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Deriving the unbent side profile
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10106&t=55758		 Page 1 of 1
Author:  bcombs510 [ Wed Jul 12, 2023 8:43 pm ]
Post subject:  Deriving the unbent side profile
Hey folks,

I'm not sure who is still paying attention down here in this forum, but.... :)

I'm spending some cycles on learning how to create a side profile template. I see these from LMI, SM, etc... and many plans have them as well. The profile of the unbent side where along the edge of the side which will meet the back you have the taper and radius factored in already. I know you know what I'm taling about, but here is a video anyway - https://youtu.be/7oojobi72mE

There are a set of known dimensions, the unbent side length, the length of the box, the radius in question, neck block height, tail block height, etc... I'm expecting there is not a way short of modeling all this up to derive the profile to use for the unbent side. Is that correct? I didn't want to head down the rabbit hole of modeling it all up only to learn there is some easier way to arrive at that shape.

Note: I mean arrive at the shape on the computer. I'm aware of how to trace the shape with the mold using a washer and pencil, etc... what I mean is arrive at the shape in CAD.

Thanks!
Brad
Author:  Chris Pile [ Wed Jul 12, 2023 11:27 pm ]
Post subject:  Re: Deriving the unbent side profile
I read it, Brad.
As a long time CNC guy, and there's no easy way - you gotta do the math. But sometimes it's hard to figure out what math to do. Good luck.
Author:  bcombs510 [ Thu Jul 13, 2023 10:19 am ]
Post subject:  Re: Deriving the unbent side profile
Chris Pile wrote:
I read it, Brad.
As a long time CNC guy, and there's no easy way - you gotta do the math. But sometimes it's hard to figure out what math to do. Good luck.

Thanks, Chris!

Yeah, I’m expecting to have to model it all up. What I didn’t want was to get way down the rabbit hole and then have someone point me to R.M. Mottola’s online calculator or some such. :D

Brad


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Author:  Marcus [ Thu Jul 13, 2023 11:03 am ]
Post subject:  Re: Deriving the unbent side profile
I know some more advanced programs can do it, but I can't remember off the top of my head which ones. I think I remember reading that Fusion 360 can do it in "Sheet Metal" mode. I've been meaning to try it out for awhile.
Author:  Jim Watts [ Thu Jul 13, 2023 5:31 pm ]
Post subject:  Re: Deriving the unbent side profile
Use masking tape to tape up the side of one of your finished guitars and then peel it off. this will give you a flat pattern for the sides.
Author:  Durero [ Thu Jul 13, 2023 7:28 pm ]
Post subject:  Re: Deriving the unbent side profile
I can confirm that there are functions in Rhino3D to show the flattened version of curved surfaces. I'm guessing that most other CAD packages have similar functions. Which one are you using Brad?

But yeah those functions presume you already have the 3D model done.
Author:  SteveSmith [ Thu Jul 13, 2023 8:27 pm ]
Post subject:  Deriving the unbent side profile
Jim Watts wrote:
Use masking tape to tape up the side of one of your finished guitars and then peel it off. this will give you a flat pattern for the sides.

That’s what I do too but I figured Brad
was talking about a new design.


Steve
Author:  bcombs510 [ Thu Jul 13, 2023 9:18 pm ]
Post subject:  Deriving the unbent side profile
Yeah, I want the shape in CAD. It’s long winded, but suffice it to say I want to do more than just make a side template out of acrylic with the knowledge. :)

I’m using Fusion 360 and Marcus had me on the right path. I’ve got a set of steps using the sheet metal unfold approach. Working through it now.

Thanks all!


Sent from my iPhone using Tapatalk Pro
Author:  10WChris [ Tue Jul 18, 2023 9:18 am ]
Post subject:  Re: Deriving the unbent side profile
Hi,
im pretty confident, that every decent CAD-App has commands for that kind of operation.
rhino has two commands to do that task, and I use them to do side-templates:
- one for a curve: CreateUVCrv
- on efor a surface: UnrollSrf
best regards
Chris
Author:  GregHolmberg [ Wed Nov 20, 2024 4:15 pm ]
Post subject:  Re: Deriving the unbent side profile
OK, it's over a year later, but maybe this will still help someone.

I model acoustic guitar bodies using onshape.com 3D CAD. It runs in your browser (so nothing to install) and is free to use. However, your plans will be visible to others and can be copied.

Here's an example body: a Martin OM.

This was modeled using the techniques proposed by R. M. Mottola and used in his "G Thang" tool. It is fully constrained (i.e. it won’t fall apart if you change something), and is also parameterized, so you can just change dimensions in the variable table, and the model will update.

In the model, I converted the surface of the sides to sheet metal, and then unwrapped the sheet metal to be flat.

From the flat view I converted and exported a DXF file, which I took to my local plastics shop (TAP Plastics), where they cut it out of 1/4" acrylic using their laser cutter. This was pricey, but now I have a template to route to with a trim bit.

I've since bought a CNC machine (a Laguna IQ 24x48), and I can cut my wooden sides directly. onshape is still working on their CAM module, but for now I'm using the free Kiri:moto plug-in to onshape to generate G-code for the CNC. It does the job.

Hope this helps,

Greg
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