I received a drill press from a friend of mine. near as i can tell its a "no-name" import one with 5 speeds. Problem is that it does not have an RPM chart for adjusting the belt. I dont know which wheels are for what speed. I was able to find out which is the fastest and which is the slowest but beyond that I don't know what speeds they are. Is there any way to find out? I didn't see any make or model info on the drill itself but found the sticker/plate where it was most likely attached :) any ideas? Thanks
Won't be exact since you're not using pitch diameters of the pulleys but will be close enough for practical application:
First measure (Dial or vernier outside calipers recommended) the overall diameter of each step in each pulley. You could use the diameters at the bottoms of the groove, but the ODs will be closer to the pitch diameter and, therefore, more accurate, especially for the smaller pulleys.
For each set of pulley steps, let: A = Diameter of a step in the Motor Pulley B = Diameter of the corresponding step in the Quill Pulley M = Motor Speed - Probably either 1725 or 3450 rpm. Should be stated on the motor's nameplate along with voltage, etc. Q = Quill Speed
Then, Q = M * A/B when the belts are running in that particular set of pulley steps.
With only 5 speeds, it's unlikely that you have two belts and a stepped idler pulley like that on my Jet. But, if you do, then it's slightly more complex.
Let everything be defined as before plus:
I = Speed of Idler Pulley D = Diameter of the Idler pulley step corresponding to the Motor Pulley A E = Diameter of the idler pulley step corresponding to the Quill Pulley B
Then I = M * A/D And Q = I * E/B
Or, combining the two equations, and eliminating I,
It wouldn't be too hard to make your own chart. Either measure the pulleys & calculate from that, or turn motor pulley by hand until quill pulley has made a full turn. repeat for each pulley step combination, a little division & multiplication, and there you are. The motor is almost definitely 1750 RPM ut it should be on the motor nameplate just to be sure.
If you need more detail post a question or you could find the explanation on the web somewhere I'm sure.
Put it on the second slowest speed and leave it there. If you're doing something exotic there's about a 95% chance your slowest speed isn't slow enough anyway.
Second that- though I leave mine on the slowest speed. It gets used for steel as well, so slowest is best in my case. Even though you could jack up the speed for smaller bits in wood, I've never seen a real advantage to that.
Can you explain why that is? 60 cycles per second = 3600 cycles per minute. So how come motors spin at 95.8% or 47.9% of the frequency of the AC supply, instead of 100% or 50%?
ARGH!!!!! Apparently I can't read today. The above is a completely irrelevant reply.
So - do this. Measure the pulley on your motor. Then measure each of the other pullies. Do the simple math to determine the ratio, then apply the ratio to the motor speed.
'Tis so for induction motors, not synchronous. Stator windings induce magnetic field in rotor. Field in stator rotates, in effect, and line freq. With no load, rotor essentially does same. With increased load, rotor speed droops from no-load.
In engineering classes, arm-waving was used to explain why.
To make a synchronous motor, the rotor is a permanent magnet (or polarized electromagnet). Permanent magnet has problems: it's weaker than electromagnets, and iron bits get caught in the works. Polarized electromagnet has problems: you have to provide current to the rotor, and it's harder to make balanced than a simple lump of iron.
So, you use a lump of iron (with some addons, lamination and conductive rivets), and it gets magnetized by the stator. When the motor is asked to do hard work, the magnetic field lags the stator field (if it didn't lag, there would be no torque), and when the motor is fully loaded (and about to reach thermal or other limits) it's typically five percent phase lag, i.e. 95% of the speed of a synchronous motor. A synchronous motor would also have a phase lag, but it doesn't re-imprint the magnetic field of the stator onto the rotor, so the lag doesn't remagnetize the rotor and it isn't usually the rotor part of a synchronous motor that burns up at stall...
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