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gnm109
08-12-2009, 10:46 AM
I have an original 1959 Craftsman drill press with the round column floor stand and a 1/2" capacity Jacobs chuck. It's the model that has 4 level step pulleys and part of the body casting which covers the front pulley. The head, table and base are all of cast iron construction and it's rather heavy. It's still in great condition and I use it all of the time.

By the way, I was mildly disappointed when the original Craftsman motor burned out after only 40 years of constant use so. LOL I replaced it about ten years ago with a new motor, a Taiwanese 1/2 hp, 1750 rpm.

One thing that has always bothered me about this drill press is that the lowest speed is really too fast for drilling larger holes, like 1/2" or more. The large pulley on the quill is about 4" in diameter and the small pulley on the motor is around 1-1/2" in diameter. That means that the ratio is around 2.66:1 which translates into around 650 rpm, more or less, as the lowest speed.

Since I've been watching this site, I've learned about VFD's. I notice that the ones I've looked at provide speed control with frequency change but also convert single phase into three phase.

My question then, is how to get speed control on the drill press? I don't want to change the pulley system and, even if I did, the front casting which covers the step pulley on the quill would make it difficult.

I'm not adverse to spending a few dollars to provide a lower speed since the drill press is sort of an heirloom. I also don't want to modify the mechanism at all.

Can a VFD also provide speed control for a single phase motor? If not a VFD, then what other unit could do this?

Comments gratefully received. :)

Forrest Addy
08-12-2009, 11:03 AM
I have the same drill press almost to the last detail. Mine's a floor model but the table doesn't tilt. The lowest speed is a bit too fast for drilling 7/16" and larger holes in steel.

I solved the problem by replacing the motor with a 2 HP 3 phase motor I happen to have and unstalling a VFD on a piece of sheet metal I mounted under the motor base. The metal was wide enough to extend off to the side to accept the VFD so the face controls are handy. I plug mine into 230 single phase but I put it together before the 115 volt input VFD's came out.

I suggest you replace your existing motor with one that's three phase. I reccomend 1 HP so you have a little extra oomph for tapping. Purchase a 115 volt input VFD. They put out by means of black magic 230 three phase variable frequency. Here's a link to one I think suitable. There are plenty of other sources.

http://dealerselectric.com/item.asp?cID=28&PID=611

No a VFD will not work on a single phase motor. You need a three phase motor.

Home center single phase speed controls for ceiling fans will not work because they control the fan speed by reducing the available electricrical power to the motor. There will be no speed regulation. Fans etc are constant load. Drill press loads vary widely which means the speed will drop as the load increases ften stalling the motor entirely

You can use DC motors and controls but the motors are a bit harder to find and often more expensive.

You will still need the step pulleys for the mechanical reduction. Motors are constant torque. Halve the speed with a step pulley drive and spindle HP remains constant. Halve the motor RPM and you halve the motor HP. High school physics.

It's likely you can find a 1 HP three phase motor free or nearly so at your local HVAC contractor. They are always replacing commercial air handlers and they often are run by three phase motors. Bird dog them a while and chances are y ou'll have a lightly used three phase (dirty) motor for freee or nearly so.

sch
08-12-2009, 11:05 AM
Altho I have seen mention of 1ph speed controllers, practically they do not
exist or are formidably expensive. If an improvised jack shaft is prohibited
by cast iron and preference, the least expensive route would be a 1HP
VFD and a new 3ph motor. A bit of searching should turn up something in
the $200 to $250 range. www.surpluscenter.com has fractional hp 3ph
motors for cheap and an old style non torque compensating 1hp VFD is
in the $100-150 range. Main hassle is getting the new motor with the
same shaft size as the old so you don't have to fiddle with pulleys.
FWIW going below about 30hz is going to cut your torque a good bit
so a torque compensating VFD ($30-50 more) might be worth while.
EDIT or you can do what Forrest did and get a bigger motor.

Duffy
08-12-2009, 11:08 AM
I have an original 1959 Craftsman drill press with the round column floor stand and a 1/2" capacity Jacobs chuck. It's the model that has 4 level step pulleys and part of the body casting which covers the front pulley. The head, table and base are all of cast iron construction and it's rather heavy. It's still in great condition and I use it all of the time.

By the way, I was mildly disappointed when the original Craftsman motor burned out after only 40 years of constant use so. LOL I replaced it about ten years ago with a new motor, a Taiwanese 1/2 hp, 1750 rpm.

One thing that has always bothered me about this drill press is that the lowest speed is really too fast for drilling larger holes, like 1/2" or more. The large pulley on the quill is about 4" in diameter and the small pulley on the motor is around 1-1/2" in diameter. That means that the ratio is around 2.66:1 which translates into around 650 rpm, more or less, as the lowest speed.

Since I've been watching this site, I've learned about VFD's. I notice that the ones I've looked at provide speed control with frequency change but also convert single phase into three phase.

My question then, is how to get speed control on the drill press? I don't want to change the pulley system and, even if I did, the front casting which covers the step pulley on the quill would make it difficult.

I'm not adverse to spending a few dollars to provide a lower speed since the drill press is sort of an heirloom. I also don't want to modify the mechanism at all.

Can a VFD also provide speed control for a single phase motor? If not a VFD, then what other unit could do this?

Comments gratefully received. :)
Get a VFD with 120V input and 220 3ph output and a 220V 3ph 1/2 or 3/4Hp motor. Not REALLY that expensive-a Teco VFD is $109.00 and I am told that fractional hp 3ph motors are only about $25.00 or $50.00. I know that HVAC companies are continually removing and trashing perfectly good units. It is all a matter of warranty and callback on replacement systems. Duffy

TxBaylea
08-12-2009, 11:47 AM
I had a similar Sears drill press and had a third step the pulley that was supported at the top of the column. It was mounted on a shaft set eccentrically in a plug fitted into the top of the column. It worked well and speed changes were relatively easy.

My son has that drill press now but he is out of the country until mid September so I can not get pictures for you.

Vernon

gnm109
08-12-2009, 03:56 PM
Thanks for the responses. That's sort of what I thought with regard to three phase. I will start looking for a suitable 1 hp 3 phase motor. I've seen lots of them around but I never had any interest in them until now. If the motor has a larger shaft, I will either bore my pulley to suit or get one with a larger hole to match the front one.

Once I get the motor, I'll add a VFD and that wil be that.

Thanks.

Black_Moons
08-12-2009, 05:11 PM
There are a few other options since your dealing with fractional HP:
You could get a DC motor, like from a treadmill and wire up a new control (or reuse the existing one) I seem to recall theres a following on treadmill motor to drill press speed control conversions online.

Alternatly you could buy a new 6 step pully (or two) and see if it fits, or buy another 4 step pully and a two bearing blocks and add another intermediate pully.
those '16 speed' drill presses just use 3 pullys.

The Artful Bodger
08-12-2009, 05:20 PM
I have seen this problem solved although you may consider the method rather a kludge. A jack shaft was made that fitted in the place of the motor so in the case of your drill press the original pulley set would be unchanged. The motor was re-mounted with the pulley end down ( the direction of the motor has to be reversed) and another pair of pulleys to give the desired reduction.

gnm109
08-12-2009, 08:48 PM
Yes, I shall have to do some sort of jackshaft. After a quick look at eBay regarding three speed motors, they are very pricey nowadays.

The cost of a motor and VFD plus shipping for both and it's over budget and all of the fun is gone from the project.

An extra shaft and step pulley like a Mill Drill will do the job. It can also be a bolt on so that no permament modifications are made. (no holes drilled in the original structure anyway). I suspect that I've got most of the parts except for another step pulley lying around already.

Thanks to all.