Shopsmith Forums

Dusty
Just wondering------ Did you calibrate the tach that you are using?
Also with a quill speed of over 7000RPM the Auxiliary shaft will be in excess of 11000RPM!!! Not good for that "water pump bearing".
I was always under the impression that because of the frequency of the power lines and the design of an electric motor in conjunction with the number of poles that the RPM would be very close to what is specified. Is my impression wrong?
Bill V

3450 Is the 'advertised' rpm at rated load - 1/8 hp. At lesser loads it will be faster.

Under load the rpms at slow/fast will be slower.

To elaborate on JPG's reply, the "synchronous speed" of a 3450 RPM induction motor is 3600 RPM. (1 rev/cycle * 60 cycles/second * 60 seconds/minute = 3600 rev/minute, where a cycle is one AC electrical cycle)

The motor will approach synchronous speed when running under no load, as Dusty's measurement confirms. But a "slip frequency" between the AC power source and the rotor speed is necessary in order to induce rotor current and thus generate torque. This "slip frequency" is roughly proportional to the motor output torque (and power), and reaches about 4% when operating at rated motor power. Which works out to about 3450 RPM.

wa2crk wrote:Dusty
Just wondering------ Did you calibrate the tach that you are using?
Also with a quill speed of over 7000RPM the Auxiliary shaft will be in excess of 11000RPM!!! Not good for that "water pump bearing".
I was always under the impression that because of the frequency of the power lines and the design of an electric motor in conjunction with the number of poles that the RPM would be very close to what is specified. Is my impression wrong?
Bill V

I think the greater than 7000RPM number to which you refer is history. I believe I now have it back in the 5200RPM range but I will check that with my tach before I run it much more. Thanks for the alert.

No, I have no reference against which to check the tach other than other uncertified devices..

OKAY Do I have my machine all screwed up.

The upper shaft, the one to which a saw blade would be attached, is operating in the 5200rpm range at high speed.

At the same time, the lower shaft is in the 8500 rpm range.

Dusty
5200 and 8500 sounds reasonable. The aux shaft should be around 8300 but considering all of the variables I think that it is OK
Bill V

As I have read through this article I am amazed at how many of you actually know what RPM your SS's are turning at. Don't get me wrong, I understand why the RPM ranges are so important and I have considered getting a tach to check my machine but to see that so many of you know this really kind of baffles me. Did I miss the sale on tachometers at HB or have you all found something better to measure RPMs with?

Toys, Toys, Toys

Knowing or being able to measure RPM is really not all that important. A tachometer is NOT a required tool. The Shopsmith can be PERFECTLY WELL MAINTAINED with out one.

The one I have cost me less than $10 (I don't remember the exact amount) and I purchased it online from some outfit in China. Details are available somewhere here on the forum.

This is the tachometer that I have. I paid a little less than this but with free shipping this is almost as good a deal. For what I use it for, I am quite satisfied.

http://www.ebay.com/itm/New-Digital-LCD ... 4ad739cf9c

greasemonkey2275 wrote:As I have read through this article I am amazed at how many of you actually know what RPM your SS's are turning at. Don't get me wrong, I understand why the RPM ranges are so important and I have considered getting a tach to check my machine but to see that so many of you know this really kind of baffles me. Did I miss the sale on tachometers at HB or have you all found something better to measure RPMs with?

Ask Dusty how much he paid for his!

Never mind, he already did. Way less than $10 as I recall.

wa2crk wrote:Dusty
5200 and 8500 sounds reasonable. The aux shaft should be around 8300 but considering all of the variables I think that it is OK
Bill V

I have heard that the ratio between the two shafts is 1.6:1.

So 5200rpm * 1.6 = 8320rpm ....close enough for most government work. Remember that my 3450 rpm motor is running a bit fast too.