Projection gauge?

[polkat]

Several luthier supply companies sell a violin projection gauge, which is simply a straight bar with two dowls (pins) sticking out on opposite sides of one end. You lay it on the fingerboard and the pin just touches the top at the bridge area if the projection is corrent. There's a pin for with or without fingerboards. You've all seen these.

Seems to me this would be a very simple device to make, but does anyone have any idea of the lengths of each pin? My guess is that the longer pin is around 27mm (standard projection heigth) and the other is less the fingerboard thickness. Sound right? Or should one consider that the pins don't drop straight down, but at a slight angle=maybe longer? Thanks.

[Andres Sender]

See Michael Darnton's posts in THIS THREAD (link).

(My rather oblique point being that setting the projection with a couple rulers is so easy, and since the exact measurement is not set in stone, it might make more sense to put time into an angle gauge.)

[M_A_T_T]

I made one from a bar of aluminum with a brass screw set at 27mm, and the pin is set perpendicular to the plane of the top. I glue my fingerboards on 'permanetly' when making the neck so I only require the one pin.

[Brad Dorsey]

"My guess is that the longer pin is around 27mm (standard projection heigth) and the other is less the fingerboard thickness. Sound right?"

Yes, that's right. But since the thickness of the fingerboard can vary a bit, the proper length of the shorter pin is not exactly defined. I made several fingerboard projection gages for different sized violins and a cello, based on the measurements given in Strobel's book. Each gage is made by gluing two pieces of wood together in an L shape, one a little shorter than the string length and the other at right angles to the first extending from it the desired measurement. Since I always set a neck with the fingerboard attached, I don't see any reason to have a gage corresponding to the shorter pin. In addition to being used in neck setting, these gages are also useful for checking the fingerboard projection of an instrument with the neck and fingerboard already attached.

[sonnichs]

Polcat

 I have one of these "werkzeugen" in my tool chest but it

rarely comes out since I use rulers. At any rate I took it out

tonight and measured it for you-- and I was a little supirsed.

The long pin =

28.02 mm

The short pin =

16.83 mm

The additional 1.02mm of the long pin does not compensate for the

angle of the fingerboard. If you assume a fingerboard angle of 11

degrees (per Strobel) the proper length would be 27/cos(11) = 27.5

mm. Perhaps the device is poorly made, or perhaps the maker is

taking into account the "sag" which results after string tension

takes hold for a while on a new violin. The pin falls right where

the bridge should be.

 I do not use this device, mainly because one must remove the

bridge to use it accurately, and I bought it with the intention of

quickly measuring the neck set condition on a violin. (the tool

costs less than the metal to make one)

 At any rate, as others have done here,  I

cut a piece of 10mm x 10mm aluminum stock about 1cm short of the

distance from the nut to the bridge. This way I can lay it on the

fingerboard of a strung violin, between the D and A under tension,

and mark the bridge where it falls, then measure the mark., hoping

of course for 27mm in most cases.  Presumably the tension of

the strings changes the neck angle slightly (but I never measure

how much).

 I expect that the commercial

tool that you mention may be handy when doing a neck set with the

strings and bridge removed. However I have a clamping jig that I

made for neck resets and still use my aluminum bar and a ruler,

strapping the bar to the fingerboard and then adjusting the neck

angle using a ruler and my jig screws.

Regards,

Fritz

[polkat]

Thanks guys! Andres, I like Michael's angle gauge, but don't fully understand it. Say perhaps 159 degrees is desirable as a final string angle (as it seemed Michael was saying-or did I read that wrong?). With the gauge set at this, and the fingerboard raised or lowered until the gauge sits flat and also touches the saddle (with the screw over the bridge position) couldn't you have varying bridge projection based on how high the arch is? How would you maintain 159 in this case. I believe, as usual, that I'm missing something here, but I like the idea.

My confusion in the pin length is that the fingerboard is, of course, at an angle to the top of the top plate, and if the pin is 27mm long, but at right angles to the length of whatever it is attached to sitting flat on the fingerboard, the tip of the pin will touch the top at something less then 27mm (assuming the neck is loose and can be rocked until the pin touches). With the pin set perpendicular to the top as M_A_T_T does, it will give the right measurement. Based on this, the commercial gauges must be slightly longer the 27mm.

Why not use a pin 27mm long (from the bottom of the bar) and attach it on a swivle? Then you could get a perpendicular reading regardless of arch or neck angle.

[Andres Sender]

Polkat--you can also vary the saddle height and if necessary the overstand. Yes arching height affects everything else and extremes will require adjustments elsewhere to get the right angle with a reasonable bridge height (reasonable for the instrument, that is). MD mentioned 157.5 and 158 degrees as the lower limit in some threads last year.

[NewNewbie]

You might like to see this web-page if you haven't already:

http://www.dov-music.com/proddetail.asp?prod=1085

Pin is only on one side.

I have one with a pin on both sides.  Here are the

measurements.

Total Bar Length 330mm

Pin Diameter 4.76 mm - ( 3/16" )

Pin is set 1.5 mm back from edge of bar.

Total Pin Length is 56.66 mm ( both sides and bar width )

Bar Width 12.6 mm

Long Pin 26.75 mm

Short Pin 17.3 mm

I like the idea of using a threaded end for the Pins so you can

adjust the pin length.  After a few instruments and some pin

changes, you will be settled on a good general projection setting

that will allow for a certain amount of settling that will occur

after the instruments is strung up and has time to settle in.

If you can work in metric, then a 6.0 mm thread with a pitch of 1.0

mm per turn would do nicely.  If you are stuck in the Imperial

system, then a 10 - 24 thread will get the job done. One rotation

will advance the screw by 1.058333 mm, so you can see that this

0.06 mm accumulated difference can easily be handled.

Another interesting thing to consider here is that some people put

the neck in with no top on the rib frame, and so they need another

projection measure, that goes to the mold of the rib frame.

 

David Rubio did this. If you want to check out how he did it then

go here, and click on the left -  "Fitting violin neck before

closing the box"

http://www.rubioviolins.com/

---What this measurement is I don't know, but maybe someone

else will be able to say what it is.

I have also run across a projection that is given for the distance

from the end of the fingerboard to the top arch. I've seen 20 mm

usually given for this.

---Does anyone else have this measurement?

I see all these projection tools as guides to getting things

close, in the early stages, and then I would suggest that the gauge

Michael uses will help you to arrive at your final destination.

 Why I like the gauge that Michael uses is because it gets to

the heart of the matter, in a very simple straight forward manner.

 Does it surprise anyone here that Michael would come up with

this.

[NewNewbie]

" The long pin = 28.02 mm

The short pin =

16.83 mm" - sonnichs

====================================================================

The difference here in length, between the short and long pins, is

11.19 mm.  

Does that require a thicker fingerboard????

My gauge:

Long Pin 26.75 mm

Short Pin 17.3 mm

This gives 9.45 mm difference.

Does this gauge require a thinner fingerboard????

I'm surprised that the variation between the two gauges.

[polkat]

Andres, the gauge makes more sense to me now, given the possible saddle and overstand adjustments.

NewNewbie, and others, thanks for the measurements. I think this all brings it together for me. I like the idea of using the bar gauge to rough the neck in, and then using a gauge like Michaels to get specific. I had been using two rulers up to this point, and wanted something more accurate. I think I found that here. Again, thanks all!