Help! What size pulley?

[SammyQ]

I'm at last - after long term illness- finishing the renovation of an elderly Wadkin AGS 10" saw. I have a 2.0kW three phase motor for it and I have just ordered an inverter to run it, when I stopped to think:

This motor runs at 1440 rpm; the saw arbour pulley is approx 3"; surface speed on the blade should be about 12000.....

Quick calculation: [10/12 x 3.142] x RPM = 12000, ergo RPM = 4583

To get 4583RPM arbour from 1440RPM at the motor, I need a x3 Pulley step-up......9"..............!!!!!! :shock: :shock: :shock:

Is this feasible or am I am a complete and utter dork, airhead, mentally deficient etc etc? Should I go out and seek a faster spinning motor? Can I carry on and fit a pulley that would make Swartznegger pause for thought when he saw it?

This with £70-odd invested in the inverter (in the post) and SWIMBO in full nag regalia seeking a completion date (yesterday) for three outstanding jobs....did I say that the illness was chronic depression?

Sam - panicking ever so slightly.

 

[Steve Maskery]

Sammie
My brain doesn't work properly any more either. Perhaps we should start a sub-forum...it's not just us, I can assure you.
What is the problem with a 9" pulley? I've not checked your maths, but assuming they are right, 9" does not seem outrageous to me. Or you could use a 6" and 2" to get the same ratio.
Unless we are both missing something.
Keep taking the tablets. I do.
Best wishes
S

 

[wallace]

Hi Sam wheres the pictures. Heres a link to a site that made all the speedy stuff easier for my little brain to understand.
http://www.vermontamerican.com/NR/rdonl ... MChart.PDF
If you had a 6" pulley on the motor and a 3" pulley on the arbour you would get a speed of 7,536 feet per minute
If you had a 9" pulley on the motor and 3" pulley on the arbour you would get a speed of 11,304 feet per minute.
According to this site you need a minimum speed of 10,000 fpm and a maximum of 18,000.
So with a 9" pulley you should be ok. Unless you were to change your motor to a faster one 2,800rpm.
When I did my Sagar saw bench I had a problem with the pulleys, if I remember correctly the pulley I had on the motor was too big and the static converter nearly popped a gasket with all the juice the motor was drawing on startup. When it did get upto speed the noise it was ear shattering. When I did the sums it was running the blade at 24,000 fpm
HTH
Mark

 

[SammyQ]

Steve, thank you for the support. I did a quick mock-up and realised that a 9" pulley fouls the motor mounting plate sheeesh.... "BEGINNER!". Mark, those run figures agree with what I read elsewhere; I think a plan may be to switch the arbour pulley to as small as I can get 2" maybe or 1.5" and then the drive pulley on the motor will shrink to fit. Photos? Yup, I know, I keeep procrastinating, but I DO have them and they're coming!

 

[Andy RV]

Have you bought a digital inverter? If so you can run the motor at a higher frequency to up the rpm.
This is common practice on woodturning lathes as you get the torque of the 4 pole motor with the speed of a 2 pole. The frequency that you can run you motor at will depend on the quality of the motor, mainly the bearings but you should be able to safely hit 2000rpm + meaning you won't have to fit such a big pulley.
There's quite a bit of information on the web about this practice so I recommend that you have a read.

 

[WoodMangler]

I think a plan may be to switch the arbour pulley to as small as I can get 2" maybe or 1.5" and then the drive pulley on the motor will shrink to fit.

Bear in mind that the smaller the pulley, the more energy it takes to drive the belt. I found this out the hard way when I down-speeded a bandsaw to cut metal - I used 3" and 6" pullies for the step-down, and ended up having to fit a more powerful motor to compensate.

 

[SammyQ]

Thanks Andy, wasn't aware of that; got any tips please on particularly good sites you've used in this repect?

Thanks Woodmangler, that is a pitfall guaranteed to exaccerbate frustration and best avoided!

Sam, now stopped hyperventilating.

 

[Andy RV]

There's loads of information here: http://www.practicalmachinist.com/vb/transformers-phase-converters-vfd/
Also this company sells a range of inverter and motors packages using 4 pole 1400rpm motors and rating them up to 100hz allowing them to run at 2800rpm, these are just standard off the shelf 3 phase motors.

The bearings found in 4 pole motors will be the same as found in a 2 pole motor running at 2800rpm, and bearings of that size will be good to way above that at approx 15,000rpm+. I'm running the 1400 rpm motor in my lathe upto 85hz, I'm not sure what speed this is, 2500rpm?.. without any problems, I used 85hz at my max as that gives me the approximate max rpm that the lathe would of originally run at.

 

[SammyQ]

Andy, you're a star! That forum will keep me off the streets for days.....What company were you linking to please? It didn't appear on the thread? Sam

 

[Andy RV]

Oops sorry its http://www.inverterdrive.com/

 

[SammyQ]

Blimey....what an Alladin's Cave of hardware.....thanks Andy.
Sam