Gear motor for drill press

[MillWeld]

I need need to drill 3" holes in 3/16" a steel plate with a hole saw in my 1/2HP Jet drill press but the lowest speed is too fast - the saw just chatters and shakes the whole drill press. I think if I could go at a lower speed I would be more successful so I am considering this AC gear motor from the Surplus Center: Surplus Center - 743 RPM 115 VAC INLINE GEARMOTOR. What do you think about this approach?
I change the speed my re-positioning a belt on a 5 sheave pulley for rpms of 2720, 1578, 887 and 531 and I rarely ever use the fastest speed and more frequently need lower speeds anyway for 3/4" and 1/2" holes. This gear motor would give me a lowest rpm of 219 - is that still too fast? I have used a cutting torch for 3" holes before but it is so messy with me doing it I had rather drill it.

 

[Shield Arc]

I know what you mean about being too fast at times. My mil has been set on the lowest speed since the day I bought it, and when doing larges holes even with annular cutters I wish it was slower.
I made this rotating table, and circle attachment for my torch years ago, you can cut some fairly accurate holes with this setup. And if you drill a hole on the opposite side of the circle you want, you don't have to worry about blowing a hole to get started.

 

[weldermike]

May sound crazy, and I admit im rough on tools, but with the smaller non gear driven drill presses when this problem occurs to me, I will grab two of the feed levers from the side of the machine and use a lot of slow hard pressure, and let the friction from cutting slow the machine down to the desired speed. Youll hear it the instint you have the perfect pressure. Its just a little rough on your belts.

 

[BukitCase]

My press is a 16 speed, goes down to 240 rpm IIRC - that's where it usually stays, for the same reasons mentioned. I've had decent luck with large hole saws at that speed; things I usually do to cheat a bit -

Drill a 1/4" pilot hole first, then use drill rod in place of the hole saw's pilot bit.

As mentioned, use feed pressure to (slightly) slow down rpm.

Keep an air hose blowing thru the "cleanout" holes on the larger hole saws CONTINUOUSLY while cutting to help keep the saw cool. Still messy, but it's a "dry" mess. I get away with this cause my compressor is an industrial DevAir with a 5 horse Baldor and 80 gallon tank, rated for 24/7/365 duty.

Also need new belts on the press, but mostly cause it's 25 years old :=) Steve

 

[vic4news]

If you want to go really slow you could add a jack shaft with another pulley and belt.

 

[BukitCase]

Just checked your link to the gear motor - saw it's a METRIC shaft size, 16mm is almost exactly .050" over a 5/8" shaft. If you go this route, you could probably get a machinist to bore your motor pulley to an exact fit pretty cheaply.

In fact, I may order one of those for my OWN machine since I almost never use the higher speeds... Steve

Another possible problem with THAT motor - it turns CW, I know mine turns CCW (mounted shaft up, CCW motor = CW chuck rotation)

 

[MillWeld]

Another possible problem with THAT motor - it turns CW, I know mine turns CCW (mounted shaft up, CCW motor = CW chuck rotation)

:confused3: Why is that a problem? My motor turns CW (as viewed facing the shaft) and the chuck turns CCW (as viewed looking up to it from below) and drills are fluted accordingly to take advantage of that, i.e., the drills turn the right direction to make holes. Did i misunderstand something?

 

[Shield Arc]

Can't you get a variable voltage unit, that really slows machinery down? Maybe variable voltage isn't the correct term:confused3:. Seem as I've seen where people use something like that on lathes.

 

[BukitCase]

Millweld, you're right - ya caught me "overthinking" again - this time that's probably a GOOD thing, since I didn't find any OTHER motors that size that were CCW - otherwise, I might have screwed BOTH of us. Sorry, ignore the old fart in the corner... Steve

 

[MillWeld]

Millweld, you're right - ya caught me "overthinking" again - this time that's probably a GOOD thing, since I didn't find any OTHER motors that size that were CCW - otherwise, I might have screwed BOTH of us. Sorry, ignore the old fart in the corner... Steve

Been there myself - too many times. Anyway, I'm glad you thought it was a good motor for a drill press. Soon as I figure out the relay I will buy it. Thanks.

 

[MillWeld]

Can't you get a variable voltage unit, that really slows machinery down? Maybe variable voltage isn't the correct term:confused3:. Seem as I've seen where people use something like that on lathes.

I think it usually requires a variable speed motor and a controller. A better solution but too much $.

 

[Shield Arc]

Variable Frequency Drive is what I was thinking about.

Variable Frequency Drive Inverter VFD 7 5KW 380V 19A YA2 | eBay

 

[BukitCase]

See their instructions here

http://www.surpluscenter.com/Instruct/I5-1647.pdf

On the starting relay - the motor appears to have a centrifugal switch (as most do) that connects L1 to the RED wire til the motor is up to speed - This lets the 120 volts energise the starting relay, pulling in the relay contacts (above the relay coil in the drawing) -

That puts both capacitors in parallel, increasing the total capacitance for starting.

When the motor comes up to speed, the centrifugal switch in the motor drops out, taking the START capacitor out of the circuit leaving the RUN capacitor.

They claim that motor draws nearly 10 amps, but uses only 440 watts - only way I see that happening is if the amperage is STARTING amps. Otherwise, 10 amps at 120 volts would be 1200 watts. (volts X amps)

Based on that, I think that a 10 amp, 120 volt AC relay would work - one I've used thousands of times (retired instrument/electrician) is the Potter/Brumfield KRP11-AN - it has TWO 10-amp sets of contacts, so if I were doing this I would wire BOTH sets of contacts in parallel. That way you would have some reserve capacity on the contacts, and they should last a LONG time.

BTW, if this motor REALLY only draws 440 watts, it would be rated at a maximum of 440/746, or .59 horsepower - still over half horse, and the slower speed should make your press act more like it had a 3/4 horse motor.

Still seeing no prob with this, as long as you have access to a way to (1) bore out your existing motor step pulley, and (2) fab a bracket that would bolt to the end plate of the new motor and match up to your existing motor mount plate (the one you move back and forth with the tension lever when you change speeds) - I'm thinking this would basically be a large "L" bracket, with a hole for the motor shaft, holes to match the motor end plate, and more holes in the other leg of the "L" to line up with the tension adjuster carriage.

Whew - as far as I can tell, I left out any more "brain farts" - HTH... Steve

 

[MillWeld]

Thanks, Steve, if it has a centrifugal then I'm home free. That was the missing link in my understanding. Thanks for your reply - it was a great help.
Bob

 

[bigdeano]

I don't see that the motor has an internal switch. Starting relays are used on refrigeration compressors and other motors that don't have centrifigul switches. Getting the right one might take some research. I've bought them from Grainger before, but I don't remember how to find the right one.

 

[npalen]

AC Drives Overview
The VFD's (VariableFrequencyDrive) have come down in price as I see the single phase GS1 model shown here starts at $99 but only go up to 1/2 HP on 120 volt SINGLE phase. The VFD's are normally used with 3 phase motors but use solid state electronics to convert 220 volt single phase to 3 phase which drives the motor to give variable speed and reversing.
My only concern with slowing down your drill press with the GS1 drive is whether there will be enough torque left at lower speeds to run the 3" holesaw. You might visit with the folks at AutomationDirect to get their opinion.

 

[BukitCase]

Went on Bodine's site looking for a motor that matches this one - no luck so far. Did find a table of torque values on AC motors, and 44 inch pounds is typical for a 1/2 horse. If I get time tomorrow I'll check further - then at least we'll know if the motor has an internal switch or not. If not, you can get a "generic" starting relay on amazon for about $15, but I've not found concrete hookup specs on that yet either.

It would sure help if Surplus Center would print actual mfr #'s, I've been thru this a few times on hydraulic valves too... Steve

 

[mjncad]

This gear motor would give me a lowest rpm of 219 - is that still too fast?

You can do it at that RPM; but you'll still have to baby the saw to get decent cutting and acceptable chatter. Use oil to cool the saw while cutting. I've done 3" or 3-1/2" diameter holes in 1/4" steel on my 17" Jet drill press at 230RPM; but it's a slow noisy slog.

 

[MillWeld]

It would sure help if Surplus Center would print actual mfr #'s, I've been thru this a few times on hydraulic valves too... Steve

I have written SC asking if the motor has a cent. switch. I'll have to wait until next week for a reply but I have found them to be very responsive. I also wrote Bodine.

Whether or not the motor has a centrifugal switch, according to the instructions, it looks straightforward to wire in a relay. The red from the motor and the hot from the line go to the relay input. The output goes to the caps. as shown. I guess there is still the question if it is a time delay relay.
Bob

 

[jwmorris]

Get a used HandyAuto torch. Cost about the same as a new gear motor and will cut perfect holes a lot faster than a hole saw.