As I wrote last year – I think I now know how to cut a custom scratchplate, and get close to the look of Jimmy’s original. It’s been ages though, and the Dragoncaster has been consigned to its’ case ever since the neck went on, back in January. Picking up some of the outstanding tasks on other projects has, however, got me back in a bit of a groove. The weather’s good, and the workshop is, for once, a warm and pleasant place to be. The last plate I cut didn’t turn out too bad and, if it all came down to that, then I’d be reasonably happy. However, there were a couple of minor flaws and, having found one more piece of suitable polycarbonate, and one more piece of holographic foil – I want to see if I can cut the definitive plate for the project. I’m itching to finally hook up those Don Mare pickups!!
The last plate had a couple of production “issues”. Firstly – the fit at the neck pocket wasn’t quite correct, and the plate didn’t sit entirely square along the top of the neck. It’s only a millimeter or so out – but that’s enough to keep me awake at night. (Not entirely in a bad way – sometimes that’s when I get to puzzle out a lot of technique. I always liked the quote – “Perfection is not attainable. But in striving for perfection, we might fail and achieve mere excellence”).
Secondly – I’ve never really been happy with the screw holes and their countersinks. Doing this sort of thing with my drill press is tricky. The stops on the vertical motion aren’t really accurate enough – so there’s a tendency for the countersinks to end up different sizes. Too big, and they telegraph around the screw head. Too shallow, and the screwhead sits proud, with the added danger that the countersink isn’t enough to protect the plate from splitting, if the screws are tightened down too much.
Thirdly – there were a couple of issues with the holographic foil. There are a few dust humps in the finish, and if you look really close – there’s a slight crease visible, where I had to reposition the foil. You have to know these things are there to pick them up – but as usual, once you’ve seen them – you can never “unsee” them. Also – since the surface is reflective – they’re the sort of flaws that become more obvious when the guitar is moving, and under illumination.
So with one, good piece of polycarbonate left – and with a much better understanding of what I need to do at each stage of the production – one more time. This time – I want to take it step by step, and fix the technical errors as I go along. Hopefully, I’ll end up with the definitive plate for the Dragoncaster build.
The first thing I want to do, is to fix the slight mis-alignment at the neck pocket. After a few test fits – it appears that what I need to do, is to shim out the template slightly. It looks like another job for a spare piece of StewMac neck shim. These things are useful. I stick a suitable piece to the MDF using PVA wood adhesive, and then tape over the joint tightly until everything’s dry. The tapered shim is flexible enough at the thin end to bend slightly, into the curve of the neck pocket. In case there’s any ridge left, and once the glue is dry, the inside line is skimmed with filler, and everything is sanded perfectly smooth. I check the template over again – just to make sure the entire edge describes a smooth line. There are a couple of places where a router bit has bitten, and a spot where the curve is a little flat. I fill the dints with two-part filler, and then sand everything down with a block – making sure the block stays perpendicular to the edge at all times.
With the template ready, I can then cut the polycarbonate sheet to a rough, but economical size, and then stick it to the template for cutting. I use double sided tape – but I’ve learned to use thin strips, and to apply them all around the edges of the plate. If you use too much tape – the plate is hard to remove without bending. If you use too little – the plastic can vibrate under the router and “chatter”. This gives you a rough, and badly aligned result. It also helps stability if there’s tape applied close by any of the screwholes, and to the edges of any pickup cutouts.
Another thing I’ve learned – is that it’s best to complete the screwholes and countersinks before anything else. These can so easily go wrong, and there’s no point wasting a day cutting and finishing a whole plate, only to ruin it with one of the screwholes going awry. The first thing to do, is to mark the hole centres – taking the position from the template. Because the polycarbonate is clear, and the hole position is marked underneath the clear plastic – you need to accurately mark the hole centres when looking directly from above, otherwise parallax can lead to positional errors. Some of these holes – especially the one on the small tab below the control plate – simply can’t afford to stray too close to the edge of the finished plate.
With the hole centres marked, I’ve found it’s best to cut the countersinks first. I use a fairly blunt countersink bit and a hand drill. Each hole takes a while – but by cutting each in turn, slowly – you can keep checking that each hole is drilled straight, true and to the correct size. Drill and test. Test and drill. The straightness can be assessed by checking that each countersink looks central – with an evenly sized surround. The size can be checked by having a spare scratchplate screw to hand, for comparison. It’s sometimes easy to get carried away without a visual reference. Having an exact reference size to work to, helps to keep each hole identical to the others.
Once all the countersinks look correct, and their overall size is consistent – I then drill through the rest of the plate to complete each screwhole – using the countersink centres to position the drill bit accurately. An HSS drill bit seems best for polycarbonate, and drilling through onto a spare piece of wood, helps prevent chips and splits. A high speed is better, but you sometimes have to clean the drill bit off if the plastic melts onto the cutting edges. This completely dulls the cut, and can leave a little bit of rough surface contamination – but it’ll usually polish off.
With all of the scratchplate holes now drilled, I use the countersink bit to polish the countersinks and to clean up any small slugs of molten plastic, by hand. It helps to check each screwhole with the spare screw – just to make sure that a screwhead sits correctly, and that each screw will sit straight.
I’m going to attach the neck pickup in the old-fashioned way – by using pickup screws under the scratchplate. Therefore, I don’t want to cut holes for the two pickup adjustment screws, (although they’re marked on the template). There’s a real tendency for the plate to split here, and this polycarbonate won’t stand a chance. It’s so much thinner than the usual 3 or 4-ply plate materials. I need to drill a preparatory hole though the plate – to allow for the router bit to pass through the polycarbonate and to cut the enclosed, pickup opening. Remembering that parallax can make it difficult to assess the exact, true centre point of any drill hole – I carefully and accurately mark a point exactly in the centre of the neck pickup opening. A 13mm spade bit is then used to start a small hole, and then gradually enlarge it until the edges of the bit describe the full extent. As long as the bit is sharp enough, and the drill is held perfectly perpendicular, then 13mm is just enough to work for my 12mm bit – without getting too close to the edges of the cutout. You need to leave just enough plastic at each side, so that the router bit can provide a proper, smooth result.
Having done the countersink holes early – it makes sense to cut the pickup opening next, before finally moving onto the edges of the plate. The template and polycarbonate sheet are clamped down to a workhorse bench, with the polycarbonate side down – template on top. The router is loaded with a 12mm, pattern following bead and bit. The cutting section of the bit is set so that it will emerge a few millimeters below the 13mm cutout hole – with the bead above, following the MDF template edge.
The router sits flat on the face of the template when cutting – with the polycarbonate facing down. It’s important to make sure that the bit sits away from the edge of the polycarbonate before switching the power on. The bit needs to come up to speed before it’s brought into contact with the work. Then – it’s important to move the router in the correct direction for cutting. This ensures the best results, and the smoothest cut. Warning – cutting polycarbonate with a router is a messy business. You will create a vast amount of plastic “snow” – and it’s static. It gets everywhere, sticks to surfaces, and travels. You’ll be finding bits of it for weeks.
Cutting the outside edges of the plate is relatively easy. The screwholes and pickup opening are the areas where I had most trouble previously. Cutting the edges is a relatively simple matter of clamping down the work, and then running the router smoothly along each section of the edge. It’s easiest to cut the outline in a series of short passes, and I’ve sometimes found it useful to makea second, more precise pass, after checking that the cut matches exactly, the edge of the template. To get a truly accurate cut – it’s necessary to keep the router sitting flat and perpendicular to the template edge at all times. And it always helps to make sure you keep the largest possible supporting area of template, under the router. If the router bit does go off the perpendicular, it can end up creating a notch on the scratchplate. If it cuts the other way – it can eat into the MDF template. The hardest areas to deal with are always the horns, and sticky-out extremities. In such areas, it’s best to position the router over the centre of the plate, and to work outwards, along the narrow edges.
Once the plate is cut – I check the edges are smooth and clear, I’ve found it sometimes helps to polish up the cut, using a bit of 400 grit over a hard wood block. By polishing up with the plate still attached to the template block – I’ve found that you can clean both simultaneously, and end up with an accurate result. You need to make sure the block stays absolutely perpendicular, and that there’s no chance of any grit paper working over the front edge of the scratchplate. Work along the edges – not across the edges. It’s all too easy to make the cut look uneven, and risk scratching up the face of the plate.
With the plate cut, the next step is to release it from the template and then to clean it thoroughly. Any loose bits, dust, tape residue etc. will spoil the overall finish. The tape I’ve used is quite grabby by necessity – so it’s difficult to pry the plate off the MDF without bending the plate. The best thing to do is to drip a little naptha between the plate and the template. This wicks in by capilliary action, and softens the glue enough to peel the plate away without too much trouble. However – the tape residue remains quite sticky, and if you don’t remove it all carefully – it reconstitutes as a messy, sticky gloop, as the naptha evaporates. It’s important to get the edges of the plate clean too – as the sticky residue seems to survive here even when you think the faces of the plate are spotless.
Consequently, cleaning the plate takes ages. Largely down to this tape residue issue. A couple of washes with naptha eventually gets rid of most of it, and I find a few extra washes with a good, soapy, anti-static, VDU type, plastic cleaning solution – finally gets the plastic clean, bright, grease and mark-free. It’s important to keep it that way while the matter of sticking on the holgraphic foil is dealt with.
The foil I’m using comes in A4 sheets. (Actually, it’s a wrapping vinyl). An A4 sheet is literally just enough to fit the plate, with a few millimeters leeway. There’s really not much room for error – especially if you’re eyeballing the placement. It’s essential therefore to keep the foil stretched and flat. The best way to keep the foil flat , whilst positioning and sticking down the plate is as follows:
- Score two, 5mm strips across the backing paper of the foil with a sharp scalpel. The two short edges are best to score. Make sure you don’t cut through the actual foil. Just the backing paper.
- Peel off one of the strips of backing paper, and then turn the sheet so that the exposed adhesive backing on the foil is facing down, and that edge is closest to you.
- Stick the foil to the tabletop, worktop, desk – whatever you’re using, and then bring the sheet back towards you so that the stuck down edge is now the furthest away from you. This means the backing paper should now be uppermost.
- Peel off the other 5mm backing strip, and attach something useful along this edge. (I use a large-ish, 90 degree set-square). You need to be able to gently and evenly stretch the foil, by pulling this edge towards you. This keeps the foil absolutely flat before the next step. If it helps – once the foil is under some tension – stick whatever you’re using, (the set-square in this case), to the tabletop with a bit of masking tape. (Don’t do this on your posh dining table).
- Before you pull off the final, main bit of backing – clean the scratchplate one last time. In fact – clean it again, if you’re not totally convinced. You won’t get a second chance. Do a trial run to see how the plate will fit onto the foil sheet before you remove the last bit of backing. Clean the plate again if you think you need to. Make sure you’re sure you know which side of the plate is going to be stuck down onto the foil. (It’s the back side of the plate, and the side without the countersinks).
- Once you’re ready to go – pull off the final bit of backing paper, and then hold your breath. Immediately position the plate over the foil in one smooth and dextrous motion. Try and keep it as close to the foil as you can without it touching anywhere. Check the position – especially the four main extremities, double check, and then drop the plate evenly onto the foil with all the accuracy you can muster. Do not faff around. You’ll mess it up if you faff around.
- Unstick the foil from your desk, worktop, dining table. Turn the plate over so that the foil is uppermost and, working out from the centre, using a rubber squeegee or even just your fingers, squeeze out any air bubbles towards the edge – smoothing the vinyl firmly down as you go.
- Breathe again. get yourself a sharp scalpel. Trim off the excess foil using the scratchplate edge as your guide. Use a sharp blade at all times, and don’t let the blade get clogged. Follow the scratchplate curves as best you can – but don’t worry about the tight curves too much at this stage. Whatever you do – don’t let the vinyl become torn, and ensure that there are no tears which threaten to spread onto the face of the scratchplate. Don’t bite off more than you can chew.
Once the plate is trimmed – you’ll have a few bits where the blade has left a slight overhang. You need to tidy these up, along with the tight inner corners. Even if you use a narrow blade – moving a blade around these tight, inside curves can be difficult. To cut the edges cleanly, take a very sharp, new, Stanley knife blade and push it, tip first, into a wooden surface, (again – not your dining table). Position the blade so that the cutting edge is just about vertical. If you hold the plate so that the foil side is down – you can then use the cutting edge a little like a bench cutter. Move the plate against the blade with the vinyl side down. The plastic plate makes the perfect template. If you hold the blade firm with one hand, you can manipulate the edge of the plate past the cutting edge of the blade, and it’ll follow the line perfectly. It takes a bit of practise to move the plate in the most effective way – but the results are way better than struggling to manipulate the blade whilst holding the plate still.
Once the foil is trimmed properly, and I’ve ensured it’s properly stuck down all over – I then heat the foil side, gently, with a heat gun. This being automotive, wrapping vinyl – the surface tightens and the glue bond is activated. You can see the surface smooth out, and as the vinyl shrinks slightly, all the tiny imperfections seem to magically melt away. Any bits of (fluff or dust you missed under the foil will now become horribly apparent).
The plate is now virtually complete. All that remains is to punch out the little bits of foil which still run over the screw holes. I want to finish off the plate properly, and don’t want to risk pulling the foil away from the plate by driving the screws through the vinyl as it is. You can use the Stanley Knife bench trimming trick described above to clear out the holes one by one – although you may have to use a finer, scalpel-type blade. It comes in handy to check the edges of the pickup opening too. Eight holes cleared, pickup cutout checked, and all it takes is one final check to make sure the plate edge is completely smooth. No slubs or loose bits of foil sticking out anywhere.
That’s it. The plate is complete. No signs of creasing , nor of any dust contamination. It seems technique – properly applied – wins the day. My eyes aren’t still really up to checking the ultra-fine detail – so I get my other half to give things a really good once-over. Full marks. Clear round. Ten out of ten. Smashed it.
Fingers crossed – this may be my production plate.