Official Luthiers Forum!

Looking at router bits for cutting a dovetail "tenon"
104 degrees? 99?98?
What angle do you use?
Is 1/2" long enough for the "tenon"?

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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.

10 degree
https://www.woodline.com/collections/do ... etail-bits

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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

As mentioned, Martin uses 10 degrees. IMS, Gibson uses roughly 14 degrees, making the neck joints a little faster and easier to fit. Generally, the higher the angle, the stronger the joint, but given that a properly fitted dovetail neck joint is much stronger than required for the loads imposed, serviceability - which is to say ease of assembly/disassembly without damage, as well as ease of fitting - keep practical angles within a fairly narrow range for a tapered sliding dovetail.

Summary? Judging from the number of old guitars still in circulation, anything between 10 and 15 degrees seems to stand up to prolonged use in hardwood. The only time we saw issues with the higher angles was a) with less expensive guitars which used woods like poplar due to wartime shortages, and thus employed the higher joint angles traditionally used for softwood or softer hardwood in secondary structure in furniture, and b) when glues other than hide were used.

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For the times they are a changin'

- Bob Dylan

I have to disagree there is a point that the angle weakens. 10 degree is stronger than 14 I have seen many of the gibsons dovetail that sheared.
The main point is that if you are using a neck jig the dovetail will match. I have use 9 and 10.
I will agree that the better the fit of the joint the better the load will be shared to the mating surfaces

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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

The greater the angle, the greater the force required to move the joint a given amount - even without taking into account any contribution from adhesives, more surface area creates greater friction when the faces of the socket and tail are placed under load. This is why dovetails in softwoods use a higher angle than stronger hardwoods. Softwood joints can be seen at as low as 4:1 in some large timber frames, while in furniture, angles at 8:1 or higher are common in hardwoods. But as Mr. Hall alluded to, at some point, material properties dominate, and along-grain shear in weaker woods becomes the limiting factor...usually well beyond the loads where we can expect the guitar to avoid the need for repairs.

But that difference in ultimate strength of the joint does not really matter, as both a 10 degree and 14 degree joint will be many times stronger than needed in routine service. The real issue - as Mr. Hall suggested - is whether the tail is likely to fracture during a steamed removal, and we certainly saw more in the way of issues with Gibsons than Martins.

Whether due to adhesive choice, the amount of excess adhesive present and related steaming time, or quality/choice of materials, it's nearly always going to be easier to get a Martin 'real dovetail' neck off. Balancing that is the ease of fitting a higher angle dovetail...just quicker and easier. I suspect that's exactly why the two manufacturers made the design choices they did - Martin towards longevity and ease of disassembly in the bowed instrument tradition of the European craft guilds, and Gibson towards reduced fitting and assembly time stemming from more business-oriented concerns.

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For the times they are a changin'

- Bob Dylan

Just to be clear. Is the angle 10/14 degrees, whatever, between the two cutter edges, or between the center line and one cutter edge?

_________________
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.

Centerline and cutter edge.

Good to see your posts, Woodie G. The rest of you, too, of course.

FWIW, I use the 10 degree bit sold by Stew-Mac.

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George :-)

And LMI sell a 7 degree bit for their neck angle jig.......

_________________
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.

As a first time dovetailer, I've had a lot of the same questions, Colin. FWIW, LuthierTool supplied a 7 degree dovetail bit with my dovetail templates, and the directions for the Neck Angle Jig call for a 1/2" tenon with a 5/8" deep mortis.

Edit: I went out side to see which bit I have specifically. Looks like the Amana 45808.

Thanks.
5/8" or so seems seems universal, ties in nicely with the 16th fret position for resets of course.
Seems to be this bit, the Incra Dovetail Jig bit is popular with the makers of Guitar Neck Jigs.
Probably because of the overall length and cutter length necessary for both jigs
I've purchased the Whiteside equivalent, recommended my jig maker and Incra, good price and availability here.
https://routercutter.co.uk/whiteside-d7-531

_________________
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.