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When using a template with a flush cut router bit to cut out small parts like a bridge or the headstock what type and size of router bird do you prefer?

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Formerly know as Mandodiddle.

To template rout a bridge or peghead I would use a 1/2 inch bearing bit with a 1/2 inch shank in a 1 hp or larger router (PC 690). The 1/4 inch/ 1/4 inch shank bits aren't really strong enough to rout things that thick and the tiny bearings seem to fail frequently.
If you have a large trimmer and you take it easy a 1/2 inch / 1/4 inch shank bit could work.

Personally I hesitate to use a router for these tasks, and prefer a Robo-sander.

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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.

If you have good hand - eye coordination a scroll saw is another good tool to use, but template routing is quicker and requires a little less skill.

I use patterns to mark them and then cut by hand on the bandsaw followed by a sander to finish.

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Steve Smith
"Music is what feelings sound like"

I use a combination - 1/2" shank 1/2" pattern bit but before taking it to the router table I get it as close as possible with bandsaw and / or spindle sander. Especially for bridges if you are routing a profile on the edges of the wings. Getting into endgrain ebony in that area its super easy to create a missile. I had to make custom inserts for my router table to be absolutely sure there was no flex in the plate. Pucker factor of 10.

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with the bridge I cut and sand using a router is not a safe procedure on small pieces.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

First, I agree with the above posts that other ways of getting to the final shape are safer for both the workpiece and your fingers. Mark it, bandsaw to about 1/16" outside the line, then sand up to the line, either free hand on belt/spindle sanders or pattern-sanded with a robosander. To me, pattern routing small parts like bridges is part of a "factory" way of thinking about how you make guitar parts. Some factory methods wind up also being a good fit for small time builders; others are more trouble for the small time builder than they are worth. Pattern routing bridges might make sense if you need to make 100 of them in a day, but if you need to make just one or a handful at a time, you might as well just cut and sand to layout lines.

But addressing the question asked: If I am going to pattern rout a piece of wood, I like to use 1/2" shank bits, with cutters and bearings at least that size. I prefer a router table, but will use a plunge or fixed base when it makes more sense for that part.

Adding something not asked: For safety purposes, if I feel the need to rout a small part on my router table (it happens sometimes), I hold the part with a wooden clamp, like a cam clamp, and hold the clamp with my hands instead of directly holding the workpiece. I want to keep my fingers a significant distance from the spinning router bit.

I'm with Colin. I changed from the router table to a Robo-Sander years ago for these small parts. No set up time and much safer, and unlikely to blow out corners or endgrain. I use plexiglass templates.

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“ The meaning of life is to find your gift and the purpose of life is to give it away” Pablo Picasso

My bit choice is going to depend on the work. I do prefer downcut spiral flush trim bits in general.

If I'm flush trimming something larger like a mold, I'd happily take a 1/2" bit in a table. If something smaller like a headstock, I might choose a 1/4" bit depending on whether or not the headstock has any tight contours along the top that a 1/4" might be better suited for. For a bridge, I'd probably choose a 1/2", but I'd really want to make sure I had work holding figured out.

A lot of roads for me lead back to Simon Fay (thankfully he's the nicest guy). If you look at this image on his website (link), you can see his work-holding solution for the bridge. The jig pictured takes care of the belly and doesn't start or stop the cut at the bridge's corners. My bridge has contours on all four edges, so I'd need to find a multi-jig solution with good indexing to keep the bridge indexed properly from jig to jig.

If you're just doing one bridge at a time, sanding with a spindle sander is the safer solution. You can even get a sanding drum to fit in your drill press if you don't have a spindle sander. Also look up the "Luthier's Friend."

I was recently making a new side bending form on the router table. I use solid forms, so imagine a solid chunk of 3/4" baltic birch. It grabbed on the 6th layer, possibly 15 lbs at that point. Thankfully I also use push blocks to grip the wood and was able to let it go. Even still, I approach that table with extreme caution every time. When pattern routing, where you start and stop the cut is mucho imporant, and corners are always dangerous.

if it grabed it were you climb cutting?
as a machinist I will never use a downcut bit in a blind hole too unsafe the chips are pushed into the work and you build up a lot of heat and dull the tool
in our shop that would warrant a write up.
The key is SHARP use a sharp bit you won't ever go wrong.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I go over the pattern with a Robo Sander. It typically leaves things about 1/32” proud. I finish that off with a top or bottom bearing 1/2” flush cut bit. Usually a climb cut

I have never had problem with catching grabbing or tearing doing it that way.

You definitely do NOT want to use the router on something like a bridge or headstock template if there is anything over a 32nd to take off. Been there!

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

It bit on one of the corners.

You must have climbed so many get hurt not understanding a climb cut or rout cut.

rules of routers and shaper tables
NEVER START AT A CORNER
Always route cut once you break these rules you loose control of the machine and bad things happen.

I have been using these tool for over 50 years and my father taught me.
If you don't know what a climb cut is I will expain

Rout Cut
this is when you feed your work into the cutter so that the bit bites into the wood opposite of the spin
so if the tool is turning clockwise you want to feed counter clockwise.
Climb cut
to make this easy to understand , if the bit is turning clockwise and your feeding it along the way the bit spins this is climb

you can get seriously harmed so be smart keep fingers clear and don't ever reach across the cutting edge

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Hey John, when I just have a small amount of material (1/32" or less) to take off and there are curves and corners like a headstock or bridge I usually first use a climb cut as I would cutting binding channels thinking it minimizes any risk of tear out. The final pass is a rout cut.

I have not had any issues as long as the material to remove is very small. Would you use a rout cut in that situation?

Thanks

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

For heavy routing, like a solid body electric,
I cut close to the line with a band saw, then use a big 1/2" drive router, with a 1/4" template.
Less sanding, perfectly square.
Just get your template perfect first.
The extra weight of the router is safer than a 1/4" drive machine.
Still gotta be careful, and go slow, small bites.
Yes, I've had stuff happen, just be ready for it.
Alan

there are times to climb it has to do with the angle of attack of the cutter. If you rout the risk of it being thrown is reduced. But depending on grain it can tear out. With climb cutting you get compression fracture when over feeding or it can grab and throw . On a guitar body the larger the safe on small stuff like a bridge I do them with a sander and a pattern

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

if you want to do a corner never start at the corner come in from counter clockwise face then turn the corner you will get sharp corners

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

When using a table router do you like using the pattern on top or bottom?
In other words, should I get a 1/2" flush cut bit with the roller bearing on top or bottom?

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Formerly know as Mandodiddle.

You can get one with bearings on both top and bottom.

For pattern routing small stuff you might want to have the jig on top "capturing" the work piece. In some cases that will require using two jigs to fully rout the piece because you also want to make it large enough to keep your hands away from the cutter. That allows you to use a 1/2 inch shank bit with a bottom bearing when using a router table.
If you have the work piece on top/ pattern below and you use a "hardened" pattern then you can use a 1/2 inch shank/ 1/2 inch bit and ride the shank on the pattern and avoid using a bearing. There are lots of ways to do it, but doing it safely is the first priority.