VFD for drill press?

TonyS · Jan 27, 2009

I'd like to convert my belt-driven woodworking drill press to variable speed using a VFD. The machine is a Powermatic 2000, a 20" model with speeds between 130 and 2770 rpm and a 1.5HP (advertised) motor; it sees light use. For the new motor I have an unused 1.5HP 220V 3PH 1740 rpm inverter-rated TEFC Leeson motor, bought for a song on ebay to test the output of an RPC I built awhile back.

After some reading on this forum I have drawn some tentative conclusions:

1) Running this motor up to around 3000 rpm through the VFD should be no problem, so a single pulley ratio could perhaps be used to provide a speed range of 100 to 3000 rpm.

2) Running below a few hundred rpm for too long may cause the motor to overheat. At what point this occurs is dependent on the type of VFD.

3) A second pulley ratio could be used to reduce the speed if/when necessary to avoid the overheating problem, but the point of this exercise would be to avoid using it.

Questions: Am I on track? How long before it's 'too long' and overheating becomes an issue at low rpm? Can I monitor it by putting a hand on the motor? Is it worth the extra money to get a better VFD (sensorless vector)? If so, what drive would suffice without breaking the piggy bank?

Thanks,
Tony

precisionworks · Jan 27, 2009

worth the extra money to get a better VFD (sensorless vector)?

In that size, there isn't much price penalty, and the performance difference (especially at slower speeds) is amazing.

Motor overheating, on any fan cooled motor that is run below nameplate rpm, is caused by the fan moving an inadequate amount of air over the motor housing. Short of a contact temperature probe, your best bet is a small, auxiliary fan that runs at full speed no matter what the motor speed is.

Teco, Hitachi, AC Tech, etc., all make fine drives at close to the same price.

DaveKamp · Jan 27, 2009

No problem!

Here's exactly how you do it:

http://www.practicalmachinist.com/vb/showthread.php?t=152934&highlight=variation

And here's a diagram- if you follow it, yours will work fine...

And here's a power-trowel I converted, too:

http://www.practicalmachinist.com/vb/showthread.php?t=172357&highlight=1305

As for overheating, don't worry about it- pull off the shroud, yank the mechanical fan, and mount a MUFFIN fan on the shroud, powered direct all the time. BTW- BOTH these applications- I'm running the motor WAY ABOVE 60hz. The drill... I'm running that Baldor motor to 390hz. The trowel, about 240hz... In both applications, I have the belt running in a reduction mode. The radial drill actually has a typical Bridgeport backgear setup, but I've never needed it... with the motor driving spindle at 3:1, I can bury and break a 3/4" tap at darned-near no speed.

PeteM · Jan 27, 2009

I suspect you'll be delighted with the conversion. That said, you'll want to remember how to change those belts.

I'd aim for the 60 hertz speed to be around 700 rpm or so. Doubling and halving that with your VFD will handle most holes you'd want to put in wood and smaller holes in metal.

I'd want to change pulleys for drilling larger holes in steel. Ditto to get up toward 3000 rpm.

Forrest Addy · Jan 27, 2009

You don't want to run a single ratio for all speeds unless you intended to work with smaller frills or in soft wood. 1 1/2 HP at full nameplare RPM reduces to 3/4 HP at 875 and so on. If you intens to tap or use hole saws on you drill press you are almost sure to stall the motor.

Keep the step pully or V/S. You'll wish you had them when you need heavier than usual torque.

Also don't sweat fans for low speed operation unless the application is a grain auger, conveyor, or some other load requiring a high duty cycle. Drill presses are definitely low duty cycle apparatus. A cooling fan might be indicated if you are drilling bir4d blocks in a production setting but general shop use a drill press loafs most of the time. When it is heavily loaded the load is of short duration. Ths produces a pulse of heat readily dissipated via convection. Things get iffy when the drill press is used in hot weather so installing a supplemental cooling fan is not an either or decision.

wippin' boy · Jan 27, 2009

I can bury and break a 3/4" tap at darned-near no speed.

no allways our plan dave

TonyS · Jan 28, 2009

Thank you one and all, gentlemen. I'll plan for three pulley ratios and size the middle one for the most common uses. Start with a cheap strip thermometer and go to a muffin fan if, as seems unlikely, there is ever an overheating problem.

Reading the responses it occurred to me I have no feel for how much power it takes to drill a hole. What does it take to run a 1 1/2" forstner bit through hard maple? Or a 1/2" twist bit through mild steel?

precisionworks · Jan 28, 2009

a 1/2" twist bit through mild steel?

Quite a few variables, Tony. If you start with a perfectly sharpened twist drill (equal lip length, correct rake & relief), it isn't too hard to power it with only a hand held drill motor ... which might develop 1/2 hp on a good day. The better drill motors, like a Milwaukee Magnum, use planetary gear drive to reduce motor rpm, which increases available torque, to the extent that if the bit hangs up in the part the user may suffer a twisted wrist or broken arm :eek:

Since a 1/2" hole can be made with a low power motor, why go larger? A bigger motor has greater torque, will be harder to stall, can feed the drill bit more quickly through the part, will last longer, etc.

For VFD use, a larger motor is a real advantage. All motors develop full hp at full rpm. Adjust the rpm to half, and horsepower is half, etc. The larger motor allows useful power at lower rpm settings.

jim rozen · Jan 28, 2009

If one were to check in the SB forum the photos of mine, and the moderators, drill
presses will show up, where we both put VFDs on them.

Mine has a half hp motor and it will drill a hole in steel very easily.

I did not put an inverter duty motor on it and it seems to work just fine.
There is a muffin fan on the motor that comes on when the VFD gets
energized. I've never seen the motor get even warm but then it is pretty
intermittent use in my shop.

This is a pretty big photo so I won't put it up but here's the link:

http://www.metalworking.com/dropbox/SB3.jpg

What you don't see is the small box with a speed control pot that is mounted
down under the stand shelf. The VFD and motor are both made by baldor,
and the VFD is run off of 120 volts. Would be handy in a home shop. The
irony of course here is the buss duct behind the machine has factory three
phase in it!

Adapting a VFD to a drill press is an amazingly handy and convenient setup.
I am just waiting right now to get an inexpensive similar setup for my
walker turner at home.

Jim

TonyS · Jan 28, 2009

>If one were to check in the SB forum the photos of mine, and the moderators, drill presses will show up, where we both put VFDs on them.<

I'm new around here, what's the SB forum?

CalG · Jan 28, 2009

Do "typical VFD's adjust voltage with frequency to maintain constant torque? I thought that was the plan.

Regards

CalG

J Lauffer · Jan 28, 2009

Non-vector type VFDs will maintain a fixed V/Hz ratio on the output. For example, 240V at 60Hz would be a V/Hz ratio of 4.0. At half speed, the voltage would be 120V and the frequency would be 30Hz...still 4.0 V/Hz. This scheme provides good torque at higher speeds, but not at low speeds. They typically have some sort of "boost" adjustment that will increase the voltage at low speeds in order to increase the V/Hz ratio, thereby increasing the starting torque somewhat.

Vector type VFDs constantly vary the V/Hz ratio as necessary to always generate maximum torque, which is why they can generate much better torque at low speeds.

TonyS · Jan 29, 2009

What would be some good vector type VFD choices for the 1.5HP motor on my drill press? (Described in opening post)

jim rozen · Jan 29, 2009

SB = south bend forum.

The moderator there has also installed a VFD on her 14" SB drill press.

You can use the search function to find the photos there.

Jim

TonyS · Jan 30, 2009

Nice work, her and you both.

DaveKamp · Jan 30, 2009

The one I showed...

Hi Tony!

The drive I show in my post above (and the accompanying drawing) is a 'sensorless vector' drive, and it'd work perfect for a 1.5hp motor. Watch the E-auctions for type AA08A or AA12A, and wire it up per my diagram, and it'll work wonderfully.

There are others, but I haven't worked WITH them, so can't tell you for certain which ones, or how they wire up.

TonyS · Jan 30, 2009

Thanks, Dave. I read the thread on your project with great interest the other night, BTW.

TonyS · Feb 3, 2009

I will need a new drive pulley because the 3ph motor has a 7/8" shaft, somewhat larger than the shaft on the drill press's existing 1ph motor. Unfortunately, the shaft on the new motor is shorter. As a result, the new pulley, if it were to be a common multi-groove item, would only go 3/4" at most onto the new motor shaft. Is that sufficient for a three-groove pulley? If not, what possible solutions are there for someone like me who works in wood, not metal?

DaveKamp · Feb 3, 2009

My drill...

Hi Tony!

My radial drill was hexed by something similar; The motor sheave was totally missing... apparently still on the motor... which was not with the J-head when I obtained it.

I fitted the machine with toothed-belt sheaves on both the drive and driven end. This allowed more power transfer capacity (no slip) with lower belt tension (smoother running) and less wrap (greater ratio differential).

As an alternative, you could fit the motor with an ordinary single sheave, set the motor sheave's elevation to suit whichever spindle sheave you desired, and just run the VFD to control your speed. You'll find that, once the VFD is set up, you won't need to change the belt position.

TonyS · Feb 3, 2009

Perhaps a picture will explain the problem better than I can. In the attachment, note the drive pulley in the back. Where can I get pulleys like that, with the extended hub on bottom that reaches down to where the motor shaft is?

VFD for drill press?

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