graduations on back plate

[ctregan]

Started to hollow out the back plate, and had a question:
Is there an acceptable +/- factor in the final thickness? I am using a digital caliper that reads to .00 mm.
Should I aim for .01 +/-? or is .10 +/- more reasonable?
Or is .25 mm more realistic?

[ctregan]

There is a lot of real estate here.....

[Matthew Tucker]

That's a very small gouge for hogging all that wood out. Try something bigger, or at least with a heftier handle. Also, I reckon drilling too many holes is going to make the carving work harder, not easier. I use the drill holes as a depth guide only. The wood removal is done with a big blade or an arched-sole scrub plane.

[chris clay]

i'm under the impression that the flat back to the bass that i am building should have a uniform thickness across the whole area of the plate.

is this still the case with an arched back plate.... and are the plate thicknesses of an arched back thinner overall to maximise the structural efficiency of the arch

chris

[ctregan]

Originally Posted by Matthew Tucker

That's a very small gouge for hogging all that wood out. Try something bigger, or at least with a heftier handle.

I have been using a mallet with the gouges but I must be carful as the top gets thinner and more fragile.

[Darren Molnar]

Hey CT. I have a thickness guage similar to yours. I didn't pay much attention to anything past the decimal. I don't think you have to be that accurate with the bigger instruments. I'd be careful with the mallet, as you've said. A bigger, flatter chisel would help you out a bit. This tool was awesome for me:

http://www.leevalley.com/wood/page.a...=1,310&p=54888

Hi Chris, carved, arched backs are thicker in the center, and thin to the upper, lower bouts. Flat backs are uniformish, as you say. they are thicker than the thinnest parts of an arched one, but thinner than the center of one. They kinda split the difference, I think.

[chris clay]

thanks Darren...i'm not sure though if i'm totally clear.

i underestand from what you say that there is a gradation in thickness increasing from North to mid line of C-bout and then decreasing towards the South so to speak...but what about across the width of the plate

out of interest can you give some sort of guide thicknesses that might apply as compared to a flat back

chris

[chris clay]

darren...i also meant to say that the Veritas pullshave looks to be a great bit of kit

chris

[Shmelbee]

Seconded. Thanks for showing that to us.

[forester]

CT this is where sharp is an understatement...dry cherry does not like to be pushed or pulled... be wary if in some areas the grain is running away towards the outside of the back ..your gouging can chase it through.

gouge : (to cheat, defraud, swindle or extort) and, rarely, as a noun meaning a swindler (gouger).

[Darren Molnar]

Hi Chris
The last page of this pdf shows some nice graduation patterns for some fiddles. Arched basses follow along these line, but thicker. The concept is the same :

http://www.bormanviolins.com/Article...%20Article.pdf

I think, in general, arched basses start aroundish 12 mm or so at the thickest areas, and end up 5mm-ish at the thinnest.

I can't really say much about flat backs, I have no experience with them. Maybe Mathew can shed some light.I think theyare around 7mm or so?

[Darren Molnar]

Depending on wood used, etc, etc.

[Matthew Tucker]

Yes it depends on the wood. I have only experience with my flatbacks and I chose to keep them heavier in the centre of the plate, the backs have a slight convexity via the shaped braces. heavier in the centre of the plate also means there's a larger glue surface for that centre joint.

Roundbacks? Peter Chandler gives common measurements in his book; as I recall yeah its about 6mm at the edges and 8-9mm in the centre. But it depends on the wood!

I have seen a roundback get a crossbrace carved in at soundpost location.

Jean Auray has experimented with thinner back graduations and a number of integral "crossbraces" carved into the back plates. No idea what the result is.