Gearing Down A Jet Drill

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I have followed along in the forum long enough to safely ask this question. I own an older Jet bench drill it is a single phase ? 120 volt 1/2 horse 1725 rpm motor. The pulley speeds on it are 500, 900, 1600, & 2800. Yowza, can't do much with this, so I only use the 500 rpm.
I have tried in vain to find a larger pulley for it but 1) Jet remains ignorant. 2) The Farm stores carry step pulley's with little room to bore the ID out...so, Should I replace the motor with a lesser rpm range? Try to install a VFD?
What would you senior member do to bring the rpm's down to a workable range?
 
I have followed along in the forum long enough to safely ask this question. I own an older Jet bench drill it is a single phase ? 120 volt 1/2 horse 1725 rpm motor. The pulley speeds on it are 500, 900, 1600, & 2800. Yowza, can't do much with this, so I only use the 500 rpm.
I have tried in vain to find a larger pulley for it but 1) Jet remains ignorant. 2) The Farm stores carry step pulley's with little room to bore the ID out...so, Should I replace the motor with a lesser rpm range? Try to install a VFD?
What would you senior member do to bring the rpm's down to a workable range?

I have an older Jet Drill. It was a few years old when the pulley broke and I had a hard time finding a replacement. Most ordinary drill presses do not gear down very low. Even a heavy duty one that I have really runs faster than I want. One thing I have done is to replace the motors with three phase and use a VFD on them to control the speed. Even if you don't have three phase you can get VFD units that are single phase that work with three phase motors. Three phase motors are actually quite reasonably priced on ebay.
 
On a Atlas drill press I have I installed a DC motor from a tread mill. I haven't used it a lot yet but so far I've been really happy with it. I don't like the speed control unit from the tread mill, so I just ordered a real DC speed control. Hope to try it out after it warms up a little. 10 degrees is too cold to be working in the barn. :confused 3:
 
I have followed along in the forum long enough to safely ask this question. I own an older Jet bench drill it is a single phase ? 120 volt 1/2 horse 1725 rpm motor. The pulley speeds on it are 500, 900, 1600, & 2800. Yowza, can't do much with this, so I only use the 500 rpm.
I have tried in vain to find a larger pulley for it but 1) Jet remains ignorant. 2) The Farm stores carry step pulley's with little room to bore the ID out...so, Should I replace the motor with a lesser rpm range? Try to install a VFD?
What would you senior member do to bring the rpm's down to a workable range?

Someone recently posted a project where he modified a band saw for normal as well as low speed to cut metal. He added a gear motor to the system using an overrunning clutch bearing and a jackshaft. When the gear motor was energized it engaged the overrunning clutch for low speed. When the high speed motor was energized the overrunning clutch freewheeled thus isolating the gear motor. This prohibits reversing your drill press but could work. Sorry I don't remember where this was posted. Two motors on a drill press would be rather clunky though.
 
I have followed along in the forum long enough to safely ask this question. I own an older Jet bench drill it is a single phase ? 120 volt 1/2 horse 1725 rpm motor. The pulley speeds on it are 500, 900, 1600, & 2800. Yowza, can't do much with this, so I only use the 500 rpm.
I have tried in vain to find a larger pulley for it but 1) Jet remains ignorant. 2) The Farm stores carry step pulley's with little room to bore the ID out...so, Should I replace the motor with a lesser rpm range? Try to install a VFD?
What would you senior member do to bring the rpm's down to a workable range?
================================================

What model drill press, do you have ?? Should be easy enough to adapt the 3ed reducer pulley, from one of the Grizzly 12, or 16 speed models. I have bought replacement parts from them, to use on machines, that were not Grizzly--- John
 
Arknack,
Would a VFD cause the motor to stall at low speeds? In other words...would I lose my torque?
 
I am not sure about the torque. That would be a good one to find out.

There is also a question of how much torque a smaller drill can take. I have VFD units on a lathe of mine and two exhaust fans. The fans are probably lower torque units. I like the one on my lathe because it gives me the option of quickly changing cutting speeds. If you really want a lot of torque you might want to look at a larger drill. I don't think the jet I have would take a lot more torque with the chucks, pulleys, etc.
 
There are a number of options. It sort of depends on what resources you have available and what you are hoping to accomplish. It is pretty easy to spend more on fixing up a machine than it would cost to purchase a machine that would do many of the things you want. Certainly, you can put a variable speed drive on (3 phase or DC). The torque will drop off (if you slow it way down, it will drop of quite a bit - mainly because of the difficulty in cooling it).

If you go with a 6 pole motor (1150 rpm), that is physically quite a bit larger - but that would get you down to about 350 rpm (and full torque capability). You could make your own larger pulley (which still gives you plenty of torque) - how much room do you have? You could go with a DC motor & drive - often these motors are fairly high speed, so you get variable speed - but you may need an intermediate shaft to get some decent torque back. You could go with a VFD and a 3 phase motor - recommend a 6 pole motor and/or upsizing the motor to preseve torque at the low end (a very nice solution, but if you pay store price for the components it will exceed the price of a good used HD drill press). You could set up an intermediate shaft - which works great, lots of speed selections, good torque (until that wee little belt slips - unless you go to a cog belt as the second belt), but a little fussy to set up and make guards for.

I had the same problem as you (too fast a drill press). I had an 11" Rockwell drill press (1/3 HP). I put a 1/2 HP DC motor on it. It was constantly popping the over current protection.

I was able to obtain a good HD Rockwell at auction for $375. It came with a 3 phase, 6 pole motor (1150 rpm) and quite a large step pulley on the spindle. I solved the 3 phase requirement with a cast off VFD (meaning old, free and still works, albiet noisy). I then spend quite a few hours engaged in "recreational chipping" to fit the drive in a nice enclosure, make up a pretty little mount for said enclosure, wire in the 3-wire stop/start to the drive - the result is great, but I was starting with something that was well along in achieving a slow drilling speed.

I no longer have that 11" DP. I got a nice 14", which is sort of fast, but combined with the 17" the bases are covered.

Your original question was, to ask what others here would do. First of all, just use the machine as is - sure it is a bit fast, but does it really cause you problems? At worst you may get a bit more practice sharpening drill bits.
Second, I would keep an eye out for lower speed motors (single phase or 3 phase). 3rd, I'd keep an eye out for a HD drill press (running a light duty drill press at low speed, is still a light weight drill press). 4th, I'd start thinking about setting up an intermediate shaft (picking up materials etc. on the cheap) - after a few years of "First", if "second" or "3rd" had not worked out and I found there was problems - only then would I modify the drill press.

Let us know what you work out.

DSC02370.JPG DSCF2220.JPG
 
What are you starting with? Does it have 2 belts or just one?
Since you mentioned only 4 speeds I assume it has only two four-step pulleys and just one belt.

Many drill presses have 3 pulleys and 2 belts. There is an intermediate shaft between the motor pulley and the spindle pulley. It allows you to have more speed choices.
Here's my King KC122FC:
belts.jpg
and the speed chart:
speeds.jpg

It is a very simple arrangement, there is an anchor hole in the head, a crank with two pins on opposite sides of opposite ends, another 4-step pulley with bearings to mount it to the top shaft.

upload_2016-1-19_21-49-33.png
from here:
http://www.manualslib.com/manual/87282/King-Canada-Kc-122fc.html#manual

Once you figure out the belt sizes required it could give you both more low-end RPM and more high-end for small holes.

I believe I saw a thread here where someone added an intermediate shaft to their drill press.
If I can find it I will post back here.

-brino
 
Last edited:
Brino,
Thanks for the break down pic.
It appears that the center pulley is on a pivoting lever #14. Thus, you still only need the one belt tensioning mechanism.
How does the pivoting lever mount? Is it just a hole with a pin? Bearings? Anything to keep it aligned?
Thanks for the pic!!

Daryl
MN
 
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