Hello

[Craig Regan]

Thats the author of this thread drilling holes on the underside of the top. Its cold, so I am wearing a coat, hat, and scarf.

Chopping it out by hand.
At the moment, there is little, in the way of extra funding available for a power carving machine, (we are saving every penny for the fingerboard).

[Craig Regan]

I got rid of the bulk of material so the top would be easier to work with.
The thickness is about 15 mm overall, or a heavy 1/2".

Now is the time to retrieve my luthiers notebook and figure out my graduation patterns.

[Craig Regan]

I am building from a Peter Chandler plan. His graduation pattern for the top plate has a thick 8 mm center "spine" running top to bottom. Here are some ideas for different patterns, for thinning the top.

The first is a simple peanut type shape. Starts off thick in the middle and gradually thins at the edges. Seems simple and straight forward.

The second is based on a cello pattern. Ovals in the center, thinned out in the upper and lower bouts or "lungs" as they are sometimes referred to in this sort of pattern. Good pattern for cellos and violins but unsure with double basses.

What is the accepted "normal" patterns used by manufacturers past and present?

Would the tea leaf and audio oscillator set up help out in this situation?

The further I go on this project - the less I know.
If anyone wants to chime in on graduating top plates, the forum is open.

[Ken Smith]

Originally Posted by Craig Regan

I am building from a Peter Chandler plan. His graduation pattern for the top plate has a thick 8 mm center "spine" running top to bottom. Here are some ideas for different patterns, for thinning the top.

The first is a simple peanut type shape. Starts off thick in the middle and gradually thins at the edges. Seems simple and straight forward.

The second is based on a cello pattern. Ovals in the center, thinned out in the upper and lower bouts or "lungs" as they are sometimes referred to in this sort of pattern. Good pattern for cellos and violins but unsure with double basses.

What is the accepted "normal" patterns used by manufacturers past and present?

Would the tea leaf and audio oscillator set up help out in this situation?

The further I go on this project - the less I know.
If anyone wants to chime in on graduating top plates, the forum is open.

Not having ever made a Bass I have been inside quite a few of them and outside as well. My worry on the second pattern for Cello on the right is Bass bar sinkage. I think the one on the left (Peanut?) is the more common and trusted way to go.

The 6mm all across the bottom might be ok but why take the chance. Also, I have heard that Panormo made some Bass at 6mm all over without any graduations. Each piece of wood is different and has different strengths and weaknesses even within the same piece of wood end to end. What you can do is try something more on the heavier side like circles in the center 8-10mm and gradually thinning and turning to oval graduations as you move outwards. After the Bass is done you can always go back and re-graduate if you like. I have seen some Basses with a slight built up platform under the Bass Bar, the entire length (and soundpost area too). This is done to add strength to that area. If re-graduated with the 'Bar in place, it would be ok to work around it leaving the platform. My Gilkes as made that way and I know of an old attributed Maggini that was as well. Someone re-graduated that Maggini thinking it was wrongly made and guess what? The Top sunk under the Bar afterwards, so the former owner told me some 3 1/2 decades ago. Things like that you don't forget!

[Craig Regan]

Thanks Ken, The extra material under the sound post and bass bar is a good idea.

It would be interesting to take a hacklinger gauge and measure the tops on various basses. Might be the best way to get answers to some of my questions.

[Ken Smith]

Originally Posted by Craig Regan

Thanks Ken, The extra material under the sound post and bass bar is a good idea.

It would be interesting to take a hacklinger gauge and measure the tops on various basses. Might be the best way to get answers to some of my questions.

Unless the wood you are using as well as the models between Basses are exact, copying measurements might not produce the exact same results.

[Matthew Heintz]

I'm not qualified to add anything here, but I spoke with Bill Merchant not too long ago about this and he said that he has seen quite a few modern basses with 6mm or 7mm tops coming back in for repairs. He said that they sound good initially but sink over time. Then again perhaps it works with certain woods, designs etc...