# Conversion To Variable Speed



## Gill (2 Feb 2007)

I have a single speed scroll saw that I would like to convert to a variable speed. Is it possible, and how would I go about it?

Gill


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## CHJ (2 Feb 2007)

Hi Gill,

Yes it is possible but will need some research.

Two methods are available.

1. use a series (brushes) motor and control it with a speed controller (like a sewing machine.) (most likely possibility from second user parts)

2. Fit a 230 volt 3ph motor and use an invertor to supply it. (expensive)

The machine may currently have a series motor, if so all that is required is an electronic speed controller with a power rating to suit. (old variable speed vacuum cleaner for instance or the spares for such)


Major things to find out if motor needs changing, 
1. physical size of motor to be replaced and its power ratings.
2. the output shaft diameter and length (to take existing fittings).

Another way would be to research the spares situation for an existing variable speed scrollsaw of similar size and see if its motor, and or controller, would be suitable.


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## llangatwgnedd (3 Feb 2007)

Charles, Why cant a dimmer switch be wired in there somewhere?
Is it because of the induction motor?


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## Gill (3 Feb 2007)

Thanks for the advice, Chas. I've no idea how these sorts of things work and I had been hoping it would be possible to buy some sort of adapter from Maplins.

The fact that Hegner's website says it is not possible to add variable speed to their saws later because of the need to replace the motor did give me pause, so I thought I'd raise the point here. Could it be that motors which work with a variable speed unit are built differently to those with a single speed?

Gill


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## StevieB (3 Feb 2007)

I do not know the answer to this, but would advise against installing a dimmer switch if for no other reason than a lighting circuit is designated 6 amps max rating and the saw will be on a 13 amp plug and fuse. Sticking an in line dimmer switch in means the switch will go first, not the fuse. 

Steve.


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## CHJ (3 Feb 2007)

Gill":h0wj25il said:


> Thanks for the advice, Chas. I've no idea how these sorts of things work and I had been hoping it would be possible to buy some sort of adapter from Maplins.
> 
> The fact that Hegner's website says it is not possible to add variable speed to their saws later because of the need to replace the motor did give me pause, so I thought I'd raise the point here. Could it be that motors which work with a variable speed unit are built differently to those with a single speed?
> 
> Gill



Gill, It may be that Hegner use an invertor and a 3phase motor for their variable speed, given the price point it could well be, need to check their specs.

The main difference with an electronic speed controller for a series motor than a simple dimmer unit is that a motor control will have a feedback circuit to address the back emf of the motor and compensate for it to provide a better power output.

Not rocket science, and if you can provide details of motor type and rating fitted to your saw ,and it is a series motor (brushes) I may be able to provide a circuit diagram for a suitable controller. 
There is one I made about 40+ years ago currently in my shed controlling the heaters in the parrots pen. (made in the days before electric drills etc. came with variable speeds.)


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## Gill (3 Feb 2007)

Hi Chas

Thanks for the offer but even if it isn't rocket science, it's all a bit too advanced for me. It's not as if I _need _a new variable speed unit added to my Hegner 1. I just thought it might be worth doing if it was only a matter of buying a component (or two) and plugging it in.

Gill


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## CHJ (3 Feb 2007)

Gill":3jotvck0 said:


> Hi Chas
> 
> Thanks for the offer but even if it isn't rocket science, it's all a bit too advanced for me. It's not as if I _need _a new variable speed unit added to my Hegner 1. I just thought it might be worth doing if it was only a matter of buying a component (or two) and plugging it in.
> 
> Gill



I checked the specs. and Hegners have induction motors.

This would mean fitting a new 230V 3 Ph Motor and invertor for variable speed, Or a DC motor, (similar to that fitted to treadmills)

*EDIT:* looking at the Axminster Clone of the Hegner and the smaller variable speed unit it would appear that they might be using DC motors in Both.
Although the specs refer to induction motors in one breath and DC motors in another.

I had assumed it was one of the Others you were thinking of modifying.


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