Simple centerline jig

[bjansen]

I've tried a number of different ways to scribe a centerline on a glass bow blank...lasers, string lines, straigtedges and so on.  Here is the best thing  have came up with yet.  It is a simple jig to hold a pencil parallel with a table.  You can adjust the height with different pencils/markers or even wrap tape around the pencil to raise it up.  The key is to start with a flat blank and the easiest way to do that is to run your blank through a drum sander.  I was always nervous about doing that (thinking it could flip when running through and be ruined immediately) but it really works good and is more stable than I thought.  

Here are some pics of how I made it with some scrap plywood:

 

 

 

 

 

 

[White Oak]

Hey, I've been waiting for this. Looks like a winner to me Brad.I'm sure I'll be making one.
I gotta tell ya, that bow starting thru that sander looks scary.  
Can't argue with success though.
Thanks for the tip.
Ed
   

[inrut]

Here is my version from a few years back. It can be adjusted for about any width bow a bowyer would want to build.
 
 

[bjansen]

Inrut..I had a feeling yours was going to be a little more precise!  Very nice

[kennym]

Sweet!!

Just make sure the table is strait(flat)...

[PEARL DRUMS]

Ahhhhh the details kenny......

[inrut]

Thanks for the complement Brad, but I was just trying to show another perspective of the same device. I love looking at other peoples ways of doing things!!!!!! Here is the top view.
 

[bjansen]

That is excellent.  Did you turn & drill the alluminum pen holder or is that a misc. part that you made a holder for?

[inrut]

The black block is a left over piece of Micarta from a riser. The pen holder is a 1 1/8" piece of stainless steel bar stock that I drilled to hold the pen. I drilled and tapped the end of the pen holder for a thumb screw, but the taper of the pen fit the hole snug so I opted not to put the thumb screw in.

[virgil.v]

5mn to build.    
 

[Roy from Pa]

Yup Virgil, I've had one of those for years.

[Robertfishes]

I just make a grid on my back glass before glue up,after drawing my center line down the center of glass I use a small square and a extra fine sharpie and make a line every inch.. after glue up I use a string and make sure the center is still a straight line.. and then starting in center of bow I number each inch mark from bow center, Then I grind limbs to the line, I then use a compass and make sure each number is the same distance left and right of center line and also top limb and bottom limb numbers..I always end up less than 3/16 tiller on my one piece bows. This works for me, wish I had a nice thickness sander like Brads!!..  

[Roy from Pa]

Robert, that is pretty precise:)

[Crooked Stic]

Here is another way. I always run my one piecers thru the drum sander for width grinding-just need one side fairly flat to start.
 

[arrowlauncherdj]

Ha, that's my method Crooked! Lets see how it works on your swap recurve.  

[bjansen]

I have been thinking about Monty's scribing jig for almost 4 years now.  I finally made a similar jig this weekend from a 1 1/8" piece of aluminum round stock, a cut of 2" angle iron and a cam lock. I drilled the pen hole so it would hold a fine tip sharpy real snug and milled a slot so it can adjust up down as well.The bottoms are polished flat on the disc sander.  

I posted this on the knifemakers board, but the idea originally came from this post long ago.  

   

   

   

   

[Trux Turning]

That's awesome Brad- quite the upgrade from the first one.

[BigJim]

Those are some sweet looking jigs/tools. I understand the idea, but not the physics.

I mark the glass before the bow is ever glued up. After this stage, it only starts to become less consistently geometric.

If your press has side stops, the glue up will be mostly square...or so much so that a slight variance won't affect a thing.

I also never waste my time grinding the bow parallel before putting my pattern on.  Why spend all that time on sanding and money on ruining more sand paper.

I will tell you also that 90% of my bows require very little work at limb straitening after the limbs have been cut out.

Different strokes I guess.

BigJim

[JamesV]

Virgil.............

You got the real deal.

[eflanders]

Originally posted by virgil.v:
5mn to build.        
 

This simple and easy to build jig works the best for tapered limbs as it always stayed centered.