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Marking a center line on a body blank.
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10123&t=53088		 Page 1 of 1
Author:  Conor_Searl [ Fri Apr 10, 2020 2:53 pm ]
Post subject:  Marking a center line on a body blank.
Since I never paid attention in shop class, and am now later in life developing my woodworkers common sense I occasionally come across simple tasks that I'm sure I do the hard way.

I've got my center line marked on my body blank, I have a 1/2" MDF template with a center line scribed down the middle. Up to now I've been using my eyeballs to line those two lines up. The perspective looking from above is always a little askew, so I check there and then at both ends. When I'm satisfied I trace the outline of the template and proceed to my bandsaw. Its worked okay, but I'm curious if there is a more efficient, and accurate way of doing this.
Author:  Freeman [ Fri Apr 10, 2020 7:45 pm ]
Post subject:  Re: Marking a center line on a body blank.
If you are only trying to transfer the line on the template to the line on the body, use a small combination square to extend it down the face.

However I will add that I usually put some temporary lines on the body while I route the neck pocket and set the neck. Get it as good as its going to get. Then use the sides of the neck to establish your centerline on the body and use the actual neck in place to establish your scale length. Those will be your true center relative to the neck and you can use those to drill and route holes.
Author:  dzsmith [ Fri Apr 10, 2020 8:23 pm ]
Post subject:  Re: Marking a center line on a body blank.
Mark the centerlines on the sides of your template.
Author:  Freeman [ Sat Apr 11, 2020 10:30 am ]
Post subject:  Re: Marking a center line on a body blank.
Here is a procedure that has worked pretty well for me. It might need to be modified slightly depending on the type of body and joint. But basically I built the neck so it fits (snuggly) into the template. Clamp the neck and template to the top of the guitar, put straight edges on either side and center the it at the bridge location. I don't totally trust double stick tape for templates so I run a couple of flat head wood screws (countersunk of course) into areas that will be routed out (pickup cavities)

Attachment:
IMG_4685-1.jpg


For a carved top or angled neck it is necessary to angle the pocket. Usually that works by just making the top the correct angle but if you have overstand or wedges or anything like that you will need to shim your template.

Attachment:
058-1.jpg


Attachment:
060-1.jpg


I drill out as much waste as possible with Forstner bits before starting to route. I also put a piece of masking tape on the face of the template where the bearing rides - that makes the cavity just a hair narrower than the tenon. I would rather remove a tiny bit of wood to make a tight fit than to have it too loose.

Notice that in both those guitars the bridge, pickups, etc are not drilled until the neck is in its home.
Author:  Conor_Searl [ Sun Apr 12, 2020 11:45 am ]
Post subject:  Re: Marking a center line on a body blank.
dzsmith wrote:
Mark the centerlines on the sides of your template.


Hahaha, obviously. :oops:
Author:  Conor_Searl [ Sun Apr 12, 2020 11:57 am ]
Post subject:  Re: Marking a center line on a body blank.
Freeman, thanks for your in depth explanations.

The body template I have has the pickup cavities and bridge location already added, so the only place to screw the template down would be the neck pocket. I suppose a couple screws there and double sided tape would be pretty secure, but I haven't had any trouble with double sided tape. Yet.

I find it so tempting to want to get the body finished, I've just done all of the body routing before making the neck including the pocket. But I see how your method is better. I'm going to try that this time. I remember now that you mentioned the masking tape trick before that's helpful too!

As an aside, when making your carved top guitars you mention angling the top. In your picture it looks like the angle is just from the neck pickup to the body edge where the neck cavity goes. Is that correct? The rest of the top remains flat at full thickness until the carving happens?
Author:  Freeman [ Sun Apr 12, 2020 1:04 pm ]
Post subject:  Re: Marking a center line on a body blank.
You can't screw into the neck pocket, you will be routing there. About your best choice would be one of the mounting screws for bridge or pickup. I have a separate template for each and I use the mounting screws when I can. I had a template shift once with double stick tape so I'm scared of it, maybe you can get a couple of clamps on in places that won't be in the way.

An all in one template is fine, but if the neck is off by even a hair then everything is off. Once again, I've done it this way for so long with no problems that I don't want to change.

As far as the angled neck - each guitar is apt to be different. If you build from plans (and trust them), then follow whatever is shown. I have a little rule that the shape of the top really doesn't matter - what matters it that the fret plane hit the bridge location at a defined point. That comes from all the acoustics I have built - the one cardinal rule is that the fret plane hits the top of the bridge. Period. If I do that I know I can get acceptable action with a reasonable amount of saddle sticking out of the bridge and have some hope in the future of compensating for changes.

An electric guitar is the same but different. But with every one that I have built, if I have the fret plane just touching the tops of the saddles at their very lowest settings (which is the equivalent of the top of an acoustic bridge) the I have been able to adjust the action to be playable and have lots of room for future changes. There are of course exceptions - a resonator might be different but you would be surprised how well it works.

For many les paul style guitars with no overstand (that is important) a neck angle of 3-1/2 to 4 degrees will give you that geometry with a standard ToM bridge. But bridges differ so I make sure I have it in hand before I start. I also check over and over and over as I am building - I bring the neck slowly down into its pocket and keep checking where the fret plane is at the bridge location.

Hiscock has a good section in his book about geometry, I wrote a little blurb for a different forum

https://www.tdpri.com/threads/building- ... ty.991659/
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