[modeleng] Re: Fw: 12V variable speed power supply

Thanks Rich

I will keep the cheap worm drive in mind - but I think that one larger 
pulley will do the trick.   I am deliberately keeping the poly-vee belts on 
the slack side, so that they will slip, if there is a serious confrontation! 
The little countershaft cost me nothing, as I had a pair of 10mm 
self-aligning ball bearing plummer blocks over from another project, and 
odds and ends of aluminium for the pulleys..
I am going to the St Albans Model Engineering show tomorrow, where I hope to 
pick up a scrap of larger round aluminium.

Cheers!   Hubert


----- Original Message ----- 
From: "R.L. Roebuck" <rlr20@xxxxxxxxxxxxxxxx>
To: "Modeleng" <modeleng@xxxxxxxxxxxxx>
Sent: Friday, September 26, 2008 7:32 PM
Subject: [modeleng] Re: Fw: 12V variable speed power supply


> Cheers Hubert - I'll bear this in mind when I get round to looking at the
> Hobbymat (likely in a few months time).
>
> One things you could try is a cheap worm drive gearbox if you do need a
> large reduction ratio and a small space, but either way, with this much
> gearing down, might be worth providing a coupling that can slip if need be
> where you join up to the lathe - all that gearing might mean the motor
> could cause a lot of damage to the lathe if the saddle comes up against
> something hard (headstock, tailstock, chuck).
>
> (In the sense that large speed reduction means large torque
> multiplication also).
>
>
> Yours,
>
>
> Rich.
>
>
> On Fri, 26 Sep 2008, Shep wrote:
>
>> Hello Rich
>>
>> As mentioned in my last message (below) the Proxxon controller solved my
>> variable-speed problems.
>>
>> BUT the bottom speed of the rotation of the leadscrew was too fast, 
>> despite
>> the gearing of the pulleys (and the small dimensions of the lathe 
>> precludes
>> a larger driven pulley)..   I have overome this problem by installing a
>> small countershaft, which reduces the bottom speed to 7rpm.   I would 
>> like
>> this to be even slower, and if I can find a scrap of say 5" round 
>> aluminium,
>> this will do the trick.   In the meantime the turning finish at this 
>> speed
>> is very good.
>>
>> If you DO convert your hobbymat, give me your email address, and I will
>> illuminate this idea with pictures.
>>
>> Cheers!   Hubert
>>
>> 

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