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Finger Joint Jig Recommendations?


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Hi everyone,

 

I am restoring a 1946 Mercury which has ~90% of the wood frame, but I am missing the drivers door (if you have one please let me know) and will need to replace the roof headers/rails and a few other odds and ends. I am hoping there is a DIY solution for replicating the original finger joints, aside of getting custom shaper cutters made. 

 

In Roland Johnson's Automotive Woodworking, they reference Jim Dugué's radial arm saw jig but don't elaborate on how it is used or what kind of cutter he is using. Does anyone have any info on this jig and the cutter? I have seen similar jigs used for box joints, but I am not sure how to adapt that idea to recreate the original joints accurately. 

 

Anyone have any tips or ideas?

 

Thank you!  

Photo of Jig.jpg

Photo of custom cutter.jpg

Finger Joint Description.jpg

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Tapered finger joints over an inch? Yeah, they don't sell deep cutters. I am looking too, though not for a Ford woodie. Sorry I can't help, and thanks for posting the radial arm idea, though I can't see how they are doing it either. I was about to just give up and do straight finger joints. Those are possible on a table saw using a box joint jig that you can buy or make. It would give up some strength over the taper I think.

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In the March 2020 issue of the Woodie Times there is an ad for someone selling a "Shopbot" CNC Router with a $900 finger joint cutter. They want $6000 for the entire set up. I don't know if they sold the router, but you might inquire about the finger joint cutter. You can inquire at Ron_98110@yahoo.com. As mentioned, the Ford finger joint is one and three sixteenth deep so it's an odd ball. One word of caution is that these finger joint cutters are serious pieces of equipment. I have seen them in action and are down right scary. Far from me to question your ability, but you might consider having your door made by one of several Woodie craftsman that have the right equipment. You don't list where you are located, but if you want I can give you a few recommendations.

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@46 woodie you are dead on—I am not a professional woodworker or anything, and I would prefer a less industrial option where I could adapt a box jig and cut them on a table saw or something… I am in Oceanside CA, and only a couple miles from Ron Heinmen’s shop, but the fool hardy optimist in me wants to do it myself. 
 

 

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I need to make TWO joints. Maybe 3 or 4 if I screw up. These custom-made options are indeed impressive, but far too expensive to use only twice. One extremely talented individual told me he freehands them on a bandsaw. I have seen his work and the joints are tight. I have a bandsaw, but I am just not capable of that. I'll keep watching this thread and hoping a low buck (if inefficient) method shows up.

 

1 hour ago, Restorer32 said:

I would think you could do them accurately using a table saw and a tenoning jig.  A radial arm saw might be too sloppy and inaccurate.

 

That was the conclusion I came to, assuming straight fingers. Do you see a way to duplicate the factory tapered joint? I have a tablesaw here as well as a radial arm and a bunch of other woodworking tools.

 

 

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By looking at the set up that Jim Dugue' is using in his radial arm saw, it's apparent that he isn't using a set of finger joint knives, but a saw blade. I wonder if you took a saw blade to a sharpener that has the capability of replacing broken carbide teeth, they could fabricate a custom blade.  They might be able to fabricate a blade with the taper that is used on the Ford finger joints. You would need to shim the work for every cut, but it can be done.

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If you look close at the last graytone picture, the teeth on the sawblade are wedge/triangular shaped. The caption on the picture says it is a custom cutter. 46, I am a woodworker and that seems like an efficient way to do finger joints for just one car. In the picture it seems he has one side of the joint shimmed up the width of one finger. That way when he makes a pass with the radial arm sawhead he is cutting the finger and the receiving slot at the same time/same pass and it is guaranteed to fit. For the next pass, insert a shim the width of a tooth under both sides and make a pass. That way you get a uniform width finger each time without having to adjust the saw. Just stack up premade shims. This method could easily be done on a table saw also. On a table saw you could also do it the way square finger joints are made for boxes with a crosscut sled. 

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I suppose it is possible to do this on a table saw with a normal carbide tipped blade. It could be done with a tenoning jig. You would have to make a first pass at 90 degrees to get the square bottom between the fingers. Then tilt the blade and make another pass to make one side of the finger. Turn the piece around and make another pass to make the other side of the finger. This is possible but adds another layer of complexity and opportunity for error over using a custom carbide blade with tapered teeth. Again, using shims would give proper spacing.

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I though of that but I don't really see how you would get it accurate enough on the turnaround, and I think you would be shimming it from the opposite side. also the angles would have to match perfectly. Maybe. A real woodworker would have a better shot at it than me. I might try it on some scrap.

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FYI Wisconsin Knife Works does not carry the correct cutter.

 

@Tom BoehmThose were my thoughts as well. I think a regular box joint sled would work on a table saw if I had the right cutter, but havent found one yet. Custom might be the only choice.

 


 

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On 6/8/2021 at 4:01 AM, Restorer32 said:

We do our finger joints using a cutter we had made.  We use our milling machine and cut the fingers one at a time.  Time consuming but dead on accurate.

 I received a quote from Orbit Tools for a custom single-blade bit for $215 which might be the ticket if you happen to own a milling machine like @Restorer32. I'm trying to think of an industrious way to use it in a router, but only have half-baked ideas at this point (short of buying a CNC machine.)

 

He will also make a shaper bit which would cut the joint in one pass in a shaper for $425.  He says he made one that was used by the Model A Ford Museum to restore a 1930 AA Ford Passenger Bus, which bodes well. 

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14 hours ago, Alecwhankins said:

 I received a quote from Orbit Tools for a custom single-blade bit for $215 which might be the ticket if you happen to own a milling machine like @Restorer32. I'm trying to think of an industrious way to use it in a router, but only have half-baked ideas at this point (short of buying a CNC machine.)

 

He will also make a shaper bit which would cut the joint in one pass in a shaper for $425.  He says he made one that was used by the Model A Ford Museum to restore a 1930 AA Ford Passenger Bus, which bodes well. 

With a big enough router mounted in a router table you might have a chance at swinging a single cutter, but you would still have to devise a way of running the wood past the cutter repeatedly in a controlled and adjustable fashion, which is really a bigger obstacle than getting a cutter made. These are the cutters I use. I turn them with a 5hp shaper. I made the sled myself, it works well but would be an awful lot of trouble just to build one door. Also the milling machine option, not cutting a finger joint here but with the right cutter could be.

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