Today was practice day in the shop, and a mighty fine thing that it was! Today was the first booger while cutting out the practice tabletop. Fortunately it only cost me $12 worth of MDF and a broken bandsaw blade.
Moons ago I constructed an add-on bandsaw table from one of the many magazine articles on the subject and, unsurprisingly, it included a circle cutting jig attachment. I’ve cut some small circles with it before but it’s only rated to about 30” instead of the 36” I needed. I figured that wouldn’t be a big problem, I’d just flip the guide rail end for end and that would give me the ability to enlarge my circle cutting ability. In theory. In practice it turned out a bit different.
When I first constructed the guide rail I drilled the bushing hole for the pivot pin a bit too deeply (drilled through the bottom) and fixed it with a little veneer-style repair on the bottom. I never gave it a second thought because the slot that the guide rode in only has a big enough slot to allow for blade changes and the patch was fully supported, something that was no longer the case since I’d flipped the guide. I should have thought longer term for my repair and so my first mistake today was made about 18 months ago. Durned butterfly effect! After I’d measured and drilled the pivot hole in the bottom of the 36 1/2” x 36 1/2” MDF blank I moved it to the bandsaw table and at one point it slipped out of my hand and dropped onto the table from a couple inches height but then I seated it on the pivot, addressed the cutting edge of the blade to my project edge and commenced to cutting. At first things went well but as I swung the second corner around it failed to clear the riser block.
That should have alerted me to a problem right there..first corner made it, second corner didn’t. Now if I’d had Euclid as my shop aid I’m certain he’d have pointed out that since I’d started with a square I was no longer cutting a circle but since he had the day off and geometry wasn’t my strongest subject I didn’t pay attention. I merely shut off the saw, congratulated myself on having practiced first so I wouldn’t make that mistake on the real deal and used my jigsaw to cut off the corners of the blank to give me swing clearance. The deed done I turned the saw back on and continued my cut. After about 1/8 of a turn I realized I was cutting a tighter and tighter spiral, a fact driven home at that very instant by the snapping of my bandsaw blade. Crud. NTSB post-accident analysis tells me several likely things happened:
1. Flipping the guide end for end changed the offset of the pivot hole and I was no longer pivoting in line with the cutting teeth. The pivot point was actually about 3/8” behind the teeth, that was going to give me a bad circle anyhow.
2. Dropping the MDF likely broke the veneer on the bottom of the guide and allowed the pin to drop below the guide surface as I basically screwed it around which caused #3 below.
3. The MDF shifted forward (towards the blade) as I rotated it and probably pinched the bandsaw blade against the throat plate causing it to break at the weld or simply shifted the blade laterally enough to make it track at a non-survivable angle.
4. Operator inattention to the warning signs led to equipment failure and ruined materials. Fortunately no injury was caused other than to my pride. Fortunately I wasn’t an hour past my airport when the problem occurred.
I used my other blank, cut a new guide rail with the proper alignment of the pivot hole and successfully cut the second top without incident.
I’m certainly glad I practiced before just tossing a blank of cherry up there!
Then I turned my attention to a task I’ve not accomplished in my couple years of woodworking, tapering table legs. Well aware that I hadn’t done this before and mostly hazy on how it was going to work I’d purchased a $9 fence post at Home Depot and this morning I ripped it down to match the dimensions of the actual table legs. I marked my shoulder where I wanted the taper to begin and marked the foot where I wanted the taper to end and then sat and scratched my head on how to make a jig to line up those marks and hold the wood securely in place. I was tapering three sides of the leg using different tapers on the front and sides so a single use jig wasn’t going to cut it. I needed something to let me alter the angles. Taking a gander at my voumes of scrap wood and drawer full of Rockler parts and pieces I began to formulate a jig idea in my head and over the course of about an hour came up with this number below.
WARNING! This jig is horridly rough and those with easily offended sensibilities should move on now!
The MDF was cut after the mitre bar was installed so I just ripped the edge which gives me a good approximation of where the blade is going to greet the wood. Line up my shoulder and foot lines with the edge of the MDF, lock it down and presto! A taper is born. I will probably cut slightly proud of the line to allow me to finish with a pass or two from a hand plane. The center section is two thicknesses of wood with a 7/8” shallow groove gnawed around the 5/16” slot which lets a toilet bolt slide back and forth, increasing the reach of the toggle, which allows me to use the jig to cut from either mitre slot.
Simple to use instructions are placed on the board to avoid operator error in the future. The center bar also serves as a convenient place to drive the sled from and keeps hands clear of the blade although a plane tote style handle would be better. Best of all, it worked!
I haven’t seen this jig before (or I’d not have spent an hour scratching my head) but for those of you who’ve rode the ride and bought the T-shirt, I’m not claiming it’s an original. It’s just a Dynablue special.
I’m pretty happy with the jig function..not so much the form factor. I’ll probably keep this jig idea, lengthen the bar and bed to allow for longer legs and actually take some time to make it less… Halloweenish.
So all in all, not the best start to the day but things ended up okay.
Thanks for looking!
-- Mistake? No, that's just an unexpected design opportunity....