Speed reducers

Help! is there a simple plug in variable speed device that I can purchase that will reduce the speed of my floor standing band saw so that I can then cut sheet metals. I have the right saw blades but the wrong speed. I tried to find a bench top metal cutting bandsaw without any luck

Hi Anthony,
To answer the question we would need to know what type of motor is in your bandsaw. If it is a single phase induction motor I would say the answer is no. If it is a three phase motor (Which is unlikely.) you could fit a VFD. (A variable frequency inverter.) If it is a series wound motor (Also called universal.) you could use a phase angle controller (This is just a high power light dimmer.) This would work but give poor speed regulation.

Les.

Hi Anthony,

My father in law fixed a worm drive between the motor and pulley on his wood cutting band saw for cutting steel.

Hope this helps.

Peter.

To cut steel and wood on the same bandsaw you wil need around a 10:1 reduction, this is not really a suitable reduction for an electrical solution if you would like some power to cut with. A mechanical solution will be the most satisfactory, either a gear redution unit or a two stage belt and pulley setup.

Mike

Here's a solution for someone who's happier working wood than metal.

**LINK**

Neil

Interesting post from Neil. Also see old post 'Bandsaw speed control' But it doesn't answer your question easily. I wonder if any of our electrical boffins could show us how to use a washing machine motor which has a speed sensor built into it to produce variable speed 240V motors.

Thinking on from washing machines. Modern machines have very small multi groove pulleys on the motor. My bandsaw has a 'V' motor pulley of about 2". If that was replaced with a 3/4" multigroove, it would reduce the 800 f/min to about 350 f/min. BUT we are looking for 100 f/min or less I believe. My motor is 2800 rpm, but a 1450 rpm motor would just about get you there. If you do as Neil says and search Using old washing machine motors, there is a wash M/c motor controller for DIY for about £40.

We need more input from our Boffins.

BobH

Thank you all. Some enlightening observations there. I do not have the space for a speed reduction box, and whilst the washing machine pulley is a possibility as I was not aware of the pulley size, I wonder about the torque though? As time is of the essence I may just go for replacing my 1ph. 1250rpm. 850w induction motor with a new 3ph job with inverter and speed control. How is it that none of many machine tool suppliers have thought of a bench mounted metal cutting band saw. after all it surely is only a motor and pulley change. Subject to torque issues of course.

Thanks for the advice, will let you all know my chosen route soon .Off to the oncologist now.

Cheers Tony

Hi Anthony,
You have not given any figure for the ratio of speed reduction that you require. If we go by "Speedy Builder5's" figures (Which sound about right to me.) you are looking for a 8:1 reduction. Even if you fit a 6 pole motor instead of your current 4 pole motor you still need to reduce the speed by a factor of about 6. I do not think that a 3 phase motor running at a sixth of its design speed is a good idea. It will only produce about 1/6 of its rated power output so even if you fitted a 1.5HP motor you would be down to 0.25 HP. You would also have to provide aditional cooling as the fan on the motor would not provide enough air flow. An alternative approach would be to buy a 6" x 4" metal cutting bandsaw and remove it from its base and make a table mounting for it. (I have seen a design on the web for doing this but cannot find it at the moment.) This would probably cost about the same as a 6 pole 3 phase motor and inverter.

Les.

Hi

On the band saw I rebuilt with two drive motors one for wood hp 1425 rpm driving a counter shaft and one for metal 3/4 hp 1425 rpm driving a 18 to 1 worm gearbox that drives the counter shaft with "Poly Vee" belts all round

Remove the belt from the worm gearbox for wood and swap motor plugs.

Motor RPM
1425
Saw Spindle Pulley Dia
168
Counter Shaft Pulley Dia
95
Worm G'Box
18 To 1
Band Wheel Dia mm
360

Metal Cutting

Motor 1 Dia mm G'Box Dia
53 90
63 80
70 70

Wood & Composites

Motor 2 Dia mm C\Shaft Dia
50 90
62 80
69 70

Metal

Metres Min
29.82
39.87
50.63

Wood

Metres Min
506.30
706.29
898.33

Sorry about the Layout Just cut and pasted from an XLS Spreadsheet Used to find optimum ratios and pulley sizes

May be useful

Still toying with using a 1.5 hp DC motor and KB Electronics Controller and two speed pulleys.

Though two speed may not be needed as KB quotes up to 50 to 1 speed control and up to 120% max motor speed.

And 0 to 30% min speed on trimpot adjustment of controller.

Not the cheapest option DC drives. Mine is a Totally Biased opinion as a "DC Drive" and "Poly Vee" belt transmission addict.

Eric

Edited By oldvelo on 30/09/2014 04:10:54

Hi Eric,
That is very nicely presented information. It should help Tony decide on the target blade speed he wants to use for metal. Regarding the use of the 1.5 HP DC motor. Although it will give constant torque down to zero RPM (I think it is better than a 3 phase motor and VFD in that respect.) the power will be reduced in the same ratio as the speed so running a 10% speed you would be down to 0.15 HP I think your existing solution is the better one.

Les.

Dear Les ,thank's for your contribution ,I am inclined now to follow your solution of the 6x4 bandsaw idea although it would be a bit large. Space restrictions and only occasional use of the wood bandsaw might make me retire it so that I have the extra room. Thinking to do.

Thanks again

Tony