true lathe speed (tach?)

[Jake Helmboldt]

I've seen reference to putting a tachometer on a lathe to determine the true RPM. Is there a cheap and simple way to accomplish this?

[Steve Mawson]

The tach that I have has a rubber end on the tach shaft. I put it against the closed jaws of the chuck and it reads fine. If you don't have a chuck use the face plate.

[Kyle Iwamoto]

I'm just curious, why would one want to know if the lathe is spinning at 700, it's actually 705 RPM in reality.

[David Walser]

A digital photo tachometer should do the trick nicely. About $50 at Harbor Freight. http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=66632

[phil harold]

I'm just curious, why would one want to know if the lathe is spinning at 700, it's actually 705 RPM in reality.

with my variable speed motor and stepped pulleys
it does get confusing some days...

[Mike Minto]

I'm just curious, why would one want to know if the lathe is spinning at 700, it's actually 705 RPM in reality.

kyle, i'm with you on that one - i would think the 'actual' rpm, varying by only a small percentage from a digital readout, would be less important than how it feels when you are turning. even on a lathe without a readout. mike :o

[ROY DICK]

Making something for the space shuttle?

Roy

[Jake Helmboldt]

kyle, i'm with you on that one - i would think the 'actual' rpm, varying by only a small percentage from a digital readout, would be less important than how it feels when you are turning. even on a lathe without a readout. mike :o

That presumes there is a digital readout on the lathe. For lathes that don't indicate a speed (other than 1,2,3,etc) it kind of helps to know how fast one's lathe is turning. I assume my lathe isn't turning 1 RPM.:rolleyes:

[Scott Conners]

This can also be an important thing to know on lathes with reeves drives. Their speed can often change as they wear, and knowing the actual speed can be useful to know when they need to be adjusted.

[Mike Minto]

no, jake, it doesn't presume anything - i mentioned 'even on a lathe without a readout'.

[curtis rosche]

speeds you should know on your lathe. to slow, slow, good speed, fast, and oh my goodness did you see where that peice of wood went?! and when did this hole get in the ceiling??? :)

[Jake Helmboldt]

And if there is no readout, then how do you know it varies from the readout?

[David Christopher]

come on guys....is it the season....I like this forum because of the nice and friendly people....cant we keep it that way

[mickey cassiba]

I've got an optical type that plugs into my multimeter, reds a dot of reflective tape stuck on the spinning part. I suspect, though, that if you read on the OD you would really be getting surface feet per minute rather than rpm. I used to have a mechanical one with the rubber pad but it went walkabout and never returned. Miss it too.

[Steve Schlumpf]

I may be wrong here but if you stuck the red dot on the OD - every time it triggered the counter it would be one rev, nothing more. If you knew the circumference of the spinning part - then you could convert that info into surface feet per minute but as it stands, its just counting the revs.

Course, all that depends on how your multimeter converts the information.

[mickey cassiba]

I may be wrong here but if you stuck the red dot on the OD - every time it triggered the counter it would be one rev, nothing more. If you knew the circumference of the spinning part - then you could convert that info into surface feet per minute but as it stands, its just counting the revs.

Course, all that depends on how your multimeter converts the information.
No Steve, you're right...I was thinking of my old mechanical tach. That one did read SFM if placed anywhere but the center, my bad.

[Rod Sheridan]

Photo tachometers can detect a reflective strip of tape, or something similar such as painted line on a shaft or pulley.

They then count the number of revolutions, divide it be the time period, and display revolutions per minute.

Regards, Rod.

[Ken Whitney]

I picked up a photo-tach on clearance from HF (about $30). It comes with a couple of feet of reflective tape. You stick a bit of tape somewhere on the spindle, chuck, etc. You start the lathe, point the tach at the reflective area, and you get an RPM readout.

It seems reasonably repeatable. If you are really "enthusiastic" about checking the speed you can attach a bit of the tape to all of your chucks, drives, etc. and take a reading whenever you want! Not that I've done that or anything.

And Steve is right. You get RPMs, not FPMs.

Ken

[Richard Madison]

Knowing the approximate spindle rpm is probably most helpful to the relatively inexperienced turner, to learn if he/she is turning at a safe speed for the particular workpiece. Beyond that EVS with readout is most helpful, but few beginners' lathes have these features. With experience one simply turns the knob to "about there", or to an audible pitch that sounds "about right". Even so when forstner drilling I still check the tach to confirm that the speed is well within the suggested max. for the bit in use.

Meanwhile the photo tach sounds like an excellent investment. Wish I had one years ago.