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Traditional Crossbow - BP style prod

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Traditional Crossbow - BP style prod

Postby teagus » Sun Dec 26, 2010 2:23 pm

I am trying to reproduce a Ben Pearson laminated prod for a new crossbow project. This post covers the form to date.

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Starting out with 2 pieces of 1/2 thick mdo and one piece of 3/4 thick mdo for a 1 3/4 wide prod.

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Building the sandwich with Titebond II.

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A couple of brad nails on the center line to keep layers from floating around.

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Tape the pattern on and center punch with a finishing nail for locations of form bar holes and form screws.

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Screw both sides together using 8 x 1-1/4 Deckmate star drive screws. Run screws into the form. If heads stick up, they will hinder sliding the form on the band saw table. Have warm wet paper towels ready to to clean up squeeze-out.

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Drill form bar holes using 7/16 and 9/16 spade bits.

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Glue pattern onto form with rubber cement.

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Re: Traditional Crossbow - BP style prod

Postby teagus » Sun Dec 26, 2010 6:02 pm

I designed this with Autocad LT. Output a dxf file. Ran the file up to the local Fedex-Kinkos for a full size print out.

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Cut out the paper with a razor blade in the area to be removed with the band saw.

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My 20" with a brand new blade.

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The nice thing about prod forms is they are small enough to square up on the big spindle sander.

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A sanding block to finish the job. A block that does not have embossed letters on the curved surface can be coved with paper to sand inside curved areas.

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Re: Traditional Crossbow - BP style prod

Postby teagus » Sun Dec 26, 2010 6:54 pm

Adding the 3/8" thick plywood pads for the form bars.

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Formica glued to form bottom with contact cement. I assembled the top to the bottom with a hose and a pressure strip and inflated to press formica in place. Moved the form to a warm room and let the cement cure over night.

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Next up, I want to load in some glass,lams,two heat strips,presssure strip,upper formica insulator and hose to check my gap. Thinking I may need to whack a quarter inch off the upper form.

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Lots to do yet. Jigs for the riser. Shorten a spare hose. Talk to Quincy about heat strips.
First prod will have .050 glass, two .060 parallel tapers. Then add a .030 par to the next prod and a .040 par to the one after that. The Ben Pearson prod is .250 at the fades. Still playing with the string length.
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Re: Traditional Crossbow - BP style prod

Postby BK in TEXAS » Mon Dec 27, 2010 7:18 am

Very cool. Looking forward to seeing how to make one of these.
Hooked on Phonics......Helping kids read gooder since 1970.


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Re: Traditional Crossbow - BP style prod

Postby Trux » Mon Dec 27, 2010 8:00 am

I'm with BK on this one-very cool!
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Re: Traditional Crossbow - BP style prod

Postby teagus » Tue Dec 28, 2010 2:42 pm

First fixture for riser under construction. This first fixture is for back side. I took BK's advice and got the 690lr. Plus a table I won on the Bay.

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Got a 2" straight pattern bit and we rigged up a pattern drum sander with a drum from my smaller spindle sander and a rub collar.

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The sanding tube overhangs the rub collar by a 1/16" so I added a second offset line to my cadd pattern. I will flush cut to the outer line first. Then change to the drum sander which will sand smooth to the inner line. I hope.

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I made a squared-off backup block and will use the two clamps to hold the raw riser block in place.
I got the idea from Kirk.

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I'm off to make some raw riser blocks 1" x 1 3/4" x 14". Then, make the fixture to cut the belly side. The backing block will be shaped to match the back curve. I will have to go with a different clamping system due the the small size.
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Re: Traditional Crossbow - BP style prod

Postby bearauto11 » Tue Dec 28, 2010 3:47 pm

Wow! This is exciting! I can't wait to see how those jigs work out.
--Tom
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Re: Traditional Crossbow - BP style prod

Postby MOUNTER » Tue Dec 28, 2010 10:40 pm

Very cool! Can't wait to see more!
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Re: Traditional Crossbow - BP style prod

Postby teagus » Wed Dec 29, 2010 11:36 am

Shaping the template for the back side. If this works, I will replace it with a micarta plate made on a NC mill from the dxf file.

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Mounting the plate to the backing block. Shot some brad nails to hold in place. Also need screws or the clamp pressure will push the two apart. Been there, done that.

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Clamps installed. ready to go.

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Making riser blocks. The Ben Pearson riser grain looks like Zebra. So I had to go there. Bad move. Checking like crazy.

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Square up bottom on jointer.

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Re: Traditional Crossbow - BP style prod

Postby teagus » Wed Dec 29, 2010 11:47 am

Cut to 14".

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Split into two riser blocks'

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Failure. Can't get enough pressure from clamps to keep the block in place. Options are pre-shaping the block on the spindle sander to minimize wood removal. Thinking of changing to clamps I use on the mill drill. I was going to use them on the belly fixture due to the small clamping area anyway.

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