how to make edges perpendicular to complex shapes
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- This topic has 5 replies, 4 voices, and was last updated 7 years ago by Edmund.
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Dear all,
i’m trying to fabricate purely by handtools an electric guitar. See the picture attached. The problem I have is, that i used rasps and handplane to roughly make the shape. But this even after the most careful treatment caused a bellying of the guitar sides. I want to assure, that the sides are perfectly perpendicular to the back side of the guitar.Standard way how to achieve this is to use sanding table, where the sanding drum protrudes through the table, guaranteeing the perpendicularity. This permits as well to do complex concave shapes as protrusions for the hands on the electric guitar.
Any hint appreciated
(btw: only battery operated drill was used to make the skeleton you see in the picture)
thanks
david
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You must be logged in to view attached files.26 March 2017 at 1:53 pm #310531I think, a suitable body stance, secure clamping of the guitar body and practise are the main keys, plus a good square to check often.
When rasping, the hand, that is at the long end of the rasp (seen from wood) has the better leverage and usually goes down automatically. Instead, you have to keep both hands level. This is not easy and requires practise. Perhaps, you can practise on another piece of wood first. For example, just take a board with one large flat surface and get the sides square and parallel.
It also helps to clamp the guitar low in the vise, so you have your workbench as a visual reference. If that is not possible, you can clamp or superglue square wooden blocks near the edges to guide you. Of course, these blocks need to be slightly away from the edge, because if you touch them with your rasp, you will quickly get them out of square. The blocks are visual guides only.
Dieter
- This reply was modified 7 years ago by Hugo Notti.
Great project. If you did a good job with your hand plane of flattening the back of your guitar body, then couldn’t you just register the body of your square against the back and check the sides, and make any small tweaks to the areas which aren’t perfectly perpendicular?
If there are large areas out of square, then what about a scribing tool first, followed by a saw. Basically the scribing tool in this case will function like a square, but instead of the flat blade of a square, it has a pencil or marking knife at a right angle to the body. You can make one — just stick a pencil or a sharpened finish nail or etc through a flat piece of wood at 90 degrees. Run the body of the scribe along the flat back of your guitar body, and the pencil or knife will mark a line along the side where you need to cut away material. Where the side is undercut or perfectly 90, it obviously won’t draw a line. You can then fix the undercut areas later by finding them with an actual square.
If the top / front of the guitar is also flattened to a high standard, the you can do that procedure from both sides, and when you perform this procedure from the top it will find all the areas which were undercut with respect to the bottom.
Good luck, I’d love to see (and hear) the final product
Hi both,
thanks for hints. Scribing tool seems as a very good idea. Wouldn’t you have a picture of yours? IMO the only way how to produce one is to use chalk or something similar, running over the entire one side of the square such, that when i’m scribing, it shows the points of the touch in white (if the chalk is white, i have a dark wood). so i have to somehow intelligently fix the chalk into the square….. hmmm
- This reply was modified 7 years ago by dejfson.
hello
I’m not an instrument maker but if i was trying to do what you are doing i would cut two templates the same (cut and shape them screwed together to ensure accuracy) then put one on each face of your blank lining them up using a square and measuring or gauging equi-distance from the blade of a square. mark around them and work to the lines.
Two points in diagonally opposite corners (so to speak) would line them up.You don’t necessarily have to worry about coating your square with chalk or anything remotely complicated.
Just make sure your front and back are properly flattened, and put your guitar body into a vise, and scribe it in two or three steps (the vise will block access to some areas of the guitar body obviously, which is why you’ll need to take it out of the vise and re-orient it before proceeding).
Pick one side and start with that side facing you. Let’s say it’s the back. Pretend the back of your guitar body is facing you in this picture:
And the square in the picture is slightly unconventional, but you’ll get the point. The person in the picture is scribing what in your case will be the side of your guitar that you want to make perpendicular to the back of the guitar body. You’ll just run your square body registered against the flat back (at first, then the front later), and when it bumps into something, that means the side is sticking out. So mark it however you want, the person in the picture is using a pencil. Proceed all around, re-orienting the guitar in the vise as necessary, then when you’re finished with the back of the body facing you, do the scribing with the front side facing you as mentioned earlier, so you get any areas which are undercut with respect to the back face.
It’s one of those concepts which is so simple that it’s actually difficult to explain, and I apologize I’m not doing a good job conveying such a simple thing. Very frustrating, but I think once you try what’s in the picture you’ll quickly grasp the concept. Good luck!
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