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Showcase cover image for jig - excuse me I meant JIG

Project Information

This is the largest jig I've made so far. It's made with two pieces of 3/4", cabinet grade plywood. Each one measures 12"wide by 60" long, and offset by 8-1/4" - the distance from the side of the table to the blade. Currently set at a 33.125" radius, I drilled a hole through both boards with a 1/4" Forstner bit, added 1/4" bolt, two washer and two nuts(to lock in place). I drew a center line down the board from the end with several perpendicular lines for reference. Made two handles from a chunk of 2×4, set 10" on either side of the pivot point. I attached a 1"x4"x42" piece of poplar with a large hinge for the leg. Made my first 6 cuts and have 18 more to go. Have made more arched cornices than I can count, all with a jig saw. This is soooo much better. More precise and so easy.

In practice what I've found is that I use the handles to get the cut started, then about a third of the way through I grab the board itself and pull it slowly the rest of the way through the cut. I can support the weight of the board and make sure I have a smooth finish to the end of the cut. Its very comfortable, controlled and I never get near the blade. I took the pic from the sharp side of the saw, I stand on the other side when cutting.

As a side note: The top of the arches won't be seen so i only have to clean up the bottom. I tried a shinto rasp, cabinet rasp, and card scraper, but best by far was a spoke shave. I have a Stanley 151 and 51, both tuned and honed. They make short work of those tool marks. Use 120 grit paper to break the edge, done.

Additions: I'll be adding a support leg on the jig, up next to the saw. That or adding a small shelf under the table of the bandsaw to keep the jig supported from underneath. This will keep things stable while i'm getting this clamped to the saw and will prevent the jig from slipping down during use. Also take the first cut-off, secured to the table, to support the next boards as they travel through the cut.

I've used this jig for two different projects now. Saved so much time and added a level of precision that made installation of the second project almost effortless.

Gallery

Comments

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118,619 Posts
Looks like a winner.
 

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687 Posts
How do you hold the workpiece to the JIG? Double sided tape?
 

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18,205 Posts
well done! Great results.
 

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Kristoffer - Sorry, skipped that part. In the second pic you can just see two screw holes in the arched board. All of these parts i'm constructing are going to be arched top and bottom. That gives me room to put screws without marring the final product. Otherwise i'd have put on some toggle clamps.
 

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28,280 Posts
Wow, Nice fixture. You sure can control the arc with that and very accurately!! Nice job….......Jim
 

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458 Posts
This brings back memories. I used to work in a cabinet shop about 25 years ago, and upstairs, they made wooden arched windows. They used the same setup as you did, only a lot bigger; the length from the pivot point to the blade was about 10 feet, if not longer! They built big windows! Now if only I could get a shop like they had!
 

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3,214 Posts
I have cut a thousand or more arches for McMansion drywall and stucco arched openings. Often I have considered creating something similar to attach a jig saw or circular saw. Never took action. ... Lay out the arch with a tape measure, framing square and chalk line, and swing it with the tape measure and a pencil. Sadly, I never figured a mathematical formula for figuring a radius using given rise/spring and span (opening or horizontal dimension). I did have a calculator that had that ability. (Construction master 5) nice tool. Still, I want the formula it used. Maybe you know how to mathematically figure an arch?

Excellent solution, and readily modified to cut any radius within the length of the jig.
 

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if you swap in a router with a 2 flute straight bit for the jigsaw the cut will be perfect. I rough cut the piece 1/8" long and then use the router to make the final cut. The end result is perfect, no sanding or dressing
 

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Holy mackerel, BigAl…. It works every stinking time. Forget laying out arches. Math power is better than manpower.

Thanks for posting that. I probably could have found it if I knew the proper terminology… ( chord )
 

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I draw out the arch and do the math long-hand(but i'll keep BigAl's info as well). It allows me a way of double checking the numbers and provides me with other details that might come in handy.
 
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