Reducing the diameter of a V belt pulley?

[great white]

I was walking through one of those "overstock" style clearance stores and ran across a V-twin compressor pump:





Part number was TL33724. They had "4HP" on the tag, but I l looked up the part number and comes out to a 3hp, 8.8 SCFM, max 1080 rpm pump and a 9.8" pulley on it. Cast iron heads, cylinder and gearbox.

Was only 75 bucks so I grabbed it. Cheaper than I have seen anywhere else for comparable specs and decent deal, even if it is a Chinese "something or other" brand.

I only have an oiless compressor on an upright 26 gallon tank and you can't even be in the same room with it when it's running. heck, I close the door to the untility room and sometimes I don't even want to be in the garage when it's running.

Not to mention, the oiless's SCFM is (to be kind) "poor". 4.2 SCFM at 90 psi. Won't even run my good impact guns at full power. So 8.8 SCFM will be a decent step up and as a side bonus it should run much quieter.

Looked though my stash of bits and bobs and sure enough, no 3 hp motors. Lots of fractional stuff, but no 3 HP jobs. So I grabbed a fairly generic "Vevor" 3 hp motor:

Nothing special, but will get the job done.

I don't have a 230 plug in the utility room, but I'll just bring and electrician in the new year to install one. Lots of room left in the panel and the compressor goes in the utility room right next to the panel, so cost shouldn't be that bad. Main line current is something I don't mess with (other than changing the occasional light fixture, switch replacement or such), so worth the dough to bring someone in to do it for me.

The thing is, I've only got a couple 3.2" pulleys. Not fractional stuff, they're cast iron (or cast steel, can't remember) and pretty hefty. 5/8" bore, 1/2" belt.

Problem is the 9.8 and 3.2 wok out to a 1126 rpm with a motor speed of 3450 rpm. Not a lot over 1080 rpm (46 rpm over), but still over. I'm not overly uncomfortable with a little over speed rpms, but ideally I'd like to be at the compressor rating of 1080 rpm max or perhaps a touch under it.

3.1" diameter works out to 1091 rpm and 3.0" dia works out to 1056 rpm.

Can I chuck it up in the lathe and shave a little off it without negatively effecting the v belt angle in the groove or should I recut the angle if I shave that 1/8" or 1/4" off the pulley?

I could just buy another 3.0" dia pulley, but they're not cheap (for stuff that's not fractional HP) and I've already spent more than I really should. Saving a few bucks on the pulley would be great if I can make what I already have here work.

No guesses please, I'm looking for an informed answer.

 

[woodchucker]

you need to keep the angle of the sheave..
BTW, I don't know if you know this, they have adjustable sheaves. I have a bunch. you basically screw them and lock them down.
You can get the belt to move down by opening the gap, or up by closing the gap.
I have different shaft size models and sizes.

edit: btw, that looks like a two stage pump..I can't be sure, but I suspect it is. They run at lower speed..

I've been looking for a new compressor, you guys got me scared about my tank blowing. Mine is a scotts compressor, 1980s vintage. I like it's quiet run, but am concerned the tank may be getting too old.

nice pickup. for that price you can't lose.

 

[great white]

you need to keep the angle of the sheave..
BTW, I don't know if you know this, they have adjustable sheaves. I have a bunch. you basically screw them and lock them down.
You can get the belt to move down by opening the gap, or up by closing the gap.
I have different shaft size models and sizes.

edit: btw, that looks like a two stage pump..I can't be sure, but I suspect it is. They run at lower speed..

I've been looking for a new compressor, you guys got me scared about my tank blowing. Mine is a scotts compressor, 1980s vintage. I like it's quiet run, but am concerned the tank may be getting too old.

nice pickup. for that price you can't lose.

Nope, single stage. Both cylinders feed into the same manifold, not one into the other.

I didn't think twice when I saw the price, even with somewhat (at that time) "nebulous" information on it.

Around here, there's always someone watching in those types of places and if you show interest in something and put it down, they walk up behind you and buy it. Then, it shows up on kijiji or FB marketplace at twice the price....

 

[woodchucker]

another view

 

[woodchucker]

BTW you can lookup the angle of the sheave in the machinery's handbook. it will tell you the angle for a particular size.

 

[Ulma Doctor]

Unless you’re beating the compressor up by extended marathon sanding or bead/sandblasting sessions, I wouldn’t be concerned about a 100 rpm difference, so long as oil levels are checked regularly and the cooling air is not restricted or compromised.
You could certainly shave some off the OD of your pulley, if it makes you feel better, so long as the belt doesn’t bottom out in the pulley. The added friction of the belt bottoming out will wear the belt prematurely

 

[great white]

Unless you’re beating the compressor up by extended marathon sanding or bead/sandblasting sessions, I wouldn’t be concerned about a 100 rpm difference, so long as oil levels are checked regularly and the cooling air is not restricted or compromised.
You could certainly shave some off the OD of your pulley, if it makes you feel better, so long as the belt doesn’t bottom out in the pulley. The added friction of the belt bottoming out will wear the belt prematurely

It's less than 50 rpm over, 46 actually, if you take the measurements and the math as "gospel".

I was kind of wondering if it was even worth bothering with or if I was just being overly cautious. I'm just kind of picky when it comes to OEM limitations like max rpm.....

 

[woodchucker]

BTW, have you considered opening it up and cleaning it out. Knowing that all Chinese stuff might be kits, and not properly finished or cleaned.

It may save you from grief further on down the road.

 

[great white]

BTW, have you considered opening it up and cleaning it out. Knowing that all Chinese stuff might be kits, and not properly finished or cleaned.

It may save you from grief further on down the road.

Not a bad idea and I certainly have the time.

Certainly worth at least popping the crankcase cover off and having a looky see to make sure there no casting sand or other strange bits floating around in there.

I generally do that with most "import" stuff if it's not from a known supplier.

Or maybe I'll just drop my endoscope in there and have a look around rather than disturbing the crank lip seal....

 

[great white]

Just dropped a 1/2" belt into the pulley and was reminded that it's not the absolute OD of the pulley itself I need to be concerned with but rather where the angle rides the belt. So I'd need to recut the angle anyways if I wanted to reduce the effective diameter of the pulley. Lots of depth under the belt as it is, so it is an option to recut the pulley.

And with all things Chinese manufatured, I can find varying specs for rpm for the same looking 3 hp pump. 800-1100 at one "reference", 1200 rpm max in another.

Oh well, maybe 46 rpm over isn't a big a deal as I'm making it out to be in my mind......