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Old Jul 03, 2013, 08:19 AM
Registered User
South Africa, GP, Alberton
Joined May 2007
11 Posts
Question
Which Cutting Bow is better

Hello Gents
I'm looking at building myself a cutting bow, just want to find out what type would be better and what the reason would be.
Thanks
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Last edited by BDaniell; Jul 04, 2013 at 04:12 AM.
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Old Jul 03, 2013, 08:32 AM
Teddy Ong
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Joined Nov 2012
579 Posts
i would go with the right one, the PVC pipe one. looks simpler and easier to control+make.
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Old Jul 03, 2013, 08:51 AM
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United States, OH, London
Joined Mar 2013
78 Posts
I built mine from a FG driveway marker from Home Depot and some pine blocks with holes drilled through them. Very light and cheap! I notched the outside of the legs to hold the looped and twisted wire.
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Old Jul 03, 2013, 11:50 AM
Registered User
Canada, BC, Vancouver
Joined Nov 2012
20 Posts
I've tried both, and I prefer your first design. Adjustable tension is really nice, I used a heavy cotton cord/rope for the tensioner and it works the best. I use this with 175lb SS leader wire for the hot wire. Other option is to have springy arms on it to hold the wire in tension. Most wires do stretch when heated, so keeping tension on them is important to having a straight wire cut.
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Old Jul 03, 2013, 02:06 PM
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Canada
Joined Nov 2000
6,983 Posts
Stainless steel as in braided fishing leader OR control line wires, stretches MUCH less than Nichrome wire.
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Old Jul 03, 2013, 07:43 PM
Build straight - Fly twisty
Whiskers's Avatar
Australia, QLD, Little Mountain
Joined Feb 2010
4,259 Posts
Yes! Use Nichrome only if you feel the need to use an expensive and inferior product.
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Old Jul 03, 2013, 07:47 PM
Out the Window
High Flyin''s Avatar
United States, FL, Alachua
Joined Jul 2004
1,277 Posts
I have used the first design and it works for me. I have a rubber bungee keeping tension on the stainless steel single strand leader material. The rubber bungee does not need to be adjusted as it will take up the slack.
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Old Jul 04, 2013, 01:31 AM
Mark Harrison
USA, CA, Piedmont
Joined Jun 2010
2,221 Posts
Quote:
Originally Posted by BDaniell View Post
Hello Gents
I'm looking at building myself a cutting bow, just want to find out what type would be better and what the reason would be.
Thanks
I had great luck with a coping saw... I took out the saw blade and just wrapped the nichrome wire (30 gauge?) around the mounts. Tightening it up gave me plenty of tension on the wire.
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Old Jul 04, 2013, 07:03 AM
Teddy Ong
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Joined Nov 2012
579 Posts
Why not the second one? i realise you have to do the tension right the first time, since it's not so easily adjustable, but the mechanics will be simpler?
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Old Jul 04, 2013, 07:48 AM
gpw
“There’s no place like Foam”
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United States, LA, New Orleans
Joined Jul 2002
24,126 Posts
Here’s the bow we’ve used successfully for many years now... cut everything from wings to fuselages, paddle boards, and even the 10’ foam slabs for my current Foamie trailer build (the rolling Hanger)

It works ...
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Old Jul 04, 2013, 07:56 AM
I don't want to "Switch Now"
pmackenzie's Avatar
Toronto (Don Mills), Canada
Joined Dec 2002
16,672 Posts
Quote:
Originally Posted by Teddy Ong View Post
Why not the second one? i realise you have to do the tension right the first time, since it's not so easily adjustable, but the mechanics will be simpler?
For a given stiffness the wood type with the twisted string tensioner will be much lighter.
Low weight will make it easier to feel the actual cutting forces.

One change I would suggest is to only have the hinge/pivot on one side. The bow will be more stable this way.

http://www.rcgroups.com/forums/showt...61#post1475377

(Old post, I still have the same bow. It was probably 10 years old back then!)
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Old Jul 04, 2013, 08:03 AM
Slipping the Surly Bonds
dz1sfb's Avatar
Attica, MI
Joined Dec 2006
10,459 Posts
Quote:
Originally Posted by poormansairforce View Post
I built mine from a FG driveway marker from Home Depot and some pine blocks with holes drilled through them. Very light and cheap! I notched the outside of the legs to hold the looped and twisted wire.
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Nice!
Would you post some dimensions and angles?

Ken
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Old Jul 04, 2013, 11:20 AM
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United States, OH, London
Joined Mar 2013
78 Posts
Quote:
Originally Posted by dz1sfb View Post
Nice!
Would you post some dimensions and angles?

Ken
Not 100% sure but it looks close to 15 degrees on the legs. There is 24" between the 3/4" pine blocks and it will cut 27" wide. The legs project down 8" from the long FG segment. The FG just press fits into holes I drilled all the way through the pine on a drill press with a fence. Its one driveway marker cut into three pieces, if you need more length use one for the long segment and if you use a thicker block you can use two pieces for more force on the wire. It would work best if you crimped loops with fishing leader crimps. I have a 3 part video series on my hotwire table setup with a hotwire scroll saw attachment using templates. It also includes a 7 wire bow so I can cut 2" foamboard into six 6mm foam sheets or part out 6 planes at a time!
My hot wire table: part 1 (10 min 1 sec)
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Old Jul 05, 2013, 08:54 AM
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Jab69's Avatar
South Africa, GP, Alberton
Joined Sep 2009
172 Posts
Hi
I would go fort the first bow.Would just let the one leg move and use a spring to keep the tension.I let mine hang from the roof off a counter balance( bucket with weights in). When I make vertical cuts I control the cutting speed by taking weights out the bucket.
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Old Jul 05, 2013, 12:58 PM
Registered DLG addict
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Minnesota
Joined Jan 2009
1,080 Posts
I prefer the first design. I use Inconel wire for mine. Have cut about 15 wings on the same wire with no breaks. Also doesn't stretch when hot.
Stuff here,
http://www.cstsales.com/tekoa_hot_wire.html
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