Lathe rpm

[Tinker7]

I have a variable speed lathe from PSI, I like it, but I am would like to be able to know the RPM speeds that I am using.
I am considering a digital rpm meter, and I was wondering what you folks are using.

Roy

 

[Monty]

I use a "yeah, that looks about right"

 

[skiprat]

I would say that the adjustable potentiometer is fairly linear.
It is probable that the lathe has a range of around a minimum of 50rpm and maybe 2500rpm max ( perhaps with a belt change or two included)

However. spindle RPM on it's own is actually pretty useless info as the info we are actually interested in is the cutting speed. This is the speed that the workpiece and the cutter are passing.
RPM ( Revs per minute ) is not speed as it does not include a distance.
The 'distance' in turning is the circumferance of the work piece.

Now if the lathe spindle is rotating at say 100 RPM you will see that a larger diameter will pass the cutting tool faster than a smaller diameter.
You can do the math, but a diameter of say 1 inch will have a cutting speed twice as fast as a diameter of 1/2 inch, even if it's on the same workpiece.

Some may say that for pen turning, just knowing the RPM is good enough, but consider that a slimline is less than half the diameter of most of the big pens. If someone recommends that a particular material should be turned at such and such an RPM, then take it with a pinch of salt unless they say what diameter they are turning:wink:

My method is to find the slowest RPM that will give me the best finish.
You should find the optimum speed long before you get close to finished diameter. Now simply crank up the speed as the diameter is turned down ( if necessary )
You will find that the sharper your tool the slower you can run the machine and still get a good finish. I also believe that a different tool needs different RPM's. eg; a skew would need less speed to give the same finish as a scraper.:wink:

....well that's my 2p worth:biggrin:

 

[bensoelberg]

I would have to say that Skiprat's post was worth quite a bit more than 2 pence. Thanks for that.

 

[PenPal]

Roy,
Curiousity and all that wanes on exact speeds even if you have such readings its like the rev counter on my cars blessed if I ever read them but seldom for tuning. What we are dealing with is not so vital.

If it bothers you there are mechanical devices to read revs or electronic ones as well. By the time you buy them and if you have developed a need to know purchase the items you want that have the readings.

When I was 19 yrs old prior to getting married I commenced building a house with a second story room, the view was breathtaking for many miles, you know what in a few years the view was obscured by trees so much for the view. Six children later I was grateful for any spare time very little window gazing. Now at 76 yrs just as busy tend to look past incidentals like lathe speeds, drill speeds for pen making critical factors you learn along the way.But like riding a motor bike without an exhaust sometimes there are things you gotta do even if once.

Enjoy the journey and live in the day.

Kind regards Peter.

 

[JMT]

SpitRat+1

For me, it's the material more than the pen or diameter. Most stabilized wood, I fly through at a pretty high RPM. Some Acrylics are so finicky that I approach them with a MUCH slower RPM....sometimes a quarter of the speed I would be using for the stabilized wood.

 

[crabcreekind]

My lathe came with a digital speed and it works pretty good, It is interesting to watch how your lathe doesnt stay at a certain speed, it jumps around about 20 rpm

 

[JerrySambrook]

James, most of the jump is probably from the sensor vibrating

 

[shull]

Mark me down for Skiprat +1

 

[Tinker7]

I use a "yeah, that looks about right"

That's what I'm using now, an "yeah, that looks about right"!

But in my senior years, I have a burning desire to go high-tech, hence the tachometer. I recently added a digital thermometer to my cooking reportire,so I'm going hi-tek all the way.

I threw out the coal-oil TV and I now have an electrified one.

So why not get a digital read-out for my little wood lathe. :biggrin:

Roy

 

[Mac]

I find its more of, this feels about right, or thats way to slow, or waayy to fast. I had a read out on my lathe, until it broke and after thinking about it, never payed much attention to it, when it was working.
PS by the way the lathe is a Grizzly12/20var.speed and I would not recommend.

 

[GColeman]

I was setting up a VFD on for a three phase motor for a lathe. I bought a hand held digital tach from Harbor Freight to check my motor and spindle speed. After that I used it it mark the indents on my Reeves drive lathe with spindle rpm.
http://www.harborfreight.com/digital-photo-sensor-tachometer-66632.html

 

[Tinker7]

Thanks, I'll order one of those tomorrow.
http://www.harborfreight.com/digital...ter-66632.html

 

[ctubbs]

I have gone lo-tec. My lathe has five shivs to adjust the rpm of the head spindle. I chose the one that turns the wood and just leave it there, way too much trouble to change it. I know, bad idea.
Charles

 

[ossaguy]

On my Delta 46-460 there is a chart on the side that lists the speeds depending on the knob numbes so that gives some indication.I tend to keep it in the place where I've been having success at.

It took me several months to get around to getting my lathe warranty repaired.during that time,the variable speed was stuck on one speed.I turned a lot of pens in that time that turned out great ,only switching between 2 of the 3 sheaves.



Steve