This is NOT a cookie-cutter jig!
Posted: Mon Oct 25, 2021 10:06 pm
This thread is not about a “cookie-cutter” jig, per Merriam Webster’s definition above. I’ve never seen anything else quite like it.
Now pardon the double entendre, but in a different sense this thread quite literally is about a cookie-cutter jig. I designed it for chainsaw-milling “tree cookies”, aka “tree slices”, aka “tree rounds”. So without further ado, here’s a picture of the strange contraption.
What possessed me to create this thing, you ask? Well, my youngest daughter was soon to wed, and I was enlisted to produce the “tree cookies” for the wedding-reception table decorations. It’s just a matter of making some nice flat parallel crosscuts through a log, bark and all. The cookie thickness isn’t particularly critical. So it should be pretty simple, right?
Well, once I started thinking through the details, it turned out to not be quite so simple after all. I vacillated between making a sled and table extension for my 12” height-capacity Jet bandsaw , or a fixture for my Granberg G555B chainsaw edging mill. (Long-time forum members may recall that chainsaw mill from the heart-pine mantel project that I posted back in 2015.) I was leaning toward the bandsaw sled concept, and even had it roughly modelled in Fusion 360. But I eventually realized that if I went with the chainsaw-mill approach, I wouldn’t have to start from scratch. It would be a piece of cake to mount a guide board for the mill atop my portable WoodAnchor™ fixturing grid worktop, and the worktop itself would make a fine platform for holding the logs.
As you can see in the pictures, the chainsaw-mill guide board is mounted to the worktop on two 13” tall riser posts. What you can’t see is that the whole guide assembly is attached to the fixturing slots with just two tie rods running through the centers of the riser posts. It’s a simple concept, but even with a Shopsmith, I wasn’t excited about trying to accurately drill 13” long through holes. So instead, I made each post from two pieces of 2x4 construction lumber. I face-jointed the boards on my Shopsmith jointer, and then milled a 5/16” groove along the centerline of each piece on my Shopsmith OPR table. Once the halves were glued up, the grooves formed a clearance hole for ¼”-20 threaded rod. WoodAnchor sliding nuts attach to the bottom ends of the threaded rod, and the guide board has countersinks on top for washers and hex nuts. It's a knock-down assembly that goes together super quick & easy, and is absolutely rock-solid.
The challenging part of the jig design was devising a way to fixture irregularly shaped logs. After spending way too much time contemplating various ways to cantilever the logs out from a mounting bracket, it struck me that I could instead mount sliding wedges to WoodAnchor fixturing slots, basically creating split-Vee blocks that could be adjusted fit to almost any log.
My original plan was to mount the wedges directly to the fixturing-grid table. But I quickly learned that advancing the log for the next cut was no fun at all that way, as it required unstrapping and re-strapping the log for each cut. And even worse, it messed up the wedge adjustments. What I needed was a sled for the wedges and the log.
By this point I was almost out of time, so I grabbed a partial sheet of ¾” MDF that was left over from a different project, and made a quick-and-dirty sacrificial sled. My WoodAnchor router slotting guide made very short work of milling it. MDF mills easily, so I skipped the pre-slotting step, and the Whiteside router bit still cut the MDF like butter. But it also unleashed an absolute dust storm, so I was very glad that I was doing it outdoors, and wearing an N95 mask!
If I were to design a jig for serious tree-cookie production, I’d probably cook up a segmented sled, so that individual segments could be removed before they reach the cutting plane. But this sacrificial sled was just fine for my one-time use. The one pictured here yielded twenty-three 1-1/2” thick “cookies”, plus 5 taller “stands”, while consuming less than $5 worth of MDF.
The wedges, however, aren’t sacrificial. So as you feed the sled forward, you simply remove the farthest-forward wedges before they reach the sawing plane. If and when you reach the last two pairs of wedges, you’re finished with that particular log. Not shown in the pictures, I used a couple of clamps mounted to the fixturing grid for immobilizing the sled during chainsawing.
The logs were from a black cherry tree that blew over a couple of weeks before the wedding. It was our next-door neighbor’s tree, in the woods only about two feet from our property line. The nice straight 12” diameter section is to be milled into a mantel for my neighbor’s son. I basically got the firewood pieces. No problem -- the picture below shows how the adjustable half-Vee’s can conform to pretty much anything.