How to slow down a drill press

[John Schreiber]

I've been using an old (1930's) bench top drill press and am trying to figure out the speed at the chuck. Do I use the measured inside diameter of the pulley, or is there some standard adjustment based on the belt size? (1/2" x .31")

I'd like to have slower speeds available, but the bell around the forward pulleys doesn't allow extra space to add a larger pulley. Based on measurements of the pulleys, the slowest possible chuck speed would be 681 RPM (1750*0.875/2.25)

Here's a picture of a similar drill press courtesy of the OWWM site.
58189

[Don Stanley]

This is probably a streach, but we had a furnace years ago, and they installed AC, they also installed a new two-speed blower. It was powered by a belt driven motor -- looked like a typical 1/4 HP motor. Other than that, you will probably have to look into a DC motor, designed for this purpose.

-Don

[glenn bradley]

Pulleys are available in a mind-bending array of options. It looks like your rear pulley could be swapped without issue. Outside diamenter of the pulley is used in this calculator:

http://www.csgnetwork.com/pulleybeltcalc.html

Just enter the two pulley sizes and the input rpm and click calculate.

[Richard Keller]

John,

The most simple calculation is d/D = s/S

d = "little pulley" diameter
D = "big pulley" diameter
s = "slower" speed
S = "faster" speed
*note: Bigger pulley is always at the slower speed

For example if we have a motor at 1725 rpm with a 2 inch pulley, and a spindle with a 4 inch pulley:

2 / 4 = ? / 1725

solving for ? (never liked x) we get 862.5 rpm.

long story short, if you can make the front pulley large, can you make the back pulley smaller? Also, you could change the motor to a slower rpm motor, or even get a two speed motor. Old furnace blowers are usually 850/1100 rpm or 850/1725 rpm and are fairly cheap. Only problem is usually they are fractional horsepower.

Richard

[Curt Harms]

Here's a solution for when I have more money than sense:p . I have a Delta radial arm drill press and the lowest speed is around 500 RPM, plenty fast for large forstner bits, fly cutters and the like. I'm told smaller used 3 phase motors can be had for cheap. Get one of those and use of of these to power it:
http://www.factorymation.com/s.nl/it.A/id.193/.f
Programmable accel/decel & reverse.

Could make for a fun toy.

Curt

[Richard Butler]

Here's a solution for when I have more money than sense:p . I have a Delta radial arm drill press and the lowest speed is around 500 RPM, plenty fast for large forstner bits, fly cutters and the like. I'm told smaller used 3 phase motors can be had for cheap. Get one of those and use of of these to power it:
http://www.factorymation.com/s.nl/it.A/id.193/.f
Programmable accel/decel & reverse.

Could make for a fun toy.

Curt


It is a fun bit of technology and that is putting it mildly. I recently put a 1hp 3ph motor on my Delta 14" bandsaw using the FM50. Adding the FM50 has been best upgrade to any of my tools and has transformed my BS into a whole new machine. I will do my Unisaw this coming week. I will convert my DP to 3 phase sometime next month. The FM50/3 phase motor combination would also be perfect for a lathe.

Surplus Center has 3 phase motors and they are indeed cheap.

Don't wait too long to get that FM50. I believe the FM50 is a discontinued unit and is discounted right now. When the existing stock is gone, then you will have to get the new model which costs more.