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Motor reduction speed

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T.Swinfield27/06/2020 14:00:21
9 forum posts

I have an electric motor the speed is 2850 rpm , I need to reduce the speed of the motor for use on a home built power hacksaw.

First what speed would you recommend,

Second where can I buy a gear box to do the job.

From Tony, thank you for your advice.

Steviegtr27/06/2020 14:11:59
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2243 forum posts
311 photos

A gear reduction is probably going to be your only way. That motor will be a 2 pole. For half that speed you would need the 4 pole version. To use a VFD may give you reduced torque of which the hacksaw needs plenty. You could do it with pulleys rather than a gearbox.

Steve.

duncan webster27/06/2020 14:36:38
3509 forum posts
63 photos

what output speed are you looking for? ETW design (sold by Hemingway) has 90 strokes/min which seems about right. This implies ~30:1 reduction. I have a feeling you'd do better starting with a slower motor

Edited By duncan webster on 27/06/2020 14:39:52

not done it yet27/06/2020 15:13:38
6325 forum posts
20 photos

You could look up TEC gearboxes. No idea how good, bad or ugly they might be but they do offer all sorts of ratios and in different formats - spur, helical, worm-wheel - In a wide range of power rating. Reasonable price ranges, too, from light duty (as in cheap) to heavier duty specification.

Edited to add that they do motors, too.  Personally I would buy a 3 phase 1425rpm pair and add a VFD to the system - so much better operation than single phase - soft start, variable speed, remote low voltage control and safety circuits all make them worthwhile considering.

Edited By not done it yet on 27/06/2020 15:16:46

Tim Stevens27/06/2020 15:16:13
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1455 forum posts

A pair of pulleys with a V belt will give you benefits such as - fairly quiet, not 100% fussy about alignment, needs no lubrication (assuming that any extra shaft runs in ball bearings), with a small-section belt you can use a very small motor pulley and get a big reduction, and the investment can be spread over the next two or three projects as pulleys and belts are always handy to have around.

Cheers, Tim

Mike Crossfield27/06/2020 15:36:33
264 forum posts
36 photos

Tony


My Rapidor Manchester power hacksaw uses a standard ac motor which runs at about half the speed of your motor. It uses a two stage speed reduction using v belts with an overall step down of about 30:1. It works well, is quiet, and has massive torque. Only snag from your point of view is that the large pulleys are, well, quite large! Take a look at the Rapidor pictures in the machine tool archive on the lathes.co.uk website And you will get the idea. If space is not a problem it might be the way to go.

Mike

old mart27/06/2020 16:11:59
3345 forum posts
208 photos

Gearboxes come in lots of ratios, these are right angle types: **LINK**

Howard Lewis28/06/2020 17:57:29
5299 forum posts
13 photos

You are not really at the best starting point.

The most compact way of getting a 30:1 reduction would be a worm and wheel. But this would mean your motor sticking out at right angles to the machine. (Unless you fancy having two worm boxes, say 6:1 feeding a 5:1 to bring the drive lines back parallel again )

For 30:1 with belts you would need at least a two stage drive, again a 6:1 and then a 5:1. With a minimum pulley diameter of 1.5 inches,the driven pulleys are still going to be pretty large,, 7.5" and 9 " diameter.

Assuming that you are using a standard 12" hacksaw blade, a Z section belt would probably cope with such small pulleys.

Polyvee belts might be better, for small diameter driving pulleys..

With small driving pulleys, to increase the wrap around the pulley, you will need fairly long pulley centres.

A four pole motor with a nominal 1475 rpm would halve the ratios needed, allowing driving pulleys of 2" minimum, and smaller driven pulleys..

If the motor can be mounted under the machine, it could drive to the countershaft at the rear, to make things compact.

Howard

oldvelo28/06/2020 22:52:20
276 forum posts
54 photos

Hi

Poly Vee Belts with a countershaft is probably a good option with 4 ribs on the primary drive and 6 ribs on the secondary drive.

As Howard points out the small diameter need as big as possible contact area this can be done with a flat idler pulley running on the back of the belt to increase the wrap around.dscf2355.jpg

Proper Alignment and correct tension is critical on Poly Vee Belt Drives as any error in alignment they will climb over the grooves as the ribs are quite flexible rubber and unable to keep the belt on the pulleys.

Eric

T.Swinfield29/06/2020 08:22:23
9 forum posts

I would like to thank you all for sharing your ideas.

I think that I will have a try with the pulleys, I have some sheet aluminium to make the pulleys, maybe using timing belts, the HTD range look easier to make ( I hope).

That's again, Tony

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