RPM thought/question

[Murray Kish]

This is likely for Sherline owners, but if anyone else has a suggestion, feel free to offer advice.


So, I'd like some sort of way to ballpark the rpm of my lathe. I know there is a little paper cut-out thing that you can stick to the side of the spindle pulley, that will sorta give you an indication that it's spinning at, but I'm not sure I really want that (call me snobby).

However, my understanding is that it actually works quite well (with the right lighting), so I was thinking:

- could I just make several 'ticks' around my on/off knob to indicate various rpms? ie. run the lathe up to 1000rpm by checking it with the little paper cut-out thingy, and then just make a little scribe/tick on the switch somehow to indicate that this position is about 1000rpm?
- repeat for various other rpms.

Perhaps two different lathes would have different switch positions for specific rpm outputs, but would mine at least be consistent with itself? If I turned it off, then on again to that same tick mark, would the rpm at least be pretty close to what I measured it at? I think so, but am offering this up to you all for advice/thoughts.

I've just been going by 'feel' lately, but would like at least some way to ballpark my rpms. That way, if someone says, cut X material at 800 rpm, I at least can approximate it, and then adjust it up/down a bit when I'm actually making the cut?

Thoughts, other ideas?

Thanks (swarf and chips are fun.... now if only I could actually make something....)

Murray

[MPWR]

Hey Murray-

The paper cutout does work surprisingly well. You just need to use it with florescent lighting (because it flickers at 60hz, at least in the US). Using it as a reference and then marking the speed selector knob seems like it could be worth a try. I'd try it with a narrow tick mark of tape to mark a position or two, and then see if that position will consistently give you that speed. Get five or six data points, and then you could probably draw a scaled index to put around the knob. Dunno if the speeds will be proportional to knob position, or if they would be consistent from one machine to another - but it seems worth a try, and it'd be interesting to find out! (Wonder why noone has made a scale to copy and stick in around the knob before??... )

[Murray Kish]

http://www.jeffree.co.uk/pages/speedmeasurement.html

There's something here for both the lazy (like me) and the ambitious...

Enjoy.

Murray