Official Luthiers Forum!

I've made the jig and now need the bit(s). I hate to ask but I'm calling uncle on the hours of research .
I'll be using the much hated Bosch Colt (I'm already invested in multiple Colts), 1/4" collet, with a measured total runout of .001".

• With either (router bit or end mill), upcut or down cut?
• Two or three flute?
• Fish tail or square end?
• 1/4" shank or 1/8" collet reducer?

I don't have a machining background so I'm stumped.
I don't want to over think it, but don't want to under think it either. I also want to avoid multiple iterations of "learning opportunities".
This may be one of the most unforgiving processes I've encountered!

Appreciate your assistance!

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Measure Twice,

Karl Borum

I’ve gotten best results with a Freud 1/8” straight bit (1/4” shaft, the one I’m using now has 1 flute). It leaves the chips packed in pretty tight. I would like to use an upcut spiral bit to make the clean out easier, but I’ve never bought one of any brand that didn’t have some runout making the slot wider than 1/8”. I don’t know anything about end mills. I’m using a Makita R700 plunge router. If I had a router with .001” runout, I’d replace it. It would cut a .127” slot with a 1/8” bit—too wide for a 1/8” bone blank. I could use a smaller bit and make two passes, but for me, that would be asking for more trouble. I try to set things to get it right in one pass.

I prefer downcut spiral, because it is less likely to cause chipping at the edge of the slot, and evacuation of dust/chips is good enough. Whiteside RD1600 is a good choice, or you can use 1/8” shank bits from StewMac (and other places) with a collet reducer. I handle the runout issue by starting with a thicker saddle blank and thinning it to match the slot. That way, having the slot be a hair wider than 1/8” is not a problem. You don’t want a loose fitting saddle.

I use the Colt as well. Works fine for me. I just don't thickness the saddle until the slot is cut.

Makita 700 here, just a straight cut bit and I can cut pretty close to a 3mm slot with a 3mm bit, IF I clean out the collet/shank area thoroughly before I use it (and remember to tighten the router body clamp before cutting! - only forgot once!)
I only cut about 1.5 mm each pass to avoid the slot packing up with chips, and repeat that pass at the same depth to clear it.
I size my saddles after slotting.

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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.

Cleaning the collet, the bit and the bore made a HUGE difference on the runout of my router when measuring with a dial indicator. I just ordered a precision collet (made in USA on American made machines from American made metal anyway) for good measure.

I'm going to bet that routing the slot in both directions will cause more inconsistency than .001 runout. As soon I get my bits, I will be testing that theory..... I had a buddy cut some slots in 1/2" baltic ply, on his milling machine and they even came out very slightly wonky from running the cutter in both directions. We'll see...

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Measure Twice,

Karl Borum

As long as there is no slack or inconsistency in the guides for the router base, I don't see how there could be problems.

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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.

There has to be very slight clearance between the guides and the router base or the router will be stuck in place. That’s enough to make the slot a little wider when you change directions.