LumberJocks

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

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Blog entry by Rick M. posted 496 days ago 2043 reads 5 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:
Printer
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

-- |Statistics show that 100% of people bitten by a snake were close to it.|



8 comments so far

View JoeinGa's profile

JoeinGa

3187 posts in 641 days


#1 posted 496 days ago

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 Rick M.'s profile

Rick M.

3885 posts in 1014 days


#2 posted 495 days ago

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.

-- |Statistics show that 100% of people bitten by a snake were close to it.|

View Brandon's profile

Brandon

4138 posts in 1586 days


#3 posted 495 days ago

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

-- "hold fast to that which is good"

View Rick M.'s profile

Rick M.

3885 posts in 1014 days


#4 posted 495 days ago

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.

-- |Statistics show that 100% of people bitten by a snake were close to it.|

View djg's profile

djg

99 posts in 797 days


#5 posted 495 days ago

very cool.

-- DJG

View Oldtool's profile

Oldtool

1783 posts in 825 days


#6 posted 495 days ago

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 nobuckle's profile

nobuckle

1120 posts in 1395 days


#7 posted 495 days ago

That satisfied the geek in me. Totally cool!

-- Doug - Make an effort to live by the slogan "We try harder"

View Rick M.'s profile

Rick M.

3885 posts in 1014 days


#8 posted 494 days ago

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

-- |Statistics show that 100% of people bitten by a snake were close to it.|

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