Routing Top and Back Flush

[scamp]

Stupid question of the day.

Got the top and back glued on the guitar and happy with the outcome but now need to rout the extra top and back material flush with the sides.
Just purchased a Bosh Colt router to rout the binding.
I assume it makes sense to use this to rout the top and back flush.
I have no experience with a router so here is my question.

I purchased the Stewmac binding router bit for the binding and I guess I could use this with a flush bearing to rout the top and back flush..
This, however, doesn't seem correct given the large diameter of the bit and the large amount of material to be removed.
Seems like a narrower flush router bit would make more sense.
How best to do this?
Feedback welcome.

[tippie53]

you will feel how it works take it slow but a flush bit is a flush bit. I use the ridig trimmer as it readily mounts to the binding machines ,
pay attention to the angle of attack of the cutter. you will do some climb and some rout cuts
a climb cut is working with the direction of the cutter
a rout cut is going against the cutter

the weak area is the upper bout across the back from the radius and the back angle .

[scamp]

Thanks John

So it sounds like I can use the Stewmac binding router bit with a flush bearing to do the job.
I have a binding router jig similar to the True Channel jig so I can just do it slowly ( taking off a little at a time ) until it gets flush.
I was aware of the angle of attach issue with routing the back and top flush.
Basically the same routing direction recommendations as routing the bindings.

You mentioned the particularly weak area.
"the weak area is the upper bout across the back from the radius and the back angle "
Not sure exactly where you are describing.
It seems like the weakest point would be the widest part of the upper bout.
Is this the place your talking about?

[Stray Feathers]

There used to be a useful illustration of the basic principle on the Stew Mac site, but it seems no longer to be there. I found a version of it elsewhere:

th.jpeg

I prefer to use a narrower (say 1/2") flush trim bit for routing tops and backs. It's another tool to buy but not that expensive, and I use it elsewhere, saving the rabbeting bits for binding channels. Bruce W.

[Diane Kauffmds]

Yes, you can use the stewmac setup. Just use the bearing that matches the diameter of the bit (largest).

You can just use your Bosch with the stewmac bearing/bit, with just holding it, with its attached base, to flush cut your top and back. It doesn't have to be in the binding jig. This is the only time you can rout without the jig. But when your simply flush cutting, you don't need a jig.

BTW, I just use a Bosch 1/4" flush cutting bit. It runs about $20 at lowes. The Diablo is made by Freud, and can be found at Home Depot for a little more.

[scamp]

Thanks for the feedback and help.

I think I will go out and buy a separate 1/2 inch flush router bit vs. using the binding router for this as suggested.

Question..... with a smaller diameter router do you immediately rout along the wall of the guitar for a flush cut, essentially making a channel through the excess material. In this case, the excess top and back material further that 1/2 inch from the walls will just fall off?

or....

Do you grind down all the excess material, working your way from the outside in, and making dust of all the excess material?

BTW.. for those interested, here is where I am in the process.

[Diane Kauffmds]

You have a lot of overhang in some places. I would carefully trim or sand that back to about 3/8". If you cut it all at once, you'll run the risk of it beaking off.

[scamp]

Instead of sanding or cutting the excess down to 3/8 inch is it possible ( make sense ) to take multiple passes with the router, only taking a small amount per pass, to get it down?

[Diane Kauffmds]

Instead of sanding or cutting the excess down to 3/8 inch is it possible ( make sense ) to take multiple passes with the router, only taking a small amount per pass, to get it down?

Yes, but you have to control the router very, very, carefully. It's easy to lose control and the overhang will break. The bearing under the cutter, which rides the side, ensures that you won't go too deep; it offers a lot of control and balance. You won't have that advantage if you gradually cut that overhang. There's a definite difference between the router and climb cuts. Practice first. You'll quickly find which direction is easier to control. I've broken a back once with an overhang that large.

You can rout it. But practice first on scrap.

Drop only enough of the bit for the cut plus a little extra, ie. if your top or back is .010" thick, drop about .125" of the cutter. This will give you more control.

[Kevin Sjostrand]

Scot I totally agree with Diane here. They is too much over hang to attack with the router. It can grab in a heart beat and tear off a chunk with the grain. That happened to a friend of mine once.
Don't risk it. Use a file and slowly take it down to an even 3/16 or 1/8" then flush trim. You won't regret it.
I always start my cuts at the top center of each bout and work to the center of the waist or to the ends just past center. Go slow. Come straight into the side cutting till the bearing contacts the side then move slowly. One you've cut all the way around you can make a second pass going all the way around without fear of tearing out.
I think the smaller bit, 1/2" is better. That is what I use. Make sure you get a flush trim bit...bearing on the bottom.
The bearing on the top is a pattern bit. Don't buy that one for this process.

Kevin