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I was honestly surprised to see that most modern drill presses still use belts and pulleys (and the manual changing of them) to accomplish variable speeds. Does this design offer certain benefits that other less cumbersome methods don't? Or have drill press manufacturers just been slow to adopt newer technologies that could address this?

With all the LEDs and lasers that seem to be appearing on newer models, it strikes me as silly that they still sport a stack of pulleys and belts for part of its core function.

VFD explained at wikipedia.

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Modern drill presses for the home market compete largely on price and on some other features like chuck size. Variable speed machines - I have a 1200 US$ lathe with that feature - would you rather pay double for convenience?

I got the lathe for production work 10 years ago. Otherwise it would have made little sense financially.

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    The cost explanation does seem to be the most likely reason. Still, it strikes me that, at scale, the cost wouldn't be as significant as the current cost of retrofitting a multi-phase motor/vfd/etc. Unprotected (by patent/copyright) designs exist for variable speeds, and ultimately it seems the cost of additional materials plus a marginal fixed cost of implementing a design would boil down to maybe an extra $20 per unit depending on the size of the drill. It just surprises me that for every $300 drill press, there isn't a $320 or $350 model that offers the same + variable speed. – Wilco Jun 22 '15 at 17:38
  • @Wilco Can you show examples of products in the market with VFD and non VFD options where the price difference is only $20? I think you may be underestimating the cost difference, but perhaps I'm mistaken, and a few examples would help illustrate your point. – Adam Davis Dec 14 '15 at 15:33
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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.

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Just a guess, but most items with a variable speed have the power belt vertical. All drill presses have the belt horizontal. Maybe that is part of the cost of the redesign that makes it unpalatable.

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Cost is indeed the main reason. Variable-speed drill presses do exist if you're willing to pay more. Remember, price is set by percieved utility and market forces, not by manufacturing cost.

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Two reasons, cost of course is the main factor. The other is speed vs. torque - VFD drives may not supply the same torque/speed curves as the mechanical pulley ratio.

  • why are you yelling? – Steven Dec 4 '15 at 18:33
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That would just be crazy expensive. Also, the VFD drive performance in terms of torque will be unusable without a gearing system of some kind. Even if you installed a VFD drive you would still need a clutch, which would be what? A belt? So, if you are using a belt anyway as a clutch, why even use a VFD, why not just use pulleys? Of course, you could install a mechanical clutch, even more big bucks.

There are some drill presses that use a VFD in conjunction with a pulley system which has the benefits of giving a much greater range of speed controls. They cost about $2000.

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