Need two small pulleys made

[Electrojim]

My own metalworking skills extend to a drill press and a belt sander. I am into electronics, however, and frequently the two disciplines merge, leaving me needful of someone to make simple mechanical parts, hopefully at a better price than an all-CNC machine shop quotes a nuisance walk-in.

Currently I need two pulleys made. One is a simple idler pulley, 3 inches in diameter and 3/4 inches thick, with a half-inch hole in the middle and a relief on each side so that a 3/4" bushing protrudes enough to miss the thrust surfaces. That's the easy one. The other pulley is 3/4 inch diameter, but with a turned-down, crowned surface to drive a flat belt. I figured that there are two ways to go about this: either a constant radius across the driving surface, or a 'segmented' drive surface with a flat middle section and tapered sections toward each end.

I've attached PDF drawings of both parts and kindly solicit your quote and comments. These will remain bare aluminum, but of course want to be precise and look nice. Many thanks for your consideration.

 

[Janderso]

I believe the print has an error. It shows .067OD and .064" at the ends which would be a .0015 measurement.
The print shows .015".
I could certainly make these for you but I'm sure someone else would want to jump on it for the experience.
This is a simple job.
If you aren't in a hurry, I could have them done in a few weeks. We are traveling right now.
I'm cheap.

By the way, it won't change the price but would you mind sharing what you were quoted??

 

[rwm]

FYI for doing a crowned surface I have cut a few small tapers and then blended them with a file or grinder to make it look like a smooth radius. Would that approach be useful here?

 

[Electrojim]

I believe the print has an error. It shows .067OD and .064" at the ends which would be a .0015 measurement.
The print shows .015".
I could certainly make these for you but I'm sure someone else would want to jump on it for the experience.
This is a simple job.
If you aren't in a hurry, I could have them done in a few weeks. We are traveling right now.
I'm cheap.

By the way, it won't change the price but would you mind sharing what you were quoted??

Hi, Janderso, and thanks for the quick reply! You may have misread the dimensions, it's zero point 67 OD in the center and zero point 64 at the ends; a 30-thou diameter difference which is the 15-thou radius differential. (I was always taught to put a zero before the decimal.) As for the shops around here, I have not obtained a quote for this job locally. I'm located in the heart of the local aerospace industry in Southern California, and past experience has taught me that these shops don't want this kind of work... they want to do thousands of any item or it's not even worth their programming time. There are NO old-time machine shops, at least around here, with a Bridgeport and a Hardinge, and a guy who knows how to run them. Those days are definitely in California's rear-view mirror.

 

[Electrojim]

FYI for doing a crowned surface I have cut a few small tapers and then blended them with a file or grinder to make it look like a smooth radius. Would that approach be useful here?

Hi, Robert, thanks for responding. Actually, I've been advised by a mechanical engineer friend (but not a machinist, darn it!), that the 'segmented' approach to the crown is darn-near as good as a constant radius, and ought to be fairly easy to do, seeing as how only 15-thou of metal is being removed at the end of the tool's travel toward the ends of the pulley. I had a crowned pulley made for me a couple of years ago for another project that looks to have been done as you describe. I guess the filing or grinding was done by eyeball, and the belt does not track in the center of the pulley. In fact, you can see that the bulge is not symmetrical. I don't know how a constant-radius surface is created by the pros, hence my preference for the 'segmented' option that should work as well and have a more professional appearance.

 

[mmcmdl]

There are NO old-time machine shops, at least around here, with a Bridgeport and a Hardinge, and a guy who knows how to run them. Those days are definitely in California's rear-view mirror.

As it is everywhere .

 

[Huub Buis]

I don't know how a constant-radius surface is created by the pros

I am not a pro but turning a radius is easy on my CNC lathe.
On a manual lathe, a radius turning attachment would do the job. I think that the setup would take a lot more time than the actual radius turning.

 

[mmcmdl]

Those parts could be programmed and machined in an hours time on a conversational CNC lathe . While one was running in the lathe , the mill work could be completed on a BP , so no added time . Sadly , they're aren't many one man mom and pop shops left to do these small batch jobs .

 

[Electrojim]

Those parts could be programmed and machined in an hours time on a conversational CNC lathe . While one was running in the lathe , the mill work could be completed on a BP , so no added time . Sadly , they're aren't many one man mom and pop shops left to do these small batch jobs .

Exactly why I've come here for help. Another home machinist helped me fit a bearing well with Oilite sleeves a couple of years ago. Did a fantastic job at an absurdly low price. In my own element of audio electronics, I try to be as similarly useful, but I'm an old geezer myself and confined pretty much to analog, rather than digital, means of solving problems. Analogous to the Bridgeport/Hardinge machinist, I guess.

 

[Flyinfool]

I have designed and used pulleys like this for a urethane flat belt. (Glorified rubber band.) This is for a product that is now in production.
There was no difference between the radius and the faceted as far as keeping the belt centered or service life of the belt. However I did have better result with both pulleys faceted (or radiused). Under heavy load (I was pushing the limit of the belt in both speed and load.) the belt would still try to wander on the flat pulley.