# Slowing Drill Press RPM's



## slowneasy (Oct 30, 2022)

Probably like most of us, we have drill presses that were more or less designed for drilling holes in wood.  And so the RPM's are higher for this kind of use.  However, most of us probably use them as much or more so for making holes in metal.  And larger bits than say 1/2" require lower RPM's and >1" even s-l-o-w-e-r.  
I picked up a vintage King brand drill press in decent condition but the slowest RPM handles 3/8" in steel okay.  So I'm really looking hard at options to slow this (jet) motor down.  And I'm not very good at this kind of thing (or much of anything really).  It seems I have basically two options-
1) source parts for an add-on pulley with jack shaft and fabricate a mount
or
2) local a 3 Phase motor and VFD controller

I don't know anything about either.  Advantages or Disadvantages of either.  From what I've read (and don't know if true or not), on 1), the jack shaft needs to be the same diameter as the motor shaft?  If true, why?
Also, an advantage of option 1) is that I have all the torque of the motor at lower(est) RPM's, yes?
On option 2) I may not have torque at the lower speeds?  

What are you experiences and thoughts/recommendations?


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## twhite (Oct 30, 2022)

Depending on your drill press you can add a set of reducer pulleys. I have an old Craftsman 150 that I made the reducer for. Works like a champ. 
I can post a picture later if needed. 


Cutting oil is my blood.


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## aliva (Oct 30, 2022)

Cost wise a jack shaft would be cheaper than a VFD and a 3-phase motor. A VFD will give you variable speed control, but a proper sized pulley arrangement will get the rpm to you desired level. Concerning shaft diameter having to be the same as the motor I can't see why, other than maybe being able to handle the torque. You didn't mention if the drill press already has stepped pulleys to vary the rpm. 
If you decide on the jack shaft option here's a site to help you with the rpm calculations.





						Pulley Calculator. RPM, Belt Length, Belt-Surface Speed, Animated Diagrams - Metric
					






					www.blocklayer.com


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## great white (Oct 30, 2022)

My King 13” drill press will go down to 220 rpm:




it has three pulleys though. Might have a look at yours and see if a simple pulley swap might give you low enough rpms (spindle speed) for what you want to do.

Power wise, pulleys will be better. It allows you to run the motor full speed (ie: better cooling, better torque, etc) while still keeping your spindle speed low.

Some might comment that swapping belts on a pulley system is a PITB, but mine almost exclusively does metal work so I don’t change the spindle speed very often.

YMMV…..


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## Jimsehr (Oct 30, 2022)

Could you find a motor with lower rpm? Both options below cost about the same? $159 bucks. I think I would GO wiTH anew motor for cutting metal.


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## Bi11Hudson (Oct 30, 2022)

+1 on using a jack-shaft. It will be necessary to increase the reach of the pulley enclosure, but they are usually light sheet metal. You might find it advantagous to reinforce the area where the jackshaft is mounted. That depends on the construction of the OEM machine.

A while back(20+years) I needed a drill press with lower speed. My solution, while not entirely satisfactory, did get the job done. What I *should* have done was acquire a magnetic drill and build a stand to run it horizontally. Or dismantle the small tractor and use a regular drill press on the part. What I actually did was *(heaven forbid) buy* a Craftsman 17 inch floor model, find a piece of tubing for a short mast, and using "C" clamps hung it on the machine. It worked, with a few busted knuckles and considerable frustration. 

Today, I have several drill presses, some are used on wood, some on metal. I ran into work that required a slower drill speed than even the big floor standing machine so acquired a Horrible Fright mini-mill to regulate the machine slow enough. It doesn't have near the torque of the full sized drill press, but does the work I need it for.

There are several disadvantages to using a 3 phase / VFD to get slower speed. An extra step (or two) of pulleys will provide the necessary speed reduction much better. And take much less engineering to fit to the machine. At the slow end of the belts, gear reduction may be advantagous. I include a document to make a geared speed reducer from automotive parts. It looks complex but is doable on a mini-lathe and Wally World drill press. Fitting it to a small drill press will take some finagling, it was first tried on a small lathe. But the ~3:1 reduction works fine and doesn't take much space. A *possible solution*. . .


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## RJSakowski (Oct 30, 2022)

slowneasy said:


> Probably like most of us, we have drill presses that were more or less designed for drilling holes in wood.  And so the RPM's are higher for this kind of use.  However, most of us probably use them as much or more so for making holes in metal.  And larger bits than say 1/2" require lower RPM's and >1" even s-l-o-w-e-r.
> I picked up a vintage King brand drill press in decent condition but the slowest RPM handles 3/8" in steel okay.  So I'm really looking hard at options to slow this (jet) motor down.  And I'm not very good at this kind of thing (or much of anything really).  It seems I have basically two options-
> 1) source parts for an add-on pulley with jack shaft and fabricate a mount
> or
> ...



If you choose to use a jack shaft, keep in mind that you will have to flip the motor pulley.  You might want to use the motor pulley on the jack shaft and a new cone pulley for the motor.


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## slowneasy (Oct 30, 2022)

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.


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## C-Bag (Oct 30, 2022)

slowneasy said:


> 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.


Hmm, you mention you already have a 3 pulley system, what is your lowest rpm now? Your best bet is just changing pulley’s as you are already as good as a jackshaft setup would be you just need the correct size pulleys.


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## GeneT45 (Oct 31, 2022)

Don't rule out a DC motor.  A friend picked one, with controller (get one *with* a controller) off eBay for ~$50.  He retrofited his small mill with it, but I don't see why the same wouldn't work for a drill press.

GsT

Edit: meant to mention that what he got was a treadmill motor.


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## Bi11Hudson (Oct 31, 2022)

Between the metric motor shaft and the "step" in the pulley, you've *almost* painted yourself into a corner. There are some outs but the window *is* closing some. So I need to think through this as I go. And bring up some of my own machines to compare against. Not bragging, just thinking through. For the first point, I don't recall if you mentioned a lathe. If you have or have access to such a machine it would be a simple process to make another pulley opposite what is on there now. You will need another pulley anyway, why not two. Worst case, a *pair *of countershafts would maintain the pulley positioning. A PITA on a good day, but it would be a solution.

So, on to the countershaft(s). I  honestly don't know what my 17" floor model DP has for a motor or countershaft. I do have a 9 inch lathe in addition to a 12 inch. Both have smaller motors with a 3/4 inch (or are they 5/8?) shaft. But they are smaller by far than what you have. I would say at least a 3/4" shaft, a 7/8 or 1 inch would be better. If I were to finagle something like that, the pulley(s) would run on ball bearings. Or the entire shaft and pulley. That would be your call, depending on what bearings you had or could find, and the contruction of the head stock. A countershaft must be rigidly mounted but must also swing some. A 1/4 inch piece of bar stock will do, thicker would be better.

I assume the drill press is of Asian origin. Or is it European? In any case the metric motor shaft indicates overseas production. Last I heard, many years back, 99% of drill presses were made in Asia anyway. The point is that belts may be of an odd size and/or configuration. One of my machines uses a 5mm wide belt. In the Gates catalog there is also a 7mm size. My machine uses a 5M720, 5mm wide and 720mm long, with a 60 degree pitch. The 60 degrees is the kicker, A US made belt will not fit properly. I happen to like them, they are surprisingly strong and pulleys are easy to make with a "standard" threading tool. A countershaft will require another belt, make sure what type and keep to the same.

There are other considerations here, most cannot be done remotely. The post above brings up a DC motor. But without reduction, it will lose torque at a terrific rate at very slow speed. A consideration, but with losses that must be planned for.

.


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## wachuko (Oct 31, 2022)

But you mentioned having a 3 pulley system… what is the slowest setting you can get with that?


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## slowneasy (Oct 31, 2022)

Some really good questions are coming from you all...thanks!  This all should get to the bottom of what I need to do.
First off, since the name cast in the side of the press says "King" and is a vintage press, I'm going to speculate that it was made in Canada.  There is no tag with specs on the machine itself or a belt configuration label that has "RPM" speed.  There's next to no information out there that I have come a cross on vintage King drill presses.  Next, I don't know if the motor is original to the drill press.  The motor tag indicates Teco brand and the standard information tag that a motor has.  60Hz, 110/220V, 19/9.5A, 1730RPM, 1 1/2HP.  
I'm going to suspect the motor is not original because of the HP rating and shaft diameter.  Seems like a beast of a motor.  

Now, back to the pulleys on the drill press.  I haven't pulled the pulley off the spindle shaft yet so don't know if I can get it off but the intermediate one comes on/off it's mounting location ("floats" in it's mounting hole and the opposing belts keep it in place) easy enough and that one may have space to change out to a different size step pulley.  I just don't know if there'd be room within the belt housing to make much difference in the RPM.  From what I understand about an intermediate pulley, to lower my RPM's, I'd need one that had a larger diameter for the motor side and a smaller diameter for the spindle side than what it currently is.


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## slowneasy (Oct 31, 2022)

> Bi11Hudson said:
> 
> 
> > Between the metric motor shaft and the "step" in the pulley, you've *almost* painted yourself into a corner.


Boy, I hope not


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## C-Bag (Oct 31, 2022)

pulley pics please.


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## slowneasy (Oct 31, 2022)

wachuko said:


> … what is the slowest setting you can get with that?


That is a great but unknown question.......at this time.


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## slowneasy (Oct 31, 2022)

C-Bag said:


> pulley pics please.


, I'll have to put the top of the drill press back together...... but they are all in a row....1,2,3.


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## C-Bag (Oct 31, 2022)

No pics, it didnt happen.


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## 34_40 (Oct 31, 2022)

I'd suggest reviewing Page 1 posts #4 & 5..    Just need a few measurements like pulley sizes and you can match the rpms listed.  My .02.


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## great white (Oct 31, 2022)

slowneasy said:


> ....First off, since the name cast in the side of the press says "King" and is a vintage press, I'm going to speculate that it was made in Canada.  There is no tag with specs on the machine itself or a belt configuration label that has "RPM" speed.  There's next to no information out there that I have come a cross on vintage King drill presses. ........



King is a relatively new name for Canadian machinery and it's all imported from overseas. King has been around since 1910, but they only branched in to machinery since 1983. Before that they operated as a steel forge:






						company king canada KING Canada - Power Tools, Woodworking and Metalworking Machines by King Canada
					

King Canada, metalworking, woodworking, parts, accessories, automotive, products, machines, tools, compressors and air tools, material handling, outdoor, indoor, equipment, generators, log splitters, power, bandsaw, drill press, dust collector




					www.kingcanada.com
				




Lots of companies in the states have used the King name. A quick search here:





__





						Manufacturers Index | VintageMachinery.org
					





					vintagemachinery.org
				




Will turn up 5 or 6 of them.....


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## slowneasy (Oct 31, 2022)

This is just "mocked" up, the pulley on the motor is just sitting on the shaft, not all the way down


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## wachuko (Oct 31, 2022)

You do not need a VFD… if you have the belts then you have all that you need to slow that down!!


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## great white (Oct 31, 2022)

slowneasy said:


> View attachment 425225
> 
> This is just "mocked" up, the pulley on the motor is just sitting on the shaft, not all the way down


Well, that sure looks like it could have been the "King Canada" era. 

But it's definitely a rebranded import (King Canada doesn't manufacture any tools itself)...likely from Taiwan.


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## savarin (Oct 31, 2022)

stuck a treadmill motor with speed controller on mine.
Ok so very slow speeds have limited torque but it does everything I want it to.
I use 2" -3" dia hole saws at very slow speed on aluminium and steel, sometimes they grab a stall but generally keep going with enough lube.


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## rwm (Oct 31, 2022)

I highly recommend a sewing machine motor:









						Clausing Drill Press (new to me)
					

I just got this sewing machine motor in the mail today:    In spite of its small size it is rated at 1HP and goes up to 4000 RPM. I plan to replace the drill press motor with this and have the added advantage of full speed control. I hope the torque will be adequate. I plan to use the pulleys to...




					www.hobby-machinist.com
				




This guy has an eBay store. Search for "The Custom Crafter". He has several motor sizes available.


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## Bi11Hudson (Oct 31, 2022)

A  much better representation of the problem. It looks very much like my Craftsman 17" machine from ~25 years ago. First off, I will *withdraw my ramblings from last night*. You have basicly two options for using the existing belts: First is a DC motor and controller. The other is to use the gear reduction I posted earlier. I don't like VFDs, they don't work all that well at low speeds. They are good drives, but not as much as they are touted. I used them in industrial applications, they may do better in small shops.

There are some calculations you can do that will get you close for speeds. You state the motor is 1800 RPM. I take that to mean it is less "slip" which will place it at 1740ish. Basicly a 4 pole induction motor. The pulley ratios are measured by the "pitch diameters", roughly half way from the OD and the ID. Calculating from OD will get you coursely near. Figure each belt position, I would bet the lowest speed is around 200 RPM. Up or down a little, but close to it.

A "sewing machine" motor would be a good choice. In the size needed it will basicly be an AC/DC notor. Like a treadmill motor but "stouter". They are "series universal" motors and will run on AC or DC, simply by varying voltage. Most associations to a sewing machine are for the smaller home machines. A commercial machine has a motor the size of an entire home machine. Be sure the controller comes with it. A small treadle can't handle the current involved.

*Purely my perspective* here: Going much slower will be in the range of a milling machine. That's what I bought the HF MiniMill for. But I do small work, you would want something a little bigger. At very slow speeds and high torque there *may* be belt slippage. That's where the final reduction gear set comes into play. A DP has quill bearings that do well for direct pressure but are weak for side play. If you are ever tempted to do side cutting, remember that! A drill press is not a milling machine.

.


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## rwdenney (Oct 31, 2022)

I’m visually estimating 20:1 reduction in those pulleys. You should be able to get RPMs below a hundred with that. Even if it’s only 10:1, it’s below 200 RPMs. How slow is your target?

It takes a powerful and strong drill press to drill a 1” hole in steel. 

Rick “4:1 motor to jackshaft and 5:1 to jackshaft to spindle” Denney


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## slowneasy (Oct 31, 2022)

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.


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## francist (Oct 31, 2022)

It’s pretty simple to do the math but you will need to measure some sheaves first, otherwise it will stay at guesswork. There are also a number of on-line calculators available that take all the effort out of the calculations, just input the numbers. This one is from Engineering Toolbox. I’ve just plugged in what look like may be close to the sheave sizes based on the photo.


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## great white (Oct 31, 2022)

Calculator I often use:






						Pulley Calculator. RPM, Belt Length, Speed, Animated Diagrams - Inch
					






					www.blocklayer.com


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## Jake M (Oct 31, 2022)

slowneasy said:


> View attachment 425225
> 
> This is just "mocked" up, the pulley on the motor is just sitting on the shaft, not all the way down



The first thing that I'm seeing is that you appear to have four speeds on the spindle, four speeds on the idler, and three on the motor.  That screams to me that the motor and motor pulley got changed at the same time.   Part of the "magic" of these stacked pulleys is that they're a specific size in relation to each other, so the tensioner comes out right in any speed.  That might be an issue.

Looking at the available speeds you have, I would suspect that if you have the motor pulley mounted high, with the smallest pulley driving the largest idler pulley, (highest belt position) and the smallest idler pulley driving the largest spindle pulley, (lowest belt position) you "should" be at or about a hundred RPM.    If you don't have the actual RPM nailed down yet, you know the RPM of the motor-  Put the belts on the slowest speed, sharpie mark the spindle and the motor pulleys, and turn the motor pulley by hand, and count the motor rotations per one spindle rotation to get an approximate ratio.  Knowing what speed you have right now might be key information, as if you're already in the hundred RPM area (I'm visually estimating), or even in the sub 200 RPM area, I think any big upgrades are going to be well past the point of diminishing returns.

Not to knock down a project to build exactly what you want.  If that's the point and the purpose, then heck yeah, all in.  But if the purpose is to make holes, and you're under 200 RPMs with a horsepower and a half.....  You can do a lot with that.


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## Weldingrod1 (Oct 31, 2022)

I used a 900 RPM motor ony Craftsman drill press...

Sent from my SM-G715A using Tapatalk


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## slowneasy (Oct 31, 2022)

Okay, I must not be understanding/inputting the correct numbers/measurements.  Using the above pulley RPM calculator, on the smallest motor pulley and largest on the spindle, it says the RPM is 118.  hmmm


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## intrepid (Oct 31, 2022)

Here is another easy option if you have the room.


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## slowneasy (Oct 31, 2022)

intrepid said:


> Here is another easy option if you have the room.


whether I have the room or not, that is ingenious!  I really like that....now why can't I think of these kinds of setups


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## slowneasy (Oct 31, 2022)

Jake M said:


> screams to me that the motor and motor pulley got changed


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



Jake M said:


> so the tensioner comes out right in any speed


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?



Jake M said:


> belts on the slowest speed, sharpie mark the spindle and the motor pulleys, and turn the motor pulley by hand, and count the motor rotations per one spindle rotation to get an approximate ratio


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


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## C-Bag (Oct 31, 2022)

intrepid said:


> Here is another easy option if you have the room.


I don’t know about easy, but I’ve never seen that. I’ve been wracking my brain to figure out how to slow my UniDrill which has a Reeves drive and 24” radial arm which severely limits the motor size. The motor needs to be very short to clear the arm and the slowest it goes is 450rpm.
thanks for posting this.


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## slowneasy (Oct 31, 2022)

Guys, if I'm putting these measurements/numbers into these pulley calculations correctly, I may not need to do anything to make this thing spin any slower......  In this case, I hope I'm not wrong


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## Charles scozzari (Nov 1, 2022)

I would consider swapping over to a treadmill 2hp dc motor and rheostat. Plug and play with plenty of torque. Look online the pricing is  reasonable.


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## rwm (Nov 1, 2022)

I should also add- having pulley reduction is great, but the main thing I like about my drill press is infinitely variable speed on the fly. This makes if very easy to dial in the chip for any size drill and any material with minimal effort. Changing pulleys is painfully cumbersome and I always found myself avoiding it. 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.


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## C-Bag (Nov 1, 2022)

rwm said:


> 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.


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## RJSakowski (Nov 1, 2022)

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.


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## wachuko (Nov 1, 2022)

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…


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## 34_40 (Nov 1, 2022)

wachuko said:


> 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


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## Ultradog MN (Nov 1, 2022)

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


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## slowneasy (Nov 1, 2022)

ah, rub it in Ultradog MN!


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## Jake M (Nov 1, 2022)

slowneasy said:


> 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.



slowneasy said:


> 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...  



slowneasy said:


> ~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.


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## slowneasy (Nov 1, 2022)

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


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## Jake M (Nov 1, 2022)

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.


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## slowneasy (Nov 1, 2022)

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.....


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## Bi11Hudson (Nov 1, 2022)

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 (Nov 2, 2022)

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.


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## 34_40 (Nov 2, 2022)

Ultradog MN said:


> 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?


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## C-Bag (Nov 2, 2022)

RJSakowski said:


> 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.


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## wachuko (Nov 2, 2022)

slowneasy said:


> 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?


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## wachuko (Nov 2, 2022)

slowneasy said:


> 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…


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## RJSakowski (Nov 2, 2022)

C-Bag said:


> 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.


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## C-Bag (Nov 2, 2022)

RJSakowski said:


> 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.
> 
> ...


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.


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## brino (Nov 2, 2022)

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


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## Ultradog MN (Nov 2, 2022)

34_40 said:


> 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.


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## 34_40 (Nov 2, 2022)

Ultradog MN said:


> 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.


Brag all you want, that is an awesome setup!  Thanks for sharing the pics too....


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## brino (Nov 2, 2022)

Ultradog MN said:


> 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.



Yup, that deserves some bragging rights!
Brian


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## Chips O'Toole (Nov 3, 2022)

I stuck a 2-HP motor and VFD on my Rockwell 17". No problems.


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## u50067 (Nov 5, 2022)

wachuko said:


> Sorry.  Missed this post…


In addition to the jack shaft pulley, I replaced the 1725 RPM motor with an 825 RPM motor. This reduced the spindle RPM to approx 135 RPM. I think the 825 motor was a direct drive fan motor. Am not sure but believe the fan motors on the outdoor AC units are slower speed motors and would likely be 230v motors. So check the RPMs of motors at sales, etc. I picked mine up at a pawn shop and have another approx 820 RPM 230v motor I found at an auction.


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## Bi11Hudson (Nov 5, 2022)

Where the fan is located is a function of the "class" of the motor and has no bearing on the speed. On my equipment, I often use TENV (totally enclosed non ventilated) motors. There *is* a fan on the inside. A little pricey, but I like than no chips can get inside. There is a TEFC (totally enclosed fan cooled) as well, but I avoid them because of the external fans. There are many classes of motors that, as a rule, are beyond the means of a hobbyist. By no wise does the fan have anything to do with speed. 

.


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## Provincial (Nov 6, 2022)

Another way to get a reduction in speed is to use a 1200 rpm motor.  These run about 2/3 the speed of a regular 1750 rpm motor.  They commonly use a frame one size larger than the normal 1750 rpm model, so you need to have room to mount them.  Using them with a VFD is nice because running them at 150% speed is 1750 rpm!  Because they have more torque (to put out the same horsepower at the lower rpm) they still have good torque when in an overspeed situation.


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