Loud hum, Delta DJ-20 -- Answered

[R Clark]

I have a (new to me) Delta DJ-20.  Manufactured 1987.  Picked it up on Thursday and over the weekend put it into place and took it for a test spin yesterday.  Everything seems to work fine.

Yesterday, I also noticed a loud hum in the shop.  It sounds like a fluorescent fixture ballast that is getting loud.  Tonight I tried to isolate the hum by sound location and then shutting things off.  It wasn't a light, but is the jointer.  The hum begins immediately when the jointer is plugged in, and stops as soon as the machine is unplugged.

I pulled the covers to determine the exact spot of the hum.  It's not coming from the motor, or the switch, but seems to be coming from the electrical wiring box on the side of the cabinet.  None of my other machines hum in this fashion, nor have they. 

Here's the electrical box where the hum is coming from.

[attachment=39455]

Here's the schematic inside the electrical box.

[attachment=39456]

I see in the schematic that there's a transformer in this box, and based on symbology, it is the blue box in the upper left.  I'm thinking this is the source of the hum.  It's in the right area.  I am reluctant to touch anything in this box while the machine is energized.

Is the hum a precursor of failure?  

Is there any way to test using a multimeter?

Is it possible that this is actually a switch problem?  How would I test?

Thanks in advance...

[TDKPE]

It's the transformer.  And it's not a sign of imminent failure.  If it bothers you, try putting grommets between the back panel and the transformer case, and also under the mounting screws, with it unplugged of course.  The screws don't have to be tight, either; just snug enough to hold the xformer from flopping when moved. 

That's a top-shelf industrial low-voltage motor control, by the way.  I bought a new one on ebay for cheap (seller didn't know what he had) and use it on my 2 hp 12" Delta RAS. Delta made a number of different versions, including 3-phase, and they were all similar in appearance.

[R Clark]

It's the transformer.  And it's not a sign of imminent failure.  If it bothers you, try putting grommets between the back panel and the transformer case, and also under the mounting screws, with it unplugged of course.  The screws don't have to be tight, either; just snug enough to hold the xformer from flopping when moved. 

That's a top-shelf industrial low-voltage motor control, by the way.  I bought a new one on ebay for cheap (seller didn't know what he had) and use it on my 2 hp 12" Delta RAS.  Delta made a number of different versions, including 3-phase, and they were all similar in appearance.

Thanks, I was hoping you'd respond.

I may try your suggestion.  The hum isn't THAT bad, but it was a new sound, and so I was compelled to track it down.  I first thought it was a ballast; one of the lights has been acting up.

Merry Christmas!

[TDKPE]

I may try your suggestion.  The hum isn't THAT bad, but it was a new sound, and so I was compelled to track it down.  I first thought it was a ballast; one of the lights has been acting up.

Merry Christmas!

Any kind of soft rubber, like small o-rings, on either side of the xformer, with the screws going through them (to hold them in place) will work.  That's how I mounted my lathe motor, but with a stack of them under and over the base, and under the mounting board between the lathe legs.  More for the ability to jump belt grooves without loosening anything than for vibration mitigation since it's a 3-phase motor, but it's a common vibration isolation technique, often using springs on both sides.  For noise transmission, something very soft is best, like low durometer rubber. 

Or just don't worry about it.  I can hear the xformer in mine if I listen hard enough, but it spends its life unplugged, so I don't care.  The lights are louder anyway.  Hmmm - note to self: gotta replace those fluorescents with LEDs.  


And Merry Christmas to you, too.

[attachment=39469]
[attachment=39470]

p.s. The motor is not actually tilted from belt tension; it just looks like that in the crappy phone photo.

[toolmiser]

I will have to try this method of using rubber on my drill press. It took me a couple years to figure out where that was coming from, I thought it was the fluorescent lights. Eventually I just added a switch to shut everything off when not using it.

[kurt18947]

I will have to try this method of using rubber on my drill press.  It took me a couple years to figure out where that was coming from, I thought it was the fluorescent lights.  Eventually I just added a switch to  shut everything off when not using it.

I have a crappy Asian Delta drill press that vibrated whenever it was on. When I removed the motor and step pulley to replace them with a VFD powered 3 phase motor and single groove pulley, the vibration went away. I'm guessing it was a poorly balanced step pulley on the motor. I guess I should be glad the step pulley on the quill shaft seems balanced.