CROWNARC Tube Bender Instructions
- June 9, 2024
- ARC
Table of Contents
CROWNARC Tube Bender Instructions
Instructions
Screw your new CROWNARC to 2 pieces of 2 x 4 using the 4 holes. Then, mount the 2 x 4‟s to the wall. You‟ll have best control when the CROWNARC is just above waist level.
To crown a bow: Lay a piece of straight tubing across the 2 lower roller wheels. Turn the top adjusting bolt until the middle roller just starts to tighten on the tubing. Remove the straight piece. Insert your bow ( as shown in Sketch A) , tighten the bolt 1/2 to 1 turn, and crank the bow through. If you wish some more arc, tighten some more and crank the bow back. Repeat as necessary.
Don‟t forget to allow some extra width, because the rolled crown will take up width. The higher your crown, the more width you lose. Crowning will also reduce your leg angle. You should leave the legs angling farther out than you need, because the crown will pull the legs in. ( See Sketch B.)
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Turn the adjusting bolt only when the “elbow” is under the center roller & the bolt is loose.
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Tip: Try bending your bow 1/2″ wider for each 15″ of width to allow for the crown. (So, if you need a 75″ wide bow, bend it 771 /2″ wide and an average crown will reduce the width to 75)
A WELL PLACED PIECE OF WOOD CAN MAKE YOUR NEW CROWNARC WORK EVEN BETTER
Screw a piece of wood to the wall about 20 inches above the
CROWNARC. Be sure it projects out from the wall just enough so the legs
of your bow are exactly straight up when resting against the wood. (Not tipped
in or out)
While you are cranking the bow through the Crownarc, be sure the legs
lightly brush the wood. That way your finished bow will be crowned straight
up, not tipped fore or aft. You can crank with your right hand and hold a bow
leg lightly against the guide board as you push with your left hand.
Here’s a basic way to calculate your bow:
When you crown your bow, you must allow for the arch. The crown (an upward curve in the B to C dimension) allows water to drain off the finished top. Crowning creates 2 changes: The B to C dimension (the width) shrinks, and the legs drop. To allow for the “shrink” in width (B to C), try adding 1/2″ for every 15″ of width. Example for a bow that’s 75″ wide: 75/15 = 5. 5 × ½ = 2 ¾. 75+2 ¾ = 77 ¾. So in this case measure, cut & bend the bow as if it were 77 ½” wide, because when you crown the width will shrink toward the 75″ you really need. This is a guide not a hard rule. If you want a higher crown, try adding ½” for each 12″ of width. Crowning also drops the legs so leave them high! You can bend the legs down more, later if needed, but you can‟t raise them once they are bent.
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Measure the distance from A to B, from B to C, and from C to D and total these 3. (Remember, the B to C dimension is always increased to allow for the crown – see above)
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Subtract from this number:
5″ for a 6″ radius Bendarc
6 7 /8″ for an 8″ radius Bendarc 8
1 /2″ for a 10″ radius Bendarc
101 /4″ for a 12″ radius Bendarc -
Cut a piece of tubing that long and mark the midpoint.
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Put the tubing in your Bendarc and align the midpoint mark with the number on the scale that‟s the same as the adjusted B to C distance (the width). Clamp & bend a leg.
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Turn the tube around; align the midpoint mark on the scale again and bend the 2nd leg.
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It‟s important that the 1st leg bent is straight down when it‟s turned so that the 2nd leg will come down in line with the 1st. Accurate guide boards will help.
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If you‟re bending matching bows, each one must follow the same crown pattern as the 1 st one. Example: You turn the adjusting bolt down ¾ turn, then turn it down another ¾ turn on the 2nd pass, and then ½ turn on the 3rd pass to get the crown you want. Each matching bow must follow the same sequence.
Here’s how to adjust the Slide Block Assembly behind the center roller:
- Loosen the set-screw on the back side of the Crownarc behind the center roller.
- Tighten the center roller shoulder bolt from the front until the roller cannot slide.
- Loosen the center roller shoulder bolt enough to barely permit up & down sliding.
- Tighten the set screw in the rear to lock the adjustment in place.
- Lubricate all sliding parts with axle grease when new and yearly
The objective is to tighten the center roller‟s up & down motion as much as possible using the procedure above. The tighter the sliding mechanism, the less wobble there will be in the center roller. Less up & down wobble yields truer, straighter crowns. (Side to side movement doesn‟t matter.) When we assemble the new Crownarcs, we call this adjusting the slide so it drags.
Crownarc Maintenance
Remove the 3 rollers.
Apply a film of axle grease to the inside of the metal bushing and to the back of the steel gears as well as to the inside of the hole of the gears. Do not get grease on the plastic surfaces. Spray silicone on the center holes of the rollers.
