Need two small pulleys made

[Electrojim]

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.

My application also uses a flat urethane belt, half an inch wide. And the driven part is a 13.5" diameter turntable with a crowned 3/4" edge. The edge was originally flat and I went to a local machine shop to have that part just crowned, which cost $150. They did a beautiful job, though, and with a part that diameter I didn't have many options but to bite the bullet and live off popcorn and candy bars for a couple of weeks (not really, but...).

 

[mmcmdl]

Analogous to the Bridgeport/Hardinge machinist, I guess.

I have 1/2 of a Hardinge left here , but the Bridgeport just left . I'll rebuild the shop once I can get into the other basement . I used to make some beer money and have fun doing it .

 

[extropic]

Suggestions:
Regarding the motor pully, because I assume you want a fine fit on the shaft (and your 8 mm is untoleranced) I recommend you get more specific about that diameter. If you can measure the shaft, to .ooo1 resolution, and add a note to the drawing, that would help.
Alternatively, you could either specify a tolerance for the hole or send the shaft (motor) to the selected maker.
Regarding the idler pully, essentially the same concerns regarding the central hole. I would like the bushings and shaft in hand to end up with a fine fit. Alternatively, you could specify tolerances.

I'd like to make these for you, but I'm away from my shop for a few more weeks. If the thread is still active when I get there, I'll contact you.

 

[rwm]

@extropic is correct. These are real concerns. If your shaft is actually 8.01mm this will not work out.

 

[Electrojim]

@extropic is correct. These are real concerns. If your shaft is actually 8.01mm this will not work out.

You guys are right, of course, and with other jobs in the past I've sent motors, gears, etc. to make sure things fit. I'm not as worried about the idler, however, as the pulley is loaded laterally quite symmetrically about its width by the belt going around it and pressing it against the shaft. Even with some slop between bushing and shaft, it shouldn't wobble significantly. Now, I can see eyebrows arching, but I have crafted (and I use the term loosely) these pulleys out of wood (using my drill press as a lathe and a hacksaw blade as a cutting tool), and despite a good deal of run-out, things seemed to run remarkably smoothly. I've attached a snapshot of the motor pulleys I used to determine the correct diameter to keep the motor in optimum range. The 20:1 pulley turned out the winner.

 

[rwm]

A belt drive will allow slop. I was more worried about an interference fit. If you could mic the shaft and make sure it's 8mm that would be great. I could hit 8mm +/- .02mm (.001') but I would prefer to use a reamer (I don't have an 8mm reamer, only Freedom Units)

 

[Flyinfool]

Another trick with the set screws.
Unless you are aiming at flats already on the shaft, put the set screws at 120° apart. This will give you 3 points of contact with the shaft that are equally spaced.

In this case it does not matter much as the load on a turntable is near nothing. I was putting about 1.5 HP thru the 1 inch wide x 1/8 thick flat belt with the drive end turning 7,000 rpm with only a 4:1 reduction to the driven end. That belt had about a 4-5,000 hour life.

 

[Janderso]

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?

That is a good method. I'll have to remember that one.
I have no way of cutting the radius so I would cut the angles and blend.

 

[Electrojim]

A belt drive will allow slop. I was more worried about an interference fit. If you could mic the shaft and make sure it's 8mm that would be great. I could hit 8mm +/- .02mm (.001') but I would prefer to use a reamer (I don't have an 8mm reamer, only Freedom Units)

My "Aerospace" brand all-mechanical dial caliper (from an offshore manufacturer) says 0.314". My dad's 1930s vintage Brown & Sharpe micrometer (in mint condition, by the way, including a little card with decimal equivalents on one side and a picture of their factory spewing smoke into the air on the other) also says 0.314. If I were asked to interpolate ten-thousandths by eyeball, I couldn't do it, as in both cases the markings lined up right on the nose. I'm impressed.

Another trick with the set screws.
Unless you are aiming at flats already on the shaft, put the set screws at 120° apart. This will give you 3 points of contact with the shaft that are equally spaced.

In this case it does not matter much as the load on a turntable is near nothing. I was putting about 1.5 HP thru the 1 inch wide x 1/8 thick flat belt with the drive end turning 7,000 rpm with only a 4:1 reduction to the driven end. That belt had about a 4-5,000 hour life.

I'm assuming you mean two setscrews at 120°? I figure two would be best, as with three you might have four points of contact with the shaft: three around the bottom and one wherever the top of the pulley gets cocked against the shaft; in fact, it might even rock some. Two screws, separated by maybe 60° to 120° would determine a virtual line of contact the whole length of the pulley opposite the center between the two screws. Have I got this right?

Also, this is a recording turntable (yes for phonograph records!), which requires a bit more horsepower as the cutting stylus bites into the lacquer surface of the blank disc. Moreover, the load increases as a groove is modulated more heavily during loud music passages. With underpowered consumer recorders of the 1940s, it was common to note a pitch change as the music got louder, especially near the outside edge of the record.

 

[rwm]

Also, this is a recording turntable (yes for phonograph records!), which requires a bit more horsepower as the cutting stylus bites into the lacquer surface of the blank disc. Moreover, the load increases as a groove is modulated more heavily during loud music passages. With underpowered consumer recorders of the 1940s, it was common to note a pitch change as the music got louder, especially near the outside edge of the record.

Fascinating! I hope you will start a thread and show us more.