Bow Limb Lamination Grinder … What?

base piecesEight cuts of MDF. They will form the base of the grinder.

BrokeStick bow building got to the point where it needed a lamination grinder — a device that would not only grind a stick of wood to a desired thickness, but grind a taper into it as well. Didn’t need to search far and wide. Fortunately, a guy named Jim Thorne (AKA jwillis) built one and was generous enough to share the design with the world.

But does it work? Especially in the inept hands of the BrokeStick cohort?

I can’t imagine this will be interesting for anyone but the most desperate lam grinder seeker. Like the rest of the posts on this blog, I’m doing it primarily to track my progress or lack thereof. Public notebook sorta thing. For those who want to go straight to the source, here’s Jim Thorne’s lam grinder page. Godspeed and thank you Jim Thorne.

From here on in this series, I’m going to walk more or less step by step through the BrokeStick process of building this thing. After it’s built, I’ll test it and return the results. Does it work? Or does it not?

Step One: What’s a lam grinder?

Zebra riser gap right

In the photo above, all those different colors of wood are laminations. Laminations because they’re glued together in layers. That curvy guy top right needed to be ground. There were two times in the bow-making process I could do that: after the glue-up and cure; or before.

The bows that I’d made to this point, were simple laminations. For instance, ipe glued to bamboo. After the glue cured, I’d remove wood, first to shape the bow’s limbs, then to tiller them. Tillering is the process of getting the limbs to curve gracefully, evenly, and sweetly so they don’t, among other things, break or shoot funny (funny usually meaning less than optimally).

The tools you use to remove wood, fast or slow, include saws, files, rasps, Shurforms, teeth, nails, belt sander, cabinet scraper, float, knives, maybe some others and I was kidding about teeth and nails. Not that you couldn’t use them.

Post glue-up grinding works fine if you’re building a simple flatbow or longbow. It’s not a terribly difficult process. (Tillering can be a maddeningly difficult process, but mostly because it’s so easy — both to do and to screw up.)

But removing wood from limbs becomes a mite trickier when you introduce reflexes and recurves. Or really thin fiberglass from which there isn’t a lot of material to remove before eating through to the next layer. (A bowyeristic no-no.)

So what you do in those cases is determine how thick you want your finished limbs and then grind one or more of the lams (bowyer talk for laminations) to the necessary thickness. And one more thing.

Those limbs? They need to be tapered. Not as thick in mid and end limb as they are closer to the handle or “riser”. And both limbs need to be tapered equally. Otherwise one limb is thicker, doesn’t bend equally with the other and you get a scrude up bow. Soul crushing. I know.

So how do you get that taper? Especially a .001″ per inch taper?

Well, you buy them from 3Rivers or Bingham. Or you grind them yourownself. And that’s where the lam grinder comes in. Because you can’t afford a $6,000 (or even $600) drum sander. (If there are other, cheaper ways to procure a lam grinder without building your own, I don’t know them. Please tell me.)

So, to answer my own question: a lam grinder is a device that allows you to more or less inflict a desired thickness and taper on a piece of bow limb wood.

Having said that, I feel, once again, that I’ve raised more questions than I’ve answered.

Yeah well … you ain’t seen nothin’ yet.

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