Share:
Notifications
Clear all

Bending a top / back

10 Posts
5 Users
46 Likes
205 Views
tv1
 tv1
(@tv101)
Illustrious Member Customer Registered
Luthier
Rep Points: 27896
Joined: 4 years ago
Posts: 3017
Topic starter  

Let's imagine that I was vaguely considering making a hollowbody-esque but wanted to avoid the excitement of an @JamesBisset vacuuming-bending-splitting (repeat) saga.

Let's also imagine that I had the opportunity to acquire a rosewood top & back set of ~3mm thickness.

Could I ....

  • Make some shaped internal braces of appropriate widths (top side of brace is curved, bottom side is flat)
  • Gradually, encourage the top/back to adopt the curved shape of the braces (wet, heat, weight)
  • Avoid the JamesBisseting (now Scottish rhyming slang for splitting)
  • Once the shape is formed in the top/back, then glue the top/back to the braces
  • Then fit the braces into some central supports and the sides (not fully worked that bit out yet)
  • = One shaped top/back guitar body.

?

Online guitar making courses – guitarmaking.co.uk


   
Koendb, Robin, swepri and 1 people reacted
Quote
jamesbisset
(@jamesbisset)
Noble Member
Luthier
Rep Points: 1440
Joined: 4 years ago
Posts: 285
 

I reckon ‘gradually’ is the secret ingredient here.

Question though: if it has never been done before, why not?

Jack of all trades and master of my own destiny. It’s only a small destiny.


   
Koendb, tv1, Robin and 2 people reacted
ReplyQuote
Rocknroller912
(@rocknroller912)
Illustrious Member Customer
Luthier
Rep Points: 8383
Joined: 4 years ago
Posts: 1149
 

@tv101

Steam box would be the best way to soften wood to make a difficult shape but I think 3 mm will be a bit thick. Some makers only use a steam box to shape the ribs, them clamp to a dry form and leave for a few days.

Alternatively you could try a lute style construction which is used for bowl back instruments. A former is made which is a bit like roof trusses with a curve instead of an apex. The pieces are put together long ways and fixed to top/bottom blocks. 

Some people call me a tool, others are less complimentary. Tools being useful things.


   
Koendb, tv1, Robin and 2 people reacted
ReplyQuote
tv1
 tv1
(@tv101)
Illustrious Member Customer Registered
Luthier
Rep Points: 27896
Joined: 4 years ago
Posts: 3017
Topic starter  

Posted by: @jamesbisset

Question though: if it has never been done before, why not?

Said James Bisset, watching the Wright brothers' inaugural flight .... 🤣 

 

 

Posted by: @rocknroller912

Alternatively you could try a lute style construction which is used for bowl back instruments. A former is made which is a bit like roof trusses with a curve instead of an apex. The pieces are put together long ways and fixed to top/bottom blocks. 

That's what I have, vaguely in mind, @rocknroller912.  I thought I'd try to make a frame, like an aircraft wing, with shaped top & back but with the addition of some vertical side pieces too.  Then gradually encourage the top & back to adopt the curved shape of the frame.  The vertical side pieces would then fix to the (also bent) sides of the guitar.  

Maybe.

 

Online guitar making courses – guitarmaking.co.uk


   
Koendb, Robin, Russ and 1 people reacted
ReplyQuote
Rocknroller912
(@rocknroller912)
Illustrious Member Customer
Luthier
Rep Points: 8383
Joined: 4 years ago
Posts: 1149
 

@tv101 

Will you use your cnc to make the frame. Flat sawn wood will take a curve more that quarter sawn i think as it warps naturally to a curve over time so you will just be accelerating the process.

Some people call me a tool, others are less complimentary. Tools being useful things.


   
Koendb, tv1, Robin and 2 people reacted
ReplyQuote
Clinton
(@clinton)
Famed Member
Luthier
Rep Points: 4944
Joined: 4 years ago
Posts: 726
 

Surely can do. Steam, a radius dish and go bar clamping would make your life so much easier.


   
Koendb, tv1, swepri and 2 people reacted
ReplyQuote
tv1
 tv1
(@tv101)
Illustrious Member Customer Registered
Luthier
Rep Points: 27896
Joined: 4 years ago
Posts: 3017
Topic starter  

Posted by: @rocknroller912

@tv101 

Will you use your cnc to make the frame. 

 

Probably @rocknroller912 - just because I've got one to use 😉 

I should design it properly.  Get the span dimensions and curves properly modelled, for maybe 3 or 4 horizontals and maybe a centre line too.  Sort of like an aircraft wing.

Probably be quicker to do it the Bisset-way ...

 

Online guitar making courses – guitarmaking.co.uk


   
Koendb, Russ, Robin and 1 people reacted
ReplyQuote
Robin
(@robin)
Illustrious Member Customer
Luthier
Rep Points: 16756
Joined: 4 years ago
Posts: 1061
 

@tv101 

I should design it properly.  Get the span dimensions and curves properly modelled, for maybe 3 or 4 horizontals and maybe a centre line too.  

I could probably model that on SolidWorks for you, given a sketch and some dimensions. I don't know how the model translates into your CNC program though, what format would you need the model saved as.


   
swepri, Koendb, Bpower and 2 people reacted
ReplyQuote
tv1
 tv1
(@tv101)
Illustrious Member Customer Registered
Luthier
Rep Points: 27896
Joined: 4 years ago
Posts: 3017
Topic starter  

Hi @Robin - that is (a) most kind and (b) would probably save me weeks of trying to understand 3D modelling!

 

Apparently, the application I use to generate the toolpaths (and do the design work, though I've really only done 2D stuff), says that it can import STL or DXF files - and a whole load more besides, but I think those are standard formats?  I suppose the spans would only need to be 2D anyway - the "3D" aspect would come from the thickness of the material that I cut them out of. 

 

I was thinking of making a hollow body Bandsman style guitar, though my thinking hadn't got a lot further than that.  Maybe I'll try some rough sketching next.

Online guitar making courses – guitarmaking.co.uk


   
swepri, Russ, Koendb and 2 people reacted
ReplyQuote
Robin
(@robin)
Illustrious Member Customer
Luthier
Rep Points: 16756
Joined: 4 years ago
Posts: 1061
 

@tv101 

Apparently, the application I use to generate the toolpaths (and do the design work, though I've really only done 2D stuff), says that it can import STL or DXF files - and a whole load more besides, but I think those are standard formats? 

Yes, I can export either SDL or DXF, there's settings for tolerances, the tighter the tolerance then the bigger the file. It might need a little experimentation.


   
swepri, Russ, Koendb and 1 people reacted
ReplyQuote
Share: