Help me figure out my Drillpress speed

Thanks for the link Count. The thing is I mostly drill small stuff so I might be better off keeping the faster speeds. What I would really like is more speed options but for that I'll probably just buy a variable speed drillpress in the future or run one off a vfd with a 3 phase motor.

Karl, maybe if I had 3 drillpress but I only have one and drilling at the same speed with a 1/2” bit and a 1/16” bit is not really working for me. ;)

Thanks James, that is a good idea. I could do it for just one pulley to see how close I am and extrapolate the rest.

Chuck, thanks for the link. Not the right manual for mine (later model with 4 speed pulley) but very useful website in any case.

Thanks again for all your help guys. :thumbup:
 
I have 4 drill presses but I only use 2 for drilling holes. Sounds like you need to add one so you don't have to change speeds every time you change bit sizes.
 
When budget permits maybe. Or a variable speed one but I may have to sleep in the shed for a while for that one. ;)
 
The tachometer arrived yesterday so as promised, here are the results.

First let me just say that for about 25$, this is a nifty gadget to have. Should have bought one a long time ago. You just stick a piece of reflective tape (included as well as a little carry case) on what you want to measure, turn the machine on, point the tachometer and click. Voila! instant speed reading.

drillpress_tachometer1.JPG


Here are the speeds I came up with with pulley measurements (close as I could get to pitch diameter) : 422, 607, 1031, 2013, 3671, 5350 rpm

Tachometer results: 410, 607, 1055, 2093, 3848, 5545.

Pretty darn close, just a little faster on the 2 higher speeds. More importantly now I am sure. Since I want to do a better job of it and stop guesstimating cutting speeds, I will now measure everything that spins in the shop, starting with the lathe. I will also use it on the new bandsaw with variable drive to see where the appropriate speeds are. (no digital reading of the speed on the drive).

Thanks again for your help guys and once again I highly recommend you get one of those tachometer.
Feel free if you have any questions.
 
Very close numbers.

Now you can click the grinder to make sure you don't fry the bearing on the small wheels.
 
Patrice Lemée;12472591 said:
Pretty darn close, just a little faster on the 2 higher speeds. More importantly now I am sure. Since I want to do a better job of it and stop guesstimating cutting speeds, I will now measure everything that spins in the shop, starting with the lathe. I will also use it on the new bandsaw with variable drive to see where the appropriate speeds are. (no digital reading of the speed on the drive).

Thanks again for your help guys and once again I highly recommend you get one of those tachometer.
Feel free if you have any questions.
Click to expand...

I've been in machining and general fabrication for many years. Often times, especially in smaller shops, the machines are not capable of reaching the recommended RPM, especially with carbide tooling. Cutting a bit too slow is better than cutting too fast, both in tool life and quality of work.

The feeds and speeds recommended are good starting points, and generally should be followed somewhat closely, but also are not set in stone, especially once you have lots of "post-paying attention to speeds/feeds" experience. I've encountered cases where I've had to go wildly faster with insane feed rates, or slow to a crawl, to overcome surface hardening or other characteristics of materials.

Cooling is every bit as important. The more heat you draw from the cutting area, the less likely you are to lose temper and start to cause erosion of the cutting edge. If you are using cutting oil and seeing smoke, that is a good thing. It means that the smoke is carrying away a large portion of the heat from the bit. No smoke/steam at all can be a good or bad thing... either you are cooling VERY well, or the coolant (oil or water based) isn't reaching the cutting area. Plenty of cutting oil also allows a superior thermal interface between the tool and the material, so more of the tool's heat is lost into the workpiece, also extending tool life.

Proper speeds and feeds combined with proper tool and a bit of experience can do amazing things... hundreds of holes in stainless from a single high quality drill bit, with only minimal damage/wear.
 
out of curiosity, have you checked you drive wheel rpm. I don't know if you have a direct drive or not, but it could be interesting to see drive wheel rpm, expected vs actual. You got your hands full with your new surface grinder, though.
 
Thanks for the additional info vintagefan. :thumbup:

Doc, just measured the motor speed:

Rated: 1725 RPM
Tested: 1781 RPM

Surprising.
 
Patrice Lemée;12483378 said:
Thanks for the additional info vintagefan. :thumbup:

Doc, just measured the motor speed:

Rated: 1725 RPM
Tested: 1781 RPM

Surprising.
Click to expand...

Would have guess that it would be closer. Is there a way to calibrate the tachometer? I wonder what you could use as a true standard. I wonder what motor rpm deviation is considered within normal range.

Thanks. I gotta get one of those.
 
Doc, I looked but I don't think that you can calibrate the machine. It is pretty basic stuff but I would not expect more for 25$. Now that I think about it, I do have a mill that I know the speed of (if they are what they say on it of course) so I will give that a try to see if it matches.
 
Motor RPM is based on the line frequency and the number of poles on the armature. Since the line frequency is a tightly regulated thing by the power companies, a free spinning motor ( no load) should be very close to the plate speed. If I had a reading of a free spinning motor that was much off the plate speed, I would suspect the tachometer first.
 
It's a four pole motor on 60 herts power, so it is theoretically 1,800 RPM except for slippage. If it is rated at 1725 under a load, 1781 isn't an unreasonable measurement.
 
Here are the 3 speeds I measured on the mill:

Mill: 730-1140-2580
Tach: 767-1122-2610

So obviously this is not exact device or the mill is not running as posted speeds but I think it's close enough for a "pretend" metal worker like me. ;)
At least I will stop trying to drill with a 1/16th drillbit in stainless at 470 RPM. :o

Thanks again guys.
 
As Stacy and Nathan say, the synchronous motor speed in RPM is the mains frequency in Hz x 60 (seconds/min) divided by the number of pairs of poles in the motor. A 2-pole motor (one pair) will run at 3600 RPM when it is synchronous with US mains, a 4-pole at 1800 RPM.

When it is synchronous, the motor will develop zero torque, so can't do any useful work. As it loads up, the motor slows down, developing "slip", which causes the torque to increase and allows the motor to do work.

The rated speed is given at a rated power, so when the "1725 RPM" motor is loaded to produce it's rated power, the speed will have been reduced (the "slip" will have increased) to 1725 RPM. At lower loads, it will be turning faster.

You can usually check a optical tachometer by pointing it at a single fluorescent tube; it will read twice the mains frequency in cycles/min: around 7200. It will vary a little, as the grid frequency changes very slightly with the total load on the grid. Here in the UK, we are on 50 Hz mains and I typically see a reading of 6000 cycles/min plus or minus about 20; there is a slightly widerr short-term tolerance on grid frequency, but the daily average is very tightly controlled.
 
Thanks for the explanation Tim, very interesting stuff. :thumbup:
I checked the fluorescent and got 7200 right on the money. Cool trick!
 
You must log in or register to reply here.
Back
Top