More torque

If the mill had been operating for a few hours without problem and then started to trip, as you wrote heat build up in the motor is the likely cause. Hobby machines are not usually rated for continuous duty.
 
The overload could also be faulty and tripping prematurely (I have seen this happen with MCBs operating under there stated rating).
 
There's one other cause or two. The drill bit is poor quality and breaking down causing the material to work harden , or the material itself is hard or case hardened . I've seen guys weld drill bits in holes trying to push thru. If the drill bits not cutting chips it's not cutting at all. The more pressure will not make it cut. Most run drills to fast for the material being cut. Drill presses are almost always way to fast even at the lowest speed. My guess his bit wasn't sharp or it is cheap China junk. Just my thoughts.
 
Here's a shot of my little stock Grizzly minimill drilling a 1" dia. hole in two cast iron weights. I started with 5/8" pilot hole.
Couldn't believe how easy it was. The mill just purred away. The drill was sharp. I've never experienced an overload kickout off the power supply.
This was a used machine to start with, otherwise it is stock, no new motors or controllers.
SHARP TOOLS!
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I have a Real Bull mini-mill that I converted to belt drive (which had the unfortunate, undesired side-effect of actually LOWERING the torque), and I have no trouble drilling deep 1/4 inch holes in mild steel. I keep my bits sharp (at the risk of starting a debate, thank you, Drill Doctor!), and clear the chips from the hole every so often. I use cutting fluid while drilling (I use Re-Li-On for this). I have cut 1/2 inch holes, though I definitely step up to this size, probably drilling 3/8 inch before drilling the 1/2 inch. I think there have been a number of excellent suggestions above and won't repeat them here. The one that I will add is that a boring head would be a useful way to make larger holes with minimum machine load, though the increased number of passes needed means it will take longer. Good luck, and let us know how you make out!
 
I have a small machine similar to that. Originally for drilling the edge of thin plexiglas but now as a general purpose drill press. It came with a 1/2" chuck and has been used for a 7/16" drill, in mild steel. I have had trouble with the speed regulation circuit board. A component was out of tolerance. I repaired it myself, that's my real job.

It sounds here that if your drill is sharp, even moderately dull, it should at least squeal if the metal is too hard. If that hard, I wouldn't try a HSS tap in it. I know what happens there. That has arisen also, but years ago. I didn't draw a temper enough. Know better now, but when you're new...

Maybe it'll help. Those circuits are Chinese and if the magic smoke ever gets out, it will drive you nuts trying to figure out how to get it back in. Good luck with it... Bill (Old Man) Hudson
 
Shawn,

I finally got back to testing my little 1/4hp drill press. This little drill press usually lives at my electronics bench in the basement, but I took it to the shop to help contain the swarf.

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I used a decent (not perfect) 1/4" drill bit at 1100rpm. No cutting fluid. No centre hole. Drilling thru a 1" piece of mild steel.
The camera (phone) was propped up on a cardboard box on the bench between me and the drill press, so please forgive the extra movement....

Attached is a video. As you can see chip ejection was good, but I did manage to stall the motor(twice) when the bit broke-thru of the backside.

Just meant as a comparison to your results.

-brino

EDIT: I guess the video didn't make the first cut....I thought I had uploaded it, so I must not have "inserted" it....or something......let's try again......Nope, maybe it's too big!

Oh well, nothing earth shattering anyway. I drilled a 1/4" hole thru a piece of 1" steel on a small crappy and loud drill press.
 
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To start with HP = torque x RPM. or HP/RPM=torque. Bottom line halve the speed =double the torque. Do not use electronic speed control to lower speed it will also lower torque, change some belts or gears. gear boxes are known as torque multipliers for this reason.

Do not be afraid to run well below recommended cutting speed with HSS. HSS is very forgiving whereas carbide is not.

Check your motor is actually running at it's rated power.

Be wary of putting a more powerful motor on your machine. certainly not more than 1&1/2 times original power, should be a maximum. You might break something

Ensure your tools are sharp, really sharp. If you are not an expert , I mean "toolmaker expert" at sharpening drills , get yourself a drill doctor. HSS will always require less torque than carbides for the same job.

Use pilot holes when drilling. especially in hard materials. consider boring larger holes, on your small machine probably anything over 3/8 inch, certainly over 1/2 inch in mild steel
 
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