Slowing Drill Press RPM's

[C-Bag]

The sewing servo motor goes all the way up to 4000 rpm so the pulley reduction that is in place already multiplies the torque considerably.

Think about it, sewing machines need high torque to start and often heavy work slowly. Treadmills the motor is more of a calibrated brake then actual power at low speeds. That’s why the totally screwy HP rating. I didn’t even use the motor on my wife’s treadmill and got a better workout with it off. The sewing machine motor is an A/C servo with close to full power slow, DC speed is voltage controlled and the slower the weaker. The only way DC works is with ratio reduction and in this case the OP has 1 1/2hp motor w/double reduction able to get down around 200rpm. That’s slow enough for large bits. And while changing belt speeds is a pain 99% of the time mine is set at the lowest speed as I drill almost all steel.

A real industrial DC motor with controller is several hundred $$. A 1hp sewing machine motor is around $100. With the added benefit of being very compact.
YMMV.

 

[RJSakowski]

A DC motor can still provide appreciable torque at lower than rated rpm with the appropriate motor controller. I have a treadmill motor on my lathe and can operate at less than 2% of rated speed with usable torque. I use feedback coupled with an encoder a PWM circuit and if it senses a slowdown in rpm due to load, it will apply up to full voltage to restore the speed. Basically, I am limited in torque only by the stall torque of the motor at full voltage.

 

[wachuko]

I still would like to know if you have tried just installing the belts and testing it’s slowest setting…

Inquiring minds want to know…

 

[34_40]

I still would like to know if you have tried just installing the belts and testing it’s slowest setting…

Inquiring minds want to know…

Yeah.. what he said! Wire it up and fire it up! LOL

 

[Ultradog MN]

It is about choices.
I never felt much inclination for woodworking so have no need for woodworking machines.
I bought a drill press for metal working.
I haven't come across a situation where I needed it to go faster. Or slower .
Oops

 

[slowneasy]

ah, rub it in Ultradog MN!

 

[Jake M]

My thoughts exactly but in this case, I don't think it was a bad thing (yet)

I don't mean that the motor is a bad thing, just that keeping the original pulley would have been nice... But it may not be a problem at all.

How would I know if it is correct or not? And if I could find a stepped cone pulley that had smaller/larger sizes than what is on it now, would it automatically work or not?

There's a lot of geometrical witchcraft that goes into those step pullies. A matched set will be designed (usually) to crazy wierd dimensions, with the largest or smallest (sometimes both) pullies sized to some recognizable number. The whole thing is set up in such a way that on any setting, the belt tension is correct at the exact same center distance between them. A mismatched set will require readjusting the belt tension at every speed change.

That "may" not be a problem. Most of us who are stuck with (or choose to be stuck with) a "woodworking type" drill press will play with the belt some, and eventually it migrates to the slowest possible speed (typically 250 to 400 RPM ish), and the drill press just lives in that speed for the rest of it's life. Because it works. If you're doing production runs (or hobby jobs similar to that) it might be worth moving the belt, but for just a few holes, you just make the best of it. A little slow for the tiny drills, you have to peck and cool, peck and cool when you start plowing huge drill bits at the limits of your horsepower.... But it works fine for a couple of holes.

In your case, you are gonna be WELL under 200 rpms, with you motor pulley in the top position. You also have the idler/spindle relationship to consider. You've got three ranges that will be very easy to change quite quickly. The back belt (which I suspect will mess with the overall length) could stay at the top, and you would probably have a range from very slow (to the point that those of us with "woodworking drills" would be jealous of, to probably in the 350/400 range, which is a very good range for where many drill presses literally, after the new wears off, will spend their entire lives...

~1 turn (on the spindle) to 10.5 turns (on the motor). So 1:10.5?

OK, so my calibrated eyeballs were off a little yesterday. You said (I think?) you had a motor with 1750 on the tag? That over ten and a half gets you a final reduction of 167 RPM. That puts you in the working range of as big of a drill bit as you'd want to power with that single V belt on the little pullies, and then some. So, we've determined that you should not trust my calibrated eyeballs too much, so let me suggest to set up the same sharpie marks you already made to check for the motor revolutions to spindle revolutions, but this time in slow on the motor belt (highest position on the motor and idler), and fastest remaining speed for the spindle belt (the spindle belt in the second highest position on the idler and the spindle). See what RPM that gets you calculate there. I think you're gonna like this drill press.

 

[slowneasy]

I'm still trying to figure out this RPM chart over at the blocklayer site. I'm not understanding something with their input requirements concerning "large pulley" and "small pulley". Placement matters or should I say location matters with regard to where the pulley size is located and placed within their diagram. (Did I mention I'm s-l-o-w at comprehended simple things?) Forget about complicated things.
I'm trying to "read" their diagram from L to R in relation to the pulley locations on my drill press. It doesn't like my "input" when the intermediate pulley has a larger diameter than the spindle pulley or when the motor pulley is larger than the intermediate pulley. In my thinking, I can't reverse those locations on their chart by putting the smaller size in first when it's the motor that is providing the default RPM. Doesn't it have to go in order?
I'm probably confusing this and myself. Yes, I'm dim

 

[Jake M]

Most people have at least somewhere in their home, a special switch that will illuminate some number of lighting fixtures at varying intensities. Sometimes dim is a good thing. Or at least I tell myself that.

So, I think I flubbed up in my mental math, and mentally put a belt on the wrong pulley set. I stand by the 167 low speed, but I think adjusting only the front belt, you'll get way more than 400 RPMs. Maybe twice that.

As to the calculator, they're gonna be off, because you will be off in your measurement. Belts in a pulley don't follow the exact outside diameter, but a "pitch diameter". That's the point on the side of the groove where the belt surface and the pulley surface travel at the exact same speed. It's not far below the surface of the belt, but it's below the surface. And it varies depending on the belt profile and the pulley size as to just how high or low that pitch diameter is will actually change. It will have more influence in the smaller pulley calculations than it will in big ones. So measuring is an approximation at best, therefore their outputs will be an approximation at best.

As to the online calculator not accepting certain things, it's just math behind it. Maybe or maybe not accounting for pitch diameter versus outside diameter. Maybe written by a commputer programmer who's great at math but couldn't understand why you'd underdrive one pulley set and overdrive a second attached set. Or maybe it has a special purpose to some application that inspired somebody to write something which wouldn't account for other possibilities. It's hard to say, but all the calculators (for anything) that you find on the internet are hit and miss. Bookmark the good ones, and verify all the unknown ones. My suggestion with installing belts and using a sharpie mark- That MEASURES the math, giving you the end result directly. When I measure the width of a board, I don't count growth rings and look up the climate for the last 40 years, I just use a tape measure. I like to know how to calculate things, because sometimes you have to calculate things... The sharpie marks are your tape measure. They will be correct (to whatever resolution you read them), regardless of what the calculators say.

 

[slowneasy]

Awesome posts Jake M! My dimmer switch moved to be a little brighter! (Not much but it ain't a 6 watt bulb at the moment, lol). I'll need to figure out more of the pulley ratios with other settings and use those calculations for my RPM's. That's for another day.....