New drive for old Buffalo drill press? VFD or DC?

Recently purchased a Buffalo 16 bench drill press. Looking to put a variable speed drive on it and looking for input on the different options available.
My electrical knowledge is pretty thin and I see there is information on VFDs and DC motors (treadmill?)out there, but it's confusing to me.
Not looking to cheap out with some farmer type setup.

Original motor was 3/4 hp (maybe), and slowest speed around 400.
Thinking I need to get down to around 150 rpm for hole saws, bigger holes in steel, etc. I have single phase power available.

Main question at this point is what are the pros and cons of VFD (with a 3 phase AC motor) vs DC drives?

Thanks for any help.

Mel in WA said:

Recently purchased a Buffalo 16 bench drill press. Looking to put a variable speed drive on it and looking for input on the different options available.
My electrical knowledge is pretty thin and I see there is information on VFDs and DC motors (treadmill?)out there, but it's confusing to me.
Not looking to cheap out with some farmer type setup.

Original motor was 3/4 hp (maybe), and slowest speed around 400.
Thinking I need to get down to around 150 rpm for hole saws, bigger holes in steel, etc. I have single phase power available.

Main question at this point is what are the pros and cons of VFD (with a 3 phase AC motor) vs DC drives?

Thanks for any help.

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Drillpress wants lots of torque as you drop the RPM. DC can be MUCH better at that.

I doubt you'll get away with running these old warhorses at HIGH RPM (for tiny, tiny holes), where the AC+VFD is the better choice, as the DP bearings simply won't stand that.

"Treadmill?" Not on my watch. Pretty sorry examples of Dee Cee motors.

But I can afford to be smug! I had grabbed-up a BUNCH of Reliance RPM III "Type T" 180 V Dee Cee motors already. One of my smaller ones and a NEMA 4-X cased KB-Penta drive, PloyVee belt, and I'd soon be done.

My own "big, OLD DP", a 1950's Alzmetall AB5/S has been allowed to keep its 7 HP 3-P motor OTOH. I have a suitable FIVE HP Reliance RPM III, but it weighs nearly twice as much (180 VDC windings do that..) would need a shaft reducer and for-damned-sure could shred the PIV Werner-Reimers variable drive the Alzmetall used.

Waay too MUCH torque, some DC motors can put out. Two to NINE times nameplate peak torque (per Reliance themselves..) if the DC Drive controller is not set to limit that sanely.

Do set such a limit if you go with DC. It is a nice thing to be able to have it just keep hauling the heavy load. It is something else again to snap drills or slowly wrap the spindle shafting itself into a helical twist-drill shape!

You'd need only a 1/2 HP 180 VDC motor if you can find a "Type T" (TR or TX). Those are the ones specifically meant for smooth, wide, RPM power band in variable-speed machine-tool, hoist, and elevator use. A 1 HP is about as small as you are likely to find. My smallest is a 1 1/2 HP with integral 120 VAC mechanical brake, itself a nice-to-have feature.

2CW

Simplest thing to do would be to add a 3rd pulley to get lower rpm, yes it takes a minute or 2 to change belts around, but its dead simple. Or check out Mr. Petes latest vids on the pull gear, kinda neat idea, never seen one myself, but you might find/make one.

I'm not too much of a fan of vfd's, especially not on old machines, its like putting spinner wheels on a classic car. I'm sure others here will disagree, but my experience with vfd's is that they have no torque at low rpm's.

If you want a good treadmill motor, look for a commercial type treadmill, ie something from a gym, the consumer grade TM's have small motors and funky mounts. The motors out of the commercial units tend to have traditional foot mounts, and come in both 90v and 180v configurations. But again, low rpm = low torque.

dalmatiangirl61 said:

I'm not too much of a fan of vfd's, especially not on old machines, its like putting spinner wheels on a classic car. I'm sure others here will disagree, but my experience with vfd's is that they have no torque at low rpm's.

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More like putting a high-reving motor that gets a nominal 300 BHP, but... at 5800-6000 RPM, into a dually that was geared for a nominal 180 BHP Diesel that made its bones with over 600 ft lbs of TORQUE ....down around 1800 RPM.

dalmatiangirl61 said:

Simplest thing to do would be to add a 3rd pulley to get lower rpm, yes it takes a minute or 2 to change belts around, but its dead simple. Or check out Mr. Petes latest vids on the pull gear, kinda neat idea, never seen one myself, but you might find/make one.

I'm not too much of a fan of vfd's, especially not on old machines, its like putting spinner wheels on a classic car. I'm sure others here will disagree, but my experience with vfd's is that they have no torque at low rpm's.

If you want a good treadmill motor, look for a commercial type treadmill, ie something from a gym, the consumer grade TM's have small motors and funky mounts. The motors out of the commercial units tend to have traditional foot mounts, and come in both 90v and 180v configurations. But again, low rpm = low torque.

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I already have a Delta drill press with the slow speed 3rd pulley set up. Ready to change over to something variable speed.

This is a working drill press, not a valuable antique, so I have no qualms about putting a new drive on it.

I'm actually seeing more people that favor a VFD over the DC drive.

Mel in WA said:

I'm actually seeing more people that favor a VFD over the DC drive.

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More people eat at McDonald's combined outlets in a single hour than have enjoyed a meal at the Island Shangri-la, Hong Hong or "Paris 1930", the Ritz, Taipei, in a whole year, too.

Doesn't change MY elitist-bastard mind one wit.

As with Thermite, I am a fan of DC motors when I need variable speed drives. An I am referring to industrial grade motors, not overrated non-sealed treadmill motors.

Why?
-lots of torque
-easy to setup and wire
- no high pitched whine of the VFD
- If you shop carefully on Ebay, you can get new or close to new motors for a reasonable price
-Industrial motor controllers are pretty cheap used on ebay.

I usually use NEMA 1 enclosed dc drives, as they have the power switch and speed potentiometer built in. They also sealed up. Most low cost VFDs are really meant to be put into another enclosure. A lot of folks do not, but I really do not like the exposed high voltage screws and non-strain relieved cables.

I find dc motors cost a little more but the drives can be cheaper. But I may just be a good shopper
-

crrmeyer said:

As with Thermite, I am a fan of DC motors when I need variable speed drives. An I am referring to industrial grade motors, not overrated non-sealed treadmill motors.

Why?
-lots of torque
-easy to setup and wire
- no high pitched whine of the VFD
- If you shop carefully on Ebay, you can get new or close to new motors for a reasonable price
-Industrial motor controllers are pretty cheap used on ebay.

I usually use NEMA 1 enclosed dc drives, as they have the power switch and speed potentiometer built in. They also sealed up. Most low cost VFDs are really meant to be put into another enclosure. A lot of folks do not, but I really do not like the exposed high voltage screws and non-strain relieved cables.

I find dc motors cost a little more but the drives can be cheaper. But I may just be a good shopper
-

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Tell me more, I'm trying to learn here. What size DC motor would you recommend? Is there a power loss at low speed?

I have a 21 inch Buffalo.. Mine is driven from a four speed transmission out of a Dodge M37 military truck .. Motor is 3hp three phase 1725 rpm...For bigger drills backgear is a must as the large V belt drive I installed will slip in direct drive.. It is great for drilling and tapping as well as I have instant reverse.. Have tapped on inch std holes.. Ramsay 1

If you go VFD a 6 or 8 pole motor is a decent answer to low speed torque issues. For machine tool drives 1200 or 900 rpm is a much better starting point given the need for grunt at low speeds and the inherent tendency for torque to drop significantly once the motor is outside the nameplate ± 1/3 rd or thereabouts speed range. However miraculous the VFD electronic innards.

Here in the UK used industrial strength DC motors and controls are thin on the ground with prices to match rarity so its not commonly viable despite the DC motors inherent low speed torque advantages.

However over here I can pick up a new 1 hp 8 pole motor for around £150 delivered and a basic "DOL soft start" starter substitute VFD, Eaton DE 1 series in this case but there must be others, for about £100 brand new. US prices are usually better than Blighty ones so ....

Over here the Eaton drives are a bit of a dark horse on the VFD market. Fixed parameters, unless you buy the adjuster dooby, no frequency display and no separate switches. Turn the power on and they run up in 5 seconds, turn off and its 5 seconds ramp down. Simples. There is a speed pot input if you need it tho'.

At that money not worth messing around searching for used equipment that might or might not do. The older I get the more attractive buy new and it works gets. I'll save my engineering and fiddling time for things that need it. These days motor drives certainly don't. Speaking as one who has built his share of static, rotary and DC drives back in the day.

Clive

Clive603 said:

If you go VFD a 6 or 8 pole motor is a decent answer to low speed torque issues. For machine tool drives 1200 or 900 rpm is a much better starting point given the need for grunt at low speeds and the inherent tendency for torque to drop significantly once the motor is outside the nameplate ± 1/3 rd or thereabouts speed range. However miraculous the VFD electronic innards.

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One one hassle I have with 6 or 8 pole 3 phase motors is they are really big. The GE 3 phase 3/4hp 1200 RPM motor in the photo below is 80 lbs and has a 7/8" diameter shaft. The larger shaft diameter probably means you would need to find a replacement step pulley with the larger bore. A 1HP 1750rpm Leeson DC motor probably has the same 56 frame size and 5/8" diameter shaft as the motor he is proposing changing on the Buffalo drill press. So bolting it in place should be easy.

When I was hunting for slow speed 3 phase motors for a reasonable price they were a lot harder to find. Maybe they are more plentiful in the UK, but not as much in the US.