I usually have a few pieces of acrylic, polycarbonate or perspex knocking around the workshop. Sometimes, it can be useful for framing applications – although the softer types of acrylic are, all too easily scratched and marked. I think a harder polycarbonate sheet might serve me well for my first scratchplate experiments.
This off cut doesn’t have any protective film left attached – so it might get marked and scratched during the process. Normally, I’d cut a blank off – leaving the protective film attached until the very last minute, but this is all about experimentation and first steps. It won’t matter too much if things go wrong. I should still be able to use the results for finishing tests, and the like.
I cut out a small piece to use as a scratchplate blank. Roughly a centimetre, or so, larger than the MDF template in all directions. I use double-sided sticky tape to stick the clear polycarbonate to the template – noting that I’ll need to stick the plastic to the MDF with the “finished” side to the front.
I clamp the work down to a small work horse – with the intended work area off to one side. I can then sit astride the bench, and drape the router cable safely over my shoulder – well out of the way of the cutter. The work is clamped down so that the MDF template sits on top of the plastic sheet. I’ll be using the same, 12mm top-following cutter as I used for cutting the actual template. This time, however, the cutter depth is set to maximise the depth of the following bead. I’m hoping this will give additional stability, and ensure that the cut is perpendicular.
Again, the cutting blade should follow the template from right to left. As the plastic sheet is cut, the work is rotated and re-clamped as required. It’s much easier to cut with the following bead, with a complete template to follow – and soon all of the edges of the plate are trimmed to exactly follow the template.
To cut out the pickup rout, I need to use a 13mm spade bit and a drill press. This isn’t the ideal tool to cut plastc – but it’s all I’ve got. I drill the holes with the plastic side of the work face down. This allows me to check the clearance through the template cut-out. I set the drill to maximum speed, and then try to let the sharp points of the spade bit do all the cutting. It helps to back off the bit a few times, and to clean off any melted plastic before pressing on. Drilling plastic often seems to melt the work – as opposed to cutting cleanly through it. You need to take things slowly. In the image above – you can see how the hole on the right has cut correctly – wheras the one on the left has, only partially cut. Here, the plastic has melted slightly, and the outline is ragged. Fortunately – I only need one hole to get the router into position for cutting. With the work clamped down, as before – it’s easy to follow, and cut the pickup rout.
Then it’s back to the drill press. This time, the screw holes are punched through the plastic. I position the work each time – using the holes in the template to locate the drill bit. An HSS type bit appears to give the best results – but again, you need to let the bit do the cutting, and clear away any melted plastic. If you let the bit get clogged – or push the bit down before it’s cut properly, then you risk splitting the plastic – especially close to the edges. (See “Things I’ve learned”, below). In this case, once of the small screw holes adjacent to the pickup rout has split. These two holes are really close to the edge of the plastic. I don’t actually need to drill these holes for this particular plate, of course – but they’re obviously a test of technique. I’ve already anticipated that they’ll be difficult. And it was all going so well. Good job this is just a test.
I change the drill bit for a countersink bit, and then countersink each hole in turn – trying to keep the size of each countersink consistent. (The pickup height adjustment screw holes are not countersunk). With the plate now completely shaped, and with all the holes drilled and countersunk – the plastic plate can be separated from the MDF template. Inspecting the work – it seems the blade has wandered off vertical in a couple of places, and has nicked the template. These will need repairing with two-part. This one, (below) is mostly just on the face of the template, but it has just extended far enough to cause a tiny flaw on the edge of the acrylic sheet.
There are a few other faults – (detailed below), – but, for a first attempt, the result isn’t actually too bad. When I check the fit against the guitar body – I can see a few areas which look to be slightly off. The little nub of a horn below the neck pocket is quite small, and it looks as if the cutter has gone slightly off line there. I think I need to be extra careful cutting around the neck pocket – so perhaps I need to look at the template again here. Also, the chrome control plate doesn’t quite fit into it’s semi-circular opening, (wheras the template fits perfectly). This suggests I might not have followed the edge of the template exactly with the following bead – or perhaps the sides of the template aren’t precisely perpendicular, or consistent.
A quick mock up with the body, control plate, bridge and scratchplate also shows that the extension by the control panel – cut flush against the rest of the plate – appears to push the control plate a little out of line. The control plate looks to be lying slightly off parallel with the bridge plate. It’s difficult to tell, to be honest, without actually screwing the metal plates into position, but something doesn’t look quite right to my eye. It’s very minor – but I may have to refine the template further – as I come to fix the bridge in place. And that isn’t going to happen until the nitro has cured.
I’m now sure I’ll have to cut a more accurate template, (or modify the existing one), and tailor it to exactly fit the body’s geometry. Importantly however – I don’t now see it as a task which has to be offloaded to someone else for custom manufacture. I think I’ll be able to make the necessary adjustments, and learn how to get the best out of my setup. I’m sure I’ll be able to improve my technique with a few more practice runs – in order to get my desired result.
In the meanwhile – this plate will allow me to check the overall positioning, and fit of the plate on the body. It will help me refine the template, and test cuts will help furnish me with blanks to make a few finish experiments and mock-ups.
Things I’ve learned
- Don’t use too much double-sided sticky tape! Presumably, if I’d had the protective coating in place, I could have sacrificed the protective film – making the task of separating the finished plate from the MDF template a whole lot easier. As it turns out – my sticky tape is extremely grabby, and it’s virtually impossible to pry the finished plate away from the MDF without breaking it. In the end, I have to drip lighter fluid down between the two, until the adhesive on the tape softens. Even then – it takes a lot of naptha to break it down, and it only stays soft enough for a few minutes. Once the naptha has evaporated, the adhesive reverts, and creates a horrible, sticky mess. It takes a lot of naptha, and a lot of clean, soft cloths to eventually clean the whole thing up.
- The cutting blade needs to be kept absolutely perpendicular to the work at all times. Even the slightest deviation can cause the blade to cut into the edge of the template. Where this happens – small indents can be translated to the edge of the plastic sheet. It’s possible these might polish or sand out – but if they’re missed, they’re likely to be picked up by the following bead on the router, next time. Any nicks in the template need to be filled with two-part, and smoothed, before any more plates are cut.
- Despite using a square gauge to check the end of the control plate extension – the template is, quite clearly, not quite finished square. I’ll need to fix it before the actual production plate is cut. It’s also possible that the edge isn’t quite perpendicular here – it’s quite hard to keep the router completely flat over such a thin area. I may need to re-cut the extension a tiny little bit shorter, to make sure I get it right. Any areas where the edges of the template are not perpendicular to the faces of the template will result in cutting inconsistencies.
- When you’re cutting the pickup opening – LET THE ROUTER COME TO A STOP AWAY FROM THE EDGE OF THE WORK. If you try to lift the router with the blade still turning – you risk nicking the edge of the template with the blade – and any slight nick will transfer itself to your, otherwise nicely cut, plate.
- When drilling any screw holes through into the acrylic sheet – if you let the cutting bit get clogged – or push the bit down before it’s cut properly – then you risk splitting the plastic. Especially when they’re close to the edges.
- For the countersinks, it helps if you calibrate, and use the stop adjustments on your drill press, (if you have such luxuries). Otherwise, it’s hard to keep the countersink holes looking consistent, and easy to cut them too deep, or too shallow.
The main thing I’ve learned is that the process of cutting a scratchguard myself, is likely to be a gradual, tailoring excerise – with quite a few steps before the template is perfected. And that’s before the final plate can even be cut. I may also have to cut a few plates before I get one that’s exactly right. I should have plenty of “mistakes” to experiment on, with finishes.