DP speed formula?

"AAvK" wrote: (clip)does anyone know the math formula (clip) ^^^^^^^^^^^^^ Multiply the motor RPM by the motor pulley diameter, and divide by the driven pulley diameter.

You are trying to reduce your minimum speed by a factor of 3.5 to 4--so if you decrease your motor pulley size, and increase your driven pulley size so the product of the two changes is in that range. you will get it. IOW, if you double the driven pulley diameter and halve the motor pulley diameter, you will reduce the speed by a factor of 4. But these numbers may not be physically attainable. Doubling the driven pulley may take more space than you have. Halving the motor pulley may call for a size that does not exist.

You may have to resort to a jack shaft.

You have been given the answer already, now, if you are interested in knowing where the answer comes from:

if "D" is the driver pulley and "d" the driven pulley, "S" the motor speed and "s" the driven pulley's axis speed:

The driver pulley "D" perimeter is = Pi x D and since it is rotating at a speed "S", it will travel a distance = Pi x D X S every minute The driven pulley perimeter is = Pi x d and you want it rotating at a speed "s", so it will travel a distance = Pi x d x s every minute

The distance traveled by the driver and driven pulleys must be the same (assuming no slippage), therefore:

Pi x D x S = Pi x d x s dividing for sides by Pi: D x S = d x s dividing both sides by "s": (D x S) / s = d So the diameter of the driven pulley is equal to the diameter of the driver pulley multiplied by the speed of the motor and all that divided by the intended speed of the driven pulley. Something else you can notice is that: S / s = d / D in your case (selecting 200rpm):

1700 / 200 = d / D or 8.5 = d / D which means that the ratio driven pulley to driver pulley is a factor = 8.5, in other words, that the driven pulley has to be 8.5 times the size of the driver pulley. If you had a 2" diameter driver pulley, in order to obtain 200rpm you would have to use a 17" driven pulley, that is a big pulley!!

Guillermo

Now That's an amazing bit of math work I must say! I am quite impressed. I have ADHD myself so I could never get educated along the lines of numbers, I only have it at the most rudimentary level. I envy you wholesomely! With ADHD I can sit in a classroom and have absolutely Xero in my mind for what is going on within a glorious spectrum of black and white television snow and the noise to go along with it! Oh well.

Looks like 17" is too big, there isn't that much room, it would run into the drive pulley, I think I need to come up with another idea, Leo's idea of a jack shaft or put a center pulley off to the outside where there is room. Thank you* very much for the calculation. Incidentally I did find this website, you might toy with it, it's a java calculator for pulley speeds, you could experiment comparing your results with it's results:

.Alex

Mechanics aside another approach to this is to install a shaded pole or universal type motor and you could install a speed controller on the press to reduce the speed down. Be forewarned you will lose horsepower doing this.

I wouldn't mind having a powerful DC motor with a speed control, unfortunately such a set up is highly expensive, even if used.

Alex

Hi Alex

I agree with what the other Leo said (:>

Use a jack shaft. Go to the place you bought your drill press and have a look at the dp's that have 15 or so speeds, (if they have any) els you will have to go some other power tool place, you will see that they are almost the same as your dp but for a 3th pulley on a swing arm in between the motor and quill pulleys, they use 2 V belts, I think that is the easiest way to go, you get 15 speeds and a much lower low speed, you might eve be able to purchase the parts needed, anyway have a look and see for yourself.

Have fun and take care Leo Van Der Loo

AAvK wrote:

Yes I already knew that actually, from a while back. Your suggestion is like the Grizzly G7943 I'd like to have for benchtop use. 12 speeds, three 4-step pullies though they could put in 5-steppers too. But that shipping is too much, since there is no California outlet, and only three locations in the U.S. then they are making a profit on the shipping cost. And there is not a single reason not to open in L.A. unless it is because they like that profit too much.

But take a look at this nice drill, the man added his own:

I just have no means with whichto do it. There is another way to do it that is worse, the motor becomes mounted up-side-down, mounted outboard on extended boards, is the jack shaft (a shop mandrel) with the very large v-pulley at the bottom of it and a step v-pulley mounted at the top which drives the front driven pulley, we get 4 or 5 permanent slow speeds. If you want the .pdf plan for that I can email it to you, or anyone, it is small enough.

Alex

It's not that bad, because drill presses aren't hugely powerful. I've a number of variable speed devices here (coil winders, ball mills) that use small DC motors from lab stirrers. One problem is that the simpler circuits tend to limit torque badly at low speeds.

If you have a three-phase spindle moulder (large shaper) then the economic way to convert it to single phase is often to re-motor the main drive but keep the 3-phase motor on the power feed, using a VFD (variable frequency drive) to do phase conversion. This small feed motor is a funny size and hard to replace, it's a low power so the VFD isn't too expensive, and you gain good speed control with hightorque, right down to a crawl - useful for a powered feed.

I don't think you can speed control a shaded pole motor though ? I'd always thought "shaded pole" motors were self-starting synchronous motors. Low power and accurately speed-locked to line frequency. I'd be surprised to see one of those in a machine tool, let alone try to speed control it. Does it mean something else in the USA ?

Can be free if you either catch someone throwing away a treadmill, or ask the folks at your local refuse operation/recycling barn/transfer station to give you a call when one gets dumped. Can be pretty cheap to buy such a setup surplus, as well. Divide the claimed HP by two, still plenty for a drill press of normal size. They'll run a lathe, so they'll run a drill press.

Andy,

I didn't completely follow your post but here is a shot at an answer. I recently purchased a 1/4 hp DC motor for an industrial sewing machine from the local sewing machine supply company that sells both home and industrial machines. (I do boat seats).

It has two ranges High and Low, it is completely variable throughout it's ranges. It has a place for the treadle pull rod to attach that control the motor speed. There is a variable limit adjustment for setting the maximum motor speed. There is a switch to select motor rotation direction.

While sewing marine vinyl I find it necessary to set the speed limit quite slow for use when going around tight corners. I find no loss of torque. Being designed for industrial use it can run for long periods without overheating concerns

The cost was $160.00, for my application that was a "give away" !

If you don't find a dealer that has such a motor, I got mine at Missouri Sewing Machine Company in Kansas City, MO, USA

Don Dando

This link outlines the formula if you read through the posts.

The speed ratio is (diameter of drill pulley)/(diameter of motor pulley).

Since you do not state the diameter of either pulley then a value cannot be calculated.

I expect you will have a difficult time finding a set of pulleys which will give this speed reduction. The motor end pulley will need to be quite small, and may slip if too small. You will likely not be able to fit the drill pulley size needed within the existing case.

Dave Paine.

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

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

Removing the belt and running with 'no load' didn't make a difference.

I use one for my Bosch 1617 router without any problems.

Anyone know if one of these can be used in this case with some adjusstment or is the problem (stalling) just due to the different types of motors (router vs DP)?

Ron

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.

Routers use brush type (universal) motors. You may change their speed by changing available voltage/current. They will typically run on AC or DC - making them *universal*.

Drill presses are almost always AC INDUCTION motors. No brushes, their speed is determined SOLEY by the number of poles in the motor and the frequency of the AC power. (i.e. 60hz) This is a fixed relationship. Some motors are wound with multiple pole taps for speed control, for instance, your furnace blower motor and few washing machine motors.

So, no, you cannot vary the speed of an induction motor with a light dimmer. You CAN succeed, however, in eventually destroying the motor.

FWIW,

Greg G.

Yeah there were some great replies and good help! Guillermo replied the following (just in case you missed it), there's no way I can do what he can do with math:

------------ You have been given the answer already, now, if you are interested in knowing where the answer comes from:

if "D" is the driver pulley and "d" the driven pulley, "S" the motor speed and "s" the driven pulley's axis speed:

The driver pulley "D" perimeter is = Pi x D and since it is rotating at a speed "S", it will travel a distance = Pi x D X S every minute The driven pulley perimeter is = Pi x d and you want it rotating at a speed "s", so it will travel a distance = Pi x d x s every minute

The distance traveled by the driver and driven pulleys must be the same (assuming no slippage), therefore:

Pi x D x S = Pi x d x s dividing for sides by Pi: D x S = d x s dividing both sides by "s": (D x S) / s = d So the diameter of the driven pulley is equal to the diameter of the driver pulley multiplied by the speed of the motor and all that divided by the intended speed of the driven pulley. Something else you can notice is that: S / s = d / D in your case (selecting 200rpm):

1700 / 200 = d / D or 8.5 = d / D which means that the ratio driven pulley to driver pulley is a factor = 8.5, in other words, that the driven pulley has to be 8.5 times the size of the driver pulley. If you had a 2" diameter driver pulley, in order to obtain 200rpm you would have to use a 17" driven pulley, that is a big pulley!!

Guillermo

Alex and Morris a quick and dirty way to find the speeds goes like this,

motor pulley 2" spindle pulley 4" makes spindle rpm 1/2 X motor rpm motor pulley 4" spindle pulley 2" makes spindle rpm 2 X motor rpm Motor pulley 2" spindle pulley 6" makes spindle rpm 1/3 X motor rpm etc., etc., etc.,. most regular partial horse power motors run approx., 1740 rpm at our 60 hertz power and 1425 rpm on 50 hertz power like in western europe. so to get lets say 174 rpm you would have to get 1/10 X motor rpm, like

2" on motor and 20" on your spindle, wow that's one large flywheel (:>).

Have fun and take care Leo Van Der Loo

Morris Dovey wrote:

Thank you very much, dank u. I think I need to buy a new drill press for pete's sakes.

Alex

My server did not have the posted question, or all of the replies, but I find this online calculator useful quite often.

can put in different size pulleys and your motor RPM's, and it willcalculate speeds, belt size, etc... for you.