aux motor for SS

peterm · Post by **peterm** » Sat Sep 25, 2010 5:47 pm

I do not have a speed reducer but want to run slower for certain lathe turnings and am wondering if the temporary setup in this marked up photo would work without damaging the Shopsmith:
[ATTACH]10502[/ATTACH]
I was intending to leave the SS unplugged but the aux motor would be turning all the internals in the headstock. I saw the similar idea on this blog: http://shopsmith-tool-hunter.blogspot.c ... ark-v.html
where they put the SS to ``fast`` to loosen the belt, which I think is not necessary for a speed reduction.
What do you think...........

dusty · Post by **dusty** » Sat Sep 25, 2010 6:07 pm

I have seen this same approach in two or three different locations. I really do not see why the inner workings of the Mark V would be damaged by this.

.............
Speed control - just thinking. Speed control - could it be used while driving with an external motor.

8iowa · Post by **8iowa** » Sat Sep 25, 2010 8:01 pm

In effect, using the headstock as a variable speed "gear" box. Keep in mind the fact that reducing the speed in this manner may increase the output torque beyond the capability of the belts and pulleys in the headstock. I'm sure that the headstock was not designed to produce output torque beyond that at the present 700 rpm slow speed setting.

peterm · Post by **peterm** » Sat Sep 25, 2010 8:29 pm

8iowa, I assume you are responding to dusty's speed control comment, and not to my question. Correct?

rlkeeney · Post by **rlkeeney** » Sat Sep 25, 2010 8:59 pm

I can't think of any reason why this would not work.

I think that running the head stock up to it's highest speed is a good idea. If I'm seeing this correctly in my sleepy brain this should make the the head stock motor easier to spin and spin it slower. There are way to many parts involved for me to do this in my head but there might be a chance you could spin the head stock motor to fast if you did this with the head sock speed set to slow. Depending on the auxiliary motors rpm and the pulley sizes.

I can't think of anything you could do where torque would be an issue turning wood. I'm assuming you are not going to use a 30hp 3 phase motor and turn lead spindles.

You might want this to run on the other side of the headstock as well. The you could run your band saw real slow.

If I had a motor laying around I think I might have to try this.

SDSSmith · Post by **SDSSmith** » Sat Sep 25, 2010 9:25 pm

dusty wrote:I have seen this same approach in two or three different locations. I really do not see why the inner workings of the Mark V would be damaged by this.

.............
Speed control - just thinking. Speed control - could it be used while driving with an external motor.

Based on the proposed set up the only thing the Shopsmith speed control will do is determine how fast the Shopsmith's internal motor will be turned by the external motor.

damagi · Post by **damagi** » Sat Sep 25, 2010 9:42 pm

http://mkctools.com/jackshaft.htm

Here is the article which it is based on:
http://books.google.com/books?id=9tsDAAAAMBAJ&pg=PA198&lpg=PA198&dq=shopsmith+jack+shaft&source=bl&ots=tKmaZ_RFi1&sig=-Ilpy_xysnhVvIlAjZHdCjP5ltI&hl=en&ei=1qSeTOzYFYy8sAPz_ejVAQ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBQQ6AEwAA#v=onepage&q&f=false

peterm · Post by **peterm** » Sun Sep 26, 2010 1:14 am

Thank you for the comments so far, they lead me to the following logic:

Assume the SS speed dial is set to slow speed. If a 10"diameter pulley is on the upper shaft of the SS and a 2" on the aux.motor, giving a 5 times reduction, and the aux motor runs all the way up to 3450rpm , then the SS upper shaft turns at 3450/5= 690rpm, which is roughly the same as the slow speed setting. Thus the SS motor will be spinning at its normal top speed.

However I expect to use a variable speed dc aux.motor running at perhaps 500rpm, so the SS upper shaft will be at 100rpm and the SS motor will spin at roughly 1/7 normal speed. I also hope to use a bigger than 10" drive pulley, so I think this scheme will work fine. If you see a flaw in my thinking, your caution would be appreciated.

I won't get to try this for awhile, but will post a followup eventually. Too busy having fun refurbing an old greenie right now.

dusty · Post by **dusty** » Sun Sep 26, 2010 5:15 am

Remember that when doing this the motor in the Mark V is functioning like a generator. All be it an inefficient generator, the power cord for the Mark V should be treated as a "hot connection" and must not be plugged into a wall outlet.

SDSSmith · Post by **SDSSmith** » Sun Sep 26, 2010 10:44 am

Setting the Shopsmith speed control at "Slow" and driving the headstock externally via the top SPT shaft would result in the headstock motor turning at about 5 times the input speed. The headstock yields a speed range of 700 to 5200 rpm from a 3450 rpm motor. So the effective speed ratios motor/quill are approx. 1/5 (Slow speed setting) and 3/2 (Fast speed setting). Reversing the input and driving through top SPT shaft the ratios "flip" for the quill/motor ratio and are 5/1 (Slow speed) and 2/3 (Fast speed). When driven externally, the headstock motor will turn at its fastest with the speed control set at the "Slow" speed setting.

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