DP speed formula?

"drive pulley ratio"

viable calculation.

Thanks.Measure the width of the pulley's. That will give you your ratio. If thedriving pulley is 3" and the driven pulley is 2" then you have a 3 to 2ratio. If the driving pulley is 2" and the driven pulley is 3" then you havea 2 to 3 ratio. If the driving pulley is 4" and the driven one is 2" thenit's a 2 to 1 ratio. It's simple fractions

"drive pulley ratio"

viable calculation.

Thanks.As someone else already said, the drive pulley ratio between the drive anddriven pulleys diameters, this ratio basically says: the drive pulley is "X"times bigger than the driven pulley. If for instance the drive pulley is 4"and the driven one is 2", the ratio is 4 / 2 = 2 meaning the drive pulleyis 2 times bigger than the driven pulley. If the drive pulley were 4" butthe driven were 8", then the ratio would be 4 / 8 = 0.5 meaning the drivepulley is 0.5 times bigger than the driven one, which in turn means thedrive pulley is half the size of the driven one. BTW, I took a look to the calculator and you really don't need togive it or need to know what the pulley ratio is, if you leave the check boxat the side of the pulley ratio field checked, you are telling the programthat value is a variable and therefore should be calculated for you when youenter the drive and driven pulley values.Guillermo

Router speed controllers are unsuitable for drill presses. Universal motors, those with brushes, work on AC and DC and smoothly reduce RPM's with a reduction in the supplied voltage. AC motors such aa capacitor motors or split phase motors commonly used on drill presses determine RPM by the applied frequency. RPMs drop off precipitously when a certain voltage is reached but this is not a design feature of the motor. This is approaching failure. Motor winding temp is going to go up and power provided is inadequate for much. Don't use a router speed controller on a drill press. You can replace the DP motor with something like a router motor and it will respond to the speed controller. Only problem is the number of belt speed reductions needed from the usual 20 - 30 thousand free running RPM of these motors can be inconvenient to set up. The other solution is a variable frequency drive. Commercial variable speed drill presses cost more. There's a reason. Ain't cheap to provide. Variable sheave "V" pulleys are probably the most practical in the speed and power range desired.

bob g.

R> I WAS about to suggest a Router Speed Controller like this one

> HOWEVER, I just tried it on my benchtop drill press and the motor just > stalls,> even on the Variable 10 (max) setting.> It works fine on the FULL setting though, which is probably just a 'pass> thru' setting.

How to calculate pulley/rpm problems is pretty trivial and has been beat to death. What's the most practical way to get yourself a low speed/variable speed drill press at minimum effort and expense? Anybody got a prime example lying around?

bob g.

Charles T. Garrett wrote:

The ratios are exactly as he has stated. Common sense dictates that a smaller drive pulley to a larger driven pulley gives a speed reduction. Little pulley on the motor, larger pulley on the spindle. Slows down. How much? The ration of the pulleys. 1 /58 to 6, 2 to 3, whatever it might be times the motor speed gives the spindle speed. If the motor pulley is larger then the spindle pulley then the whole things reversed and the spindle speed will be greater than the motor speed. Use logic and don't get bogged down in the "rules" of how to calculate this.

bob g.

the need for a web site calculator to calculate the ratio of two pulleys if gross overkill. Everybody here has at least the microsoft calculator with w>

Same way you get that for that on a lathe. Pick up a treadmill VS DC motor for free at the recycling barn, or for cheap by paying a surplus outfit or buying the used treadmill in the classified ads. Yank motor and controller, slap into drill press, vary torque by belt setting and speed by control knob.

[Repost - Qwest ate original response]

Alex...

I haven't seen a formula - but I probably missed some of the responses, too. It looks to me like one formula might be:

motor RPM x drive pully diam = spindle RPM x spindle pulley diam

You'll need to measure your drive pulley before you can do the calculation.

I missed the original posting. However you are right. The OP needs to measuer pully size [diameter]. The ratio of speeds is the ratio of the diameters. I think of two wheels, one 1 unit, the other 2 in diameter. As the belt moves around the larger, which turns once, that same distance is covered by the smaller which must turn twice, and vice versa. To slow down, the larger must be on the spindle, the smaller on the motor.

I don't know the drill setup, but most these days are fixed sets. If there is room to change pulleys, just divide 1700 by 200 to get 8.5, and the front pulley must be that much bigger than the rear.