Form Tool or other way?

Hi all,

I am going to be making a 2" round belt pulley for one of our textile machines (and easy early project I thought!). Here is the drawing for it:

Am I right in thinking that the best way of turning the internal radius, where the belt sits, is with a series of stepped cuts to remove the bulk of the waste, followed by a form tool created to the correct radius? If so, what is the best method for creating the form tool? Ground Flat Stock, shaped and hardened? Or HSS ground?

If Ground Flat Stock, will 10mm thickness be sufficient? If HSS, do I have to re-harden it afterwards?

Many thanks in advance for your help!

Kind regards,

James

Edited By James Jenkins 1 on 19/05/2016 16:27:42

Edited By James Jenkins 1 on 19/05/2016 16:31:00

Edited By James Jenkins 1 on 19/05/2016 16:31:26

If this is a recurring job, I suggest having a custom tool ground on a HSS blank. If this is a one-off job, make a button from hardenable rod and screw it to a steel shank. Ivan Law's book on gearing shows how button cutters are made.

Hi James

You seem to have an error on the drg, at the top you show 0,375" diameter but at the btm you quote 0,203" radius, does this mean a 3/8" belt running in a wider groove ?

Not that it makes much difference to the tool, if you can grind a HSS blank to the required radiused end with good clearance angles you could use it as ground, it wouldn't need further hardening. Even after roughing out some material it is quite a long cutting edge so I believe you would need to turn at low rpm with lubricant to avoid chatter marks.

Emgee

Easiest is FGS, shape when soft, harden & temper, or button tool from Silver steel. 10mm thick is plenty.

Tony

You can get carbide button tools, certainly as big as 8mm and I wouldn't be surprised if you could get 10mm. 10mm is 0.394 which is close to your 0.203 dimension. If this is too expensive then as John Reese says, make one out of silver steel, or if you're really strapped for cash grind down an old square file to the required end radius. With carbon steel go slow or you'll overheat and kill the hardness

I have never tried this but I would make a holder that could press a 3/8" endmill against the edge of the pulley and allow the side flutes to shave the metal off.

Mike

3/8 sq tool steel with a hand ground radius

Clamp the tool steel in a vise with the top surface just below the top of the vise jaws use a 3/8 drill shank end as a guide and a carbide scriber to mark out the radius then grind on a bench grinder and finish on an oil stone .

Set your grinder rest up on centre height of the grinding wheel this will give you enough relief angle under the cutting edge

Your biggest enemy will be chatter , i would stop just shy of the required depth and shut the lathe off then use hand power to rotate the chuck and feed in the tool a few thousndths every second rotatoin of the chuck this will clean up the chatter .

Then give it a polish with some fine emery , the most important thing is that the bore and the surface where the belt runs are true with each other and the surface the belt runs on is smoothe and remember it is a pulley not a precision gear so you have a little bit of room to play with

Steps as you said and round file?

Forget this idea. It will only work if the end mill can be rotated at the same time as it is pressed against the rotating pulley.

Mike

Weld a 3/8" ball bearing to a stick of metal for the tool, then grind half away, instant, simple form tool already hardened.

JB Cutting Tools have this **LINK**

Bernard

It's going to be one hell of a width of cut if you use a semicircular tool, something like 15mm along the circumference towards the end. Don't imagine it will be easy to avoid grievous judder unless you have a beast of a machine.

I made some mandrels in steel for my pipe bender - looked similar before I cut the wheel into 3 sectors although somewhat bigger. I turned the bulk by eye with carbide tooling and although it was pretty good, it wasn't perfectly circular by the time I declared I was finished.

If you have one of those radius tools for turning balls etc, they give a very precise finish particularly if you use a (round) profile cutting insert, judging by photographic evidence. I thought about using a milling cutter (3/8" in this case) but don't think it would have been easy going.

You might want to consider using a V profile on the pulley. My Wizard lathe is designed for round belt but used a V shaped pulley. Best way to cut a V is do a parting cut down the centre then a cut on each side to establish the angled face.

Thank you so much everyone for your input, really, really helpful. I certainly don't have a 'beast of a machine', just a treadle powered Drummond M! The measurements came from a commercial pulley design and they seem to make the internal radius just over that of the band, so who am I to argue?

Whilst spending £20 on a tool with JB Cutting, that I might just never use again, seems rather extravagant to make a simple alloy pulley, it does mean I have one less thing to learn/worry about (tool making) in these very, very early days of learning to use the lathe. I am sure in a years time I will look back a laugh at money wasted and the fact that I didn't just make one. But I tend to find that if you don't make learning new skills as incremental as possible you quickly get overwhelmed! Maybe that's just me.

I saved a few pennies by buying an off cut of aluminium on eBay, which will help pay for it and hopefully this tool will also give me the best chance of succeeding as well (which is also a key part of learning I tend to find!)

I'll let you know how I get on.

James

What is the pulley material? If you can, choose something easily machinable.

I agree a silver steel button on a steel shank is the easiest way, with the top ground to give some top relief.

Roughing the groove will help reduce the work to be done and avoid over-heating the tool.

I made a 3/8" concave form tool in 1/8" gauge plate and that was ample for brass.

If chattering is a problem, grind two tools that are a quarter circle on the end - one for each side of the groove, it won't be hard to align the second cut with the first.

Neil

Neil,

Drawing says Aluminium.

Tony

Obviously I don't know the application, but for round belts it is usual to make Idler pulleys with a groove radius slightly larger than the belt but to use a V section for Drive pulleys.

HTH,

Rod

Treadle lathe, 3/8 dia TC button tool? That sounds like hard work!

Personally I'd use a small button tool and CNC it, but not on a treadle lathe...

Now that's really got me going, CNC conversion on a treadle lathe, come on someone must be up for a challenge

Since you are using a treadle machine you certainly do not want wide tool contact. Why not grind up a graver with a radius and finish the groove free hand? Unless the belt running in the groove is under extreme tension the groove need not be the exact radius.