motor advice

[wallace]

Hi all, I have an old sagar saw bench which is next on the spruce up list. When I first got it about ten years ago It had the original Brooks 3 phase motor which was about 5hp. Being alittle naieve and not knowing about converters and such I scrapped it and put 3hp single phase in its place. Since then I have accumulated quite a bit of old iron, so have got myself a converter of 5.5kw. On a little job recently I was ripping some 6" sleepers up and I found the saw alittle lacking. So when I start to spruce up the sawbench I thought I may aswell remedy the lack of power. Which way should I go Stick with single phase or utilise the converter to go back to 3 phase. Will I be able to run a 5-6 hp motor on my coverter? Any advice much appreciated.
Mark

 

[9fingers]

If the original machine designers fitted a 5hp motor then we have to assume that it was needed. So it is not surprising that a 3hp motor is a bit inadequate.
3hp seems to be typical for a 10" saw and some 12" saws - you don't say how big the blade is on your Sagar

If you converter is rated at 5.5kW then it should be able to run a single motor up to 4kW and a minimum of 0.75kW. When running multiple motors, the full load of 5.5kW can be realised - this is based on the data for a transwave 5.5kW static converter.
If your converter is a rotary type. then there will be no minimum load requirement, and it will run a single motor up to its rated capacity.

hth

Bob

 

[wallace]

Hi Bob, thanks for the advice most helpfull as usual. The converter I have is a transwave static one. The blade I was useing was a bit of a beast, I think it was about 18-20" so thats maybe why the 3hp wasn't upto the job. I popped into my local motor rewinders and asked him to keep an eye out for something old and heavy similar to the original brooks one I stupidly scrapped. He asked if I would prefer 2 or 4 pole. Which would suit this application? I think a 4 pole does 2800rpm?
Mark

 

[9fingers]

No, more poles = lower speed.

Have a look at my motor paper and you will find further information.

The blade speed on my saw is about 11000 fpm so you could scale this to your blade which would give around 2500 rpm at the arbour.

HTH

Bob

 

[tool613]

Mark nice saw i would love to see it.

18"/20" blades need a bit of power as the cutting edge is so far from the privet. I would say 5 HP minimum and the problem with the static converter is you only get about 2/3 of the motors HP so your 5 hp motor is only going to give you about what you have now for HP/kW in the single phase. VFDs and RPC(rotor phase converters) will give full hp out put to any 3 phase motors(if sized proper) and would be a better chose for phase conversion IMO. you could use the static as the start to a home made RPC tho.

I think you are on the right path as to getting 3 phase over single. ever one knows real machines are 3 phase :lol: .3 phase motors are very simple and not much to go wronge while on the other hand single phase motors are an after thought in motor design.

Bob is a master at this and he may have more to add in the way this works in England.


jack

 

[wallace]

Thanks again Bob, I have re-read your sticky. Another factor which will have to be addressed when I do the sawbench is how to tension the belts properly. Originally belt tension was provided by the weight of the motor which was in excess of 10 stone. I have been attempting to stop slipping by just putting a lever on the motor. Jack I have found an old book were it states that the power required on average work for a 18" blade is 2.25 - 3 BHP. I never really checked the suitability of the single phase motor I stuck on, I think it came from a compressor.
Heres some pics of the bench

It has a stamp on table saying its from the 50's
Heres the blade that came with the sawbench. 20"

 

[tool613]

love the fence. So its only rise and fall?
does it have the tags?

jack

 

[wallace]

Hi jack, Yes just rise and fall. I saw a nice wadkin PK on ebay and was sorely tempted. It hasn't got any spec tags just a sagar label and the table is stamped.
Mark

 

[tool613]

Thanks Mark
ya I bet the PK went for some money too. The table on your Sagar is planed not ground(that's what those rows in the top are). This is very nice to have on a saw. you don't see that much any more. Really the best way to flatten cast ARN. Sagar in many ways was better than Wadkin. Wadkin closed down Sagar after the take over as Sagar machines mirrored many of Wadkin's. It was one way to take the market. Only a few of the Sagar designs(mostly thicknesser) were kept but were built at the Bursgeen shop intil the 90s when it was closed down. You have a real fine example of early Sagar piece there.

BTW i did not have a chance to congratulate you on that fine restoration of the wadkin press.

Hat is off sir.

jack