Friday, October 24, 2008

Dust collector

My surface grinder makes a lot of dust. If I want it to coexist nicely with the rest of my machines, a dust collector is a must. Holescreek posted some photos and a description of his on Practical Machinist:

Several members of this board (myself included) have posed questions as to what everyone else uses for grinding dust control in their home shop. I read the few threads in the archives on both boards and ended up with more questions than answers. Most of the web sites I googled cater to wood dust.

In my little home shop I have one surface grinder, a couple of snag grinders, and a small belt sander that I use only for metal. The surface grinder was my primary concern so I based all of my requirements for dust collection on it. I watched industrial Torit type units on Ebay for several months hoping that I could snag one close enough to home to pick up myself and save freight. Not having a forklift to unload a semi is one drawback, then having to either buy yet another VFD or change a motor out was another.

I refined my list of requirements to fit my wants: single phase, fine filtration, mobile, quiet, safe (from fires) and CHEAP. My wants pretty much decimated the majority of dust collectors available on the net. A friend gave me an old furnace blower so I started prototyping a dust collector around it. I figured that I'd just start trying stuff. I pulled the covers off of a Torit #64 at work to see what they did. To make a long story short, the furnace fan wasn't feasible (but it was quiet) without using a 10" duct. I was about ready to give up when I found a damaged 650CFM HF dust collector on Ebay for $30. I wasn't going to use the broken part anyway, and it was about an hour drive each way to get it. The noise that it made measured out at 95dB sitting on the floor. Putting it in the box I had left from my furnace blower attempt dropped it to 85dB and adding the insulated exhaust stack took it down to a manageable 75dB. Since this is a prototype I figure that I'll remake it out of steel on a smaller scale to fit the HF impeller later on. I used MDF for the current case. I know it can burn, but I often use MDF for impromptu welding jigs and seldom do I ever get a flame from stick welding directly against it. I've got around $50 in everything so far, and the suction is very strong. The 5 filter bags were picked up at a local flea market. I found them in the McMaster catalog as polyester filter bags rated at 25 gallons/min. I think the catalog had the mesh size at around 2-3 micron. I held a piece of filter over a butane flame and it melted but would not catch fire. I added the close weave furnace filter on top for good measure, and the whole tray slides out for maintenance. I’m sure there’s a few things I can come up with to improve on it, from what I’ve read, I could use a lot more surface area on the filter bags. I’m open to suggestions from the group.

Matt Isserstedt had the following to add:

Wondering if a large 90 degree square "elbow" on the exhaust stack would further reduce the noise level.

The egg-crate/waffle foam is a wonderful idea, however noise that radiates "straight up" can still escape...if there were another foam surface directly above that might absorb some more. Might be able to accomplish the same thing with a "cone hat" type of cap lined with the foam and then exhaust air escapes 360 degrees around. Thinking somewhat like the drip cap on a fireplace's chimney.