Slowing Drill Press RPM's

[Bi11Hudson]

Figuring the speeds based on "pitch diameter" will get you close, but. . . One method is time consuming, but "brute force' simple. All done by hand, a "sharpie",(nearly universal shop tool) and the ability to count. Mark a spot on the motor pulley, and a corresponding mark on the shell of the belt cover, Do the same on the quill end. Rotate the drive pulley and record the number times, or turns, it takes to turn the quill pulley once. Record each pulley combination, redo if anything distracts you. This will get you the ratio of each pulley step. Then calculate speed based on the motor speed. If it is indeed an 1800 RPM motor, 4 pole, the running speed will be around 1750 RPM at no load.

If you have a need to calculate closer,(not likely) get an optical tachometer. A strobe light that counts a reflector on the quill. In any case, keep in mind that the machine will run a fuzz under indicated speed when loaded. The heavier the load, the slower it runs. By a very few RPM, in most cases you won't be able to measure the difference.

The "Cardinal" drive above is a commercially produced device that many people have shop built. It still is belt driven at the quill. My gizmo a few pages back gives a gear reduction at the quill. In either case, need for one is rare. Once you have a chart of belts vs. speeds, there are several methods of displaying it on the machine. Each more complicated than the last. Simplest is taping a copy nearby.

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[savarin]

Sometimes I think my total lack of training is worthwhile.
I never try to figure out what speeds to use I just go for it and turn it up or down depending upon how it feels when cutting.
Having the treadmill motors of my lathe and drill press make that so much easier I wouldnt go back to the original motors.

 

[34_40]

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

So is there a favorite RPM setting? Do you feel like there's a "one size fits all" more or less?

 

[C-Bag]

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.

So is there an off the shelf equivalent? I know the controller I’ve got for my treadmill motor doesn’t have the feedback as its puny when turned down.

 

[wachuko]

Thank you all for these ideas, this is half the fun (right?)!
This drill press is a 17" with a 1 1/2hp motor spinning a 24mm shaft. The motor tag (only tag/identification on this machine) states the RPM at 1730. The spindle is a 3MT. It has three pulleys, a three step cone on the motor(which as it is now, can not be flipped upside down; the small step in on the top), a four step intermediate in the middle and a four step on the spindle.
I do realize that going with a jack shaft pulley setup, that it will require either removal or modification of the belt cover but I am unsure if the jack shaft needs to be the same diameter as the motor shaft. Doesn't really matter to me, I just need to know and would like an understanding as to why?
I really want to avoid the three phase honestly simply because out of convenience of 110v outlets. So definitely leaning towards the jack shaft mounted pulley. But nothing is in stone yet.

So the issue is that you want to go lower than 200 rpm?

 

[wachuko]

Yes, I would also estimate the current lowest RPM to be around 225-240. I would like to see at least 150 RPM at the lowest setting. 100 RPM would be icing on the cake. I'm not sure what I could see if I only changed the intermediate step pulley. I will look into that but not expecting to get what I'd like to see
I would definitely like to put 1" holes in steel but I always start with smaller drills first. Not just starting with a 1" drill. I do have a handful of 3MT/2MT drills as well that would be nice to use them as well.

Sorry. Missed this post…

 

[RJSakowski]

So is there an off the shelf equivalent? I know the controller I’ve got for my treadmill motor doesn’t have the feedback as its puny when turned down.

I don't know of an off the shelf equivalent. I decided to build my own when I came to the realization that I wanted something that used simple components that would be likely to still be available ten or fifteen years down the road. and with circuitry simple enough in design that I could still understand it with my advancing age and diminishing mental acuity. I chose not to go the route of a microprocessor as they have an annoying habit of fading from existence as time goes by. Controlling something like a lathe can have serious consequences if things go south. I have personally had that happen with my Tormach CNC mill where the controller failed and a carbide end ill redecorated my table. Fortunately, it was drilling at the time and I was able to plug the holes but the thought of the lathe suddenly going berserk and revving up to 1,000 rpm as I was threading to a shoulder.

The circuit uses pulse width modulation for the driver control and it is fed by line voltage converted to DC by a full wave bridge rectifier and filter to give a no load voltage of 176 volts and 120 volts under load. A custom encoder monitors motor speed and when it senses a decrease in speed, the circuit increases the pulse width up to a full on condition, if necessary. This would be analogous to the operation of a vehicle cruise control when you come to an incline. The difference being this cruise control operates down to zero mph.

There is a limitation due to the encoder design. I used a Hall effect switch with 80 magnets embedded in the intermediate pulley which amounts to a pulse for every 18º of motor rotation. When the speed is low enough, the motor cogs much like a stepper motor as when the position is between the magnets, it translates as zero rpm and sends the full 176 volts to the motor. This limits smooth operation down to around 3.5 rpm at the spindle (with the belts configured for lowest speed). Even at that speed, there is a belt slipping amount of torque. I am in the process of building a Prony brake to measure that torque but I am confident that it is sufficient for any lathe operation.

All the components are common, low in cost, and have been around forever and not likely to disappear. At any rate, I have an ample supply of parts on hand to meet any maintenance needs. Once I can put some numbers to the performance, I will post the detailed build.

 

[C-Bag]

I don't know of an off the shelf equivalent. I decided to build my own when I came to the realization that I wanted something that used simple components that would be likely to still be available ten or fifteen years down the road. and with circuitry simple enough in design that I could still understand it with my advancing age and diminishing mental acuity. I chose not to go the route of a microprocessor as they have an annoying habit of fading from existence as time goes by. Controlling something like a lathe can have serious consequences if things go south. I have personally had that happen with my Tormach CNC mill where the controller failed and a carbide end ill redecorated my table. Fortunately, it was drilling at the time and I was able to plug the holes but the thought of the lathe suddenly going berserk and revving up to 1,000 rpm as I was threading to a shoulder.

The circuit uses pulse width modulation for the driver control and it is fed by line voltage converted to DC by a full wave bridge rectifier and filter to give a no load voltage of 176 volts and 120 volts under load. A custom encoder monitors motor speed and when it senses a decrease in speed, the circuit increases the pulse width up to a full on condition, if necessary. This would be analogous to the operation of a vehicle cruise control when you come to an incline. The difference being this cruise control operates down to zero mph.

There is a limitation due to the encoder design. I used a Hall effect switch with 80 magnets embedded in the intermediate pulley which amounts to a pulse for every 18º of motor rotation. When the speed is low enough, the motor cogs much like a stepper motor as when the position is between the magnets, it translates as zero rpm and sends the full 176 volts to the motor. This limits smooth operation down to around 3.5 rpm at the spindle (with the belts configured for lowest speed). Even at that speed, there is a belt slipping amount of torque. I am in the process of building a Prony brake to measure that torque but I am confident that it is sufficient for any lathe operation.

All the components are common, low in cost, and have been around forever and not likely to disappear. At any rate, I have an ample supply of parts on hand to meet any maintenance needs. Once I can put some numbers to the performance, I will post the detailed build.

this would be very helpful as you can imagine. I don't know if you can drop it down into granny gear so a dim bulb like me with only high school electronics can grok, but I will be on the lookout if you ever get to that post. I have a really nice hi end treadmill motor I'd like to put into use but am waiting for something like this solution to show up. It's on my many side lists of project solutions that have not gone critical because the motors on my lathe and mill are still functional. But it would be nice to be able to slow the lathe down as right now it's slowest is 120rpm.

 

[brino]

Understanding all the math is great, and really not too tough if you start with a simple two pulley theory and move on up from there.

Also, a laser tachometer is always useful in the shop.....
https://www.amazon.com/s?k=laser+tach&crid=20UW1RH9O3XWW&sprefix=laser+tach,aps,174&ref=nb_sb_noss_1

Brian

 

[Ultradog MN]

So is there a favorite RPM setting? Do you feel like there's a "one size fits all" more or less?

I am not in a hurry so I generally run it slower.
Usually in the 120-720 range.
Ran it at 60 a few times to tap a bunch of 1/2-13 holes.
I drilled some 25/32" holes the other day.
1/4" pilot holes first.
It has power feed and walked right through.
I have the drill head mounted to a massive 1 3/4" thick cast iron table. The first hole I ever drilled was 1 1/16" in the table top. No pilot hole.
I set it at 60 rpm, feed at the lowest .004/rev and let it go.
Couldn't hear any strain on the motor.
Sorry for bragging but yeah, I'm proud of it. My one, really nice machine.