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  #1  
Old 12-22-2017, 04:07 PM
Carl1Mayer Carl1Mayer is offline
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Default Cylindrical top guitar build

Ive decided to start building a new guitar with a cylindrical bend in the soundboard. I had previously built an upright bass using a similar approach to get out of having to carve the top (and to get out of paying ~$400 for a blank of spruce that big).

Its documented here if anyones interested https://www.talkbass.com/threads/alm...-bass.1194755/

I was happy with the result and pretty impressed that a minimally braced 1/8" plywood top could hold ~400lbs of string tension (the steep break angle on a bass bridge directs ~100lb of that normal to the soundboard). Since I typically play guitar more regularly than bass I started digging to see if anyone uses a similar approach with guitars and found out the Howe-Orme company had stolen my good idea about a century before I thought of it (pictured below from google). In addition to the Howe-Orme guitars I would be remiss if I didn't mention Nigel Forster (http://www.nkforsterguitars.com) who is a modern builder using this approach as well, and from the sound clips Ive been able to find he's using it to great effect.



Since the bracing used isn't well documented for the original Howe-Ormes and would depend on how tight of a radius I decide to put in the top I did a bit of finite element modeling to come up with a bracing pattern where the stresses don't exceed what a traditional flattop sees while also cutting weight as much as possible





(Max Deviatoric Stress image is the mostly blue one out of plane displacement is the mostly green one)

Comparing the unbraced soundboards you can see that adding the radius to the top only gives you a little improvement when you put a sound hole in the middle of it because its almost flat on either side of the hole making it much weaker than the rest of the top. Moving the sound hole off of the radiuses part makes the radius much more effective. Another option would be to use a smaller oval sound hole like the Selmer jazz guitars.

Anyway after experimenting with a few design iterations I got the stress pretty comparable to a representative flat top (roughly based on a gibson L00) with only 63% of the weight using a pretty simple X brace pattern (Im using the max deviatoric stress as the metric since wood has pretty significant tension-compression asymmetry). At the same stress the Z displacement for this design is also more meaning it should in theory move more air and be louder.

Next step is to start on all the molds and other such prepwork.

Last edited by Carl1Mayer; 12-29-2017 at 09:36 AM. Reason: (broken image links)
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Old 12-22-2017, 04:19 PM
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I can't understand how your cylindrical top #2 can see more stress with the parallel bracing than the unbraced variant.

it doesn't pass the sniff test. Did you alter the boundary conditions or something?
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Old 12-22-2017, 09:10 PM
Carl1Mayer Carl1Mayer is offline
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The unbraced ones are all .125" thick (as well as the braced flattop per its plans) while the braced cylindrical ones I reduced the top plate thicknesses to cut weight until the stress was about the same as the flattop (at the original 3mm even the unbraced cylinder top is just as good as the braced flattop but you don't get that much weight savings that way). For the x braced one that ended up around .09". Both the x and parallel braced ones shown are modeled at that thickness but since the parallel bracing wasn't as effective I didn't bother spending the time to further optimize the thickness on that one to match the braced flattop.
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Old 12-24-2017, 12:43 PM
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I believe the Larson brothers used a 12' radius cylindrical top on some of their designs. I've built a couple with cylinrical tops.
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Old 12-25-2017, 02:24 PM
Carl1Mayer Carl1Mayer is offline
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Happy holidays all, catching up on some of the progress Ive made while I'm on a train.

I have all the side and soundboard molds made up (just plain 3/4" particle board) and then faired in with durhams wood putty. I made the side molds in two pieces so I can use it as a half mold for forming the sides and a whole mold for holding the body shape when I glue the top.





The sides I laminated out of 3 layers of 1/16" maple with the center ply orthogonal. I got a bunch of plies from roarocket (http://www.roarockit.com/skateboard-.../#.WkFqn2Uyk-I). They're intended for making skateboards but hard maple is hard maple and the price is right. I used a bike inner tube to pull the plies into the mold which works pretty well for awkward shaped things if you don't have a vacuum press set up.



I also got the soundboard joined and thinned down to .100" and it pulled down to the arch without much trouble.



Next up will be the neck and end blocks, and trimming the sides to the top contour.

Last edited by Carl1Mayer; 12-29-2017 at 09:38 AM. Reason: (broken image links)
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Old 12-26-2017, 08:56 AM
Carl1Mayer Carl1Mayer is offline
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Quote:
Originally Posted by Rodger Knox View Post
I believe the Larson brothers used a 12' radius cylindrical top on some of their designs. I've built a couple with cylinrical tops.
How'd they turn out and do you have any pictures? I couldn't find any on your webpage. Also what type of bracing approach did you settle on if you don't mind me asking?
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Old 12-26-2017, 10:57 AM
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The two parlors (Hauser model) and the paduc back & sides are cylindrical tops, they use an unorthodox bracing pattern. There are too many differences to draw any meaningful conclusions about bracing or the cylindrical top.
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Old 12-26-2017, 12:04 PM
LouieAtienza LouieAtienza is offline
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Quote:
Originally Posted by Carl1Mayer View Post
Ive decided to start building a new guitar with a cylindrical bend in the soundboard. I had previously built an upright bass using a similar approach to get out of having to carve the top (and to get out of paying ~$400 for a blank of spruce that big).

Its documented here if anyones interested https://www.talkbass.com/threads/alm...-bass.1194755/

I was happy with the result and pretty impressed that a minimally braced 1/8" plywood top could hold ~400lbs of string tension (the steep break angle on a bass bridge directs ~100lb of that normal to the soundboard). Since I typically play guitar more regularly than bass I started digging to see if anyone uses a similar approach with guitars and found out the Howe-Orme company had stolen my good idea about a century before I thought of it (pictured below from google). In addition to the Howe-Orme guitars I would be remiss if I didn't mention Nigel Forster (http://www.nkforsterguitars.com) who is a modern builder using this approach as well, and from the sound clips Ive been able to find he's using it to great effect.




Since the bracing used isn't well documented for the original Howe-Ormes and would depend on how tight of a radius I decide to put in the top I did a bit of finite element modeling to come up with a bracing pattern where the stresses don't exceed what a traditional flattop sees while also cutting weight as much as possible





(Max Deviatoric Stress image is the mostly blue one out of plane displacement is the mostly green one)

Comparing the unbraced soundboards you can see that adding the radius to the top only gives you a little improvement when you put a sound hole in the middle of it because its almost flat on either side of the hole making it much weaker than the rest of the top. Moving the sound hole off of the radiuses part makes the radius much more effective. Another option would be to use a smaller oval sound hole like the Selmer jazz guitars.

Anyway after experimenting with a few design iterations I got the stress pretty comparable to a representative flat top (roughly based on a gibson L00) with only 63% of the weight using a pretty simple X brace pattern (Im using the max deviatoric stress as the metric since wood has pretty significant tension-compression asymmetry). At the same stress the Z displacement for this design is also more meaning it should in theory move more air and be louder.

Next step is to start on all the molds and other such prepwork.
Cool...

I believe Nigel Forster worked with Stefan Sobell, of who he learned the approach from...
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Old 12-29-2017, 07:10 AM
Carl1Mayer Carl1Mayer is offline
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My day job has been light over the holidays so Ive been making some good progress on this thing. The neck and tail blocks are glued in and I have the rim planed level.





The soundboard is coming together nicely as well. I glued some temporary braces outside the section Im going to use just to help hold the contour before its glued to the rim. They'll be trimmed off later.




I stuck PSA sandpaper on the top former and used it to fit the braces (I got the idea for the sanding guides from http://acousticsoundboard.co.uk/thre...larson?page=15 , its a shame his bracing was too light and it folded at the sound hole). All the braces are glued and will hopefully Ill have the shaping done today. I used a layer of aluminum flashing between the soundboard and sandpaper so I wouldn't get a bunch of nicks in it, which is especially important since I don't have much soundboard thickness to sand into.





Next up will be adding two more layers of maple to the rim to serve as linings and then cut the cylinder top profile into the rim

Last edited by Carl1Mayer; 12-29-2017 at 09:42 AM. Reason: (broken links)
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Old 12-29-2017, 08:31 AM
redir redir is offline
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I don't see any photo's in this thread except for the Howe-Orme.
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Old 12-29-2017, 09:45 AM
Carl1Mayer Carl1Mayer is offline
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Quote:
Originally Posted by redir View Post
I don't see any photo's in this thread except for the Howe-Orme.
Sorry about that, apparently dropbox can't publicly host images any more but I could still see them. Anyway I switched over to imgur so let me know if there are any new issues with that.
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Old 12-29-2017, 01:36 PM
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Very cool. Looking forward to watching your progress.
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Old 12-29-2017, 02:09 PM
LouieAtienza LouieAtienza is offline
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Awesome!!!
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Old 12-29-2017, 08:49 PM
Carl1Mayer Carl1Mayer is offline
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So Im designing an adjustable neck joint to use with this guitar (cross section below). It'll be similar to the ones used on the original howe-ormes in that you'll be able to change the neck angle from outside the guitar easily. What I didn't really like on their design was that all of the load on the neck is directed through two threaded studs so I changed it to have full wood to wood connection at the top of the neck joint (through a radius at the base of the neck and a complimentary block attached to the body) and moved the threaded adjustment to the bottom of the neck heel. I also included a mortise and tenon slot to help keep it aligned to the body. It probably isn't necessary but I can use it for a more traditional bolt-on neck if this idea doesn't pan out.




Since the body will be ~5" deep where the neck attaches Im considering joining the main part of the neck to the long heel through a finger joint like whats shown below plus a few dowel rods. Have any of y'all tried something like this? I already have a bunch of leftover 1/4"x2" maple strips I can laminate it out of but maybe its not worth the time.

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Old 12-29-2017, 09:20 PM
LouieAtienza LouieAtienza is offline
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That's pretty cool... I did something somewhat similar a long while ago, except I had the configuration the other way, the bearing surface was on the neck and the "saddle was a separate piece on the guitar, and the bearing surfaces were slightly eccentric so that when the action was raised, the neck actually pulled toward the body and vice versa. I also pocketed the heel into the body to make it less "visible". I also used a heavy spring to keep tension on the lower bolt, so the neck wouldn't move if I changed strings. Unfortunately I knocked the guitar over and I took too much off the heel block and the whole thing exploded before I could touch it up! But cool ideas here..

The only thing with the finger joint is that it may look a little funny once you carve the heel area...
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