J. Phil Thien's Projects

Sorry if I'm keeping the Peanut Gallery in suspense, but I'm in the middle of a project that is going to keep me pretty busy for the next couple of months, and I just lost a weekend making a base for my mortiser so I can move on to the next phase of the project. I won't get around to making a couple of modifications to my DC separator until this project is at least into the finishing stages.

But stay tuned...

Thanks for the suggestions. Most of the inside of the separator is already extremely smooth. I faced the inside with 1/8" UHMW instead of hardboard. It was secured using a combination of double-sided fiberglass tape (works extremely well with UHMW) and countersunk flat-head bolts. I even ran a patch of packing tape over the heads of the bolts to ensure even the slots in the screw heads wouldn't introduce turbulence. The top and bottom are "virgin" MDF which is also very smooth.

However I have a REALLY THICK baffle - two layers of 1/2" MDF - and the edges are very crisp. I don't recall the drop-slot size, but I think it's 1 1/4". So obviously based on your experience there are two things I can do immediately - thin that baffle (maybe by sharply beveling the edges??), and increasing the size of the drop-slot.

Quote from: retired2 on January 08, 2012, 04:16:08 PMfour simple vanes installed axially in the pipe.  I think this would be easier to fabricate, it would be sturdier, and it would stop the air rotation.

I think you're probably right - I always try to make things more complicated than they need to be!

However, I'm trying to analyze what is happening. We have a material (Byrd head-produced shavings) that are more prone to remaining airborne than what I was previously putting through my separator - chips produced by HSS knives. This is causing this material to get caught in the air-flow into the output pipe. What I'm visualizing is a "cloud" of shavings circulating around the separator rather rather than a "sheet" of chips caught in the slower-moving laminar air-flow around the outside of the separator, and thus ending up on top of the baffle rather than falling into the collection drum.

One of the other things that I've observed is that the chips in the collection drum always form a lopsided inverted cone which is consistent with them falling from around the sides of the drum below the drop-slot. What I noticed about the Byrd-head-produced flakes is that this cone is much deeper, having a much steeper slope from the outside of the drum toward the apex of the "cone" at the bottom. I think this attests to the tendency of these chips to resist the pull of gravity, and therefore to remain airborne a little longer.

So, it seems that the trick is to get the flakes to hug the outside of the separator, which the increased velocity from the air-flow "straightener" may help to achieve, but I'm trying to think what else I could do to get enough differential in the air velocity between that outer layer of air above the drop-slot to get the wood flakes to drop. I'm not sure what effect the thickness of the baffle has on all this, other than the "thinner is good" rule-of-thumb, but perhaps someone could help me determine if thinning my baffle might also help the cause.

Ok - so I'm on my own, huh?  ;D

I may make my outlet pipe just a tad longer if for no other reason than to give myself something more substantial into which to install the "straightener" elements. right now that tube (as you can see from the picture) is only about 6" long at most.

Since I'm only running about 1 1/2 HP (you may recognize the blower and filter assembly as being salvaged from a Harbor Freight DC unit), I'd like to really minimize any restriction, and may play with the idea of making some kind of "egg crate" insert if it's not too hard to fabricate.

Well! That's quite a thread.

Just a few thoughts:

First - I lined my top-hat with 1/8" UHMW. It doesn't allow you to see what's going on inside, and right now, I wish it was plexiglass, but it was extremely easy to work with.

Second - I have a very thick baffle, and could make some improvement there. I believe from what I've read around here at one time or another that I could make it somewhat thinner, but also taper the edges to improve performance.

Third - the "straightener" outlet would be an easy fix, but I think I'm also hearing that making the outlet pipe longer will also improve performance, so doing both might help.

Whaddya think?

Here's a picture of my rig. Based on the lack of dust at joints and stuff, I think it's pretty leak-free. Just before I had this marathon milling session where I observed this problem I thoroughly cleaned the filter, so it's definitely not clogged.

Quote from: retired2 on January 05, 2012, 03:49:09 PMNow, the bad news is that is possible that none of these suggestions will help, and you won't know until you've gone to the all the work of making the changes!!

Aye! There's the rub!!

Quote from: galerdude on January 05, 2012, 03:51:03 PM
Now here's a crazy thought  ;D. Could you put a leaf shredder/blower after the planer to shred the "feathers" before they go into the DC line?

Hah! Gettin' closer to a Rube Goldberg setup ever' day...

Like feathers - yeah, that's an excellent way to describe them!

Increasing the depth of cut might slightly change the thickness of the chips, but would probably be offset by a slower feed rate so I think I'd be back to the starting point.

Very interesting that a similar problem has been observed with cyclones! (and here I was thinking that I might have to invest in a cyclone to solve the problem!!)

I'm trying to visualize what's happening inside the separator, and I'm thinking that because the chips are lighter they aren't being forced against the sides as strongly by centrifugal force, and are getting caught by the baffle, and that maybe increasing the size of the drop slot would improve the situation. Then again, it could be that they're simply remaining airborne long enough to get caught by the baffle at the end of the drop slot, instead of falling into the drum, in which case changing the width of the slot would have little effect.

I built an MDF top-hat to fit on top of a 60-gal plastic drum, with a 6" inlet and a 5" outlet that fits a commercial DC blower (about 1.5 HP). A pretty straightforward design with the only innovation being a lining of 1/8" UHMW to minimize wear on something like 1/8" hardboard.

Up until recently, everything was working good.

But last week I was milling 110 bd-ft of cherry, and noticed a large quantity of chips ending up in the DC bag when usually I'd only get a smattering of dust. It appears that the Byrd heads on my jointer and planer are creating much thinner, fluffier chips than the old HSS knives did. The effect is that the chips actually seem to be collecting on top of the baffle, rather than all falling through the drop slot, and thus getting sucked up through the blower and into the bag and filter assembly. This starts with the drum almost empty, and gets progressively worse as it starts to fill. I even thought about actually cutting the baffle out of the bottom of the top-hat, but wisely restrained myself.

So, I'm trying to figure out what to do.

The outlet extends into the separation chamber about 2" (the chamber is about 6 1/2" tall), and the drop-slot is about  1 1/4" if I recall correctly. I'm wondering if shortening the outlet tube, or widening the drop-slot might improve the performance.

Thanks.

Sneezy - don't give up on the bag idea!!

I have a 60-gallon plastic drum (they can be had very cheap or free - find one that was used to hold foodstuffs rather than something toxic), lined with a 2.7 mil plastic bag that comes on a roll from McMaster-Carr. (www.mcmaster.com). Cut a piece of laminate (WilsonArt or Formica) the height of the drum, roll it into a cylinder that fits easily into the drum, and fasten it with pop rivets. Put a couple of 1" holes at the top with a Forstner bit to make it easier to grab, then slip this inside the bag. This will keep the bag from getting sucked up into the separator, and when the bag is full, it literally just slips out, you close the top of the bag with a piece of duct tape, lay the drum on its side and slide the bag out. I can empty my drum and have it back in operation in about 5 minutes.

Quote from: gregascull on August 27, 2010, 05:20:54 PMHope it helps

It does indeed. Thanks!

Sorry - one other question I forgot to ask.

Did you use the original 5" inlet on the blower, or did you remove the inlet flange and make a new flange with a 6" inlet? Since your picture show it already assembled, I'm trying to figure out how to configure the top. I have everything cut out and am to the point of starting to assemble, but the top is still solid - haven't cut a whole for the blower inlet yet.

Thanks!

Okay - thanks for the tip, Greg.

Thanks for the feedback - that IS impressive performance on a crappy little HF dc motor and blower. Odd that you're getting the CB trip only after the unit is sitting idle for a few days.

Thanks again.