Craftsman/King Seeley 9x30 Lathe #3: Measuring lathe speed with an ink jet printer and fluorescent light

  • Advertise with us
Blog entry by Woodknack posted 04-21-2013 11:15 PM 5914 reads 6 times favorited 8 comments Add to Favorites Watch
« Part 2: Shop made disc sander lathe attachment Part 3 of Craftsman/King Seeley 9x30 Lathe series Part 4: Lathe tool holder and disc sander »

After switching my lathe to a variable speed DC motor I had no way of knowing it’s range so rather than buying a digital tachometer for a one off measurement I used some old tech… a homemade strobe tachometer. A google image search yielded a variety of discs designed for measuring speeds from 60 rpm up to 7200 rpm. After printing out 4 papers discs I found my lathe is capable of 240 rpm up to an estimated 2,800 rpm (estimated because this method jumps from 2,400 to 3,600 rpm). I did hit 3,600 rpm by loosening the bearing retaining nut but I don’t want to run it that way, 2,800 is fast enough for 60 year old bearings. In the video you’ll hear a knocking sound, I don’t know what that was but after filming I removed/replaced the arbor and fixed it.

The stationary band tells me the lathe is running at 300 rpm

Materials needed:
Strobe tach disc (from internet or homemade)
glue (spray glue or glue stick)
Wood to mount the paper disc
Fluorescent light

To make your own start with an image search for “strobe tachometer disc”. If you live in the U.S., lights operate at 60hz, overseas they are 50hz, so make sure you are using the right disc or your results will be off. It is possible to make your own and I’ll cover that further down. Print the disc to fit inside the swing of your lathe, mine are 5 inches diameter, and carefully cut it out. Cut a wood circle, drill a hole in the center and true it using a lathe, disc sander, drill press or whatever you have. Actually I guess it doesn’t have to be a circle, a square would work fine. Center the paper disc on your wood and glue it down. Mount the disc to your lathe or drill press (I used a screw chuck on my lathe) and turn off (or point away) all light sources except for one fluorescent above the machine. Incandescent bulbs will not work, neither will energy saver fluorescent bulbs (the kind that replace normal bulbs). Turn on the lathe and slowly adjust the speed until one band appears to stand still.

If you want to make your own disc from scratch, here is the math. Neither the length of the bars nor the distance between them matter, all that matters is they are equally spaced. Rather than make a circle, you can make them in a line and glue it around the outside edge of a wood circle.

Formula: 120 x hz/rpm=equally spaced bars or 120 x hz/bars=rpm

So to make a strobe disc for 480 rpm in the US (60Hz)
120×60/480= 15 bars equally spaced

In Europe
120×50/480= 12.5 bars (doesn’t work out evenly so we’ll adjust the formula to work with whole bars)
120×50/13 (bars)= 461.5 RPMs (fraction)
120×50/12 (bars)= 500 RPMs (nice even #)

Quick Reference Chart

-- Rick M,

8 comments so far

View JoeinGa's profile


7741 posts in 3065 days

#1 posted 04-21-2013 11:50 PM

Dude! That is so cool!
Couple questions…
In the topmost pic (above) there doesn’t appear to be any numbers, yet when the vid started I could clearly see the numbers on the disc. So when it’s spinning, can you read the numbers to tell what speed it’s at as each band “stops”? Or do you just hafta know what speed each ring represents?

And second… why oh WHY would anyone want to try and make their own disc, when you can just print them off the Interwebs? :-)

Neat demonstration. Thanks for sharing

-- Perform A Random Act Of Kindness Today ... Pay It Forward

View Woodknack's profile


13552 posts in 3438 days

#2 posted 04-22-2013 12:33 AM

There were 4 different discs and the pics and vids were made at different times. You just have to know what each band represents. I thought about making my own disc but it wasn’t worth the effort with so many available but it would have been convenient to have a disc with just the speeds I wanted.

-- Rick M,

View Brandon's profile


4381 posts in 4009 days

#3 posted 04-22-2013 03:15 AM

Yes, this is all sorts of cool. Thanks for sharing.

-- "hold fast to that which is good"

View Woodknack's profile


13552 posts in 3438 days

#4 posted 04-22-2013 03:57 AM

This was my goal. The numbers correspond to the band# then afterward I cross referenced with the wheel to find out the speed. So line #1 was 300 rpm, line #4 was 600 rpm.

From that I made this graphic. I’ll print this on paper and tape it temporarily behind the dial. After verifying the lines are in the right place, I’ll make a cut vinyl version and apply it to the control panel.

-- Rick M,

View djg's profile


160 posts in 3220 days

#5 posted 04-22-2013 09:09 AM

very cool.

-- DJG

View Oldtool's profile


3208 posts in 3248 days

#6 posted 04-22-2013 10:20 PM

That’s slick. I gotta try the just for giggles. Thanks for the video.

-- "I am a firm believer in the people. If given the truth, they can be depended upon to meet any national crisis. The point is to bring them the real facts." - Abraham Lincoln

View Doug's profile


1241 posts in 3818 days

#7 posted 04-22-2013 11:50 PM

That satisfied the geek in me. Totally cool!

-- Doug

View Woodknack's profile


13552 posts in 3438 days

#8 posted 04-23-2013 08:57 PM

It would be interesting to do this and check it against a calibrated digital tachometer, I bet it is pretty accurate.

-- Rick M,

Have your say...

You must be signed in to post the comments.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics