Gretsch G5420T Thinline Conversion



August 2017.
I don't normally get intimidated or nervous when I'm asked to do serious repairs on an instrument. Usually they are in such a bad way that I can't possibly make them any worse.
This time though I was asked to take a pristine archtop guitar & cut down the body thickness by approximately 1" to convert it into a unique thinline model.
To pile on the pressure, it happened to be a limited edition of 250 instruments.
Now, I would not normally be the type of person to agree to hack up a guitar & ruin its value. Nor would I be the one to alter an expensive instrument without having a reasonable grasp of the consequences on the constructional & tonal integrity that such a modification might have.

The owner was adamant that he wanted to risk it & chop it down.
I asked him at least a dozen times if he was absolutely sure, & each time he answered 'Yes'.
He explained that he loved this guitar but due to mobility problems in his shoulder he found it too difficult to play. He had reluctantly decided to sell it & purchase a thinner bodied model. He had a buyer standing by whilst he tried just about every thinline make & model he could lay his hands on. He found them all more comfortable to play but they just didn't match up to the playability & tonal dynamics of his favourite instrument. 'So why should I sell it & have to have something I don't like as much?' he asked me. 'If you can modify it & it retains even part of its character then I'll be happy'. That's why I agreed to take it on.
I hold the belief that instruments are made to be played & loved by musicians; not be hoarded by collectors & hung on a wall just for show.
I know of people who hold a different view to mine & that they will horrified to hear of what I've done.
Well I've probably increased the re-sale value of the remaining 249, & hopefully created a very limited edition of 1 special instrument that he can continue to enjoy making music with for as long as possible.

So having agreed to do it, I now had to plan out how I would approach it.
I've had the backs off many instruments for repairs, but they had already been damaged or started to come away at the seams. So it has always been fairly straight forward to either apply a little heat or steam to the seam & pop the back right off.
This time I wanted to keep everything in the best condition possible for re-use. So trying to remove the back binding & getting my steamer into the back seam wasn't really viable. Also if I removed the back I would then still have to accurately cut down the flimsy sides, which didn't seem the best approach.
After considering different methods I finally decided that I would make a cut around the periphery at 28mm distance from the back. Using my Dremel mounted in its router base, and using a circular cutting wheel, I could track around the edge & produce a very clean cut.
Of course there is the neck heel, neck block & heel block which I would have to carefully cut with a hand-saw afterwards because the Dremel cutter diameter is too small to cut through them. Also there is a central post glued inside the guitar between the top & back, just underneath the bridge. I will have to deal with that after I've completed the peripheral cuts. The glue joint between the post & the back is visible through the pick-up cavities in the top, so I can get my steamer nozzle through to pop the joint quite easily.
With the back section off it will be possible to apply heat/steam from the inside to separate the back cleanly from the still attached portion of the sides & kerfed linings.

Now it was time to begin.
I have to admit to feeling a bit jittery at this stage, knowing that once I made a start on the cut, I must finish the project no matter what problems it would throw up at me. A solution would have to be found to resolve every difficulty that cropped up.

The first stage was to take measurements of all the critical parameters of the instrument: Action height, neck angle to body, etc, etc, & note down every important dimension I could imagine.
Next, I stripped out all the hardware & electronics & stored them away for a while.

I taped right around the side of the guitar & marked a guide line 28mm down from the back. The guitar was mounted back-side-up in my universal holding fixture to keep it stable during the process.

I set my Dremel cutter to the required dimension from its base & very slowly & carefully ran it around the periphery.
I cut right through the thin sides and just a little way into the neck heel & end blocks to mark the cutting line.
Then I had to handsaw through the heel & internal end blocks. I cut at a slight incline through the blocks to ensure that I had enough material to permit height levelling later.
The back portion was now only being held in place by the internal central support post positioned below the bridge.
A quick shot onto the post joint with my steam nozzle softened the adhesive & the back section came free.

Now the back section was off I used the steam nozzle from the inside to loosen all the joints and separate the back & kerfed linings.

A bit of cleaning up of the old glue remnants & the parts are ready for re-use.

The end blocks required levelling & the central post needed shortening to suit.
The kerfed linings were glued into position & left to dry.
They required a little sanding to smooth them off level with the sides & blocks.

To prep the body ready for the top I had to ensure the neck to body angle was set to match its original height at the bridge position.
To achieve this I strapped a straight edge to the fretboard & clamped the other end over a correctly sized block at the bridge position.
The back was then glued & clamped in position.

A new binding channel had to be cut - that's another job for the Dremel.

And it's ready to accept the binding.

Originally it had an off-white binding but I was asked to fit a contrasting black binding instead.

With the binding trimmed flush it now required a neck heel-cap to compliment it. A nice piece of black Ebony was fashioned into shape & glued in place.

All the hardware & electronics was re-assembled followed by a restring plus a set-up and it is back in playing order.

The incredible thing is that it has maintained its sound characteristics without incurring any detrimental affects when being played both acoustically & plugged in.
In fact I'm convinced it actually sounds a bit better acoustically, though perhaps that's just the new strings.