Build 12.5 - Prop

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joel
Blackwood
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Location: Brisbane, Australia

Build 12.5 - Prop

Post by joel » Sat Mar 18, 2023 11:24 pm

All righty. I'm approaching gluing the top onto my sides. Build Section 12.5 is all about checking the geometry. Well, my top has flattened slightly longitudinally (from the neck to tail ends). According to the text this might be expected of falcate braced tops. I have 1.2mm too much space between the straight edge and a 2.5mm drill bit. If I put the top into my radius dish, it's clear I have some longitudinal flattening of the top (across the top is fine).

In the text of 12.5 it says "a central "prop" may have to be provided" when gluing the top to the sides to ensure correct geometry.

Question: what are people using as this "prop"?
- If God had intended us to drink beer, He would have given us stomachs. - David Daye.

- The mouth of a happy man is filled with beer. -

AKEric
Myrtle
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Re: Build 12.5 - Prop

Post by AKEric » Mon Mar 20, 2023 11:33 pm

I use the appropriate number of layers of masking tape to fill the gap. Usually just a few layers.

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joel
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Re: Build 12.5 - Prop

Post by joel » Tue Mar 21, 2023 10:36 am

Hi Eric,

I was envisioning some sort of post inside the body to restore the longitudinal doming whilst the edges of the top are weighed down to the rims. I'm unsure how to envision what you're describing. Got any pics?
- If God had intended us to drink beer, He would have given us stomachs. - David Daye.

- The mouth of a happy man is filled with beer. -

AKEric
Myrtle
Posts: 50
Joined: Fri Sep 28, 2018 1:29 pm

Re: Build 12.5 - Prop

Post by AKEric » Wed Mar 22, 2023 2:35 am

I guess I build a bit differently. I have the top sucked down to a vacuum dish with the appropriate radius and have the rim over the top of it. The masking tape under the top raises it enough to account for the flattening of the upper transverse brace and neck block.

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joel
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Joined: Thu Oct 11, 2007 7:55 pm
Location: Brisbane, Australia

Re: Build 12.5 - Solved

Post by joel » Wed Mar 22, 2023 10:39 am

Fancy! Thanks for the description.

I actually found the root cause of my problem. I found I had to clamp the neck end of the top down to the head block! The UTB was correctly flattened, but longitudinally the top still had too much doming there. Once I clamped the top at the head block, the 2.5mm spacing at the saddle magically appeared! Now I have to wait for a relatively dry day to glue it down.
- If God had intended us to drink beer, He would have given us stomachs. - David Daye.

- The mouth of a happy man is filled with beer. -

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