Drill press power?

[jdm]

I have got a bench drill press for cheap and it works well enough.

Today I was able to fix the annoying noise it was making, caused by the sliding square sections of the spindles having too much play. Used a strip shaped shim cut from an oil can, and now is totally silent.

What I'm not sure is the good working of the motor. I can drill 13mm in one pass on free machining steel, but with other less friendly materials it stalls easily. The label on the motor says 250W, and it has a fixed speed of 1450 rpm. I haven't took it apart but I believe it's of the brushless type. I found that (wearing a glove) I can stop the motor pulley without effort. Is that normal?

 

[spectre6000]

<= Wood/metal worker/drill press owner/restorer.

For a the little cheap models (like Harbor Freight and equivalent), there really isn't much torque. They're made for hobbyists to make small holes in soft wood about three times a year, and last about five years. As long as ~90% of them work out of the box (hence the generous return policies), they call it a win. The nicer bench top models also don't make much torque, but they're more precise (you won't be shimming shafts) and last longer. My 1939 floor standing Delta has a 1/3hp or 1/2hp motor (I forget which motor ended up on it), and due to the way the belts are tensioned, it'd probably stall if I was really aggressive in something thick and hard, but that's due to a design issue that was rectified 70 years ago, and there are ways around it...

You should probably be able to pull the motor and check it out. I'd be looking at the belt, pulleys, and motor shaft first. I'm not really sure what a brushless DC motor looks like mid-failure though... I'm wracking my brain, and I'm not sure I actually own a single tool with a brushless DC motor, and I'm pretty certain I haven't had one fail on me.

[HectorLooi]

Could we have a picture of the drill press?

You got to be pretty strong to stop a 250W motor at full speed. ( that's 1/3 hp )

[JohnR725]

8 hours ago, jdm said:

I found that (wearing a glove) I can stop the motor pulley without effort. Is that normal?

It would be really nice to have a picture to grasp what sort of size were looking at. I was just thinking about my drill press I like my fingers I most definitely would not try to hold the pulley. Although I might be able to hold the drill chuck but I really don't want to think about that. I know that if I was drilling something and carelessly or stupidly didn't use a clamp to attach it to the table and something went spinning it was always in my best interest to keep my fingers away. A lot of this depends upon the size of the drill press.

[jdm]

9 hours ago, spectre6000 said:

I'm not really sure what a brushless DC motor looks like mid-failure though..

It's an AC induction (brushless) motor, 18 x 18cm. As I said I can prevent it from start, or even stopping at its pulley using minimal (for anyone) force and without any risk.

[HectorLooi]

Ok. I see. It's an AC brushless motor. Not DC.

TThis is probably a single phase AC induction motor with a run capacitor. It sounds like the run capacitor is failing.

Look for a cylindrical object. It could be an aluminum can or plastic cylinder. If you can remove the capacitor, look at the rating and capacitance. If you have a multimeter with a capacitance measuring capability, measure it to see if the value is still within specs.

A failing capacitor can cause an AC induction motor to seize or hum. 

[jdm]

1 hour ago, HectorLooi said:

This is probably a single phase AC induction motor with a run capacitor. It sounds like the run capacitor is failing.

Good point, thanks. I had neglected this basic test on the assumption it was a start capacitor, while the motor starts and runs. Cap is rated 6 μF but it measures zero, and 48 Ω resistance. Without it, motor does not start or run. Since this is the first time I use my new DMM for that I verified the instrument measuring another small one which reads correctly.

Edited May 3, 2020 by jdm

[nickelsilver]

It does sound like Hector was right. But also,  what rpm is the drill spinning? 1450 would be a bit fast but still OK for free machining steel with a 13mm drill, you'd want to go 500 or so for stainless. For that size motor at any rate 13mm would be what I'd consider about the max size for steel. I imagine you have 2 or 3 steps on the pulleys that you can switch to? My "big" drill press has a 1/4hp (200w) motor, though 3 phase, and a max drill size in the chuck of 1/4"(6.4mm). 3 steps on the pulleys, and they can be switched from motor to spindle so 6 speeds from 650 rpm to 12,200 rpm. I leave it on 650. Running a drill too fast is much worse than too slow, the former you toast the drill, the latter the hole just takes a little longer to make.

[jdm]

1 hour ago, nickelsilver said:

But also,  what rpm is the drill spinning?

Just like most other drill press of its class mine has 5 steps pulleys. I use some reference tables to set speed based on drill size and material, then augmented by experience and observation. I like to set the correct speed aiming to get a nice swarf like the below.  I'm very curious about which effect a new capacitor will have, it might turn it into a beast, LoL.

Edited May 3, 2020 by jdm

[spectre6000]

Disregard my post above. I missed or misread the power rating, and thought we were talking about some little generic Ryobi kinda thing. I second (or third, or whatever we're up to) the cap diagnosis.

Edited May 3, 2020 by spectre6000

[jdm]

Replaced cap but no change. I thought of bringing this to a community that deals with that stuff daily

https://www.practicalmachinist.com/vb/transformers-phase-converters-and-vfd/250w-weak-motor-377260/

[HectorLooi]

Check for belt slippage and stiff bearings.

[jdm]

1 minute ago, HectorLooi said:

Check for belt slippage and stiff bearings.

There is none, as explained above and shown in the video I stall the motor pulley. No belt or bearings involved.

[HectorLooi]

Just watched your video clip. Never tried that before.

Were you wearing a Kevlar glove?

[jdm]

2 minutes ago, HectorLooi said:

Were you wearing a Kevlar glove?

Cut prevention gloves from the hardware store.

[HectorLooi]

When I get a weak motor, the 1st thing I  do is check it with a wattmeter. Or a ammeter and work out the power drawn. If the measured wattage is below the rated power, then suspect coil faults or switch and fuse faults.

[jdm]

1 hour ago, HectorLooi said:

When I get a weak motor, the 1st thing I  do is check it with a wattmeter. Or a ammeter and work out the power drawn. If the measured wattage is below the rated power, then suspect coil faults or switch and fuse faults.

Can't measure because ATM I don't have a clamp meter and my DMM manual says no more than 25VAC in 6 or 10A ranges. I measured resistance at the motor poles, with no cap, at 85Ω

Tried bypassing the switch / protection and that made no difference. 

Took apart the thing, no signs of rubbing, overheating or other damage.

 

Edited May 6, 2020 by jdm

[HectorLooi]

I was watching your video again. The motor seems a bit slow. Do you have any way to measure the rpm?

[jdm]

8 hours ago, HectorLooi said:

The motor seems a bit slow. Do you have any way to measure the rpm?

The best answer is the one I got on the other forum:
250W at 1400RPM comes to 1.7 N-m of torque (or for us, 15 in.-lbs.). That is roughly what it takes to open a typical jar of pickles

Furthermore, 250W drawn can be, best case, 1/5 hp output, which is about 0.1 kgf. Not much really, but as mentioned above is enough anyway to drill using some craftsmanship, so for now I'll be happy with that.

Edited May 7, 2020 by jdm