Opinions on my small jumbo

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Jeremy D
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Opinions on my small jumbo

Post by Jeremy D » Mon Oct 07, 2013 6:06 pm

I have been designing a small jumbo. I have based it loosely on the j-185 shape. Mine has a smaller lower bout and slightly different curves. I also hope to incorporate a scoop style cutaway.

Specs are
Body Length 514.35mm
Width 406.4mm
Scale length 645.16mm
14th fret body joint
46mm nut
56mm at 14th
99mm Sound hole diameter
Bridge plate is 60mm tall.

I have made all the bracing 6.3mm (1/4") except for the UTB and the splay of the X brace is 100 degrees.

I wonder if anyone would care to share some comments on the shape and bracing layout? It will be my 3rd guitar and my first not taken directly from a plan. Also happy to share the cad files if anyone is interested.

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Re: Opinions on my small jumbo

Post by nnickusa » Mon Oct 07, 2013 6:57 pm

My opinion is it looks like a small jumbo. Look forward to the build thread.
I wish I was half the man my dog thinks I am....

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Nick

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Jeremy D
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Re: Opinions on my small jumbo

Post by Jeremy D » Mon Oct 07, 2013 6:59 pm

Haha cheers Nick!
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Trevor Gore
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Re: Opinions on my small jumbo

Post by Trevor Gore » Tue Oct 08, 2013 8:25 am

Are we looking from the inside or the outside?

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Re: Opinions on my small jumbo

Post by Jeremy D » Tue Oct 08, 2013 9:25 am

Hi Trevor,

Looking at the inside as the bracing would be glued on. Think I have it for a right handed guitar? Funny thing is I think the first guitar I built I got it around the wrong way. Sounds fine though :).

BTW I wont be tucking the lower legs of the x as per your book.
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Trevor Gore
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Re: Opinions on my small jumbo

Post by Trevor Gore » Tue Oct 08, 2013 8:07 pm

The bracing is typically right handed, if we're looking from the inside. The bridge (saddle slot) is therefore left handed.

I have a mate with a really good D28. It's a right handed one but he's left handed so he had it converted. Then (as musos do) he decided he needed to sell it, so had it converted back to right handed. Most people, including me, reckoned it sounded waaaaayyyyyy better in left handed config, which basically means it has the lower face braces on the opposite diagonal. One data point, but it seems you may have another...

Are you aiming for the J45 style diagonal dipole, having placed the lower face braces parallel?

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Re: Opinions on my small jumbo

Post by Frenchy » Tue Oct 08, 2013 9:49 pm

pm sent ;)

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Re: Opinions on my small jumbo

Post by Jeremy D » Tue Oct 08, 2013 10:17 pm

Trevor Gore wrote:The bracing is typically right handed, if we're looking from the inside. The bridge (saddle slot) is therefore left handed.

I have a mate with a really good D28. It's a right handed one but he's left handed so he had it converted. Then (as musos do) he decided he needed to sell it, so had it converted back to right handed. Most people, including me, reckoned it sounded waaaaayyyyyy better in left handed config, which basically means it has the lower face braces on the opposite diagonal. One data point, but it seems you may have another...

Are you aiming for the J45 style diagonal dipole, having placed the lower face braces parallel?
Hi Trevor,

The bridge is facing the front. I just quickly placed it on the layout so I could see how it fits over the bridge plate and bracing.

I am going to try for the diagonal style dipole of the j45 in your book. I am a long time player but I don't have a lot of experience playing different instruments (especially hand made) so I would really just like to try a few things to see what I like the sound of. I was hoping to get to the Melbourne Guitar Makers festival and try out some others designs but unfortunately I cannot make it this year.

I really just wanted to make sure that it was a viable design. For me at the moment its all about the joinery and build quality. Hopefully after a couple more I will be in a position to try falcate bracing or at least have a better understanding of the sound I want to shoot for.

Oh and hopefully next year you might run a course in Brisbane :D .
Jeremy D

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Tom West
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Re: Opinions on my small jumbo

Post by Tom West » Wed Oct 09, 2013 2:52 am

BBK: If it was me doing this, the bridge would grab more of the X brace with a smaller bridge plate. But that is just me.
Tom
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Mark McLean
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Re: Opinions on my small jumbo

Post by Mark McLean » Wed Oct 09, 2013 10:45 pm

Jeremy
I built one from the OLF-SJ plans, and I have the plans in front of me now.
I am not saying what is right or wrong, but here is the specs:
Upper bout width 290mm, lower bout 390mm. Body length 500mm
The X-brace angle is 93 degrees, which has it more upright, and less splayed than your plan. This means that the bridge overlaps the X-brace by a significantly greater margin than you have drawn. The bridge plate height is 45mm. The two tone bars are parallel.
cheers
Mark

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Re: Opinions on my small jumbo

Post by Jeremy D » Thu Oct 10, 2013 7:32 pm

Thanks Guys,

I might have to go back to the drawing board and study Trevor's books some more :).

Specs on the OLF-SJ are interesting too, thanks Mark.

Cheers.
Jeremy D

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Bob Connor
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Re: Opinions on my small jumbo

Post by Bob Connor » Thu Oct 10, 2013 9:17 pm

Looks fine to me.

I'd build it like you have planned and use it as a basis of how you would change the bracing for your next one.

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Bob, Geelong
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Re: Opinions on my small jumbo

Post by Jeremy D » Sat Oct 12, 2013 3:30 pm

I have made some changes, Hopefully for the better.

Scale length is now 632.46mm (24.9")
13 fret body join
X is 96 degree.

I think I like the idea of the shorter scale length and 13 fret body join. The sound hole and X has been moved towards the tail by 7mm and there is a lot more of the bridge overlapping the X brace.

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woodrat
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Re: Opinions on my small jumbo

Post by woodrat » Sat Oct 12, 2013 5:39 pm

Looks Good Jeremy....what program did you use to produce that drawing? ...I am a pencil and paper man myself but I would like to have a go at designing like you have here...

John
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Re: Opinions on my small jumbo

Post by Jeremy D » Sat Oct 12, 2013 6:18 pm

Hi John,

This is how I go about it.

I used "G" Thang (http://liutaiomottola.com/formulae/gthang.htm) software to layout the body shape, sound hole and fretboard relative to the sound hole (using scale length etc). It draws really nice arcs and its easy to tinker with and get a nice shape based on other makers or your own design. I then turn off the fretboard and go file->export as .dxf.

The other software I use is DraftSight (free: http://www.3ds.com/products-services/dr ... /overview/) or AutoCad.

The thing I like about DraftSight is that it is so lightweight and does everything I need (as long as its 2d).

Now you can open the .dxf file in DraftSight and start laying out the braces etc. The first thing I do is draw a center line. Everything else I do will now be relative to this.

Make sure you have eSnap and eTrack buttons clicked at the bottom.

A really nice way of placing things is using the eSnap overrides. You can choose the line tool, right click on the workspace and choose eSnap, then choose from. This will let you click on a spot, move your mouse in a direction you want the line to start from (e.g. center line) then type how many mm and press enter. This will start your line exactly that many mm from the first click point.

For doing angles I find it easiest to draw a line vertically or horizontally, then choose modify from the top menu and rotate.

When using cad tools you always need to keep an eye on the command window down the bottom. It usually tells you what you need to do next. It seems unintuitive at first but becomes second nature. You get out of any commands by pressing escape and you move to the next step by pressing enter.

The bridge I just did in DraftSight, its actually the bridge I am putting on the one I am building now. Its a nice feature that you can just import any other drawing and place it where you like.

If you have any other questions let me know, happy to help (with my limited knowledge) :)
Jeremy D

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woodrat
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Re: Opinions on my small jumbo

Post by woodrat » Sun Oct 13, 2013 1:10 pm

Cheers Jeremy....I will have a look at those sites you mentioned....

Thank You

John
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