Top thickness

[lacrombie]

I have started my first guitar build and have been working on the top. I think I may have made it to thin - it is 2.2mm. What effect will this have on the structural integrity, tone, balance etc.

[ozwood]

Hi Lacrombie,

I'm only Three guitar's into my Luthierie Journey so you may want to wait for More Qualified advice , but for my Two Bobs worth, if you want to keep that top ,You may want to consider a latticed braced top, I have a friend who only uses this system And all of his tops are around that thickness , allowing of course for the species and the Variables particular to each top, as each species have different qualities, in terms of stiffness and weight . Sitka Spruce is both Stiff and Light so it can be Thinner than say Western Red Cedar , which is a bit lighter again but less stiff . Double tops use two layers of between 0.5 mm and 0.8 mm with honeycomb Nomex in between , and only need minimal bracing. so I guess in short I would take into account the species , the Tightness of the grain and then Seek advice from the wealth of Knowledge available on this Forum as to the most appropriate Bracing for that top. I'm sure Someone will come up with a Solution.

Regards,

Paul

[kiwigeo]

Welcome to the forum,

Your question is a bit hard to answer as you haven't told us what sort of wood your top is or what sort of guitar you're building.

If as you say you think you've gone too thin then sometimes it's possible to compensate by going for heavier bracing.

Making a guitar top is all about finding that sweet spot where the wood is thin enough to vibrate as freely as possible but not so thin that it has no structural integrity and collapses at first string up.

2.2mm (0.087") is getting very thin for a spruce top for a steel string and its the lower limit I go to on my classicals which have Lutz. Sitka or Engleman spruce tops.

Determining when your top is at the right thickness is a matter of flexing the wood between your fingers and judging how flexible the top feels. I also tap the top at regular basis listening to the tone and sustain. if your top is floppy like cardboard and has a dull tap tone then its likely youve gone to thin.

Anyway if you post up more details of your top then Im sure there'll be a flood of responses from others in here.

Cheers Martin

[lacrombie]

Hi Paul and Martin, the top is sitka spruce and it is a OM style. The top still has stiffness and a tap tone but as I am a complete novice I'm not sure what to look or listen for. I am intending to use X bracing with lattice bracing in the lower bout.

Thank you for the advice.

Leigh

[kiwigeo]

2.2mm is getting thin for Sitka. Like I noted earlier beefing up the bracing is an option.

For the record my last Sitka OM had a top that was 0.125" around the bridge area and thinned out to around 0.108" around the periphery of the lower bout and waist. Upper bout was a uniform 0.108 - 0.110". Bracing (standard X brace plus two tone bars, all braces scalloped and shaped) was a bit lighter than specified to compensate for going a bit thicker than I could have.

Cheers Martin

[Bob Connor]

By the time you get that top glued on to the guitar and finish sand it you'll probably be closer to 2.1mm which is getting close to the lower limit for an OM.

It could be done. I have on OM sitting next to me with an Engelmann top with a 2.2mm top on it. It's about 5 years old and while it does have some deformation of the top around the ends of the bridge it has still retained it's geometry.

If this is your first I would put that top aside for when you want to build a parlour or smaller guitar and use another top that's been thicknessed to around 2.75mm.

I use the lattice bracing in the lower bout to evenly spread the load over the lower bout but I also use a larger bridge lalte than most to counter the rotational forces of the bridge. So you need to design your bracing system to suit the the top you are using, the style of guitar (body shape), what guage of string you intend to use and whether the person who will play the instrument is a heavy handed strummer or a delicate fingerpicker.

Lots of things to chew over.

If you do decide to use this top and it doesn't work it's not a difficult job to take the top off and replace it.

Oh, and welcome to the forum. Do you have a name other than your login?

Regards

[lacrombie]

Hi Bob,

Thanks for the advice. There is a lot to chew over but I think I will persist and use the top. I will use the lattice system with slightly higher braces and perhaps 11 to 48 strings instead of 12 to 52.

Cheers

Leigh

[Allen]

Things to do with this top Leigh. Regardless of what type of bracing you go with below the sound hole you will want to beef up the rest of it.

Don't skimp on the upper transverse brace. Might even want to add a second one or go with the popsicle brace between it and the neck block.

Use a sound hole patch to add some reinforcement besides the typical sound hole braces. Go with a bigger footprint on the bridge patch, Take it a bit further into the x-brace and a bit further behind. On a top that thin what you will most likely see fairly quickly is a V shaped dip in the sound board right in front of the bridge, Down the track you will see deformation around the sound hole. Behind the bridge you're going to notice a belly. A little is alright, Looking pregnant is not....at lest on a flat top guitar.

My suggestions will take care of most of the stuff in front of the bridge. The rest you'll need to nut out when you plan the rest of the bracing.

[TedvV]

Hi Lacrombie,

For what it is worth for all. I once had some damaged Bunya pine and by the time I had it sanded smooth , the thickness was less then 1.6mm.
I decided to glue two pieces (soundboards) together and finished to the required thickness. The steelstring guitar I used this board on sounds good to me.
May be not a desirable way of construction , however in my opinion it worked.

regards.
Ted

[lacrombie]

Thanks Allen, your advice has giving me some good points to consider. This guitar is my first build so it is a fast learning curve for me and I have already learnt a lot of what not to do.

I appreciate you advice.

Leigh