Official Luthiers Forum!

I’m not sure why I didn’t do this sooner, but it is pretty convenient. Use the top template as a clamping caul to protect the spruce from any dents from the go-bars.

I can’t think of a downside. Anyone else?



P.S. glad to have Presidents’ Day off to finally get a few minutes in the shop!

Brad


Sent from my iPhone using Tapatalk Pro

_________________
Insta - https://www.instagram.com/cbcguitars/
Facebook - https://www.facebook.com/cbcguitars

Thumbs up from me.

_________________
"Act your age, not your shoe size" - Prince

Good for protection, but something thicker would spread the force out more evenly. However, I don't think you'll have any problems with that.

Pat

_________________
Pat

You could add a little foam...
The foam was from a discarded marble race track. (pipe insulation cut in half)
It is glued to an oversized pattern so the high point of the foam bears on the edge of the top/side.

I found that when I clamped my template onto the top it put a lot of unnecessary force in the middle of the guitar. Since the soundboard has a slight radius to it, it's going receive some extra pressure from an unradiused template. I can't say that the amount of pressure is even problematic, but I discarded the idea anyway.

_________________
-Marcus
http://www.bailieguitars.com
Instagram | YouTube

When I was at Greenridge, we made up cauls from thin temperboard (0.100" fiberboard/'masonite') which is textured on one side and smooth on the reverse. These cauls were slightly oversized (1/8") such that the go-bars set 1/4" in from the edge would land on the caul over the lining to side joint, avoiding issues with applying pressure where there is little or no supporting structure. The photo shows a collection of cauls, and the method by which a single caul may be made for a given body shape to address both full and cutaway side profiles. The cauls are used smooth-side-down and the textured side up so as to provide some additional grip should the bar not be set vertical between the points of contact (the force applied is always in a line between the tips of the bar, no matter how bent the bar might be).



On thickness...the thicker the caul, the farther the clamping pressure is spread, and the lower the average clamping force over that larger area. For these materials, clamping forces may be considered to spread from point of application in a cone of about 45 degrees from the axis of application. For a 0.100" caul and 0.095" back plate, that suggests no more than 2 x 0.195" = ~ 3/8" between bars, while a 1/4" caul would give just over 11/16" between bars. We typically used a thinner caul and lots of small bars (24" x 3/16"...about 7-9 lbs per bar) versus a thicker caul...primarily to get higher glue line pressure. Also note the extension to ensure pressure on the neck block area...this avoids having to use a separate caul, but may be an issue for archtops with a string recurve in that area.

A guitar rim supported by a radius dish can take a distributed load of well over a ton, so the 700-800 pounds of clamping pressure generated by 80-100 bars of concern only if the top plate on the go-bar deck is not stiff enough to retain shape.

_________________
For the times they are a changin'

- Bob Dylan

Years ago a bought a bunch of spool clamps. When I started using go bars I found a use for some of the spool clamp parts.

This is a pretty old picture, I use 1/4” carbon kite rods now.

I would also worry about pressure/damage on a domed top using a full template as a caul.

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.

I'm the same as Woody, thin hardboard (UK term for Masonite) rough side up around the rim area and overhanging slightly with lotsa go-bars.
I used to use small blocks of 3/4" ply faced with cork round the rims, much the same as Terence, but the new way is just quicker and simpler for me, as long as I can find my jigsaw to cut them out!

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

The thing I like about the foam pipe insulation is it holds the caul off the plate and applies the pressure to the glue joint, but allows you to jam the go bars (or place clamps) quickly over the entire surface - a little less fiddly than fitting them around the edge.

I've been using my clear flexible templates to protect the top in the go deck for years, works great. My templates are shop made from flexible acrylic, no issues with pressure on the center of the top.

_________________
It will probably be alright.