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| Scarf joint gluing jig http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10101&t=51969 |
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| Author: | doncaparker [ Sat May 25, 2019 9:57 am ] |
| Post subject: | Scarf joint gluing jig |
I put this scarf joint gluing jig together recently. It worked so well, it felt like I was cheating. I thought I would share some pics. Here are the front, top and bottom, respectively: Attachment: Scarf joint jig front.JPG Attachment: Scarf joint jig top.JPG Attachment: Scarf joint jig bottom.JPG As you can see, there is a base, and there are two adjustable supports: One for the neck, and the other for the head. Here are closeups: Attachment: Scarf joint jig neck support.JPG Attachment: Scarf joint jig head support.JPG In the scarf joint gluing method described in the Cumpiano/Natelson book, there are stop blocks at both ends, but I have found that, by using supports that index off the face of the neck wood instead of the edge, I really don't need a stop block for the neck. The neck won't move if it is securely clamped to the neck support. On the head support, an adjustable depth stop is needed, however. I just use a threaded insert and a knurled jig knob with a bolt. The end of the bolt has been smoothed so it won't leave a mark on the head. Here is a closeup: Attachment: Scarf joint jig depth adjustment.JPG Here are photos of the jig with a neck in it. I have left off the four C clamps that actually clamp the joint, just so you can see everything better. The cauls are cut from a regular 1/2" thick HDPE kitchen cutting board, useful because glue won't stick to HDPE plastic. Attachment: Scarf joint jig with neck.JPG Attachment: Scarf joint jig closeup of depth adjustment.JPG The open space between the two supports is open for a reason; it makes cleanup easier if the glue can drip down. If joint alignment is harder without a support directly under the joint, you can just put some packing tape on a small bit of plywood and put it under the joint. I have not yet had a problem that required that solution. Only small mis-alignment happens with this jig (if at all), and that is easily cleaned up after the glue dries. The two supports have over-large holes in them, so that they can be adjusted for proper alignment prior to the gluing operation commencing. I set the neck on its support, clamp it, loosen the head support, hold the head against the neck where I want it, move the head support into position, adjust the depth stop, tighten the adjustment bolts, re-check everything, and then get cracking. This all starts with a great fitting scarf joint. It also relies on the edges of the neck blank to be perfectly square to the gluing faces on BOTH sides, not just one side. Why? Because, when you flip the head, you are registering off the opposite side of the head. I get my scarf joints where I want them with a combination of my table saw, band saw, and 12" disc sander, with jigs for the band saw and sander. Like the gluing jig, my scarf joint cutting/smoothing jigs feel like cheating, compared to other methods I have used. Those are pretty machine-specific, so no photos of those, unless requested. |
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| Author: | Joe Beaver [ Sat May 25, 2019 10:54 am ] |
| Post subject: | Re: Scarf joint gluing jig |
I made something like that last year. Mine is not near as nice and well thought out as yours. Great job! |
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| Author: | Colin North [ Sat May 25, 2019 12:35 pm ] |
| Post subject: | Re: Scarf joint gluing jig |
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| Author: | meddlingfool [ Sat May 25, 2019 12:51 pm ] |
| Post subject: | Re: Scarf joint gluing jig |
Nice! |
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| Author: | George L [ Sun May 26, 2019 7:53 am ] |
| Post subject: | Re: Scarf joint gluing jig |
Thanks for sharing! And it would be great to see the pics of your related jigs as well. |
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| Author: | Ruby50 [ Sun May 26, 2019 10:05 am ] |
| Post subject: | Re: Scarf joint gluing jig |
Don Well thought out and built - worth a look. If you put another of those special knurled nuts on the inside of the end piece, it would prevent the positioning bolt backing out when you don't expect it. Also, testing has shown that tapping wood with a standard metal tap is an excellent substitute for a metal sleeve. I have done them with standard metal taps, not even the long nose version in the video. I have also coated the threads with CA glue, then re-tapped to further strengthen the wood https://www.google.com/search?source=hp&ei=3KvqXIvJF9Lr5gLChpqwAQ&q=tapping+threads+in+wood&oq=tapping+threads+in+w&gs_l=psy-ab.1.0.0j0i22i30l3.1169.5977..9220...1.0..1.203.1710.19j2j1......0....1..gws-wiz.....0..35i39j0i131j0i67j0i131i67.XrULaJxqoQw#kpvalbx=1 Ed |
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| Author: | SteveSmith [ Sun May 26, 2019 3:17 pm ] |
| Post subject: | Re: Scarf joint gluing jig |
+1 on putting CA on the threads and running the tap through again. |
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| Author: | doncaparker [ Sun May 26, 2019 4:00 pm ] |
| Post subject: | Re: Scarf joint gluing jig |
Ed (Ruby50)-- Thanks for the link on tapping holes in wood. That's certainly an option. I've kind of got my handle on inserting threaded inserts now (after years of messing it up), so I'll stick with the familiar. I've threaded wood before, but I'm used to the inserts. And while on the topic of inserts, the combination of having a threaded insert inside that piece of wood on the jig and having the knurled jig knob on the outside means there is no slippage, once I tighten the knurled knob. It's very secure without another knob. For George--Here are some photos and explanation of the cutting and smoothing jig. Like I said above, I get my neck blank edges perfectly square to the faces using the table saw. I should have also mentioned my drum sander, which (along with some modest resawing on the band saw, if needed) allows me to get the thickness of the blank just right and the faces parallel. I then lay out where I want the cut lines to be. From there, I go to the band saw and use my cutting and smoothing jig. Here is are photos of the jig: Attachment: Scarf joint cutting smoothing jig front.JPG Attachment: Scarf joint cutting smoothing jig top I.JPG Attachment: Scarf joint cutting smoothing jig top II.JPG The front edge of the jig is specially designed to work with a Kevin Ryan style disc sander. By that I mean: My sander has a lip between the work table and the disc. The lip is 1/8" thick, about 1/4" tall, and it sits 1/8" away from the face of the disc. So, if I make up a pattern jig that has a rabbet at the leading edge that is 1/4" deep and 3/8" tall, I can template sand flat or convex parts (like tail blocks or, in this instance, the gluing faces of a scarf joint) to a precise shape, up to about 5.5" tall. On this jig I have cut that rabbet, but then relieved the edge on the left (nonworking) side of the jig, to allow more air to flow. Here is the front edge of the jig: Attachment: Scarf joint cutting smoothing jig front edge.JPG Here are photos of the jig on the band saw, first empty, then with a neck: Attachment: Scarf joint cutting smoothing jig on band saw.JPG Attachment: Scarf joint cutting smoothing jig on band saw with neck.JPG The cut quality is OK, but it needs smoothing. Also, since this jig does not have support for the head that is cut off, the head falls off with some extra wood on it (due to the angled nature of the cut). That would be a nuisance if I were trying to hand plane the cut after this, but I'm sanding it, so the extra wood gets sanded off very quickly. So, now the jig goes over to the disc sander, and the rabbet is shoved flush with the lip: Attachment: Scarf joint cutting gluing jig on disc sander.JPG Here is a close up of the jig on the disc sander: Attachment: Scarf joint cutting smoothing jig on disc sander close up.JPG The neck and head are separately slid along the jig to touch the disc. This cleans up the gluing surfaces to near perfection in seconds. Note that this sander turns clockwise, so the right side is the business side. The angles on the neck and head are just right, the surfaces are smooth, and everything fits together very well. Like I said above, it all feels like cheating, it's so easy. |
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| Author: | George L [ Sun May 26, 2019 4:18 pm ] |
| Post subject: | Re: Scarf joint gluing jig |
Thanks, Don. I've hacked together a couple of jigs for this, but I like yours better.
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| Author: | rlrhett [ Wed May 29, 2019 4:54 pm ] |
| Post subject: | Re: Scarf joint gluing jig |
Very clean. Better than what I have. I'll be remaking my. On a related note, tell us about your DIY disk sander. I have been thinking about doing my own, but I don't know where you get a flat large disk that spins balanced on an axle of some kind. I've been working out solutions, but can you tell me about yours? A new thread might be in order if you don't want this one high jacked. |
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| Author: | doncaparker [ Wed May 29, 2019 8:24 pm ] |
| Post subject: | Re: Scarf joint gluing jig |
I cheated regarding the disc sander. The disc is a steel 12” one I bought used on eBay. I think it was from an old Delta that had been parted out. I got the matching shaft, matching bearings and pillow blocks, matching pulley, and belt from McMaster Carr. The electric motor and motor pulley I harvested from a cheap Harbor Freight belt/disc sander; it’s a great way to get a low speed motor for woodworking tools. The plywood is just plywood. I doubt I have any more than around $150 in the whole thing, but it gives me a Mac daddy 12” disc sander that runs smoothly and accurately. I highly recommend putting one together. |
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| Author: | doncaparker [ Thu May 30, 2019 8:34 am ] |
| Post subject: | Re: Scarf joint gluing jig |
Here's a disc not too different from what I used: https://www.ebay.com/itm/Delta-30-120-1 ... Swx59c5wIG |
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