How to measure grain mill rotational speed?

[GlowingApple]

At the moment I'm using an adjustable Milwaukee drill to drive my grain mill (eventually will upgrade to a motor, but don't have the space or money for a pulley-driven system right now). I'm sure that at full speed it is way too fast, but I can easily adjust it down to a crawl by squeezing the trigger less tightly.

I've read a number of guides/forum threads talking about optimum RPM (seems to be around 300 or lower), but I'm not sure how to tell what RPM the drill is actually going? I'm also not sure how much the roller size makes a significant difference (1" diameter rollers at 300 rpm are going to crush much slower than 2" diameter rollers)?

I assume there are a number of ways to do this; I'm looking for something cheap and simple that will get me by until I can get a mounted motor for my mill.

Any suggestions?

 

[Singletrack]

Use a large hose clamp to pull the trigger, so you can adjust it and keep it constant. Then, count revolutions. 75 revolutions in 15 seconds is 300 rpm. (I realize counting 5 rev each sec is a little challenging, but I believe in you! Note the speed and position of the clamp so you can repeat in the future. Can't count that fast? There is no magic at 300 rpm exactly. Crush slower to be "safe." If you like the crush, then you can speed up until you don't like it anymore -- or not. I turn the crank, so it's pretty easy for me to keep the speed under control.

 

[Bobby_M]

You can get a free tachometer app for your smartphone. Put a tab of masking tape on the shaft and hold the phone's camera such that the tab of tape passes the camera. I know... they've thought of everything.

 

[JONNYROTTEN]

You can get a free tachometer app for your smartphone. Put a tab of masking tape on the shaft and hold the phone's camera such that the tab of tape passes the camera. I know... they've thought of everything.

This is fantastic info.I always wondered what speed I was at

 

[GlowingApple]

Use a large hose clamp to pull the trigger, so you can adjust it and keep it constant. Then, count revolutions. 75 revolutions in 15 seconds is 300 rpm. (I realize counting 5 rev each sec is a little challenging, but I believe in you! Note the speed and position of the clamp so you can repeat in the future. Can't count that fast? There is no magic at 300 rpm exactly. Crush slower to be "safe." If you like the crush, then you can speed up until you don't like it anymore -- or not. I turn the crank, so it's pretty easy for me to keep the speed under control.

My drill actually has a trigger lock, but it doesn't work all that well. Never thought to use a hose clamp; will try it! My phone has a time lapse video mode, so I can try recording for a set time and should be able to count the revolutions that way!

You can get a free tachometer app for your smartphone. Put a tab of masking tape on the shaft and hold the phone's camera such that the tab of tape passes the camera. I know... they've thought of everything.

This would definitely be the easiest solution! I looked around the app store and only was able to find apps that use a strobe light (which are limited by how fast the iPhone can flash the LED) and one app that uses a camera but is still in the design phase (so not available for download) and the developers claim they can only get to 200 rpm at best. Do you have any app names I can look for?

 

[planker101]

Laser tachometer $10.50 shipped from ebay. I use mine for all kinds of things!