Duo Jet Project

rmconner80

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Hey folks, been a while since I was on the forum. Years in fact. In the meantime I set up a sweet shop and got down to business. I'm here to share some progress photos and inevitably ask for some help.

Instead of Les Pauls however I've set my sights upon the Gretsch Duo Jet. Have had some serious shop time as of late with the holiday vacation and a bit more leave tacked on beyond that due to a lapse in appropriations here in the DC area...

I decided to do a Duo Jet because I love them but the ones available from Gretsch have pencil thin necks. Also I like nitro and tall frets. Since I'm insane I decided to just go ahead and build my own. Besides, I've already got three les pauls from Gibson.

The basis for my plans / templates come from 1) my 2006 Duo Jet, and 2) details observed or interpreted from this video:


The duo jet is cool because it's a thinline mahogany back with a 1/4" three ply maple arch top plate on top, just like the top or back you'd find on a Gretsch hollow body.

My templates all index to two screws on (well close) to centerline on the front face of the mahogany back. One screw hole ends up in the neck mortise so it gets blown away, the other is under the bridge area and gets covered by a shim and the archtop plate anyway so it's invisible.

First step is to route the three cavities through from the front.

View media item 108874





Second step is to route rear cavity cover recess / lip.

View media item 108873
 

rmconner80

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Next I route out the chambers

It takes two overlapping templates so the router stays supported. Even then I found I had too large an opening and have a third step to route out the middle of that big swimming pool with two guide boards the same thickness (1/2") as the templates.


View media item 108910
Here's the top template screwed on. Takes some time but I like to use pencil to hash out the areas for routing out so I don't zone out and mess up. It's a lot of standing at the drill press trying not to zone out.





Hogging out material to a depth shy of the router depth using a few different forstners. I aim for the back thickness to be .500 but it ends up somewhere between .450 - .550.






 

rmconner80

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Next step is to finally cut out the body shape. I always want to cut out the body first but one has to keep all that surrounding material to support the templates and all the work preceding cutting out the body...

Relief cuts

Bandsaw as close as possible to the line

Final route on the router table with template followed by some 240 spindle sanding to smooth it out a little. Will need more sanding inevitably after the bearings hit the side multiple times for binding channel (haven't gotten that far yet)


Some finished backs. I've been working on a few as I'm not sure how many will make it to the finish line.



This is the last one, in korina. The others are honduran or african mahogany.


 

Frogfur

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I love this stuff. Especially woodwork.
 

rmconner80

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Ok separate from the solid backs are the archtops. I spent many many months thinking this through / testing and below is the method I decided upon. It's not perfect but it works pretty well.

My initial plan was not to make the plates at all but instead use two 16" Gretsch factory archtop plates that I had purchased on eBay which were from the late 70s / early 80s. These are the exact plates Gretsch used on Jets. There's a guy (still) selling a bunch of old Gretsch stuff on eBay though most of the cool stuff is long gone. However I wanted to do sparkle tops (Delmar Drum Wrap which Gretsch used/uses on their drums as well as their Sparkle Jets) and I couldn't figure out a way to effectively laminate that on top of the existing plates. Also I didn't want zero margin for error with only two plates handy. If I messed up one or both I'd be SOL.

I decided to reverse engineer my own. As far as I know Gretsch, Gibson, etc. use a massive press, steel molds, and a lot of heat to manufacture their archtop plates. Obviously that was out of the question for me. Instead I used a vacuum press. I used a large bag press from Roarockit which is an outfit selling presses and materials for homebuilding Skateboard decks.


The key for my needs was to develop the form or mold for the plate. I thought for months about this and figured I'd try to make a solid mold in the same way that folks here do their carved tops, ie. a series of concentric templates, routing, and sanding it smooth. I messed around with this and even cut up some MDF templates but eventually gave up on it because I couldn't get the 3D shape / carve right.

Eventually I had a bit of an epiphany to use one of the Gretsch factory plates as the mold.



This required me to use solid reinforcement under the plate or else the press would flatten it out completely and probably ruin or break it.


To account for spring back after removing from the mold as well as the fact that I was using the top of the factory arch shape as the inside curve I set the inside reinforcements a bit taller than the normal curve of the final plate. What I ended up with is great but not perfect, and shows a bit of flattening at the apex of the curve due to the solid mold but I can live with it. I've had plates sitting around for 8-9 months and they have not lost their curve. Also the curve is important but does not have to be perfect - it gets reinforced / held to shape using shims when attached to the body (more on that later). The Gretsch factory plates have a form / curve but it's not as exaggerated as you see on the guitars.

For materials I used thin maple veneers sold by roarockit. The plates are three ply, with a cross grain middle layer. Top layer is Delmar drum wrap in various sparkle finishes.


Bulk cutting 16" ply to shape for tops


Three ply matched up for pressing


As far as glue I tried using DAP weldwood and Titebond I. The weldwood basically melted my plastic Delmar tops when offgassing. I don't know if this is due to the vacuum press or if this is just due to not waiting enough for the weldwood to dry - you're supposed to let it dry and get very tacky before joining. The issue with this is that the bending / press process requires slip of the faces before setting up. The weldwood is tacky enough to interfere with this. Or when it's not it offgasses and melts plastic. My tests of flat joins show weldwood might be a tougher adhesive but I was blowing through too much Delmar wrap ($$$) doing my testing and settled on using the Titebond. So all my finished tops are using Titebond, very very slightly thinned to extend open time. I haven't had any delamination of the wrap from the tops but it's possible that this will happen when I do binding.

After a lot of testing, wasted material, and failures / refinement, I got a reliable and consistent process to produce the plates.

I have some video of the prep / press. I basically sand all three maple ply on each surface and scuff sand the back of the Delmar (required...), then clean and residue plus the sawdust off using acetone.

After that it all gets put onto the form and then into the vacuum press. One must work fast due to the glue set up but not too fast as to make errors. In the video I am taping the top but stopped doing that as it left visible impressions in the top. Without the tape however one must be very careful getting the finished product out of the bag in one unit with the mold in order to transfer the center line from mold to finished plate. Because the sheets / layer may creep slightly in the press, the plates are oversized compared to the guitar and you therefore can not have a center line scribed prior to being formed in the press. If you do it may be off.



A lot of my Delmar is one off, off-cuts picked up from supply houses but I did spring for a couple full sheets; though I only got three tops out of the first one (two wasted, one completed) I got creative and was able to squeeze out four on this one (one wasted, one completed, two more unused)



The delmar wrap has a tough protective plastic peel on top. It needs to stay intact until I’m ready to shoot the finish, or at least until I have scraped the binding, to keep scratches off.

 
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rmconner80

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To afix the tops to the backs I would rough cut the archtop plate in a shape close to the body but with some overhang / excess. After reviewing my 2006 Grestch Jet I noted that the body shape doesn't come out of the middle portion of the archtop plate, rather it is shifted to the very top. The bulk of the bottom of the plate ends up waste. This means that the neck join area gets the benefit of a maximum expanse of flat (makes sense for the neck join right?) and then at the other end i.e. the south side the top rise / curve begins pretty quick from the edge on the bottom / widest bout of the body.

Also, the inside chambers of the body have been designed / cut strategically to provide support wood for the pickups and to reinforce where the bridge / a bigsby would rest (both would produce a lot of downward pressure on the top). These areas are reinforced with shims glued to the mahagony 'arms'.

The shims are glued up out of the same maple ply as the arch top (basically plywood). The bridge location is the highest point and the top tapers towards the neck, with those shims having a taper built in / sanded to shape. These are glued to the body and then glued to the top when the top goes on to provide support and reinforcement structurally to the top.

In this photo you see the shims however the bigsby shim is missing. I glued up several forgetting this piece but wedged / glued them in after the top was on from the control cavity.


The glue up of the plate to the body was a challenge. I thought on this one for a while and came up with a jig / caul to ensure the tops didn't creep wildly under all the clamping pressure.

First the underside of plate gets centerline plus a small notch cut at north and south edge on the centerline. These same notches are present on both Gretsch factory plates; this is what got the wheels turning for me.


The jig has to fixtures to match these notches. The little notches fit into the back side of razor blades that are inset to blocks and clamped where you need them depending on the body and the top.





Once positioning is triple checked it's time for Titebond and clamps.






i went a bit nuts with the clamps but oh well.

Blue Sparkle


Champagne Sparkle


Tangerine Sparkle


After 24 hours the join is well done. The next step is to trim it close to flush on the band saw without ruining the past 10 hours of work and then get it on the router table with a flush edge bit to take the archtop flush to the body.


Here's a router slip on the cavity lip I need to fill.



Here you can see a missing bigsby reinforcement shim which I had to wedge / glue in at a later date having forgotten it before the top went on.



After routing flush:




A couple glued up:

 

rmconner80

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Early duo jets had rosewood fretboards with block or ‘humpblock’ inlays. Gretsch then phased in ebony with the cool ‘thumbnail’ markers. I’m doing thumbnail / ebony but eventually couldn’t resist also doing a rw/block board also. The thumbnails were much easier! I would have preferred a humpblock and rw board but lacking an example guitar to measure the humpblock dimensions I took a pass on that. Also would have been a nightmare to route / chisel those shapes.

I got my boards preradiused and slotted from LMII. The radius is 12” and the scale 24.625.

Here’s my measurement table for the thumbnails.

I used celluloid rather than real MOP. I cut the material using a cheap desktop CNC and the Easel program. Cutting the board for inlay was simply a matter of using the right size Forstner on the drill press and positioning it right.




Glued in with CA


Tapered board next to untapered


For the rosewood board with block inlay I spent a couple hours routing with a dremel and did such a poor job of it I decided not to use that board. Rather than ordering another blank from LMII I grabbed an amazon rosewood blank from my stash to work up from scratch. Sounded straight forward and fun at the time, but with building a workable fret slot jig / mitre box, slotting of a template using another board, planing the blank flat, slotting the blank from the template, at least 3 hours radius sanding the board, and then finally getting down to redoing to the actual inlay routing, it was a couple day long tangent which is still not compete. But good experience and real happy with the result, and the Amazon rw is beautiful if not the toughest wood planet (not really but it sure felt like it when radius sanding).


Tape guides from positioning inlay celluloid shapes

Routed close to line and then chiseled edges clean



Slots and inlay

Glued in



Now I’m out of photo media storage and am up to date. I’ll try to update as I move forward. I have a few more boards to finish up and then bind the bodies. After that is the neck which I’m dreading a little, and also routing / drilling the body control and pickups.

 
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The_Nuge

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Very, very cool thread an eexcellent work!
I have plans to build a Billy Bo myself, but I've only come so far as to buy a router....
 

fatdaddypreacher

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and how were they off? if they are correct distance apart from one another, except the scale is incorrect, save for another build and adjust accordingly. if they are incosistent, i get your drift. sure is a shame. nice looking board
 

mistermikev

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wow, some really cool stuff there and amazing attention to detail. I have always been a fan of the gretsch duo jet. My name is Mike and I love sparkle. I was not aware that the duojet was A) ply top and B) bent... i just assumed they were carved maple. You learned me - thanks for that!
 

DaveR

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Sorry to hear about the fretboard. That hurts.
 

rmconner80

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Thanks for the interest everybody!

and how were they off? if they are correct distance apart from one another, except the scale is incorrect, save for another build and adjust accordingly. if they are incosistent, i get your drift. sure is a shame. nice looking board
Yeah they are off all over the place, clearly my slotting jig was not quite up to the task. Twas a great piece of rosewood though.

wow, some really cool stuff there and amazing attention to detail. I have always been a fan of the gretsch duo jet. My name is Mike and I love sparkle. I was not aware that the duojet was A) ply top and B) bent... i just assumed they were carved maple. You learned me - thanks for that!
Yep they call it “arched laminated maple” on the thinline jets and penguins with mahogany backs.

In terms of progress I’ve routed the binding channel on the bodies. I went to a .110 channel for the nominal .120 binding as I always have a gap when I match the cut to the nominal width. I can scrape or preferably sand or flush route that fraction of overhang. Getting the depth right was a stressful business as the base of my jig (3/4 ply) is not (surprise surprise) not perfectly straight and true in x and y planes and so it was producing some depth variation as I rotated the body. The jig only suspends the router and doesn’t have one of those donuts that ride on the carved top. Because the top on these is perfectly flat at the edge, and because I can not sand out any marks or scuffs that may appear in the top, I did not use that approach. In the process I learned how to mitigate the variable depth enough to satisfy myself and not ruin anything; this was thankfully possible since I was progressively routing both width and depth and therefore had some room to play with.


Today I hope to build a jig for consistently prebending the binding for at least those sharp bends in the cutaway and horn. My fingertips are already sore just playing around with scrap and heat...


The fretboards are on hold while I catch up with the replacement for the one above. Those get binding and then frets next.
 

mistermikev

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"Yep they call it “arched laminated maple” on the thinline jets and penguins with mahogany backs." well... I learn something new everyday!
you are a pleasure to watch. that blue is just amazing and w the binding looks really good.
 

61LPSG

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Great thread :cheers:
Too bad about that fretboard... been there done that.
Looking forward to the next installment.
 

rmconner80

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Feels like lots of work done, but only a few photos. Starting with the fretboards, I’ve been binding. Had to work up a bit of nerve to do it as I usually find multiple ways to screw it up, but I worked out the bugs on my practice fretboard and alll came together pretty well.

Five boards, fifth one went ebony. No more rosewood and blocks, instead it’s pure solidarity.


Here’s the bound boards before sanding the binding flush. I suspect I’ll be re dying these after sanding. Also I plan to glue them to neck blanks before fretting so I can do a final radius sand so as to: build in some guaranteed relief using the radius beam / truss rod backbow, get the neck and board perfectly true, and also radius sand a bit of fall away in the highest frets. All of this makes it sound like I know what I’m doing, and I guess I know, but only from reading, and not much actual hands on experience.


Hoping the extra glue will sand off and clean up nicely. I did clean out the fret slots where needed.

I built a jig for prebending the toughest curves on the body binding and it works great aside from the constant struggle to heat the binding enough to reshape it awhile not heating it too much. What a pain.


So far four bodies bound and one to go. They are coming out well but the blue one has some pretty shallow binding routes unfortunately. I guess the guy doing the routing was a knucklehead...

The binding is two strips, a inner BWB and outer white. I tested various glues for this job for permanence and also compatibility with the plastic sparkle tops. Stew Mac BindAll works great but is mostly acetone, just the shortest duration of contact with the plastic Delmar sparkle top test piece melts it quickly. It can’t be cleanly wiped off in the inevitable case of squeeze out, so I went instead with super thick CA for the inner strip of binding for attaching to the wood. The CA squeeze out can be wiped off with no mark on the top, the downside is short open time, finger fatigue holding the binding tight against the wood, and occasionally gluing appendages to the guitar. The plastic protective film helped but didn’t prevent all squeeze out from getting on the top, given that infamous wicking action and the natural pull away of the film from the edge of the Delmar. Some CA did afix under the plastic film to the top; won’t be able to assess the extent of this until I pull the film which will be delayed as long as possible to protect the tops from the shop environment; hopefully won’t have to remove it until right before spraying. This fugitive CA on the tops will either be ignored or gently scraped down a bit, I’m hoping it will be minor or not show once buried in sealer and clear.

I still used bind all for the outer binding layer as it’s got a longer and more forgiving open time and works great. Squeeze out was successfully quarantined to the plastic binding and didn’t get on the tops.



One left to bind tomorrow. Then corner radius the backs,and scraping / sanding binding flush. After that it’s on to necks which I’ve been dreading and procrastinating. Still trying to decide between a beefed up version of the traditional dovetail used originally by a certain Brooklyn guitar factory or a regular square mortise and tenon. There are some tricky issues with the dovetail but I’m going to at least test it on scrap to see if I can make it work. On the full arch tops they cut the dovetail tenon like an acoustic, straight through, then attached a mahogany neck / fretboard extension using I guess a lap joint, but not so on the jets. The jets have one piece necks ie no lap joint extension. This one piece extension requires routing in a different axis and then chiseling square. Or alternatively an dovetail bit that has a six inch long shank and would work in a router (I don’t think so). It will be interesting to figure this out, once it’s the only thing left I’ll have no excuses or other work to do and will figure it out.
 
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rmconner80

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Quick question - can anyone recommend a good wood filler (not a grain filler)? I need to plug a small wormhole in Korina and fix a small router slip on a control cavity plate recess. What works and takes a finish ok?

Thanks!
 




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