Mitred Purflings

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Dave M
Blackwood
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Mitred Purflings

Post by Dave M » Sat Jul 13, 2019 12:57 am

I was reasonably pleased with my latest classical. First time not using Maple for back and sides so I had to think about the purfling scheme.

However I was reminded by what Robbie Obrien said in in a recent video - and Trevor has said - that if you are going to do mitered joints then they have to be good. Mine weren't! I could kick myself. My excuse is that I had had a huge struggle getting both the binding and the home cooked purfling lines to conform that I just wanted to get it finished.

A lesson to be learned.

Only consolation is that it does sound good and the geometry is exactly where I wanted it for a change.
Attachments
mitre 1 v small.jpg
cutaway 1 v small.jpg
front 1 v small.jpg
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Dave

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Mark McLean
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Re: Mitred Purflings

Post by Mark McLean » Sat Jul 13, 2019 8:39 am

You are right Dave - they make absolutely no difference to sound or playability, but a big contribution to the “snazzy factor” of the look. I haven’t perfected it yet either, but I know a few elements that make a difference:
1. Wide purflings like yours are harder to get right. Even a slightly “off” angle will make a visible gap.
2. Dark colour purfling material, like black, makes it easier to hide gaps. Ebony sawdust and CA glue will hide most mistakes. Light coloured purfling tends to reveal attempts to fill.
3. If you are doing the angled cuts with a chisel, it helps to have a highly polished surface on the flat side of your chisel and to use the reflection to judge the angle of the cut. When it is a 45 degree angle you can eyeball a right angle in the “mirror” and get it spot on. When it is a different angle it is harder, but the reflection still helps you get it close to perfect.
4. Measure it (twice) but cut it over-length. Then gradually whittle it down to exact length with fine cuts using a sharp chisel. If it is too long you can always make it shorter. Once it is too short, you are buggered.
5. You need really good light, and magnifying lenses unless your eyes are phenomenally good. A magnifying visor or large lens with built in illumination is a real boon.

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Allen
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Re: Mitred Purflings

Post by Allen » Sat Jul 13, 2019 4:44 pm

1. Razor sharp chisel and polished back to see the angle is crucial.

2. I have to use a magnifying visor as my regular reading glasses just aren't good enough. And pretty much everyone I know even with good eyesight would benefit from the use.

3. Don't ever think you can hide a small gap at a mitre. If it isn't right, make another one.

4. I also try to have the depth of purfling to be just a hair high so that I don't have to remove hardly any material to level them. Then I will put a slight undercut to the purfling. This is so I can really push what will be the show face of the mitre tips closer together. If it's the other way then it's vitually impossible to get the show surface to fit correctly as the bottoms will interfere with getting a tight joint.

5. If a light colored timber use a touch of PVA glue on the end grain of the purfling to both pieces. CA glue will almost always make a dark line even if you had a perfect fit.

6. You can also try and have the mitres cut just slightly more acute so that the tips come together with a slight spring and compression of them. This gives the same effect as the undercutting I mention in step 4.
Allen R. McFarlen
https://www.brguitars.com
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Dave M
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Location: Somerset UK

Re: Mitred Purflings

Post by Dave M » Sun Jul 14, 2019 2:09 am

Thanks Mark and Allen. I feel really stupid but thought throwing the pics up might help other starters like myself to get it right.

Your suggestions are all correct and I thought I had absorbed those lessons, but that quick rush to the head betrayed me.

I think this is a general lesson for we amateurs. You just can't take your eye off the ball at any stage of the process. Particularly at the end when you really want to hear what the thing is going to sound like.
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Dave

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