Useful info on drills

RVA

RVA

Ambassador
I was researching whther to buy a drill press with a belt ot a variable speed motor, and I came across this seeming acurate explanation, which had a lot of useful info
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The reason is that while VFD is modern and sounds cool, it is a really poor substitute (which is true for a lot of modern electronic gizmos).

Like all machines, an electro motor has an ideal range of operational speed. Electro motors are admitteldy much closer to "perfect" machines than for example combustion engines (which cannot run slower than about 800 RPM at all, and only start to deliver serious torque at about 3,000 RPM), but they still aren't perfect. There is still a "right" and a "wrong" way to use them.

For drilling, you will usually want net speeds from as low as 100 (possibly 50) RPM up to about 3,000 (possibly 4,000) RPM, and you want this speed as steady as possible, with no vibrations, sudden decelerations, locking or other undesirable artefacts.

While torque in an electro motor very favourably starts -- even at very low speeds -- with an almost perfectly straight, high plateau up to about 4000 RPM (after which it slowly decreases to about 50% at 8,000 RPM), things are not nearly as ideal when it comes to current, power, and power efficiency. Electro motors have their peak power plateau between approximately 4,000 and 12,000 RPM. Before that, power output (unsurprisingly, being the product of torque and rotational speed) goes up linearly with rotational speed. Power input, on the other hand, is exceedingly high on very slow rotating motors and even goes down as output goes up.

Efficiency increases with rotational speed following a "kind of" negative exponential saturation curve reaching a plateau of around 70-95% depending on the quality of the motor (actually the curve goes down again at high speeds, but for "reasonable" speeds we may assume that it looks like a saturation curve). A motor running at 20% of its maximum speed is usually less than half as efficient as a motor running at 60% of its maximum speed.

That suggests that a motor should preferrably run faster (indeed, much faster) than needed -- ideally near the end of its torque plateau -- and then have the speed reduced mechanically to whatever is desired. It may lose a small amount of torque if it runs too fast beyond the max-torque plateau (gaining efficiency in return), that torque will however be regained in excess from the speed reduction, and it will be much more power efficient. Which also means less heat and less wear on the motor.
The starting current, which may be forbiddingly high on a powerful motor, is significantly reduced, and rotational speed is a lot more constant in presence of any environmental effects that might occur (inhomogeneous material, bit locking, power grid fluctuations, whatever).

A speed-reduced motor is therefore win-win in every respect, compared to a slower turning motor.

Now, why belts, and no gear? Gear makes a lot more noise, and it's more expensive, too. Belt-driven drill presses are silent enough to be used without hearing protection (I rarely ever recommend not using hearing protection with any kind of machine, but I can lead a normal conversation with my drill press running without being disturbed in any way).

Add to that the fact that variable speed electronics are delicate circuits which may (will) eventually fail whereas a mechanical belt has hardly a way of failing.
Before someone yells out: "Sure, a belts can rupture!", as an anecdote from my life, I got my drill press from a bankrupt tool manufacturing company 24 years ago (the drill was used for making tools, they didn't make drill presses). It had been in use for around 20 years at that time already, but apart from obvious usage marks it was in good shape, and it's still working with the same belt, same everything today.
In the very worst case, a ruptured belt is easily replaced, too, whereas broken VFD logic means "trashcan" to anyone who doesn't have a degree in electric engineering.

Belts provide the desired mechanics as efficiently and silently as possible, they cost next to nothing, and they practically last forever.
 
gasket said:
It mystifies me that anybody would consider anything other than belt and pulleys for a workshop pedestal drill.
Click to expand...
Actually, I am! Please tell me why. A variable speed is only $ 80 more. Why tinker with belts with 5 speeds when you can have a dial adjustment for speeds between 560 and 3100 rpm? I would greatly appreciate your advice.

Here are the 2 options I am considering

Variable speed

https://www.amazon.com/dp/B00HQONFW...olid=2WXVMBD3ZS1LS&psc=0&ref_=lv_ov_lig_dp_it

Belted

https://www.amazon.com/dp/B005UKGLA...olid=2WXVMBD3ZS1LS&psc=0&ref_=lv_ov_lig_dp_it
cleardot.gif
 
Must you physically ADJUST (I know how you love adjusting things Ray) the belts for the variable speedS?

seems the dial a knob non belted is a more practical option --- for the home hobbyist or part time carpenter....
 
eSGEe said:
Must you physically ADJUST (I know how you love adjusting things Ray) the belts for the variable speedS?

seems the dial a knob non belted is a more practical option --- for the home hobbyist or part time carpenter....
Click to expand...
Yes. You must unplug the machine and physically relocate the belt to a new track

Skil-Drill-Press-Variable-Speed-Belt-System.jpg
 
Refer back again to your "seeming accurate explanation". haaa haaa
OK, not interested in a drawn out debate about $120 machine tools but my idea on the subject is ...
Belts are simple, reliable, inexpensive and work. Usually home workshops use drills within such a small diameter range speed changing isn't done very often. I can compensate for slightly too fast or slightly too slow by feeling and adjusting the pressure on the feed lever. It's really a matter of "KISS" = Keep It Simple Stupid.
If I want to change the speed because the job material is seriously different to the typical mild steel work I do or the drill diameter is very small or large, so what, lift the cover and roll the belt onto a different pulley combination.
 
gasket said:
Refer back again to your "seeming accurate explanation". haaa haaa
Click to expand...
I always qualify my input when I personally know so little on the topic.

Your point about simplicity certainly makes sense. So, if you were going to set the belt for a speed that will likely be good for most purposes, at which speed would you set it?
 
Its a shame that the belt ratio can't change automatically with the load.
Like a snowmobile or minibike torque converter.


But belt driven drill presses are all I've ever used.
Ratio changes are a simple no tools needed operation. Just derail the belt and select another ratio.
The beauty of this method is the motor runs at a constant speed, drill speed and torque is determined by the ratio selected.
Small drive pulley with large driven pulley is low speed , high torque operation.
Large drive pulley with small driven pulley is high speed low torque operation.
 
Hackmaster said:
Its a shame that the belt ratio can't change automatically with the load.
Like a snowmobile or minibike torque converter.


But belt driven drill presses are all I've ever used.
Ratio changes are a simple no tools needed operation. Just derail the belt and select another ratio.
The beauty of this method is the motor runs at a constant speed, drill speed and torque is determined by the ratio selected.
Small drive pulley with large driven pulley is low speed , high torque operation.
Large drive pulley with small driven pulley is high speed low torque operation.
Click to expand...
Thanks Hack. How often do you actually need to change the belt/speed? Have you found a speed that works most of the time?
 
RVA said:
if you were going to set the belt for a speed that will likely be good for most purposes, at which speed would you set it?
Click to expand...

Way back when I was an apprentice all of this stuff was on the tip of my tongue, it had to be to pass exams but these days I just look at the speed and job and know that it's within an acceptable range or not.
Mr. Google has these charts available.


Drill-Speeds.gif
 
Guys Ray likes to adjust stuff--- a LOT-- he will be opening and closing that lid so much the hinges will drop off!!!!! :)

rumor has it he buys pickup set screws in weight bulk (like 25 lb boxes) because he wears them out adjusting things up and down and up and down

sorry its Friday eve and Im in a mood :)
 
RVA said:
Thanks Hack. How often do you actually need to change the belt/speed? Have you found a speed that works most of the time?
Click to expand...
The speed / torque is determined by the task at hand.
I supposed a middle ratio would be an all around handy speed for most projects.
The ability to adjust this up or down is golden.
Too high of speed ruins bits due to heat. I always use a lubricant when drilling any steel.
When using paddle bits or hole saws, ones first inclination is to bear down full speed ahead, just to get the job done.
But going slowly will be kinder to the tools and the work at hand.

FYI, I don't have a proper drill press.
I just use a hand drill chucked up in one of those drill stand thingies.

The drawback is one speed only, and the paddle bits have just about killed my drill motor, due to the torque needed for use.
 
eSGEe said:
Guys Ray likes to adjust stuff--- a LOT-- he will be opening and closing that lid so much the hinges will drop off!!!!! :)

rumor has it he buys pickup set screws in weight bulk (like 25 lb boxes) because he wears them out adjusting things up and down and up and down

sorry its Friday eve and Im in a mood :)
Click to expand...
You ain't wrong. I like options! I have "adjusted" almost every guitar I touched in the last month. I have been known to start a fret level at 11pm and continue until it is finished
 
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Hackmaster said:
The speed / torque is determined by the task at hand.
I supposed a middle ratio would be an all around handy speed for most projects.
The ability to adjust this up or down is golden.
Too high of speed ruins bits due to heat. I always use a lubricant when drilling any steel.
When using paddle bits or hole saws, ones first inclination is to bear down full speed ahead, just to get the job done.
But going slowly will be kinder to the tools and the work at hand.

FYI, I don't have a proper drill press.
I just use a hand drill chucked up in one of those drill stand thingies.

The drawback is one speed only, and the paddle bits have just about killed my drill motor, due to the torque needed for use.
Click to expand...
What lubricant do you use for metal drilling?
 
RVA said:
What lubricant do you use for metal drilling?
Click to expand...
Any thing handy. Motor oil in a squirt can, WD40 or PB Blaster.
The lube cools the work as well as lubricates.
They also make commercial cutting fluids for sawing & drilling, probably available at Lowe's or Home Depot.
 
You know, Mods, we should have a section for tools.
Most of us use all kinds of tools daily.
It could be an add on to the Garage. Like Fender - Squier, Gibbo - Epi, and Other Electric Guitars is a sub forum for Twang Terrace.
 
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