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cross-grain Dilema


al heeley
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Cross-grain dilema

So this final chunk of mahogany left from the old fireplace unit is about 22" X 14" but the grain runs width-wise instead of length-wise.

I'd like to use it for another body, probably another maple-cap build, but I've been told it's only good for a chopping board or a bedside table, as the grain, running width-wise may introduce dimensional instability in the guitar. This is why you never see a guitar with the grain direction running across it's width.

What is the general consensus on this? Am I likely to get into trouble after a season of damp and heat?

Should I just go for it and use it as a side table once it falls apart?

Do I really have nothing to worry about as it's a good, dense, single piece of premium Honduras Mahogany, and I will be putting a 5mm maple cap on it anyway?

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Cross-grain dilema

So this final chunk of mahogany left from the old fireplace unit is about 22" X 14" but the grain runs width-wise instead of length-wise.

I'd like to use it for another body, probably another maple-cap build, but I've been told it's only good for a chopping board or a bedside table, as the grain, running width-wise may introduce dimensional instability in the guitar. This is why you never see a guitar with the grain direction running across it's width.

What is the general consensus on this? Am I likely to get into trouble after a season of damp and heat?

Should I just go for it and use it as a side table once it falls apart?

Do I really have nothing to worry about as it's a good, dense, single piece of premium Honduras Mahogany, and I will be putting a 5mm maple cap on it anyway?

14 inches wide? Then make a 14 inch long body :D Something cool. Or a mini-strat/lp. That'd be cute

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NFG, don't forget about string tension, no way to balance the effects of temp and humidity. One day your strings will be loose and the next they will be super tight. But hey, if you want to give it a whirl then have at er! How many cross grained guitars have been made? ZERO? Then there must be a reason. :D

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A front AND back cap would strengthen the body considerable.

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The real issue with cross grain stability has to due with the way wood shrinks and expands. In the Longitudinal direction wood does not change much, along the radial and tangential it changes much more (tangential generally being the highest shrinkage). Woods that have closer rad. to tan. shrinkage percentages are less likely to cup,twist, warp (and of course closer to flat or quartersawn will minimise the likely hood of these things). Gen. Mahogany has very close rad. to tang. (making it a very stable wood). However cross grain shrinkage is still going to be much greater than with the grain (Longitudinal). The shrinkage and expansion occuring in line with your scale, as well as an increased risk of cupping and warping along the bridge to neck line is not a really good idea. So you can do it and it will string up. You can set it up, and it will play just fine. The test will be when the humidity levels change over time. Will your action change slightly, and enough to be significant. Remember the cupping may amount to a small dimensional change, and I am sure you have a lot of string clearance (like your action good and high?). A slight amount of dimensional shrinkage or expantion in your scale length probably won't be noticed (you don't set your intonation all that close do you?). So point being- Yes it wiill work. No- it is not optimal. How acceptable this is depends on the person.

Here are a couple links that may give you some extra info or better explanations-

Simple explanation of shrinkage

Better explanation and suggested cures if wood warps during drying

Humidity and wood- nice little table

Answers to just about every wood question asked on this board (great resource)

Peace,Rich

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Thanks for the reply, thats really useful information. Maybe I won't spend 60 hours making a body out of this piece if it's likely to cause problems in the long run, unless I use it as a test bed for some new designs. I think a nice chopping board or strat-shaped side-table could be a fitting end to this learning curve :D

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Maybe you could use it for the wings on a neck-thru design. Doesn't seem like that would cause so many problems.

Thats true. The effect would not impact the neck section. That would only leave you with a couple issues. 1-looks (but that is totally subjective). 2- potential issues with glue joints (end grain sucking up too much glue starving the joints, but that can be dealt with by a little pre-soak).

For what it is worth. Another topic that had not really been addressed when talking about using a cross grain configuration is velocity of sound across the grain. There is a section in the last reference I attached above that talks about this. If I remember correctly virbration will travel cross grain at a rate of about 20% of the rate with the grain. Of course I am not sure exactly how significant that would be in a body, as the vibration in the body is not going to be as linear as you would expect in a neck (of course it is going to oppose the neck grain, so it will have an effect for sure). I would bet as wings the effect would be less of an issue.

Peace,Rich

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