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Neck Jig refresher course (for me)
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=48344		 Page 1 of 2
Author:  Mike OMelia [ Fri Sep 30, 2016 7:00 pm ]
Post subject:  Neck Jig refresher course (for me)
I got the Jig all squared up using the wood alignment beam. Platform is 90 degrees to aluminum bar. Dial indicator is zeroed to wood alignment beam. I put the body in the Jig and presses in towards dial indicator 0.186". I am aiming for 0.385" at saddle location. Bridge is 0.375, add a tenth for fret height.

Do I need to account for fret board thickness?

Do I tilt platform till zero? Then count to 0.385?

Please dont say "RTFM". And you probably know why. gaah

Mike
Author:  Mike OMelia [ Fri Sep 30, 2016 7:01 pm ]
Post subject:  Re: Neck Jig refresher course (for me)
Forgot the picture
Author:  Mike OMelia [ Fri Sep 30, 2016 7:03 pm ]
Post subject:  Re: Neck Jig refresher course (for me)
If fretboard is 1/4" (typical), then do I subtract that and fret height estimate off of .375" (bridge height)

Edit: this seems wrong. See below
Author:  Mike OMelia [ Fri Sep 30, 2016 7:48 pm ]
Post subject:  Re: Neck Jig refresher course (for me)
How about this. In TFM, it says once you tilt it back to zero set, then add height compensation. But no examples. My fretboard is 1/4". My fret wire is 0.039". My bridge is 3/8", and my saddle height is around .23" (same as slot depth).
Author:  Mike OMelia [ Fri Sep 30, 2016 7:51 pm ]
Post subject:  Re: Neck Jig refresher course (for me)
So, would height compensation be 0.25 + 0.039 - 0.375 - 0.23 = -0.316" ??

So, once zeroed, I move it another 0.316" away from zero datum?
Author:  Clinchriver [ Sat Oct 01, 2016 6:39 am ]
Post subject:  Re: Neck Jig refresher course (for me)
Mike O'Melia wrote:
So, would height compensation be 0.25 + 0.039 - 0.375 - 0.23 = -0.316" ??

So, once zeroed, I move it another 0.316" away from zero datum?


I don't think so, if you look at reference A, I see your neck without a fingerboard and the top of body in-line dial indicator zeroed. I would shoot for .080 to .100
Author:  Mike OMelia [ Sat Oct 01, 2016 7:20 am ]
Post subject:  Re: Neck Jig refresher course (for me)
Right. That's the number I get if I don't factor in saddle height. That's correct t?
Author:  Clinchriver [ Sat Oct 01, 2016 7:46 am ]
Post subject:  Re: Neck Jig refresher course (for me)
Mike O'Melia wrote:
Right. That's the number I get if I don't factor in saddle height. That's correct t?


yep :mrgreen:
Author:  Mike OMelia [ Sat Oct 01, 2016 7:48 am ]
Post subject:  Re: Neck Jig refresher course (for me)
From same document;

Remember with the dial indicator at zero represents the same projected plane for the top of the neck to the point where the saddle will be placed. With this setting you now have a surface that you can calculate the difference between the bridge, saddle height, finger board, string height, fret height, etc. This number will become your height compensation. This distance may be different for the type of guitar you are building.
Author:  Clinchriver [ Sat Oct 01, 2016 8:10 am ]
Post subject:  Re: Neck Jig refresher course (for me)
Mike O'Melia wrote:
From same document;

Remember with the dial indicator at zero represents the same projected plane for the top of the neck to the point where the saddle will be placed. With this setting you now have a surface that you can calculate the difference between the bridge, saddle height, finger board, string height, fret height, etc. This number will become your height compensation. This distance may be different for the type of guitar you are building.


Again yep, what are you asking now? With the neck and body "in-line" establish your saddle location, zero the dial indicator and tilt till your .080 to .100 over the top. Route your neck, dovetail or tenon, body the same then fit your neck and you should be off and running.
Author:  Mike OMelia [ Mon Oct 03, 2016 12:39 pm ]
Post subject:  Re: Neck Jig refresher course (for me)
Been on vacation. So, when cut and fitted, fingerboard with frets and bridge in correct location, a straight edge across frets, extended to bridge would be about 0.1" above bridge. Correct?
Author:  Ken Jones [ Tue Oct 04, 2016 12:23 am ]
Post subject:  Re: Neck Jig refresher course (for me)
I find that around .050" projection above the bridge works out about right. That's the number we use as a target when doing resets. I find much more than that, and the saddle is a bit too exposed.


Sent from my iPhone using Tapatalk
Author:  Ken Jones [ Tue Oct 04, 2016 12:29 am ]
Post subject:  Re: Neck Jig refresher course (for me)
Off the top of my head, once you zero the dial indicator on the body, the height compensation is the difference between fretboard plus frets (roughly .290" nominal) and the ideal projection over the bridge (roughly .425" nominal), so around .135". My fretboards and bridges are usually a little under those numbers, but the offset is similar. I'll check my notes tomorrow to confirm.


Sent from my iPhone using Tapatalk
Author:  Woodie G [ Tue Oct 04, 2016 6:52 am ]
Post subject:  Re: Neck Jig refresher course (for me)
On the bare body/bare neck measurement, we use 0.085" + the correction for the reduced neck angle with a tapered heel/curved neck block area.
Author:  James Orr [ Tue Oct 04, 2016 12:01 pm ]
Post subject:  Re: Neck Jig refresher course (for me)
Woodie G wrote:
On the bare body/bare neck measurement, we use 0.085" + the correction for the reduced neck angle with a tapered heel/curved neck block area.


Woodie, I'd love to hear more about what you mean by the correction for the reduced neck angle? I'm not sure I understand. I thought that the gap above the soundboard (.085" in your case) was to account for the neck angle? I always get a lot out of your posts, so I feel like I'm about to discover a new secret :)
Author:  Woodie G [ Tue Oct 04, 2016 5:15 pm ]
Post subject:  Re: Neck Jig refresher course (for me)
Secrets? Goodness, no! But thanks for the kind characterization.

The attached illustration shows the reason for the need for a correction. For our SJ body, which has a fair amount of curvature across the neck joint, there is about .040", so a big impact on neck angle off the neck jig if not corrected.
Author:  Mike OMelia [ Sun Oct 09, 2016 1:18 pm ]
Post subject:  Re: Neck Jig refresher course (for me)
Ken Jones wrote:
Off the top of my head, once you zero the dial indicator on the body, the height compensation is the difference between fretboard plus frets (roughly .290" nominal) and the ideal projection over the bridge (roughly .425" nominal), so around .135". My fretboards and bridges are usually a little under those numbers, but the offset is similar. I'll check my notes tomorrow to confirm.


Sent from my iPhone using Tapatalk


Ken, once more. Could you explain "ideal projection over bridge"? I guess I don't understand .425". Is that distance from the projection line over bridge area (location) to the surface of the top?

Edit: OK. I see. Bridge height plus projected height above bridge or 0.375 + 0.05 = 0.425. This site (http://www.buildyourguitar.com/resource ... aangle.htm) suggests 1/64" to 1/16", or 0.015" to 0.0625"
Author:  Mike OMelia [ Sun Oct 09, 2016 4:13 pm ]
Post subject:  Re: Neck Jig refresher course (for me)
Additional info: My tops are domed. 25' radius. I take great care to get sides square. I can measure angle between top and side at neck joint. It is ~1.4 degrees. This indeed closely matches design (OLF Medium Jumbo, 1.5 deg). Dome center height is at center of X brace, and saddle sits back further (of course). So its on the "down slope" if you will. Angle at tail block to top is ~0 degrees, again by design.

I clamped a fingerboard with frets to top, taped bridge in correct location, and used a straight edge and measured an "as is" projection height above bridge as 0.05". (Bridge is 3/8" tall, fretboard & frets is 0.29"). On the jig after a very careful setup, the dial indicator says 0.251". If the top was dead flat, i would bump into the bridge 0.085 below the top of bridge. As it is, I am 0.05 over top (domed top result). I am between the 1/64" and 1/16" range (mentioned in link). Ken says he shoots for 0.05. I could go another 0.0125 to hit 1/16".

I think the domed top is what makes me over-think this. Tan(0.251/11.5) is 1.25 deg. So its close (11.5" is saddle location).

It just seems to me that if top is truly flat, then projection height will be 0.29-0.375=-0.085 (its below top of bridge). So you have to take out that 0.085 and an additional 0.05" to 0.0625". Note what Ken said above: 0.085+0.05 = 0.135". This makes perfect sense for a flat top. But with a domed top, I have to make measurements to see where I am. And take into account. I am 0.05 already above. I think my height compensation should be 1/16" -0.05" = 0.0125
Author:  Mike OMelia [ Mon Oct 10, 2016 12:04 am ]
Post subject:  Re: Neck Jig refresher course (for me)
For a true flat top, height compensation is bridge height + desired clearance(relative to top of bridge) - fretboard height - fret thickness
Ken's example: 0.375 + 0.05 - 0.25 - 0.04 = 0.135" (the theoretical amount I tilt jig past zero dial indicator reading)

For a domed top, make same calculation, but subtract off bridge height + measurement (relative to top of bridge) - fretboard height - fret thickness

Obviously, this results in a simpler equation: height compensation is desired clearance(relative to top of bridge) - measurement (relative to top of bridge)

In the case of a true flat top, (above) this 0.05 - (-0.085) or 0.135

In my current case, this is 0.05 - (+0.05) = 0.0

Why does this equation not involve bridge height or fretboard & fret height? Because there is a measurement BASED on them. I am suggesting that you cannot use a neck jig with a domed top without a measurement. But in either case, if you use a straightedge measurement, you only need to know two things.

The amount of the desired clearance is still subjective. Based on what one believes a guitar will do under full tension and proper relief.

Someone care to evaluate my suggestion?

Mike

Edit: The 1.4 deg angle I mentioned earlier has nothing to do with this. The jig takes that out so that the surface of the neck plane is planar with the top. Some adjustment beyond that is needed to create the correct projection height (above). The hope is, I think, that it will not be too dramatic as to create a noticeable hump as the end of the fretboard is bent down to meet the top (this assumes a careful crafting of the body)
Author:  Woodie G [ Mon Oct 10, 2016 6:34 am ]
Post subject:  Re: Neck Jig refresher course (for me)
I am not sure top shape (domed, flat, cylindrical) makes a difference - aren't we just attempting to set the height of the neck plane against a fixed point on the surface of the body to a fixed value? If we substituted a true flat top for a radiused top body in the neck jig, what would change, beyond the need to wedge or taper the extension to fit to the body?

We still have to set the neck angle to achieve a set saddle height above the top whatever the physical shape of the top. The only values that I can see that are not measurable and/or known are the body distortion under string tension (so-called 'top' rise...we use 1/32" to 1/16", depending on body size and shape, and top wood and bracing) and a correction for use of a tapered heel on a curved neck block. Fretboard thickness, fret height, and desired string height are all established by design or materials choices. Even bridge thickness should be a known value, because the desired saddle height above the bridge may be subtracted from the height of string at the bridge to determine bridge thickness, and the bridge fabricated to known dimensions.
Author:  Mike OMelia [ Mon Oct 10, 2016 6:57 am ]
Post subject:  Re: Neck Jig refresher course (for me)
Woodie, I finally see what ur saying about tapered heels and body curves at neck joint. I'm using a D heel, no taper, nothing to compensate for.

Look at these pics. The neck is not involved. This is just looking at the geometry of the top. Here, there is a 0.049 height above bridge. There will of course be some adjustment in the neck angle, at least or near 1.4 degrees. More or less than that to achieve final result.

My pictures show that the top geometry alone with FB & frets and bridge provide almost the correct value.

.
Author:  Woodie G [ Mon Oct 10, 2016 9:07 am ]
Post subject:  Re: Neck Jig refresher course (for me)
There are two conditions here: the body and bare neck in Woolson-style neck jig, and assembled body and neck with fretboard and possibly frets after milling the neck joint. For the first, the bare neck is used with bare, undistorted body, and the milling angle for the joint is set. For the second, the fret plane is used to check for the ROT 1/16" clearance.

My comments earlier in the thread address the first condition, but I would think that for the second condition, we would want to be careful and assess the actual clearance of the fret plane over the bridge with a tool that contacts the frets or fret plane (we fret after the neck is finished and on the body) at at most two points, such as the 1st and 12th or 14th frets (we use the 12th for consistency, as we build both in a variety of scale lengths), thus, eliminating any departure from a true representation of the neck/fretboard plane due to distortion of the fretboard extension or fretting irregularities which would normally be resolved in the fret dressing process.

We have used a couple different gauge designs for the job, with the early model (bottom in the photo) still a quick go-no/go tool which required the use of shims to measure height above bridge and can be knocked out of alignment by temperature changes, rough handling, etc., and the revised tool (the uppermost in photo) used for most measurements in this shop. The disadvantage of the improved gauge is the need to zero the tool on a dead flat surface or a stable straightedge prior to use; the advantage to that approach is that any change in tool geometry is corrected each time it is re-zeroed. There is still room for improvement - the tool needs other bodies for baritone and bass guitar use, and the Stewart MacDonald dial gauge mount is mounted with set screws instead of a quick release.
Author:  Mike OMelia [ Mon Oct 10, 2016 9:34 am ]
Post subject:  Re: Neck Jig refresher course (for me)
I understand how to set the neck angle by tilting the table to zero the gauge. In the pictures below, the table angle is 1.5 reg after zeroing dial. That's going align the bare FB plane with the top at the joint. The actual neck block itself is tapered by design by 1.5 deg. If all I do is this, then how do I adjust further (after milling)?
Author:  Pat Foster [ Mon Oct 10, 2016 10:12 am ]
Post subject:  Re: Neck Jig refresher course (for me)
Wow. I didn't know this was so complicated.
Author:  Mike OMelia [ Mon Oct 10, 2016 11:19 am ]
Post subject:  Re: Neck Jig refresher course (for me)
I personally do not think it is that complicated. The problem is the number of conflicting ideas.
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