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.