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LMI Neck Jig
https://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=48927		 Page 1 of 3
Author:  JoeM [ Sat Jan 28, 2017 7:07 pm ]
Post subject:  LMI Neck Jig
I bought the LMI neck jig and it doesn't seem to work for me at all.

When I cut the joint with the dovetail templates, using their dovetail bit, the joint doesn't seem to fit right. It doesn't wedge together, the fit is wrong. It rocks up and down (in line with the joint, not side to side) by 1/8".

I got one joint (out of three) to fit by doing a lot of careful paring on the male dovetail.

Since this is a tapered dovetail, I'd expect the joint to slide together and wedge right off the fixture, but the dovetail doesn't seem to touch everywhere. This is really frustrating.

Has anyone had better luck with this?
Author:  James Orr [ Sat Jan 28, 2017 8:54 pm ]
Post subject:  Re: LMI Neck Jig
Not with the dovetail, but the tenon is oversized as well. I had to shave mine with a smoothing file, which made me worried about losing that great geometry.
Author:  Ben-Had [ Sat Jan 28, 2017 9:36 pm ]
Post subject:  Re: LMI Neck Jig
I have used this jig on 50 plus dovetail joints with zero problems. One thing I don't do is cut the mortise on the guitar, I cut the neck block first in a fixture I made up and then glue it to the rim (centers better for me that way). So I only use the jig for the neck. When routing the tenon I start by having it too long, so it sits about 3/8" to 1/2" proud and then I slowly rout it down until it is about 1/32" proud and hand fit it from there.
Author:  Woodie G [ Sun Jan 29, 2017 9:35 am ]
Post subject:  Re: LMI Neck Jig
So what is the correct terminology here? A mortise is a mortise, and a tenon is a tenon, and both seem to have parallel sides, even if they are stepped or haunched or keyed. But reading the discussion, is a dovetail joint composed of a tail (the male part, if we insist on gendering inanimate objects) and the socket (the female part) as per the terminology in use where I work and in carpentry and timber framing, or have we adopted the mortise/tenon nomenclature for both joints?

To complicate this, when we cut dovetailed joints for drawers, a group of sockets is referred to as 'the pins', so even the guys here in the shop have different usages, depending on whether they come out of a cabinetmaking background or framing and construction, where a dovetail joint usually has just one tail and one socket.

Usual disclaimer about the desire to ensure accuracy of terminology in our shop building guide.
Author:  JoeM [ Sun Jan 29, 2017 8:04 pm ]
Post subject:  Re: LMI Neck Jig
I've been doing some checking, but I'm no closer to making this work. I cut another neck blank and it has the same problem, it rocks up and down right off the fixture.

I cut the male part of the joint off a ruined neck, and while it does fit (and doesn't rock), it doesn't seat all the way. I suspect that like the tenon fixture it intentionally makes it oversized so you have to hand fit it th get it to fully seat.

The problem seems to be where the end of the neck abuts the outside of the guitar body. Undercutting this lets the joint fit further into the body, and reduces the rocking a little. Maybe "flossing" would help dial this in.

Also, the fixture doesn't hold the neck centered over the template. Maybe I was off in assembling it, but I was really careful in putting it together. You can see it's off by 1/8" or so...and there isn't ay adjustment in the fixture to help.
Author:  Ken McKay [ Sun Jan 29, 2017 8:39 pm ]
Post subject:  Re: LMI Neck Jig
Hey Joe, Hang in there. We can help.

Looking at the picture, there seems to be a problem. Can you shoot a picture of your routing templates.
Author:  Ken McKay [ Sun Jan 29, 2017 9:10 pm ]
Post subject:  Re: LMI Neck Jig
Image
does your template look like this?
Author:  JoeM [ Sun Jan 29, 2017 11:25 pm ]
Post subject:  Re: LMI Neck Jig
Yep, that's what my templates look like.

I suspect that there is some error in my assembly of the jig that accounts for the mis-alignment side-to-side. Probably on the hinged part that supports the neck. The holes are all laid out on the wood, so I'm not sure how that happened (or what to do about it now).

As far as the fit, it has to be some interference with the end of the guitar body because the dovetail itself (sawn for the end of a ruined neck blank) doesn't rock. So something is keeping it from fitting. It's annoying that the male part is oversized because that means that I have to shave down the heel of the neck carefully to fit the body, AND have to shave down the sides of the male dovetail because when the male part is machined the right length for the socket it's too wide to come close to fitting.

I'm going to try again, and make sure the male part is the right length, even though it won't fit into the socket, and then focus on shaping the heel carefully to get it to seat against the end of the body...and then file the sides of the dovetail down to let it settle all the way into the socket.

But having to adjust both to get it to fit is a drag. I guess I could change the guitar design and make the area where the neck seats perfectly flat side to side and top to bottom (it is, top to bottom, but is rounded side to side)
Author:  Ken McKay [ Mon Jan 30, 2017 12:39 am ]
Post subject:  Re: LMI Neck Jig
Joe, your mortise looks like a straight one, not a dovetail. Can you explain that?
Author:  Mike OMelia [ Mon Jan 30, 2017 10:28 am ]
Post subject:  Re: LMI Neck Jig
I use the Luthier Tools jig. I found it difficult to cut the D/T as well. And as I do mine on the body, I wasn't willing to risk it. Maybe one day.
Author:  JoeM [ Mon Jan 30, 2017 11:22 am ]
Post subject:  Re: LMI Neck Jig
Ken McKay wrote:
Joe, your mortise looks like a straight one, not a dovetail. Can you explain that?


Hi Ken -- the slot is the 1/4" x 3/8" truss rod slot that fits over the alignment pins in the fixture to center the neck. You can see the truss rod slot is centered, but in the fixture the dovetail will be off-center. I can't imagine how I could have assembled the fixture inaccurately Everything is positioned by LMI (pre-drilled holes for the templates, slots for the parts to fit in, marked screw holes, etc).
Author:  bcombs510 [ Mon Jan 30, 2017 11:24 am ]
Post subject:  Re: LMI Neck Jig
LMI support has been good to me. Did they have any input?
Author:  JoeM [ Mon Jan 30, 2017 11:32 am ]
Post subject:  Re: LMI Neck Jig
Mike O'Melia wrote:
I use the Luthier Tools jig. I found it difficult to cut the D/T as well. And as I do mine on the body, I wasn't willing to risk it. Maybe one day.


I was looking at that jig last night, wondering if it would work better for me. Just a little put off by the price given that I'm a beginner and amateur. But it looks like it has adjustments to make sure the neck is centered and square. That would take care of one of the issues I'm having. I'll have to look at the LMI jig today and see if there is any way to get the neck centered. In theory I could re-drill the holes the alignment pins fit into, but that is going to be dicey to get it done accurately.

I just subscribed to Tom Bills' site to see how he does the neck dovetail, maybe I'll get some ideas from that.
Author:  Ben-Had [ Mon Jan 30, 2017 1:03 pm ]
Post subject:  Re: LMI Neck Jig
Have you watched Robbie O'Brien's video on the LMI site to compare to how you are cutting yours?
Author:  George L [ Mon Jan 30, 2017 2:07 pm ]
Post subject:  Re: LMI Neck Jig
Ben-Had wrote:
Have you watched Robbie O'Brien's video on the LMI site to compare to how you are cutting yours?

Just what I was going to recommend. It's possible there is something wrong with your particular jig, but the odds here are on operator error. I base this on my own experience of making just about every mistake imaginable at least once and hope you won't be offended. [:Y:]
Author:  Clinchriver [ Mon Jan 30, 2017 5:36 pm ]
Post subject:  Re: LMI Neck Jig
JoeM wrote:
Mike O'Melia wrote:
I use the Luthier Tools jig. I found it difficult to cut the D/T as well. And as I do mine on the body, I wasn't willing to risk it. Maybe one day.


I was looking at that jig last night, wondering if it would work better for me. Just a little put off by the price given that I'm a beginner and amateur. But it looks like it has adjustments to make sure the neck is centered and square. That would take care of one of the issues I'm having. I'll have to look at the LMI jig today and see if there is any way to get the neck centered. In theory I could re-drill the holes the alignment pins fit into, but that is going to be dicey to get it done accurately.

I just subscribed to Tom Bills' site to see how he does the neck dovetail, maybe I'll get some ideas from that.



The Luthier Tools jig once sorted out is very precise, and repeatable.
Author:  JoeM [ Mon Jan 30, 2017 6:52 pm ]
Post subject:  Re: LMI Neck Jig
I just watched Robbie's video, I'm doing what he shows. LMI support suggested that too

The misalignment problem of the neck in the fixture is a problem with the manufacture of the jig, if you look at the alignment holes you can see they are offset from the laser engraved center line by about the same amount as the neck is offset from the template.

As far as the rocking, I'm stumped. The only think I can imagine is that the geometry of the end of my body (well, guitar body, not *my* body) is somehow uneven. I made sure to sand it flat from top to bottom so it was straight.
Author:  murrmac [ Mon Jan 30, 2017 6:58 pm ]
Post subject:  Re: LMI Neck Jig
Woodie G wrote:
So what is the correct terminology here? A mortise is a mortise, and a tenon is a tenon, and both seem to have parallel sides, even if they are stepped or haunched or keyed. But reading the discussion, is a dovetail joint composed of a tail (the male part, if we insist on gendering inanimate objects) and the socket (the female part) as per the terminology in use where I work and in carpentry and timber framing, or have we adopted the mortise/tenon nomenclature for both joints?

To complicate this, when we cut dovetailed joints for drawers, a group of sockets is referred to as 'the pins', so even the guys here in the shop have different usages, depending on whether they come out of a cabinetmaking background or framing and construction, where a dovetail joint usually has just one tail and one socket.


There are few more pedantic than I when it comes to correct terminology ... (I scream silently when I see "kerfing" used as a noun) ... but I have no problem with "mortise" and "tenon" in this instance.

What does bug me is when I see references to "flossing the cheeks" when fitting a neck, when what is really meant is "flossing the shoulders".

The "cheeks" are the internal sides of the dovetail tenon, the surfaces which are glued to the sides of the mortise. The end-grain surfaces of the neck heel which abut the upper bout are the "shoulders".

I have, however, long since ceased to care about the perennial and ubiquitous misspelling of "heel" as "heal".
Author:  Alex Kleon [ Mon Jan 30, 2017 8:28 pm ]
Post subject:  Re: LMI Neck Jig
murrmac wrote:
Woodie G wrote:
So what is the correct terminology here? A mortise is a mortise, and a tenon is a tenon, and both seem to have parallel sides, even if they are stepped or haunched or keyed. But reading the discussion, is a dovetail joint composed of a tail (the male part, if we insist on gendering inanimate objects) and the socket (the female part) as per the terminology in use where I work and in carpentry and timber framing, or have we adopted the mortise/tenon nomenclature for both joints?

To complicate this, when we cut dovetailed joints for drawers, a group of sockets is referred to as 'the pins', so even the guys here in the shop have different usages, depending on whether they come out of a cabinetmaking background or framing and construction, where a dovetail joint usually has just one tail and one socket.


There are few more pedantic than I when it comes to correct terminology ... (I scream silently when I see "kerfing" used as a noun) ... but I have no problem with "mortise" and "tenon" in this instance.

What does bug me is when I see references to "flossing the cheeks" when fitting a neck, when what is really meant is "flossing the shoulders".

The "cheeks" are the internal sides of the dovetail tenon, the surfaces which are glued to the sides of the mortise. The end-grain surfaces of the neck heel which abut the upper bout are the "shoulders".

I have, however, long since ceased to care about the perennial and ubiquitous misspelling of "heel" as "heal".


Language is the virus. Single malt is the cure (remedy, anyhow). ;)

Alex
Author:  Terence Kennedy [ Mon Jan 30, 2017 9:09 pm ]
Post subject:  Re: LMI Neck Jig
Man those holes are WAY off. Better send that one back and tell LMI.
Author:  Ken McKay [ Mon Jan 30, 2017 10:45 pm ]
Post subject:  Re: LMI Neck Jig
try pulling the pin for centering with the truss rod and do it by eye.
Author:  JoeM [ Wed Feb 01, 2017 11:02 am ]
Post subject:  Re: LMI Neck Jig
I drilled new holes for the pins, but the laser-engraved centering line isn't centered under the template either. That seems like something that should be adjustable, of the jig should be precisely made so that it isn't an issue. (LMI support has been silent since I sent them pictures of the mis-aligned holes.)

But that's the smaller issue frankly. The main issue is the rocking. Very, very frustrating.

Here is what I did.

I checked everything with a caliper and straightedge to see if I could identify something that was out of wack. Nothing seemed wrong. The body dovetail had flat walls and a consistent depth, although there were a few spots where I pared it to fit the original neck I made (plans had the wrong dimensions -- THAT neck fit, go figure).

So I put the body back in the jig and cut the female socket a little further into the body (toward the back) just to clean it up and give the joint a little more grip area.

Then I cut the male joint oversized and started hand fitting. It's still a little off center, but I'm hoping that will not affect playability. I used dental paper to check the surfaces and pared a little at a time off the end of the neck, the sides of the dovetail and the end of the dovetail. As best I can figure the rocking is caused, at least partly, by the curvature of the body at the neck joint. I'm going to make that area dead flat side-to-side the width of the neck in the future!

I started with the neck protruding 5/8" above the soundboard, I'm down to about 1/16" now and the rocking is gone. Lots of work paring and flossing to get it to this point. I'm going to cut it to the right width before I fit it the rest of the way, but I think I'll be able to make this one work.

Holy S*** this was a pain in the butt. I think working to a dead-flat plane will make this easier, but I like the continuous curved shape better. This is an area where I need to get a lot better in both skill and process.

I'm curious how others do this, I'll search the forum, but if you have any hot tips I'd love to hear them.
Author:  SteveSmith [ Wed Feb 01, 2017 11:05 am ]
Post subject:  Re: LMI Neck Jig
Curve shape 'shouldn't" be that big of a deal, I would think. Most of mine are curved and I see no difference.
Author:  Ben-Had [ Wed Feb 01, 2017 4:06 pm ]
Post subject:  Re: LMI Neck Jig
Remember when you profile that neck done to the FB width and floss the heel shoulders during your final fittings before attachment I would bet most of the rocking you are experiencing will go away. The neck is still in the early stages in my mind. I do like the area under the heel to be near dead flat on my guitars.
Author:  Terence Kennedy [ Wed Feb 01, 2017 7:20 pm ]
Post subject:  Re: LMI Neck Jig
Looks like you have a little curve in your upper bout which is fine but even after undercutting, a tapered heel against a curved upper bout will rock a little in the middle.

Put a ruler against a pop can so it is in line with the can and it fits snug. Rotate it a little and it only hits in the middle and rocks.

I would get your heel taper and width pretty close to final specs, undercut to leave maybe 1/8-3/16" actually bearing against the body and floss to fit. I usually outline the neck width and taper with a fretboard in place and draw lines and then cut just outside those lines with the bandsaw.

Image

This thread has some useful info as well as pictures of a slotted fretboard surrogate for flossing that has helped me a lot.

viewtopic.php?f=10101&t=48494&p=640550&hilit=Flossing#p640550

Don't be too hard on yourself it took me quite a while to wrap my head around juggling neck angle and heel body fit.
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