More fun in the shop

[Ken McKay]

This is a back plate with an X-braced pattern. I designed it by the highly scientific method of "seat of the pants".

It might sound like poopoo? who knows. It rings at about a open D. And the top at E one step above.

[Paul Warburton]

Beautiful Ken....So tell us about the two shorter lower bout braces angling from the X brace.

[Ken McKay]

Originally Posted by Paul Warburton

Beautiful Ken....So tell us about the two shorter lower bout braces angling from the X brace.

It is a lot like an acoustic guitar top bracing and the transverse braces are for stiffness in the lower bout. The whole idea is to add some stiffness similar to a carved plate and/or the usual 3 or 4 across braces if a flat back, yet allow the plate to expand and contract without cracking.

The braces are curved so the back of the plate is actually dome shaped about 10mm or so with its center at the post area.

[Jake deVilliers]

That's cool Ken - very 'Martin'. It'll be interesting to hear what that bass sounds like!

[ctregan]

Good idea, looks like fun in the workshop!

Will the sound post land on an X-brace or the disc on the side? It seems like you could get more drive if it hit one of the braces?

[Matthew Tucker]

Show us yer label!

How much extra weight does that bracing add to the back? Doesn't look like it would be much lighter than a standard cross-bracing pattern.

Is your back graduated evenly or is it thicker in the middle, too?

[Ken McKay]

It is all equal thickness of 6.5 mm. I didn't weigh the plate before the bracing, as I should have! It is too heavy for my little 5 Lb scale...darn.

The post will sit on the pad which is laminated and pressed into the dome shape. It is two ply with spruce about 1mm thick inside and 0.65 mm beech showing. The grain is parallel to the back wood.

There could be a lot of theories about what would be better, the post on the X arm or off, mine is off. Where the X joint is in reference to the plate center, mine is in the plate center. Where is the post position in relation to the X center, mine is in the center. Should it be asymmetrical in stiffness? Mine is symmetrical. All of these could have a large effect on how the plate impedes the way the top can vibrate in connection to the post.

I could have created an overly complicated mess here, but my intuition is that it is acting like a carved plate in its stiffness, more than the usual 3 across. Nothing wrong with the 3 across though, many great basses have it, right? I did it for long term stability more than anything.

[arnoldschnitzer]

Ken, I worry that the soundpost pushing on the back will try to seperate it from the braces in that area. It seems you may be working against your glue joints, rather than with them.

[Ken McKay]

Originally Posted by arnoldschnitzer

Ken, I worry that the soundpost pushing on the back will try to seperate it from the braces in that area. It seems you may be working against your glue joints, rather than with them.

I was hoping for your opinion Arnold. I did some flexing and pressing in the soundpost spot and it seems to flex the whole plate evenly. The dome shape seems to help.

Do you think I should replace the pad under the post with a wide brace that connects the X? The way it is, it is pretty strong, pressing there causes the whole plate to flex.