Photo Tachometers & Spindle RPM

[itsme_Bernie]

Bernie, you lost me with this comment "The second is the Westward mechanical tach which has a rubber tip that you just stick onto a rotating shaft. I made a brass fitting to stick into a chuck or collet and measure from there. I got this for $40 on EBay once, like new."
The Westward comment lost me. I have a tach just like that one. Yours just like mine has the SW logo on it's face. Those tachs were made by Stewart Warner. I have no knowledge of any link to a Westward???

Thanks Buck

I got mixed up there. I think I Stewart Warner sells them through Grainger as well, and when I googled it, Grainger popped up, and listed it as Westward.

Even though I OWN it, I let Google tell me what it was!!! Aye yay yay

It's pretty nice though, right?


Bernie

 

[Uncle Buck]

Thanks Buck

I got mixed up there. I think I Stewart Warner sells them through Grainger as well, and when I googled it, Grainger popped up, and listed it as Westward.

Even though I OWN it, I let Google tell me what it was!!! Aye yay yay

It's pretty nice though, right?


Bernie

Those old SW tach's are nice. I thought them relatively rare when I found mine complete with instructions tips and tin can pre internet. I have since figured out they seem to be fairly common. For all I know they might still be available new. WOW, just checked Grainger, $117 for the SW!

 

[Tony Wells]

Westward is just Grainger's house brand name, not the manufacturer.

 

[bonehead]

I looked into tachometers and found out that they cost quite a bit more than i expected so i made my own. It works exceptionally well and im refitting it for a laser range finder to make it easier to set the part surface height. The instructions for making the tachometer is here: http://www.floridaame.org/Plans/Kamran Nili/rpm/tachometer.html . I didnt write this but i found it useful. it cost me around $50 for everything even the material for the case(which is a plastic cutting board i used for cheap plastic $1). I think i can go without using the microcontroller but im not sure yet if linuxcnc can accept the raw data or if it needs a different format. Dont tell my wife where the new unused cutting board went.

 

[bedwards]

Bernie,
where do you get the reflective tape for the optical tachometers from?
Have a tacho but no tape.
thanks
Frank

I use shiny finger nail polish I swipe from my wife and seems to do well with the Harbor Freight optical tachometer.


bedwards

 

[Starlight Tools]

I picked up a Monarch Phaser-Laser Portable Tachometer a few years back on ebay, it was from a company that rebuilds and re-certifies them, so came marked with the calibration sticker on it.

Got a 5 foot x 1/2" roll of reflective tape from KBC Tools

see http://www.kbctools.com page 925 in their catalogue.

To check that a photo Tach is working properly aim them at a Flourescent light bulb (,bulb must be on, LOL) and they should read 7200 RPM ( 60 Cycles / Second x 60 Seconds / Minute x 2 Pulses / Cycle = 7200 Pulses / Minute)

This works great for measuring the RPM and or confirming that the item is turning at the "proper" RPM.

With a bit of math it is easy to determine what the proper calculated RPM should be. R1xD1=R2xD2, so as long as we can determine at least three points we can calculate the missing one. IE Motor is 3400 RPM, and we measure the two pulleys and determine that on is 1" diameter and the other is 2" diameter. Then do our calculations based on that to find what the expected output RPM should be. Or if we know that we want a certain RPM on the output and we are starting with a known RPM at the input we can then determine the needed diameters of the pulleys or the gears.

I went through this with the Logan 9x28 and used the tach to verify that the spindle speeds were within a few RPM of the calculated values for each pulley combination both in and out of back gear.

As for cutting speed, that is easy to calculate, RPM=CSx4/dia CS comes from the tables in books like the Machinery Handbook and is in Feet /Minute, and the 4 factors out Pi at 3.14159 and that there are 12 inches/foot. After a few times, the CS becomes ingrained in our head, and the rest is easy calculations.

Here is a basic graphical chart for SFM.

Walter

 

[Kennyd]

The aluminum tape that HVAC guys use on ductwork will work fine as well if you know someone in the business.

 

[Starlight Tools]

Basicaly, anything reflective that is different, ie contrasts from the surface being scanned will work. If there is no reflective surface, then it will try to find a spot on the surface that is different, and sometimes that works, but often it gives miss readings. If you put on two patches you will read double the readings.

Walter

 

[Old Iron]

I use black tape on half of my spindle and left the other spot bear metal.

Paul

 

[E.MARQUEZ]

I have three MachTachs on two mills (one of them CNC) and on the shared VFD installation on the third mill and lathe. When you switch between machines, the tach shifts to the active machine. I really like these tachs.

Same here, very much like my MachTachs for my lathe.