Black Box Vac Source

[sbd1]

John, the switchbox is screwed to the underside of my table (MDF painted blue).

[crash5050]

I finally got the box cut out, flip op and all, tomorrow I will begin the assembly. I am going to assume that the joints are glued and brad nailed, and possibly some silicone to prevent leakage?

David

[JDGJr]

I hooked my new vac box to my table last weekend and ran it briefly to make sure it worked, and thought I liked the sound level.

Today, I finally got around to cutting with the vacuum on, and it has a very annoying variable vibration, with a frequency around .7-.9 hertz. I can feel the vibration when touching the box, and the pulsing sound gets annoying fast. This is with 2 of the 4 motors running.

Has anyone had this, and corrected it? I may disconnect all but 1 motor and see if that makes a difference. Any other ideas?

thanks,
John

[donek]

I hooked my new vac box to my table last weekend and ran it briefly to make sure it worked, and thought I liked the sound level.

Today, I finally got around to cutting with the vacuum on, and it has a very annoying variable vibration, with a frequency around .7-.9 hertz. I can feel the vibration when touching the box, and the pulsing sound gets annoying fast. This is with 2 of the 4 motors running.

Has anyone had this, and corrected it? I may disconnect all but 1 motor and see if that makes a difference. Any other ideas?

thanks,
John

It sounds like harmonic beats. This is what happens when you have tones that are very slightly out of tune. If you run two vacs at the same time, this will frequently happen. When tuning a musical instrument, you listen to the beats and adjust your tuning to make them go away. You are getting these beats because of minute differences in the two systems. It could be a slightly different shape to one vac impeller or one zone is not sealed quite the same as the other. If you wish to learn more about this, you can look up constructive and destructive interference.

[JDGJr]

Thanks Sean.

I will do some experimentation with different pairs of motors.

Is it likely this is directly caused by the motors, or could it largely be the cabinet reacting to them? Dunno exactly how to word the question, and sure don't know how to prove the cabinet is the main cause.

[donek]

Thanks Sean.

I will do some experimentation with different pairs of motors.

Is it likely this is directly caused by the motors, or could it largely be the cabinet reacting to them? Dunno exactly how to word the question, and sure don't know how to prove the cabinet is the main cause.

You can easily confirm it. Below are a couple of images.







You'll that there are regions of darkness in the third image as well as the second. Just like these images indicate, you'll find zones where you can not hear the beats and others where you can. It is not likely do to your enclosure. We do not use an enclosure on our vacs and can frequently hear beats. Usually when we have 2 vacs of similar age or use. As one is used more and more, it's tone becomes so out of tune with the others that they are no longer close to the same tone.

[JDGJr]

thanks again.

related to phase: should both of my 240V motors be wired the same, or should one have the 2 hot wires reversed? Currently they are wired the same.

[Josh Beckmann]

I just purchased a 5 x 10 machine. Gary, can you suggest the number of motors I should use for it?

Thanks!

[Gary Campbell]

Joshua...
Depending on how efficient your system is and what size your parts are, 4 should do the job. With that said, my usual rule of thumb is to use 1 motor for each 2 by 4 zone (8sqft). That rule would require 6.

The old system, with many variations shown on this thread, may require 6 to deliver the same performance that the new design does.

New design here: http://www.usroutertools.com/black-b...tems-s/339.htm

[Kyle Stapleton]

Has anyone bought a black box vac from the website?