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Hi,

What width do you make your plate, in building a J45 size but not strictly following the plan but using it for references, the plate on the Plan is a lot wider than the bridge footprint. Reluctant to go to wide, but then maybe it needs it as larger body?
What do you guys do or reccomend
Tia



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Added a photo as I know everyone likes a photo

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My personal "guide" is around 5-6 mm back and 5-6 mm forward if the bridge outline for larger bodies/scale length like the J 45/Jumbos, but I knew some leave them a lot tighter, especially for smaller gits/scale lengths.
I see one purpose of the bridge plate as helping to resist bridge rotation/soundboard bellying, and tend to use longer scale lengths (25.4" or 650 mm (25.6")
What plans are you using, what is the width of the plate, and of the bridge? What scale length/string weight? Several factors to consider.

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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.

25.5 scale length mate, plan shows 63mm wide plate

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I would say that's wider than necessary.
As I said, I would make the BP about 10/12 mm wider than the bridge, split between front and back, bevel the BP all round the edges, but others mileage may vary.
Some of the older J 45 apparently had quite narrower bridges and BPs than later ones with adjustable bridges, i.e. about 1 7/16" (36.5 mm) x .125" thick solid maple bridge plates. Not much wider than the bridges at all.
One discussion here - https://umgf.com/bridge-plate-dimensions-44-j-45-t57075.html
Disclaimer - I'm no expert! Just trying to help out.
Good luck with the build.

_________________
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.

Thanks as always Colin,

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I tend to go wide, but....

Back when I did more repairs I worked on a couple of old Martins that had the same problem; the bridge had pulled off an there was a crosswise crease in the top along the front edge of the bridge. These were mahogany-topped 1-15's, iirc, pre-WW1, with 'bar' bridges. The bridge plates were exactly the same width as the bridges, and carefully lined up so that the edges matched. This created a very large stress riser at both edges of the bridge. Mahogany tends to surface crush along the grain on the inside of a bend, and that's what happened to these, and then the top folded up.

Part of the repair was to extend the bridge plate well outward from the edge of the bridge both front and back. Rather than have a square edge to the plate I tapered them, so that they had essentially no thickness at the edges. This kept both the stress riser and the weight down. I have been doing the same on my own guitars ever since.

In my view, whatever other things a bridge plate might do, it's main function is to provide a hard bearing surface for the ball ends of the strings. It only really needs to be full thickness there. I extend my bridge plates out in front of the bridge by about 1/4", but they taper down starting from the saddle location and go to effectively zero thickness at the front edge. I make them a full 2" wide, but, again, taper down the back edge to nothing, starting from a point about 3/4" back from the saddle location (on a six-string). All of this keeps the weight of the plate down,and reduces stress risers, while still providing plenty of material where it's needed.

I have three different J-45 plans (but I haven't built from any of them yet). The Michael Collins and Kerry Char both show a fairly small bridge plate, approximately 1-1/4 and pretty much centered under the 1 x 6 (square) bridge. Collins shows several versions of the reverse belly bridge but I don't see anything about changing the size of the b/p. The one on the Georgia Lutherie Supply plans is considerably bigger - they show a reverse belly and a mustache bridge.

I go for 3/16th inch wider then the bridge. I've experimented with rounded back sides to sort of match the belly bridge and perhaps distribute the stress in a better way but have not noticed much of a difference. So typically I make the front and back edge straight. And I also taper the front and back edges down to zero. They always butt right up against the X-brace too.