Build 12.5 - Prop

[joel]

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"?

[AKEric]

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

[joel]

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?

[AKEric]

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.

[joel]

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.