Replacement for KMG binding jig

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Replacement for KMG binding jig

Postby Mark Parker » Tue Sep 10, 2019 6:17 pm

After much 'noodling' I have come up with a derivation of the KMG jig that works well for me. It is designed to work with my form which I built following Benedetto's book with a few modifications:
    I made it wider to better support the jig.
    I added 20 carriage bolts with 3/4 x 2" spools recessed around the perimeter. This was originally done to aid in gluing top and back to sides but is also key to supporting the sides in the form for trimming flush. I place an oversized guitar shaped piece onto the mold, secure it with the spools and flip the whole thing over. I can then use the varnished surface for the jig.
    The form is coated with shellac, varnish, and wax to create a very smooth and slippery surface
Hopefully the following pics and explanation will help. Note: it will take 2 posts to get all the pics.
Attachments
1-assembled.jpg
1) Here is the completed jig - Mk 3 since I have had to modify the prototype twice so far :P The laminate trimmer is a cheap-o from Harbor Freight. The 'micro adjuster' came with it and I modified it to use with my jig. Things to note:
The router is supported by a 1/4" piece of ash that is glued to the rest of the jig (also ash).
The router is aligned with the 'nose' using a 1/4" drill bit exactly as described for the KMG.
2-pieces.jpg
2) Here are the two pieces separated. Note:
The wide tongue and groove to keep things aligned
The two bolts to secure things once adjustment is complete.
The 1/4" notch in the 'nose' to accept the router bit
The large recess above the 'nose'. This is for the top/back overhang before it is trimmed flush.
The wide nose. The curve was adjusted to just fit the curve in my cutaway while providing as much 'meat' as possible to contact the guitar while routing.
3-routing edge.jpg
3) Here is the jig in action. The first step is to route the sides, neck/heel blocks flush and parallel to the form. To do this, I use a 3/8" bit with the nose retracted so the bit flies over the sides and kerfing. The neck/heel blocks will require additional planing by hand as the jig will only cut ~3/8" into them. This is done twice, once for each edge. Now I have a rib/blocks assembly that has perfectly parallel edges which are also parallel to the form when inserted and 'bottomed out'.
4-bit recessed.jpg
4) Here is the 1/4" flush trimming bit retracted so the nose will be the bearing surface and I can trim the overhanging top/back just a little at a time, using the micro adjuster to slowly retract the nose.
Fair Winds and Fair Tunes,
Mark (a veteran sailor and a VERY newbie luthier)
Mark Parker
 
Posts: 28
Joined: Tue Jul 30, 2019 7:19 pm
Location: Dublin, NH & Bocas del Toro, Panama

Re: Replacement for KMG binding jig-part 2

Postby Mark Parker » Tue Sep 10, 2019 6:20 pm

Here are the rest of the pics and story.
Attachments
5-flying.jpg
5) Even at the waist, the router flies above the top without touching it.
6-bit exposed.jpg
6) Sorry for the bad pic, but here you see the nose retracted to where the bearing of the flush trim bit will index the sides for the final pass.
7-flush.jpg
7) Here is the final pass with the flush trim bearing doing its thing.
8-result.jpg
8) The results. Nice and smooth
Fair Winds and Fair Tunes,
Mark (a veteran sailor and a VERY newbie luthier)
Mark Parker
 
Posts: 28
Joined: Tue Jul 30, 2019 7:19 pm
Location: Dublin, NH & Bocas del Toro, Panama

Re: Replacement for KMG binding jig

Postby Mark Parker » Tue Sep 10, 2019 6:20 pm

9) (No there isn't a 9 yet) The final step will be to route channels for binding. This will involve some trial and error with lots of practice runs on scrap. Basically, the micro adjuster will set the width of cut and the router will set the depth. Setting the width will be the same as the KMG, indexing off the nose. Because there is no bearing on the top directly, it will be harder to set the depth than with the KMG. The only technique I have come up with so far is first adjusting the bit to just 'kiss' the top. Then use a caliper to adjust it down 1/4" (or whatever you want). Obviously test on scrap, adjust, test on scrap, etc. etc. If anyone sees a better way to do this, let me know.
Fair Winds and Fair Tunes,
Mark (a veteran sailor and a VERY newbie luthier)
Mark Parker
 
Posts: 28
Joined: Tue Jul 30, 2019 7:19 pm
Location: Dublin, NH & Bocas del Toro, Panama

Re: Replacement for KMG binding jig

Postby David King » Wed Sep 11, 2019 1:15 pm

I suppose you could make up some precise depth spacers that could be used to set the first indexing height and then pulled out to let the router drop down to the full depth. It's still fully dependent on you setting the indexing depth correctly. I've sometimes used a sheet of paper or layer of masking tape to set my indexing depth assuming that when the bit touches the top it's actually a couple of thousandths into the top.
David King
 
Posts: 2629
Joined: Sat Jan 07, 2012 10:01 pm
Location: Portland, OR


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