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Drill press 2 or 3 pulley setup need help?

GoceKU

Active Member
Active Member
#1
I'm making my own drill press i have a tread down in the drill press section, now i'm at that stage where i need to plan the drive setup, i have 1400 RPM 3/4 horse motor selected for this project, i've looked at factory drill presses some have 2 pulley setup and only 5-6 gears others have 3 pulleys and more gears, i suppose more gears better but i've seen big gaps in the rpm ranges, and i'll like some advice for the size of the pulleys of a good drill press with linear rpm range, i'm more interested in the slower gears, i have a morse 4 taper sindle made to be able drill bigger holes.
 

RJSakowski

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#4
It depends on the work you wish to do. Big drills = low rpm , tiny drills = high rpm. I prefer high rpm when working wood; you get cleaner holes. I seldom run drills less than 2mm in diameter on either my drill press or my mill/drill as I have other options for those occasions.

I don't believe that you will be able to get down to 50-150 rpm with a single set of step pulleys. 50 rpm would require a 20:1 ratio. Even at 150 rpm, you would require a 7:1 ratio. and something like a 40mm drive pulley diameter will require a 280mm driven diameter. You will most likely want to use a two belt system. This will give you extended range as well as more intermediate steps.

As far as choice of pulley diameters goes, you should try to pick the diameters so the sum of the diameters is approximately equal for all combinations. This will reduce the amount of travel for the belt tightening mechanism. This is fairly easy for a single belt setup but more difficult with two belts.

My drill press has a 1hp. 1725 rpm motor and uses four step cone pulleys. The output range is 400 - 2900 rpm. I would have preferred that I would be able to get down to 100 rpm. My mill drill uses a two belt system and there are 12 speeds ranging from 95 to 2580 rpm.
 

GoceKU

Active Member
Active Member
#5
I do have i chunk of 114 mm diameter round bar and can go down to 35 - 40 mm on the small end but even with 3 pulley setup that will only gave me reduction down to 250 rpm, next i thought if i can bolt an 220 mm top pulley even then is hard to drop it down to 100 RPM, 250 rpm is to fast for a 35 mm drill bit even with and guide hole, any ideas how to avoid worm drive and get the rpm down.
 

RJSakowski

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#6
A 40/114 pulley will give you a ratio of 2.85. follow that with a 40/220 and ratio if 5.5 and you overall ratio will be 15.675. With a 1400 rpm motor, you will have a spindle speed of 89.3 rpm. I wouldn't go any smaller than 40mm on the drive pulleys and preferably larger on the secondary drive pulley to prevent torque limitation due to belt slippage. A 55mm secondary drive pulley will still give you 100 rpm.
 

Ulma Doctor

Infinitely Curious
Active Member
#8
if you can get a 3 phase motor, you can put an inexpensive VFD on the drill press and have an adjustable speed drill press
a DC motor and Pulse Width Modulator and suitable inexpensive transformer could also be employed to great effect.
otherwise you'll need to add further reduction by a secondary with some relatively large pulleys or a 3rd jackshaft for ultimate reduction
you could possibly gain reduction from a planetary gear arrangement, but the engineering and time consumption may be prohibitive to create your own.
you could steal the parts for the planetary arrangement from an automatic transmission and go that route, if you were so inclined.
i wish you the best of luck in your work! :)
 

Silverbullet

Active Member
Active Member
#10
The trouble is if i go bigger with the pulley will act as a flywheel, and that's the last thing i want when the drill jams.
Unless you use cast iron pulleys they will not act like a flywheel. I give you example lawnmowers use to have cast iron flywheel and blade they will run and start without the blade. New models use aluminum flywheel and the blade is the counter balance needed to run. It will not start without the blade . Aluminum pulley will not propell if the drill gets stuck it will either burn the belt or stall the motor if jammed bad enough.
If you run three pulleys your torque will be better. Two belts , lots of ways to get rpms and torque . Variable speed with a vfd with three phase motor. Look at some of the old set ups they have torque with overhead belts .
 

GoceKU

Active Member
Active Member
#11
I'll have to make the pulleys out of 1045 steel, it's the only material i have a big enafth piece, you can imagine 12 - 15 kg of drive pulleys at speed, i'll have to put in a disk brake for emergencies, and as RJSakowski pointed out if i go little bigger on one side of the pulleys i could go down to 100 rpm and get much more torque, i already was planning to add flood coolant and a dividing work table, this project is going to take some time but be one of a kind, thank you all that replay and more suggestions are welcome.
 

John_Dennis

Active User
Active Member
#12
making step pulleys is very complicated, making a matching pair of step pulleys is extremely complicated. If you use a 3 pulley set up, you will not need a matching set because the third pulley will tighten the belts in any configuration.
 

GoceKU

Active Member
Active Member
#13
i'm considering putting the motor on a hinge and make a strong spring adjustable tensioner to tension both belts.