Official Luthiers Forum!

I've used the same 1/4" downcut spiral router bit to cut the binding channels on four guitars and am about to start binding my fifth. I have no idea how long the bits last and how to determine when one ought to be retired.

Suggestions?

Thanks!

_________________
Peter Havriluk

If the bit is no longer shearing the wood and leaving a clean cut then it is probably time to sharpen it. Many of the spiral bits are solid carbide and will hold an edge a long time (although they are never as sharp as a HSS bit when new). For the shallow rabbets we make for binding ledges you may be able to touch up the bit with a small diamond hone when it gets dull.

http://eze-lap.com/products/diamond-hone-stone/

expect about 6 to 8 guitars by 10 they are shot

_________________
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

Thanks, folks.

I don't have experience sharpening router bits but I appreciate the advice. The time's passed when I knew whether my bit was carbide or HSS.
I'll watch for cleanliness of cut. Time's approaching when I'm inside the window of caution John's mentioned.

Much obliged.

_________________
Peter Havriluk

Another thing to watch for: Keeping the bit clean. Gunk can build up pretty easily. Any of the blade cleaners will help get that stuff off.

Measure the bit. I noticed when my bit for routing my CF rod in the neck gets tight/snug, the bit itself has a smaller diameter, even though the cutting action is still good. I use a 1/8” bit, so naturally it’ll wear faster than the 1/4” I use for binding.

I never thought of hand sharpening a spiral bit. Are you sharpening the inside of the edge like you would a straight bit?

Pat

_________________
Pat

The most recent set of binding channels I cut was the 11th on the same StewMac binding bit. It's still working fine. That includes doing test cuts on scrap wood before cutting the channels on the guitar, for each guitar. I'm guessing that the bit life could be affected at least somewhat by the types of wood it's used on.

_________________
Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Hand sharpening a spiral bit is little tricky, and commercially, many sharpening shops won’t even take this on. There are a few that have specialized machinery, but with a decent quality 1/4” carbide spiral bit only costing $10-20 the economics aren’t really there. The longevity of any cutting blade or bit will be dependant on the material being cut. Oddly the hardness of the wood is not always main dulling effect, but more importantly the silica content of the wood being cut. For instance cedar has a janka of around 900 but certain boards with high silica content will take the edge off a fresh blade quickly.
The silica content can be more of a factor of the environment the tree grew in as opposed to considering species alone.
On a side note, a dead solid carbide bit can be fitted with wood handle over the cutting flutes and used as a great burnisher for your scrapers.

B

_________________
My memory is so good, sometimes I remember things that never happened.

For cutting binding ledges you only use about 1/4 inch of the bit. You can sharpen the bottom edges and the lower quarter inch of the flutes. The rest of the bit should be relatively sharp and the material removed from honing doesn't change the diameter very much, so you can still use it for deeper rabbets and dados.

https://www.youtube.com/watch?v=fx5EwsEX-G4

I replaced my bits every dozen of so guitars when the spruce rabbit started getting fuzzy. I was surprised that they did not last longer.

I recently bought the Amana Rabbet bit RC 49357. Has blades that can be rotated when worn. U can buy more blades. And there is a good number of "bearings" (collars, 67800), though for the bit above, you would be able to purchase the smaller set. Nice bits.

https://www.toolstoday.com/woodworking/Amana-Rabbet-Bit

Mike

Just cut all the binding ledges on my project. still shows nice clean cuts, so it's used-up condition remains in the future. I got advice I can remember, too, when the edges get fuzzy, it's time for a new bit. Even I can hold that thought.

Thanks, folks, for a comprehensive course in router bits used in lutherie.

Much obliged.

_________________
Peter Havriluk

Depends on what wood you're cutting. High silica woods like Koa will do in your bit pretty fast

Brent

Many of the "new" woods for guitar building were not used formerly because they were very difficult to work with steel cutters which they quickly dulled. With the advent of carbide tooling and the increased scarcity of the more desirable species they have come on the market. Ipe, jatoba, and ovangkol are three I can think of that fall in that category.

This surprises me. I use the LMII bits, I’ve done probably 100 guitars since last replacement.

Mind you I have a separate router and bit for each cut, excess, main binding, top purf, back purf.

The excess is pretty dull but that’s ok if the edges are fuzzy cause they’re not final, the final cut bits only ever cut a very small cut...