Drill press motor swap

[ddmckee54]

RM-MN:

I have been threatening to get a tach for a while now. I'll probably get an optical tach, but one that gives me the option also getting a linear speed. It looks like they can be had for around $50-$60 for a budget model.

Don

 

[payner]

Why not use a Hall effect tachometer, leave it permanently attached, I'm using 3 on different machines . You only need a 12V DC power supply .
Google search , I have the ones from Aliexpress .
Bill

 

[ddmckee54]

I've already got an rpm display on the servo, but it only displays in 100's of rpm. The tach will let me determine whether I'm varying the speed set point in 100rpm increments, or just displaying to the closest 100rpm.

If I set the speed and it's displaying 1700rpm, but I'm reading 1725rpm on the tach - then I'll be able to determine if it's the setpoint, or the display. If I can vary the pot setting a bit, and both the servo display and the tach remain constant, then I'll know that they're changing the speed setpoint in 100rpm increments. Otherwise, I'll know that they are just displaying to closest 100rpm.

I've got a used Ametek 1726 tach coming, I've used them before and they're a good tach. I found a listing for a 1726 that was dated 2010, so they've been around for a while. The 1726 is a dual use tach, both as a non-contact optical tach and as a contact type tach. It's got a ridiculously high non-contact rpm range, 0-99,999rpm. When you slip on the contact type converter it'll let you measure up to 20,000rpm. It also has a little wheel that lets you measure linear speed, up to 20,000 feet per minute. The 1726 will also do the math for you and convert the reading into just about any Imperial or metric reading that you could want. That'll let me measure just about anything I can dream up right now.

I don't think that there's anything I can do about the motor speed/speed settings in the servo, this is just for my own curiosity right now.

When I 3D printed the pot/switch enclosure I didn't get the 0-100% speed arrow correct. It increases in the right direction, but it's upside down. I'll fix that on the next version, and add some text to the print for the switch and the pot. Plus, I STILL had to file the cable strain relief opening - I'll open him up a little more too.

Don

 

[ddmckee54]

I re-printed the enclosure, I even got a white paint-pen and painted the top of the text so that it stands out a little more. Some numbskull forgot to scale the print up to 103%, so I had to "adjust" the fit of the cover. Other than that, everything worked out OK.

I used the drill press a little bit over the weekend. I know that using a 1Hp drill press to drill itty-bitty holes in plastic parts is overkill, but at 100rpm you get a nice clean hole with no melting from friction.

I tried changing the speed setting and I could hear the pitch of the motor change, but the "Real-time" rpm indicator didn't change. I'm pretty sure that this thing is varying the speed in a linear manner, but only displaying the speed to the nearest 100rpm. The tach is supposed to show up by Thursday, so I'll know for sure then. Either way, I can live with this arrangement.

A word to the wise... If you do a similar motor change, and use the same hobby machinist circuit that I did, be sure you always leave the Run/Stop switch in the Stop position when you turn off the servo drive. If you just turn off the servo drive, when the servo boots up the next time you'll get a "Pedal Error" because the speed setting is not at the minimum position.