What RPM?

[Jester129]

Typical Question (i.e. how long is a piece of string) from a relative newbie?
What is the typical rpm on a decent, say 2hp 240v motor bandsaw please? The reason for the question is that - maybe giving the game away here - on fleabay there is a 3-phase bandsaw for sale and the motor isn't playing fair and I thought, "If I could put a single phase motor in there". Would it be almost that simple, apart from rewiring?

 

[Oddbod70]

It;s the blade speed you are interested in , which depends on the diameter of the wheels and the RPM of the motor.

I'm sure there is a "right" answer but I think it would work at pretty much any speed. (Some bandsaws have multiple speeds). That said I think running it too fast might be a fairly alarming experience!

Could you ask the seller to have a quick look at the plate on the motor? Or google the specs of the bandsaw?

If all else fails you could always fit a speed controller but i'd be very surprised if you couldn't pick up a perfectly satisfactory 240v motor and fit it fairly easily.

 

[novocaine]

for a single phase, 50kz AC 4 pole motor the speed is always going to be 3000rpm (half it for a 2 pole which will have less torque) doesn't matter.
a 3 phase motor will depend on the wiring but is typically around 1400rpm for a 3 pole star configuration at 50hz. (from memory and I might have that the wrong way round and thats for Delta)
so yes you can stick a single phase motor in there, but you will need to regear it, or stick it on a VFD.

 

[guineafowl21]

for a single phase, 50kz AC 4 pole motor the speed is always going to be 3000rpm (half it for a 2 pole which will have less torque) doesn't matter.

Other way round. 3000ish for 2 pole, 1500ish for 4 pole. Same for single or three phase - star or delta for the latter dictates working voltage.

Get a pic of the motor rating plate (not machine plate) from the seller, and post it here - it should give useful details such as frame type, speed, power, etc.

Direction of rotation is another thing to consider, but you should be able to work that out from pics of the machine.

 

[Ttrees]

Have a look to see if the motor has 220 or 240 volts stamped into the motor nameplate, not the plate on the machine .
If it does then a VFD is only `100 quid with about 15 quid for everything else, all in.

You may have to make a box for it though, if you see an old washing machine about or whathaveyou that would do the trick.

2 pole motors run around 2840 to 3000 RPM on 50hz electricity (this side of the pond) and 4 pole are half that RPM.

If you only have a 13 amp plug its an absolute no brainer to go VFD route.
My 24" saw has no issues as it can be tuned to startup in how ever many seconds you want.
Its the current from starting inertia that blows the fuse, if you've ever done so with single phase motors, it goes way way up for a second or two.
VFD's store the charge in large capacitors instead of a big surge of power needed to get going and very smooth on parts compared to single phase.

Good luck
Tom

 

[novocaine]

figured I had it the wrong way round, always got that wrong, it's why I became a mechy not a sparky .

 

[AES]

@novocaine: Also worth a look at the Tuffsaws website. Ian had (no doubt still has) a very useful table of info about saw blade speeds. From the info you've got above and Ian's info you can work out what blade speed you actually have/what you need (sorry I don't have the info in my head, not his URL, but easy to find).

 

[Jester129]

I've asked for a photo of the motor rating plate, but meanwhile this is what he's already posted and it isn't really very helpful:

 

[guineafowl21]

I think I can make out 2 pole, which chimes with 2850 rpm (giri?)

It’s also a dual voltage motor, so can be run from a simple inverter drive. This is well worth considering, depending on what ‘motor isn’t playing fair’ means.

 

[Jester129]

Dear Mr Foul21, or may I call you Guinea, or even Guin for short?
I was trying to be polite, but the motor is cream crackered and needs either a rewind (?) or replacing, so I got to thinking that if it was replaced by a 240v motor, I could get a decent(ish) bandsaw for a hopeful bargain. As a 240v one, I could use it in my garage in place of a tiny ryobi benchtop bandsaw, it being quite a decent step up.

 

[Myfordman]

Dear Mr Foul21, or may I call you Guinea, or even Guin for short?
I was trying to be polite, but the motor is cream crackered and needs either a rewind (?) or replacing, so I got to thinking that if it was replaced by a 240v motor, I could get a decent(ish) bandsaw for a hopeful bargain. As a 240v one, I could use it in my garage in place of a tiny ryobi benchtop bandsaw, it being quite a decent step up.

Look at the plate on the old motor to see what speed you need. Some bandsaws use a 950 rpm motor which is a 6 pole type but are harder to find.

 

[guineafowl21]

Dear Mr Foul21, or may I call you Guinea, or even Guin for short?
I was trying to be polite, but the motor is cream crackered and needs either a rewind (?) or replacing, so I got to thinking that if it was replaced by a 240v motor, I could get a decent(ish) bandsaw for a hopeful bargain. As a 240v one, I could use it in my garage in place of a tiny ryobi benchtop bandsaw, it being quite a decent step up.

Ah, a euphemism, as I thought! You can call me what you like...

So you need a 2-pole, 2850rpm, motor. Work out the rotation direction, or get a reversible 1ph motor.

To be determined (from motor plate, hopefully): Frame mount dimensions, shaft size.

 

[Jester129]

The seller has sent a better picture of the motor plate:

GIRI is Italian for 'turns', so it's 2890rpm.
The motor has a pulley on, so I can safely say that the saw will have one on (impressive, eh?). All I would need to do is take the one off this motor and (hopefully) put it on the 240v motor, wouldn't I? So, if I got a 240v motor with a similar rpm, amend the electrics accordingly and away I go?

 

[Ttrees]

Is this why the machine is going cheap?
Three phase motors are fairly tough.
It could only be the keyway that is damaged, if the seller has given you a short answer saying its toast.
You can buy pulleys that do not need a keyway which lock onto a bare shaft.
So you don't need to do any work to cut or fix a keyway.
If this is the case, then buy a VFD for a hundred quid, and 15 for everything else.
If its a large machine and you only have 13amp household sockets, then absolute no brainer, as the equivalent motor that is single phase will have a starting draw that will require 16a blue plug.
Once the machine is running it is not so hungry on the leccy.


Are you asking if there is another pulley on the machine that you might need to source or replace?
On most bandsaws there is another groove on the back on the lower wheel.

Hopefully the motor is good.
Tom

 

[guineafowl21]

It’s a 3hp motor - didn’t see that from the original picture. Budget for a nice new starter box with overload and NVR, and a blue plug and socket.

Frame type 90 L2 so have a look for that. Safest bet is to get the machine in your shop so you can double check measurements.

Pulley looks like it has a grub screw into the keyway, and from the look of it I’d guess clockwise rotation, with the shaft facing you.

 

[Ttrees]

What are the chances of the motor being alright, and only the flex being damaged
and tripping the breaker?

I don't see signs of burning anywhere, and that 4 core wire looks flimsy
enough to get damaged with its thin insulation.

Interesting stuff, I wouldn't order a motor just yet, but a good idea to get a figure on a price to compare.

Tom

 

[Inspector]

Get it with the motor and once in hand look the motor over. It may be something simple to fix and then you only have to worry about powering it. If it has had the blue smoke let out of it then you can look for another motor, either single or three phase as you like. I can't speak to costs where you are but rewinding motors below 60 to 100 horsepower, unless a special motor, is not economical. That came from a motor repair company when I brought in a bench grinder that was duff. Three phase motors a generally cheaper than single phase ones. Pretty much any bandsaw that has a 3hp motor is worth getting in working order unless the asking price is too high.

Pete

 

[Jester129]

As usual, the people on this platform have been fantastic, so thank you all for your help.The support and knowledge has been really helpful, I'll see how I get on with the auction now.
Thanks again.

J