Crown Tools

Hello

I wonder if I might ask some advice on pulley crowns? I've been watching David Richards's on the steam powered macine shop create these on line shaft pulleys. He turns left and right tapers then blends the two with a file. This seems an excellent and effective approach. But the crown I need is on a small (60mm diameter by about 15mm wide) aluminium part. I'm not sure the best way to do this - whether the opposing tapers method would work?

Many thanks for guidance.

Best as always from sunny springtime in Paris.

Martyn

Sounds like a job for a [very large-radius] ‘ball-turning tool’ concept.

MichaelG.

The way you describe will work I'm sure, but another method is to use a hand-held graver resting on a make-shift turning rest held in the lathe tool post. My most useful graver is a length of 1/4" sq HSS ground off at about 45 deg. and firmly fixed in a file handle It's useful for all kinds of quick finishing-off ops.

It works on Minnie flywheels.

The Ali is likely to clog the file with out some chalk dust rubbed into the teeth.

Yes I think for a pulley 60mm diam. and 15mm wide I would be tempted to file the curve on there, using a 10" flat single cut mill saw file or the like, with plenty of chalk on it as Dave H says and frequent wire brushing with a card file. A simple template made from a bit of sheetmetal or even cardboard cut to the desired radius would help. At that size it should only need 1mm or 1.5mm of dome I should imagine. You could put a little cut around each edge of the pulley blank at the target depth for guidance.

I've done it on several small pullies and flywheels, depending on width us e3 or 5 facets blended with a file, single angle lathe file is the best but a standard flat will do

3 facet just visible 

5 facet one below

Edited By JasonB on 26/02/2023 10:09:17

Edited By JasonB on 26/02/2023 10:13:46

Pulley for an Austin 7 fan? Was told that the French made Austin 7s under licence as the Rosengart

Howard

Howard

Indeed they did. Early Rosengarts are Austin Sevens built under licence by Lucien Rosengart after he left Citroën. Likewise Dixis (aka BMWs) built in Germany!

And so the the 'crown'. Thank you everyone. I think we are looking at a kind of form tool here that I had considered a possibility. Also I think the grooves at the side would be helpful; I had thought that may be the way to start.

Many, many thanks for the advice.

Martyn

Be cautious with a form tool on a small lathe, the more so with aluminium, which is notorious for clogging files., as it may dig in and spoil the work. A simple tool rest and graver may work well if you have a good eye. Noel

Unless it is for aesthetic reasons, I would use a flanged pulley with a flat surface. More contact area, tracked belt and OK for anything on old iron which is out of sight. That was what was fitted to our early 1950s Massey Harris 701 baler.🙂

I changed that pulley for a multi-grooved pulley which easily transmitted all 22HP without any slip with a twenty-odd grooved belt.

Noel. Thanks for your cautionary note. I have come up against this before. My Chester Super B probably does not have the torque to drive a form tool. I'm sure you're right, hence the graver..

As to the MH 701 baler comment. I really don't wish to be boring or set a thread bare hare running again, but, to come clean, it is for an Austin Seven (crankshaft) pulley, and with 2mm deep flanges on either side do I really need the crown to keep the fan belt on?

.

The crown doesn’t keep the fan belt on, it keeps it tracking centrally

MichaelG.

Hi Martyn,

When I restored my A7 donkeys years ago I assumed that the fan pully had deformed in some way and filed the crown off. The fan belt never came off the pully but it would sometimes ride up onto the flange. I replaced the pully when I gained a bit more knowledge. I haven't checked to see if a new pully can be bought, but I have a spare, I think...

Lee

Thinking outside the box, I recently needed to put a crown on the flywheel for my current traction engine build.

I used my little CNC mill on a hydraulic table next to the lathe to perform a simple curve cut with a lathe tool clamped to the mill table. Worked perfectly!

An excellent ‘hi-tech realisation’ of what I mentioned earlier, Les

Very impressive

MichaelG.

I would do it the hard way for lack of suitable machinery. First find out exactly what the crown dimentions were. Then turn the pulley to the maximum diameter of the crown. The diameter of the outside ends would be done with a narrow grooving tool. With a fairly narrow pulley, that would give a reasonable start for hand filing of the profile at low rpm using the back gear. The difficult part would be to make the crown symetrical.

My memory says 1/8" per foot of width (radially), interweb says 1% of width, which is remarkably close. I'd to it as a series of small steps and finish with a file, but interweb reckons parallel in the middle with a shallow taper each end will work. Look for crowning on conveyor rollers.

1 per cent of a 15mm wide pulley is 0.15mm crown. About 5 thou in old money. Thirty seconds with a flat file in the lathe would take care of that. 

Or use Jason's pictured method to create 3 flats, then finish with file.

Edited By Hopper on 28/02/2023 09:00:00

It sounds like an ideal job for the eccentric engineering Turnado but that would be quite a lot of money for a one off job and it may be a while before the next job came along. Of course once you have one it might become very useful.

Mike

Too much 'mountain out of molehill' going on here. Use a felt tip to mark the rim with lines such that there is a solid line right in the middle and edges and graded amount in between. Then file to remove the edges and not the middle one. Repeat. This helps you appreciate how much you have removed.