A great technique for establishing thickness.

[Springbuck]

  I have no luck with the thing I see a lot of you doing where you pencil in a thickness line on the sides of a squared up stave.  I have also learned that if I can successfully rough out a bow to a consistent thickness, without ruining the stave or finding a surprise, I almost always finish it at the weight I want, etc.. (the only place I destroy bows any more is when I get distracted during heat treating )  And since a lot of what I have to work with is lumpy and otherwise rough, getting to that starting point is often challenging

It recently occurred to me that I can help this process with my tabletop drill press, if I start with a stave with squared sides.  I rigged a rounded block and clamped it to the platform about 1" from the axis of the drill.  Following the grain, or the crown, appropriately, I can mark out a centerline for the limb, and place that centerline against the block.  Then if I drill a hole every 2" or so, and connect the dots, I can follow the humps and hollows of the back, on the belly.  I can split down the drilled holes, and after working the belly wdown with spokeshave or scraper, VIOLA"!  Consistent thickness.

It occurs to me that if I used several drill bits in increasing sizes, I can do the same, but establish a preliminary taper.  You could probably do this with the right miter box, as well.

  Anyway, if it helps.

T

[BowJunkie]

Ummmmm I use a pencil compass for that 
"If in the wild" I use a charred large piece of wood, on the side held by my fingers that follow the "roller coastery ride" of the back.
Bing,,,O.  Transferred thickness 

[PatM]

What wood splits along a line of holes without digging in below level from time to time?
 I'll keep using a hatchet and Farriers rasp. Don't have drill press anyway.

[bradsmith2010]

once the bow is roughed out,, the long string will tell you alot about the taper,, you are right if you have alot of dips a bumps,, you need to really go slow and use your eye by sighting down the taper on both sides alot,,
this will help once you have the general taper,, to keep it tapered,,there is no easy way,,   lots of practice does help

[huisme]

I just machete along one growth ring, then depending on ring thickness I expose a certain number of rings down the limb and call that my starting taper and start the tillering process. Leave a little more for knots, Make sure I compensate for little wiggly areas, maybe cheat in a little extra mass to keep a knot I like in the bow.

[Badger]

     For me the easist way is to take the belly down 1 ring at a time. I never use a bandsaw anymore. I did one today that was about 3" thick, I just took it down 1 ring at a time until it started to flex. I had it floor tillered in about an hour with just the draw knife. It only takes about 2 minutes to remove a belly ring once you get it on one ring. If you start floor tillering when you think you are getting close you don't take much of a chance of comming in light. White woods I tend to cheat and reduce with the bandsaw.

[Pappy]

What ever works, I just use a carpenter's line to mark the thickness  along the edge and it follows the contour of the back. Then I just rasp toward the middle on each edge at a slight angle and then take the hump out of the middle. Quick and easy. 
  Pappy

[George Tsoukalas]

Whatever works for you. I'd be afraid I'd make a mistake and drill through the stave.

With the stave I'm using now I just used a hand axe and got the limbs flexing.

Then I usually go to a dknife but I decided to give my back a rest and use my sander for floor tillering and more roughing out.

I finished up floor tillering with my surform and then used my push knife as a scraper.

Jawge

[SLIMBOB]

+1 Pappy. Facet a line and work down to it leaving a crown in the center then knifing the crown down.  Belt sander, drawknife, and SS scraper. Use my sense of touch to judge the taper.

[Badger]

  I second the facet method, I do it with the draw knife down each side and then remove the rings one by one down the center.

[Comancheria]

Do any of you ever use calipers to check taper/thickness?  I have seen a couple of methods that do, but that may have been only for board bows.

[Pat B]

I use my fingers and a pencil as a thickness gauge. I start out at about 5/8" on the sides with a slightly crowned belly. I check floor tiller then go to 1/2" along the sides. Usually from there I only use a scraper to reduce the thickness as needed for tillering and weight reduction.  As stated above I follow the contours of the bows back leaving knots slightly proud until final tillering where I reduce them until they almost begin to bend. 

[Springbuck]

Ummmmm I use a pencil compass for that 
"If in the wild" I use a charred large piece of wood, on the side held by my fingers that follow the "roller coastery ride" of the back.
Bing,,,O.  Transferred thickness 

Well, I don't know what is wrong with me, but this is exactly what the first couple sentences of the post said I can't seem to do. Just doesn't work.  I can rasp down in facets to the sides, but this gets me started quicker and better.

I think it is partly due to the fact that I work so much with small diameter trees, and rarely can or will square the sides up, nor are they very thick when I get there.

[Springbuck]

What wood splits along a line of holes without digging in below level from time to time?
 I'll keep using a hatchet and Farriers rasp. Don't have drill press anyway.

  All of them, so far or I wouldn't have kept doing it.  Part of the trick is the layout of the center line on the back.  If you do that right, the holes are automatically following the grain perpendicular to the midline of the back.

[Springbuck]

once the bow is roughed out,, the long string will tell you alot about the taper,, you are right if you have alot of dips a bumps,, you need to really go slow and use your eye by sighting down the taper on both sides alot,,
this will help once you have the general taper,, to keep it tapered,,there is no easy way,,   lots of practice does help

I've had plenty of practice, having made well over two hundred bows. I've been at this 15 years.  Remember, this is how I reach STARTING point only, but "well begun is half done."