V belt sheave design?

[Toolbert]

We use cast iron 3V sheaves, QD bushed, in a product. They're heavy, overkill, and expensive, but the stock alternative is zinc die cast/setscrew and is not acceptable.

Is there a good reason nobody offers a line of simple plain keyed/setscrew sheaves in 6061 AL? The AL seems standard for timing belt sheaves with similar speed & power ratings, typically with keyed setscrew bores, not taper bushings.

My specific query is two part - is there a reason small V belt sheaves, esp. for 3VX belts, are not common in aluminum? And second, any design guidelines for e.g. bore tolerance, length of bore, number of setscrews?

In house, figure we would blank these in 1-1/4" 6061, be generous with the bore length and hub diameter, and use a long setscrew.

I'd appreciate any design wisdom along the lines of:
- this isn't common because it's cheaper to make a volume product in cast iron
- don't do it, the key/setscrew will fail, even if I think the hub design is overkill
- don't do it, a 3VX belt will wear the aluminum; needs to run in steel or cast iron for a reason

Not doing this to save $ - its more about space and weight.

thanks,

Bob

 

[Limy Sami]

1 1/4'' dia is very small for a 3 Vx ? .typo?

 

[DDoug]

The lawnmower people have several v-belt pulleys made from pressed/spun steel.

I see them hanging on the wall behind the counter every time I
visit my neighborhood lawnmower repair shop.

Ag supply places sell pressed steel pulleys with no hub, and a separate weld on hub.

 

[johnoder]

typically with keyed setscrew bores

Only one way these won't walk - have to have matching dimple machined in shaft

I have two major maker machine tools that use set screws on ancillary drives - and they walk

B&S used 1/4" set screws and they walk more than...

P&W used 7/16" set screws and they walk less -simply because you can get them tighter with the larger hex key / Allen wrench. Naturally, big set screws require heftier hubs.

Both with 3/4" shafts

Both with keys in place

 

[Monarchist]

We use cast iron 3V sheaves, QD bushed, in a product. They're heavy, overkill, and expensive, but the stock alternative is zinc die cast/setscrew and is not acceptable.

The "Zinc" is usually one of the ZAMAK family. Cheap as they look - and ARE - 6061 is not ordinarily enough "better" for most common use to give-up the cost advantage of precision casting with zero machining, or near-as-dammit zero machining.

Is there a good reason nobody offers a line of simple plain keyed/setscrew sheaves in 6061 AL?

Yes. You already nailed it. All of these:

- it's cheaper to make a GOOD ENOUGH volume product in cast iron or ZAMAK

- the key/setscrew will fail, OR WEAR TOO FAST

- aNY VEE belt will wear the aluminum; AT HIGHER LOADING IT needs to run in steel or cast iron

Not doing this to save $ - its more about space and weight.

Then go directly from CI to a steel alloy.

No matter how fabricated, YOU will have more choices than any of Aluminium, ZAMAK, or Cast iron.

For automotive "serpentine" belts, steels outright dominate. They mostly did even in the Vee-belt era as well.

Mind - I prefer Cast Iron, and very much so.

But this ain't my machine, so..

 

[Toolbert]

Thanks for the replies. I do like the QD bushings. Maybe the answer is to make an aluminum QD bushed sheave and keep buying the bushings.

The sheaves are 2.65 and 3.35" dia. 3/4 HP driving the 2.65 at 1750 rpm, at the low end of the power rating for a 3V.

I meant blank from 1-1/4" plate - our cnc's are a waterjet and vmc, it's a wasteful way to make a lathe part but attractive for in-house work. For just the sheave with QD bore it would be 3/4" plate.

 

[Monarchist]

Thanks for the replies. I do like the QD bushings. Maybe the answer is to make an aluminum QD bushed sheave and keep buying the bushings.

Not on my dance card. QD is a taper. Shiney-wood stretches, eventually cracks in those tiny sizes.

The sheaves are 2.65 and 3.35" dia. 3/4 HP driving the 2.65 at 1750 rpm, at the low end of the power rating for a 3V.

Low end on power to be transmitted. HIGH end on wear. Look at the diff in circumference as lineal feet per.

A Monarch 10EE can run light-metal pulleys, "A" section Vee belts, paired, typical power USED mebbe 1 HP to 2 1/2 HP.

..and ... have them last for around 80 years. And still counting.

The diameters are waaay larger. The surface feet per even more so. Pi Dee thing.



BTW .. this is an application I would consider "ripe" for PolyVee or MicroVee conversion vs "wedge" type 3V belting. VERY "ripe". If you are to experiment, try that, too.

 

[Limy Sami]

If you only have a VMC you are going to need custom tooling and / or some form of rotary 4th axis.

I know it's your job on your tab - etc etc etc but ;-

IMO Small pulley's like that are so much of a lathe job, it's bordering on lunacy to try to do them any other way, ......even cutting them out of plate is about the most expensive way of getting the material, ......plate is generally a good bit more expensive than round bar and you waste more.

+ 1 on looking at PolyVee drives.

 

[Monarchist]

If you only have a VMC you are going to need custom tooling and / or some form of rotary 4th axis.

I know it's your job on your tab - etc etc etc but ;-

IMO Small pulley's like that are so much of a lathe job, it's bordering on lunacy to try to do them any other way, ......even cutting them out of plate is about the most expensive way of getting the material, ......plate is generally a good bit more expensive than round bar and you waste more.

+ 1 on looking at PolyVee drives.

Lathe is a no-brainer even if one has to sub it out.

PS: Poly/Micro vees are so shallow one can even use TUBING, separately made hub.

Not that I'd bother for these tiny diameters but on BIG ones, it can make sense AND reduce mass cheaply.