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Wood Flour


Howard
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For the longest time, I've been using up a big sack of wood flour. Light colored and very fine, I think it came from RAKA. It didn't have much odor, but I seem to recall it might have been made from maple.

 

Anyway, I ran out so ordered some new. Not the same, so I ordered from a different source. Again, not the same. Color is darker (one is clearly oak, the other is something else........color is not a worry) but both new samples are much coarser, such that the fillets I am making are rougher in texture. The previous stuff left fillets as smooth as fumed silica alone.

 

Did a little research and apparently this stuff is sized as they do sand, walnut shell, etc. Finest grade is 200 mesh screen, most often size appears to be 20 mesh, which I suspect is what I now have.

 

Anyone know more about this than I do and do you have a source for the really fine stuff?

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I can't answer your question. But I am currently dealing with the same problem, but the opposite. The new batch is lighter in shade after mixing it with the resin for seam gluing. It sticks out like a sore thumb, sadly too, since the majority of the deck is the darker and blends nicely. I have begun to blend a wee bit of black colorant with the resin only and then mix it with the hardener and then the wood fibers.

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I think I have some really fine maple from RAKA left over from a boat we finished in 09.  If I can locate it, I'll send it to you if you want to pick up the shipping.  I'd guess it's a couple of pounds worth, at least.  I just have to get to my dad's place next week.

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So far my wood flour source is DeWalt - as in wood particulate produced by my DeWalt random orbital sander. Color is dark since most flour is WRCand adding fumed silica shades it lighter, but I'm not very picky about color match.

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That is a generous offer, and would get me by in the short run, but is not as much as I'm going to need.

 

I will call RAKA and ask if they have any significant quantity of the fine maple left, or if they can get more. The stuff they sent me is oak and comparable in size and coarseness as the stuff I got from Paul at Progressive Epoxy. His website references the particle size of his wood flour as 80 mesh. Both thicken but both are leaving me with a rough, coarse textured fillet. You could light a strike anywhere match on it and with the fine maple, I doubt you could.

 

Many of the mail order places sell the products MAS epoxy packages. But they only describe it as wood flour and do not reference particle size. It appears there is a steep quantity discount for this, so I would get a 50# sack if I could find it.

 

One mail order epoxy place offers finely ground pecan shell instead of wood flour. If nut shells work, I can get walnut shell locally and it comes as fine as 400 mesh. Color would come out the same as a dark chocolate bar though.

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Update:

 

RAKA no longer offers maple flour. According to them, their supplier no longer makes it. Something about EPA regulations related to particle size? Not sure if that is entirely right, as I called a company that makes wood flour and their rep said they still made it, but their minimum order was something like a full pallet of 50 pound bags..........a truckload would be better.

 

RAKA now offers what they describe as a hardwood flour, which in my experience is the medium coarse oak. For smoother fillets, they suggested a top coating of neat (regular unthickened epoxy) using a plastic spoon or brush to smooth it. Of course if you were going to tape over it, probably doesn't matter what it is.

 

Greg:  Chuck at Duckworks tells me they have never sold maple flour. Theirs is and always has been pine, which I seem to recall that in a previous life, RAKA also offered. Back then, according to RAKA, the pine gave a light color, the maple a darker color. If you look close, the RAKA site still has a legacy reference to it, suggesting their wood flours are cheap so you should get both. If Oyster is now using pine instead of maple, that might explain the color change. Anyway, I have a sample of Chuck's pine on the way.

 

My recollection is the pecan shell will also throw a dark brown chocolate tint, similar to but perhaps a bit lighter than our black walnut. I think either would work if you wanted a darker color.

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Well, it definitely came from Duckworks, in four sealed ziplock and unmarked bags. I used one of the bags. This was purchased about 8 years ago. Now I will hunt the paperwork. I am pretty sure it was sold as Maple or Oak wood flour and I doubt I would have bought Pine, but I might have if it was cheep enough and I was experimenting at the time.

 

I cannot locate this Duckworks invoice. I trust that Chuck is correct as my memory is often missing a bolt or two. I was building several boats and had this flour sometime in 2004 or 2005, as a guess. I wonder if Chuck can locate my order from back then?

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When mixing wood flour, you can play with the color by adding talc, corn starch, wheat flour (or other cooking flour) all of which tend to lighten it up. If you use talc (yes, baby powder), it will dramatically smooth out the mixture, if the wood flour is on the coarse side. To darken it you can use dies or dry pigments. These can be purchased at artist supply outfits and online. I don't use the dies, but do use the powdered pigments and they work good, if colors are important to you. I need to them to match stuff during repairs. The nice thing about these pigments is "what you mix is what you get". In other words, once the pigment is added, it doesn't change color as it dries, like stains can. Mix the dry pigment into the resin first, before adding hardener (I'm not sure why, but it's what I've been told).

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Paul.......aside from what a person uses to make his fillets, I've found references to what is essentially scantling recommendations for sizing the fillet to the plywood being glued.

 

One reference is the radius of the fillet should be 3x the thickness of the plywood. Example......fillet for 1/4 inch plywood should have a radius of 1/4 inch x 3 or 3/4 inches, meaning the diameter of the tool would have to be 1 1/2 inches. For 1/2 inch plywood, radius would be 1.5 inches, or nearly 3 inches in diameter.

 

Second version of the story is the depth of the fillet needs to be equal to, or no less than 75% the thickness of the plywood being glued. That too would require a large radius fillet tool and even larger if the angle of the two pieces is greater than 90 degrees.

 

Early on, I only used the same 3/4 inch tongue depressor / stirring stick to make my fillets, which would have had a 3/8" radius. If the larger scantling suggestions are right, I was way off on what I did.

 

I know I have tested my fillets by glueing some pieces up, then breaking them apart. In every test, the plywood failed before the epoxy fillet did by simply pulling the wood apart. I can see where a larger fillet would increase the surface area, and also reduce the leverage force by moving the fulcrum (edge of epoxy fillet) away from the surface, effectively reducing the force of the lever?

 

Not sure if my reasoning has any validity, but in any event, does this larger scantling rule of thumb sound right?

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As with all "rules of thumb" you'll have a significant margin of error. The 3:1 rule is pretty common and one I use, when describing fillets in my plans, but this isn't the say all of fillet dimensioning. It's just a safe suggestion and for most builds, well good enough, offering a healthy bit of wiggle room, because we know that sometimes, a builder will be short of these general dimensions, yet will still have a solid, reliable joint.

 

In really, small craft like that used in canoes and kayaks, these dimensions are away over the top and probably adding more weight and bother, then absolutely necessary. This is partly because of the size and relative stiffness/strength of the materials, given the general loading they'll tolerate, but also because every once counts, so a decrease in dimensioning could be justified. There's also a practical reality to the fillet and this is, sufficient radius, so tape or other fabric will make the turn, without puckering. This is one of the biggest concerns as we've all applied 'glass over something, just to find the radius wasn't generous enough and it bubbles, puckers and generally makes you cuss a lot.

 

Now my interpretation of the 3:1 rule doesn't produce a 3/4" radius on 1/4" stock. What I tell folks is the fillet should be 3 times the material thickness in height off the perpendicular. This means the thickness of the fillet, as it bisects the joint is a fat 1/4" of goo, that tapers quickly in each direction. AT 3 times the height, it's the same as the radius, but I generally don't make circular fillets, but more like a elliptical shape. This provides more "meat" in the middle, spreads the load across a wide area, but decreases the bulk of the fillet, yet still permitting a reasonable radius for fabrics.

 

As to what you should do, well it's a crap shoot without some testing, but you'll find you'll need more fillet and fabric on thicker materials, then you do on 1/4" and smaller stock. Again this is because the relative strength/stiffness of the thinner plywood (assuming it's good stuff) is higher and typically less heavily loaded. So a common rule that can handle 3/4" plywood fillets, will be a bit over kill on 3 mm plywood. I know this isn't much help, but . . .

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Actually, it helps a lot. A person can read and research, but so much of what is out there is either incomplete, inconsistent, inaccurate, or all of the above. I have both the System 3 and Gougeon Brothers epoxy manuals, and both clearly show how to make a fillet and what to make them out of, but not how big they need to be for the job. Same with several of my boat building books, of which I have several.

 

I recently ordered a copy of Sam Devlin's book on stitch and glue boats, and he mentioned something nearly identical to what you describe above and that set off alarms and whistles. If it is that important (since structural fillets are mostly what holds your boat together......I'm guessing it is), it seems like it should be mentioned and explained in the literature a lot more than it is.

 

And now that I think about it, from a practical standpoint, tabbing structural joints with one or more layers of 12 or 17 ounce biaxial will go a lot better with a larger inside radius to lay in.

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The radius on smaller fillets is just a practical matter. They need to be large enough to permit the fabric to lay down nice. From a structural stand point, you may only need a 3/8" tall fillet, but the fabric will not lay down in such a tight radius, so . . .

 

As far as West System and the System Three folks, the dimensions of a fillet are generally application specific and of course assumingly engineered, for the tasks they'll be asked to tolerate, which is out of the "scope" of their epoxy use guides. This coupled with liability concerns, are likely why they don't offer generalized fillet specs. I do offer generalized specs for each plan set of mine, but also knowing they'll work for the specific project they have plans for. Now, that you've brought it up and we've explored it a bit, maybe I need to add a disclaimer of some sort, suggesting the specs provided are for this boat only. Damn, lawyers suck.

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No argument about the lawyers, although to be fair, it's only 99% of them that give the rest a bad name. (I'm dealing with 4 of them now).

 

Liability issues aside, my point is if it is common knowledge among designers and experienced builders that the size of structural fillets vary according to the job at hand, then that is all that needs to be said. That alone should be enough to put even novice users on notice to investigate.

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Update #2:

 

Pine flour from Duckworks arrived today. Texture is considerably finer than what I found from others. Did a test batch and the fillets were smoother too.  Looks like I have found my new source for wood flour.

 

BTW, a fillet made with a 3/4" radius is huge compared to one with 3/8". At least double, if not triple. Ouch.

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  • 1 year later...

2B4iam  (Russ)

 

  I have used wheat flower recomeded by my cousin who is a boat bulider by trade 30+ years.

 

  I have not used it my selfe on boats but use it alot in other wood working.

 

                                                                                   Russ

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  • 1 month later...

I've used cooking flour and tested it against typical purchased wood flours of various species. Rice and wheat flour compared to the hardwoods and nut shell flours within a few percent. The rice (the best of the cooking flours, by my tests) and wheat flours where slightly superior to softwood wood flour (pine, spruce, fir, etc.), but not by much. I even was making flour for a while, with an old mill, but it's a pain in the butt, mostly drying the materials and keeping moisture out of it once ground down. It's so much easier just to buy a 5 pound bag of wheat flour, which also makes a reasonable, medium to light brown glue line, then pay for shipping from some supplier. If you mix and match some purchased pecan, or maple (or whatever dark) wood flour with corn, rice or wheat cooking flour, you can move the color around quite a bit, making good looking glue lines.

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