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Drill presses?

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Hazmatt_(The Underdog)

Tue Aug 12 2008, 06:23PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Mine is capacitor start so a variac won't work. You can try it, but what you get is the press tries to continually start in bursts and of course you don't get any horsepower like that. The Ryobi might be small enough that you could phase control it, but you'll have to play around with its motor to find out.

Steve Ward

Tue Aug 12 2008, 06:47PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Yeah, the better way to get lower speeds from these things is with a real VFD controller. Im not sure if regular induction motors are even supposed to run from a VFD, but im fairly sure it will work from my understanding of how they work.

The problem with just varying the AC voltage is that its merely increasing the slip of the motor (if it even manages to run at a lower speed), and this implies that the efficiency is going way down (as Hazmatt said, the torque will be crappy). There is a reason these motors are all close, but just slightly less than synchronous speed, its because the slip is usually fairly small (maybe .05, or 5%) so they are running efficiently. The torque generally goes up as slip increases (typical scenario when the motor is under load) but at some point, the torque begins to fall off toward zero (stalled motor) and you must remove the load to start it again.

Using a VFD just changes the 50/60hz going into the motor to something more or less, so the slip can still be fairly low, but you get to change the RPM. IVe been wanting to build a VFD for my machine tools for awhile now, havent had the time though.

Steve Conner

Wed Aug 13 2008, 09:44AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I always just used a handheld Dremel for drilling PCBs. The very small carbide bits snap easily, so I just used one big enough to survive careful handheld use, and lived with all my PCB holes being a little oversize.

If it was enough work to need a PCB drill press, I'd just send the board out to one of these Chinese contractors.

I wouldn't ever think of trying to use PCB-sized bits in one of these cheap drill presses, or use one for milling. I have one of the $60 Chinese specials, and it has enough play in the quill that it'll actually drill triangular holes in sheet metal if I'm not careful

aonomus

Fri Aug 15 2008, 04:09AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

I was just at a local shop today and found a set of HSS bits in this range (at $9.99 surprisingly):

(In inches)

0.0135
0.0145
0.016
0.018
0.020
0.021
0.0225
0.0 24
0.025
0.026
0.028
0.0292
0.031
0.032
0.033
0.03 5
0.036
0.037
0.038
0.039

Now I just need to order the bigger ones from digikey... :D

quicksilver

Fri Aug 15 2008, 03:42PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

There may be a better way to get differing speeds for an inexpensive drill press.....swap out two pulleys to the ratio you need. Pulleys are available at local hardware stores that sell them for "Swamp Coolers". IF you could make them fit you could adjust the ratio to a level so low (or high) that for that one setup you'd have the speed with no damage what so ever. More minute adjustment can be accomplished by the belt thickness (height). Here you're talking about $15 to alter speed. But if those pulleys don't fit your spindle other inexpensive sources may have what you need. However, in inexpensive systems they often use very standardized part sizes.

Most anything that runs from a belt could be pressed into service. You would just need to pull off both the drive pulley and the motor pulley so the belt fits(get the right belt; it's only a few dollars) but I know this can be done for a very low cost.

This is one of the best things about an inexpensive item. They often have simple and common spindles which will accommodate the pulley of choice. It would take some time to swap them back & forth, so I leave the cover off the top- but it worked on mine.

aonomus

Fri Aug 15 2008, 04:31PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

Varying drill press speed was a bit OT since my main goal was low arbor wobble for PCB drilling, lowering drill press speed + some kind of coilform = fast(ish) coil winding jig.

Many 'fixed' speed drill presses are just a set of stepped pulleys which allow you to swap speeds, but only when the drill press is not running. Some have a 'transmission' of sorts which lets you infinitely vary the speed.

quicksilver

Sat Aug 16 2008, 04:23PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

To really consider winding a coil with it you would have to drop that rotation to about 50 rpm and lower. The way they are setup as a standard I believe that they are at their lowest (as is) at perhaps 500 rpm and that's just too fast.

ragnar

Sun Aug 17 2008, 12:22AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Winding thinner coils is not impossible at 500rpm with a proper setup; if you're using thin wire and there's no chance of finger entrapment, you can hand-feed (through a cotton handkerchief or similar around your fingers). The trick is to focus carefully, holding the wire close to your body and wind a long former.

After winding, lacquer the former as one piece, and then saw it into several smaller secondaries as needed. I wound all my 0.15mm wire coils this way and haven't had to repeat it yet. This seemed appropriate for small runs of coils with secondaries < 3" diameter.

quicksilver

Mon Aug 18 2008, 04:27PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

Pretty darn impressive! For 500 rpm: my hat's off to you. I've tried with careful setup at that speed and there seems no room for error: so I think you've "got the touch"!

Out of curiosity, what type of foot control (if any) or mechanism to you use so as to "time" the end of the coil? 500 RPM is not slow by any means! Bravo!

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