filler would probably end up in the bin when the tins turned to rust), But there's still that little voice in the back of my mind saying "If this was a good idea there'd already be GRP pulleys on every cheap machine out there".

So, What am I missing here?

Scott.

[RemanParticipant @reman]

[EmgeeParticipant @emgee]

Hi Scott

IMO not a good idea, better to get some steel pipe to match the 3 diameters and fabricate the pulley.

Emgee

[Clive FosterParticipant @clivefoster55965]

I've made several multi step pulleys, both flat belt and polyvee, by screwing and gluing individual steps together. That way you can start with close to size material for each step. Simplest way is to make them on an undersize mandrel and finish bore to size when bolted together. Need to keep your brain engaged when figuring out the sequence of tapped holes and through holes. I used hex socket countersunk screws 'cos I had a stack in a suitable size.

Sometimes I assembled the pulleys on a central tube which I finish bored to fit the shaft. Other times I just stacked them up on a mandrel. Both worked. However, on reflection, I think the best method is to use the central tube as the mandrel. Hold it in the lathe and mount the pulley blanks on it to cut to size so everything comes out true. If you don't want to put a screw or two radially down through the pulley blank you will needs an extra part fixed (grub screwed?) to the tube to hold the blanks against cutting forces. Start with the smallest of course, especially if they are crowned flat belt pulleys as doing the crown properly with larger step in the way will be a right pain.

I think I'd look for some 1" alloy plate to cut the blanks out of.

Clive

[Howard LewisParticipant @howardlewis46836]

Would be concerned about the life of a glass fibre pulley, and about the dust coming off as it wears. Could be bad for the lungs, or skin. There will be some slip, which will abrade the surface.

Wood may be, less damaging to health, and possibly longer lived

Fabricating from pieces of pipe, or shorter pieces of solid sounds a much better method..

Howard

[not done it yetParticipant @notdoneityet]

As Clive. 3 pieces of 1”, 4 of 3/4” or 5 of 5/8” as you are writing in inches. Any suitable combination of sizes would work, but the thicker the better I suppose…

TBH, I think I would be converting to a format, other than flat belting, if possible.

[Mike PooleParticipant @mikepoole82104]

I made a 3 step flat pulley from some Tufnol that was handy and free, it was not chosen for any reason apart from that. It works fine. As a piece of aluminium, cast iron or steel is going to cost a few quid then any freebie material is worth a try. The H&S concerns during machining are worth it but if it doesn’t wear in use then it won’t be making dust, if wear is severe then it might be best to abandon it but it means starting again. If you are going to the Midland exhibition in a couple of weeks then you will find a few stalls will have short lengths of large diameters often at a reasonable price and no carriage costs,

Mike

Edited By Mike Poole on 06/10/2019 09:44:01

[Dave HalfordParticipant @davehalford22513]

Barbell weights would be a better option, the chances of a pulley made from short chopped strand coming apart as big sharp chunks underload load and at speed isn't a chance I would personally take.

[Clive FosterParticipant @clivefoster55965]

As NDIY says consider an alternative to flat belts. Getting the crowning right so the belt runs true on all steps without rubbing on the side of the next bigger one at one end or the other can be a right pain.

PolyVee is easiest. The belt will run just fine on the flat pulleys at the other end. You will need a micrometer bed stop (easiest) or plain stop and space setting gauge to cut the Vees at the right intervals.

Getting pulley diameters sizes dead right so the belt tension is equal on all settings is another pain. None of my flat belt sets were perfect although they all worked. The shorter the belt centres the harder it is to get right due to the angle of the belt as it runs between different sized pulleys. Four steps are worse. Six steps, just don't go there!

Sensible man puts a spring or jockey pulley in to accommodate any variation. Makes shifting easier too.

Clive

[colin hawesParticipant @colinhawes85982]

My lathe and horizontal mill both have three step flat belt pulleys that I made many years ago from sheet metal discs with welded on sheet metal bands for the belt to run on. Tube is welded though through the centre. Perhaps I was lucky as they both ran very close to true. These pulleys have a largest diameter of about 9". Colin

[RemanParticipant @reman]

Posted by not done it yet on 06/10/2019 09:22:20:

I think I would be converting to a format, other than flat belting, if possible.

That was actually the original plan, But I've got to quite like having the "Weak link" of a flat belt running the spindle. Under normal conditions it's fine with no slip, But if I do something stupid it WILL slip and allow the chuck to stop dead without the kinetic thump of it also stalking the rest of the drivetrain and motor.

 

Posted by Dave Halford on 06/10/2019 10:37:24:

Barbell weights would be a better option, the chances of a pulley made from short chopped strand coming apart as big sharp chunks underload load and at speed isn't a chance I would personally take.

The idea did occur to me. I was thinking that for a belts and braces approach I could twist up some stainless wire  into several hoops that I could embed in the filler around 1/2" under the pulley surfaces. They probably wouldn't stop the pulley breaking if that's what would have happened anyway, but they should hold the bits together long enough for me to shut the lathe off, And it would limit how big a chunk could come flying off it it did disintegrate.

 

Edited By Reman on 06/10/2019 11:32:49

[not done it yetParticipant @notdoneityet]

Weak link? I would fit shear pins for that purpose. Slipping belts is poor engineering or necessary to cover up previous poor engineering.

[RemanParticipant @reman]

Posted by not done it yet on 06/10/2019 11:39:44:

Weak link? I would fit shear pins for that purpose. Slipping belts is poor engineering or necessary to cover up previous poor engineering.

If the choice is a belt slipping or having to replace shear pins every time I do something silly, Personally, I think I'll stick with the belt if it's all the same. 

As I said though, The belt doesn't slip unless I do something that would (If the torque DIDN'T have this easier escape route) probably result in damage to the tool and/or lathe.

Anyway, As I said at the beginning, This idea was only really me pondering aloud. I've actually got some 1" thick aluminium discs kicking about here somewhere that I could use, But before using up 30 or so quid worth of metal (That could be used for something else) on this I was wondering if I could get away with doing it on the cheap using the fiberglass filler that probably won't get used on another project.

I know some hobby lathes use molded glass impregnated nylon change gears, So the thought of a fiberglass flat stepped pulley didn't really seem that big a leap of imagination.

Edited By Reman on 06/10/2019 17:29:02

[An OtherParticipant @another21905]

Why not cast an aluminium blank, then turn it to suit. It really isn't difficult to do, using (say) the lost foam technique and almost any scrap aluminium. I've done this many times, either to replace broken parts, or to make parts for something I am making.

I would certainly prefer this to casting from resin – I once made a variable diameter pulley for a wood-turning lathe out of resin – it lasted about 10 seconds before shattering into several large pieces.

[Jon LawesParticipant @jonlawes51698]

I've machined carbon fibre components in the past and even the most hardwearing tools get very blunt tediously quickly. And the mess it makes….. I can understand your logic (my workshop runs on scraps other people throw away) but in this case it sounds like a lot of mess, work and risk to health to save yourself the price of a few beers.

I hope that comes across the way it is intended; I mean no offence.

[Author]

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