Help me figure out my Drillpress speed

Patrice Lemée

Patrice Lemée

Joined
Aug 13, 2002
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Thanks to Ocelot85 I realized that I was not using the proper drilling speeds and that I needed to start paying more attention to that. :o “Roughly” is not cutting it anymore, pun intended. ;)

My problem is that I have an old drillpress and the pulleys have been changed from the 5 steps original ones to 6 steps pulleys. So I measured the pulleys ID (inside diameter) and also OD (outside diameter). I calculated the ratio to see what it would translate using the 1750 RPM motor. Well of course it varies. I get a range of:

480 rpm – 4990 rpm using the outside diameter (OD)
355 rpm – 6180 rpm using the inside diameter (ID)

Which one of these is right? The difference is too big for me not to try and figure out the right way to do it so any help would be greatly appreciated.

Thanks

PS: I also read about the pitch diameter which, if I understand correctly, is about halfway between those. And of course it would give me a range of speed right smack between the two above.:confused:
 
Pitch diameter isn't just halfway. If you have an old belt, cut a section of it and measure how far the tensil fibers are from the OD of the sheave (put the section into the sheave), mulitply that by two and subtract it from the OD. The fibers are what the pitch diameter is measured by.

This will give you a more accurate measurement. Or just get a timing light and mark the spindle.


-X
 
Whether you measure ID or OD, wouldn't the ratio of them be the same ?


You can always try direct measurement


Digital Laser Photo Tachometer Non Contact RPM $20 ishi

Or see if a motor shop will loan you one
mechanics used to have them to set engine idle speeds in the old days of carburettors and non electrical ignition.

This is a machinist version

http://www.ebay.co.uk/itm/vintage-s...515&pid=100011&prg=1005&rk=1&sd=290941421706&


http://www.tmart.com/Digital-Laser-...aign=product&gclid=CIHOsbferrgCFYxcMgodbkUAtg
 
A larger pulley on the motor shaft will make the drill run faster. A larger pulley on the working spindle will make the drill run slower. All you need is the ratio of the two pulley sizes. You can measure radius, diameter, circumference, number of teeth (bicycles), etc. Just make sure to measure both pulleys in the same place.
 
Xander, thanks for the description of the pitch diameter. Problem is also knowing if that is the measurement to use or the OD or ID?
The timing light sounds like a great idea but I know nothing about them. :(

Count, the depth of the sheave being constant, the ratio is different using ID or OD. Take a 1" and a 2" pulley (ID) for example. Ratio is 0.5. If the sheave is 1" deep, OD is 2" and 3" and the ration is now 0.66.
Can I find a Digital Laser Photo Tachometer locally (Canadian-tire, Autopro...)?
 
If you had a belt that was 3" thick then your numbers would be grossly different using id and od for example. But the pulley would still be running at the same speed as if you used a link belt that is very thin. So using the inner diameter is the measurement that is standard. Now if you had a sheave that had a groove to accept a 3" belt it would still be running based on the inner diameter.

I would run your table of ratios and speeds based on the id. Being off by 50 rpm will not be critical. Keep in mind that many people have parked their press in the lowest rpm and just keep on drilling. Good luck.

Also keep in mind that there are drill presses that have ribbed belts that track in horizontal grooves in the pulley. In this case there is no id and od. So they must be using the id as the number for computing the ratios and subsequent speeds.
 
I have the digital non-contact gadget as well. Put a piece of reflective tape on your chuck, turn it on and shoot it with the laser!
Bang! - RPM readout.
I use it on all sorts of things.
 
Thanks guys. Found something comparable at the Harbor Freight Tachometer on ebay.ca so I'll order that and in the meanwhile I'll use the ID to calculate my speeds. I would most likely mess things up even more trying to figure out that pitch diameter. Not the sharpest tool in the shed here. :o ;)

Thanks again for all your help.
 
Karl B. Andersen said:
I have the digital non-contact gadget as well. Put a piece of reflective tape on your chuck, turn it on and shoot it with the laser!
Bang! - RPM readout.
I use it on all sorts of things.
Click to expand...

On the the chuck is the easiest.

Patrice,

If would be interesting to see if you can compare the chuck speed with the pulley/ratio formula to see how close. I wonder how close the motor rpms are relative to the motor specs.

Keep us posted.
 
Will do Doc. Looking forward to check pretty much anything that spins in my shop. :D

Ok, here is what I did. I can't really cut the belt to see where the fibers are but I know that they are usually closer to the outside part of the belt. Since my belt thickness is 16mm, I added 10mm to the ID to get a little closer to the Pitch Diameter. Figured that would get me close enough until I get a Tachometer. But even then, I only have 6 speeds so I will only be able to get close to the calculated drilling speeds needed.

It gives me these speeds: 422, 607, 1031, 2013, 3671, 5350 rpm

Only thing I am not sure is, is it better to go faster or slower than the recommended speed when you can not get the exact one with what you have available? For example, drilling in stainless with a 1/16th drillbit, I get 50fpm which translate into 3056rpm. Do I then use 2013 or 3671 rpm?
 
Patrice, I say that depends on your habbit of feed rate. If you have a light hand on the lever, then go slower. If you chuck the bit up on the flutes and really hang on it, then go faster.

Now on your calculations/estimations of pitch diameter, did you add 20mm to the ID,10 for each side? Also, if you have an old automotive belt sitting around somewhere, they are interchangeable with A series V-belts. Cut that up and check with it.


-Xander
 
As a general rule-of-thumb, I tend to assume that the effective contact between the belt and pulley is one-third of the belt thickness in from the outside. With molded-notch belts, I work on the full thickness, not the notches. I find it gives pretty good results on industrial belt drives where I can't read the original markings off the pulleys. Obviously, I'll use the marked pitch length wherever I can read it.

That seems like a very fast drill.

I've always worked on too slow being better than too fast. The most important thing is usually keeping the drill-bit cutting, rather than rubbing, in work-hardening materials. It needs a heavier hand than most folk expect and just seems easier to do at slower speeds. The cuttings, which often come off as one long razor-edged string from each drill lip, are also slower-moving, easier to see, and don't get centrifuged out as far at lower speeds, giving a slightly smaller and marginally less dangerous danger zone.
 
Thanks guys.
I have a light hand as you say but I guess I need to feed a little faster. It is just not instinctual and a little scary. Like for parting on the lathe which always scare the crap out of me. :(
Drillpress does seem a little fast. I added 10mm so 5mm for both sides. I messed up on belt thickness, it is 6mm so 2/3rd of that is 4. So I actually have added 8mm total. But in any case, the speed variation would not be that big.
I ordered the Tachometer and it should arrive in a few weeks. I'll post results when I get it.
 
Patrice Lemée;12414634 said:
Thanks guys.
I have a light hand as you say but I guess I need to feed a little faster. It is just not instinctual and a little scary. Like for parting on the lathe which always scare the crap out of me. :(
Drillpress does seem a little fast. I added 10mm so 5mm for both sides. I messed up on belt thickness, it is 6mm so 2/3rd of that is 4. So I actually have added 8mm total. But in any case, the speed variation would not be that big.
I ordered the Tachometer and it should arrive in a few weeks. I'll post results when I get it.
Click to expand...

You can convert that 2 pulley to a three.

I've got a 16 speed princess auto drill press and it's a Harbour Freight equivalent

They sell repair parts, you can get the middle pulley and bracket pretty cheaply

The pulley, the swinging bracket and 2 short belts should do it.

It drops into a hole in the casting, which you probably already have, or you make a simple bracket
 
Last edited:
The same principle applies

There is a thread on Pirate4x4.Com where he put grizzly parts on an old drill press


Pirate4x4.Com where he put grizzly parts on an old drill press


http://www.pirate4x4.com/forum/shop-tools/504982-restored-slowed-down-drill-press.html




You just need to match the belt width on the pulley

Maybe drill a hole, maybe it's there.

The new HF I have is the same casting as another that's at least 40 years old.

then you get a couple of belts.

If you use same step like a 1" difference between steps, no problem fitting a belt

The linked belts not really necessary in this thread.
 
I have three drill presses and two mills.
I haven't changed the drill press speeds since I first adjusted them. 10 years?
On the two mills I use two speeds. Fast and slow. ;)
 
If you know the RPM of the motor (3450?) could you just rotate the pulley by hand to see how many turns it takes to rotate the chuck once? Divide out the ratio and multiply by the motor RPM. If it takes 20 turns of the motor to rotate the chuck once, take 1/20 = 0.05, multiply 0.05*3450 = 172 RPM at the chuck. Mine has the original pulleys and a little sticker that shows the RPMs and recommended RPMs for different materials. But I have used this technique to figure out the ratio of a rear-end on a 4x4.

- James B
 
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