Difference between these motors? - with pics

[ELL]

So the pics of the different motor types:

Why I ask: I need a motor at least 3/4 hp for a power hacksaw I just bought.
Can I use an old motor off a cheap circular saw from FB marketplace like the first pic? Or do I need one similar to the one below? Ignore the KW on the motor in the second pic, I'm on about the design.
I know almost nothing about motors, except you get single phase,3 phase and different KW power. So, any info on what to look for would be greatly appreciated. Must be single phase, since I'm running it off domestic power supply. Many thanks lads. Have a great Friday.

 

[daleyd]

You would need some way of mounting the motor from a circular saw, which you would have to manufacture. Is the motor sealed, and not going to pull in swarf to the windings?

Fan cooling? Once you remove the motor from the circular saw you may find the fan is dangling on the end. You may need to expend some effort making sure this is shrouded.

The electronics that control the motor will probably need to be housed somewhere, if they have any (it may not, so this might not be an issue).

How long is the motor going to run for in your power hacksaw? What’s the run time of the circular saw motor? Is it for intermittent duty, cheap ones usually have an in/off duty period, maybe if only a few minutes? Is this long enough.

You then need to make a pulley for the shaft, to transfer power.

I don’t suppose there’s anything stopping you having a go, but seems a lot of effort for something that may or may not work.

 

[dieselsamurai]

I would say for the cost the extra hassle of converting the output and fabbing some sort of mount you time involved will far out wiegh just getting a foot mounted motor like the pic above.

And i say that knowing that its the sort of thing i might think about doing but from experience its just better to go for easy option , just getting the right size pully to fit will be a ball ache

 

[dieselsamurai]

Old belt drive cement mixer motors are probably the perfect size

 

[dieselsamurai]

I know its not close but they often come up free too !

Working cement mixer

Working cement mixer. Free of charge collection only. Need to be cleaned

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[Pete.]

So the pics of the different motor types:

View attachment 489078
View attachment 489079
Why I ask: I need a motor at least 3/4 hp for a power hacksaw I just bought.
Can I use an old motor off a cheap circular saw from FB marketplace like the first pic? Or do I need one similar to the one below? Ignore the KW on the motor in the second pic, I'm on about the design.
I know almost nothing about motors, except you get single phase,3 phase and different KW power. So, any info on what to look for would be greatly appreciated. Must be single phase, since I'm running it off domestic power supply. Many thanks lads. Have a great Friday.

Power tools like the one pictured have brushed motors you want an induction motor for your hacksaw. The circular saw relies on rpm to work.

I'll check my shf when I get home I probably have something suitable. What size is your hacksaw? If it's a Kennedy hexacut they take a very small motor.

 

[MetalMonkey]

Why I ask: I need a motor at least 3/4 hp for a power hacksaw I just bought.
Can I use an old motor off a cheap circular saw from FB marketplace like the first pic? Or do I need one similar to the one below? Ignore the KW on the motor in the second pic, I'm on about the design.
I know almost nothing about motors, except you get single phase,3 phase and different KW power. So, any info on what to look for would be greatly appreciated. Must be single phase, since I'm running it off domestic power supply. Many thanks lads. Have a great Friday.

A proper explanation is going to get into a lot of depth, so as a nutshell consider:

The first type of motor on the circ saw is a "univeral motor", its a brushed motor.
They have the advantage of being powerful and compact, but they are exceptionally noisy and wear out brushes, so need regular maintenance if you intend on using it continuously.
They typically run at quite high RPM

The second type of motor is an "induction motor", it has no brushes and relies on an induced electromagnetic field to turn it.
The advantage of these is they are much quieter and nothing to wear out (apart from the bearings) so last a lot longer. However they are bigger, heavier, more expensive to manufacture and don't have the starting torque.
They typically run at lower RPM, and usually are available in specific speed ratings to suit the application.

For a power hacksaws, which is going to be chugging along for long periods, you really do not want a universal motor - it won't last and will be painful to be around.
You will also have the difficulty of mounting it, and gearing it down to a suitable speed.

The hacksaw will have been designed for use with either a flat belt or induction motor.
An induction motor will be easier to mount, last better, be quieter and generally more suitable IMO.

 

[zzr1200]

The circular saw will probably run at 3000 rpm approx. you'll need a motor that run at 1400 rpm approx.

I fitted a 1hp (maybe 2hp??) motor to my hacksaw, depends on the type of hacksaw a Manchester Rapid would be good with a 1hp any larger industrial models I'd go with a 2hp (possibly 3hp). Pictures or model would help?

I found with my hacksaw, the direction of rotation of the motor was important, the design of the motor mounting bracket allowed the belt tension to loosen off allowing slip and loss of transmitted cutting power. Once I worked out what was happening changed the rotation direction (changed the wiring connection in the motor) and it became a proper saw......

 

[Erie Fred]

I sure wouldn't want to listen to that screaming brush motor running on a hacksaw....

EDIT: Also, they go up/down in speed with load.
So as it cut's, it will sound like a siren weee wooo weee wooo.

 

[ELL]

The circular saw will probably run at 3000 rpm approx. you'll need a motor that run at 1400 rpm approx.

I fitted a 1hp (maybe 2hp??) motor to my hacksaw, depends on the type of hacksaw a Manchester Rapid would be good with a 1hp any larger industrial models I'd go with a 2hp (possibly 3hp). Pictures or model would help?

I found with my hacksaw, the direction of rotation of the motor was important, the design of the motor mounting bracket allowed the belt tension to loosen off allowing slip and loss of transmitted cutting power. Once I worked out what was happening changed the rotation direction (changed the wiring connection in the motor) and it became a proper saw......

Here is the saw, 1/2 hp 3 phase was fitted with it.

 

[George A2Y]

If the existing motor is working it may be a lot easier getting a cheap inverter off AliExpress.

 

[MetalMonkey]

If the existing motor is working it may be a lot easier getting a cheap inverter off AliExpress.

^^ This.

Providing the motor can be changed to delta and run off 220v you can use a cheap VFD which is going to be the easiest way to convert the machine to run from single phase without replacing anything else. Check the dataplate on the motor.
If it can't, you could still rewire it, but that is likely to be more effort - you can get single to three phase VFDs which aren't that expensive. Or you can swap the motor to a single phase induction motor.

 

[daleyd]

^^ This.

Providing the motor can be changed to delta and run off 220v you can use a cheap VFD which is going to be the easiest way to convert the machine to run from single phase without replacing anything else. Check the dataplate on the motor.
If it can't, you could still rewire it, but that is likely to be more effort - you can get single to three phase VFDs which aren't that expensive. Or you can swap the motor to a single phase induction motor.

Even taking it apart and finding the star point is probably orders of magnitude easier than trying to cobble something together from a power tool motor!

 

[timgunn1962]

As above, universal motors are brushed motors. They can run on AC or DC and speed is dependent on the Voltage. They can run at high speeds.

Induction motors are AC only. Speed is usually pretty constant and is Frequency-dependent and pole-count-dependent. Here in the UK, we have 50 Hz mains: 50 cycles per second, 3000 cycles per minute. A 2-pole motor (one pair of poles) will run synchronously at 3000 RPM. A 4-pole (2 pairs) at 1500 RPM, a 6-pole at 1000 RPM, and so on. There's no theoretical limit to the number of pole-pairs that can be in a motor, but higher pole-counts than 4 (2 pairs) are not particularly common. As the motor is loaded, the speed will drop below the synchronous speed and the rating plate will show the speed it will have dropped to when loaded to its rated power. The induction motor pictured in the OP will run at 1425 RPM when loaded to 1/4 HP, for example. It will be a 4-pole motor.

Induction motors can be single-phase or 3-phase. 3-phase motors can be run from Variable-Frequency Drives to allow operation at variable speed. Single-phase motors generally can't (there are exceptions, but they are odd enough that they don't apply to "us").

Single-phase-in, 3-phase-out VFDs can be surprisingly cheap (I paid under 30 quid each, delivered, for a couple of 1.5 kW VFDs on Aliexpress a few months ago).

Old motors don't necessarily play nice with VFDs. It's largely down to the insulation in the windings. Older 3-phase motors also tend to be configured for 380-440V only. Newer ones tend to have 6 terminals and can be used on either 380-440V in Star or on 220-240V in Delta.

We could do with pics of the motor plate and a pic of the inside of the motor connection box to see whether a VFD is likely to be the cheapest/easist way of running your saw on a single phase supply.

The motor plate pic will also tell us the motor speed and frame size. If it's fairly common (maybe a 4-pole on an imperial 56-frame?), just swapping the motor for a single-phase one might be another cheap/easy way to do things.

 

[zzr1200]

If the motor can be run on 220v x 3ph the other big advantage of a VFD, if you buy the right one, with a knob on the front that allows you easily to reduce the speed of the motor, giving you a variable speed hacksaw.

 

[brightspark]

you dont need variable speed on the donkey saw just a half hp single phase 1450 rpm motor. the whole lots geared down to about 80rpm from memory ive had this one 55 years re built it from virtual scrap all the bearings replaced and the guide bars re ground and the worn bit of bed built up with cast welding rods and ground flat

 

[zzr1200]

you dont need variable speed on the donkey saw just a half hp single phase 1450 rpm motor. the whole lots geared down to about 80rpm from memory ive had this one 55 years re built it from virtual scrap all the bearings replaced and the guide bars re ground and the worn bit of bed built up with cast welding rods and ground flat

I don't disagree with you Brightspark, I just found that my old one even with a brand new blade sometimes felt like it was just rubbing through, not cutting as such. My replacement saw has a much heavier "Bow" with the extra weight it just digs in and cuts...

Rapidor are good lightweight hacksaws mainly supplied/used in schools.

 

[brightspark]

I don't disagree with you Brightspark, I just found that my old one even with a brand new blade sometimes felt like it was just rubbing through, not cutting as such. My replacement saw has a much heavier "Bow" with the extra weight it just digs in and cuts...

Rapidor are good lightweight hacksaws mainly supplied/used in schools.

the older lightweight bows on the saw arent much good with a course blade that the heavier newer ones use. cant remember how many tpi all mine are will have to look

 

[dan.taylor.1]

I've likely got a motor that would suit if you still need one.