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Old Apr 13, 2012, 02:00 PM
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My drop arm foam wing core cutter


I finished up the drop arm last night and tested it this morning, it turned out really nice and got a really good result with the very first cut.

I built it from a design that is already available I just refined it a little to get it to work with the rollers I purchased.

I mounted the arm to a piece of 25"X49"X1/4" MDF
I used 2 pcs of top grade 1 1/2"X3/4"X6' pine and 2. 4" pcs of a yard stick from Home Depot for the pivot plates.

I bought 6. 1" screen door rollers from swisco.com I replaced the rollers carrage bolts with standard bolts from home depot that are the same length.

here are a few pics of the assembly
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Old Apr 13, 2012, 02:01 PM
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2. pivot arm's 1 1/2"X 3/4"X72" top grade pine cut to 51 1/4"

1. table top is 24"X49"X1/4" MDF.

1. wooden home depot yard stick 1 1/2"X3/16" or equivalent.

6.1/4" 20 bolts X1" swivel bolts.

1. 1/4" 20 bolt X 2" pivot bolt.

6. screen door wheel assemblies


VIDEO
Last edited by RogueTitan; Apr 14, 2012 at 05:09 AM.
Old Apr 13, 2012, 03:26 PM
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Originally Posted by RogueTitan View Post
more pics Instructions and video coming up.
Cant wait for the video... looks awesome
Old Apr 14, 2012, 05:12 AM
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I spent a couple of hours ataching picture files and writing in captions only to have them to disappear
I will try again tomorrow.
Old Apr 14, 2012, 07:25 AM
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here is the plans and instructions to the original design.
everything is the same except the hole locations on the top and face and the pivot blocks.
The center of the top roller bolt holes on the stationary arm on the one I built are 5/16" from
the edge and the CL of the bolt holes on the face are 5/16" from the top of the arm.
All holes are drilled 7/32" diamiter and drilled 9/16" deep. this way when you screw in the bolt
it threads the hole make sure not to over tighten for this can strip out the threads in the wood
pretty easily that is why I made it so the bolts would bottom out by only drilling the holes so deep.

here is the link to the Foam Cutter Calc
https://www.rcgroups.com/forums/show....php?t=1531098
Last edited by RogueTitan; Apr 14, 2012 at 07:48 AM.
Old Apr 14, 2012, 05:03 PM
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Looks Good!
I apologize if you said this on the video but I can't play the audio right now.... Can you make angled cuts?

I like how clean the cut was... I notice mine would not be as smooth if I didn't ensure equal pressure the entire cut. I found clamping a board or level to the table acts like a fence on a table saw and helps a lot.
Old Apr 14, 2012, 09:19 PM
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snipeworm you can cut tapered chord wings with the drop arm as well as constant chord wings but you have to cut the shape of the before cutting the air foil shape.

check out the PDF this will go in depth on the procedure of cutting the blanks and making the air foils with the bow and drop arm

Check out this video it goes in depth of the procedures of cutting out the blanks and how the drop arm works with the bow to cut the shape of the air foil.
the drop arm is a little diffrent than mine but works on the same basic principal.

Hot Wire Foam Cutting (High Res for Broad band)
Old Apr 14, 2012, 10:04 PM
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Originally Posted by RogueTitan View Post
snipeworm you can cut tapered chord wings with the drop arm as well as constant chord wings but you have to cut the shape of the before cutting the air foil shape.

check out the PDF this will go in depth on the procedure of cutting the blanks and making the air foils with the bow and drop arm

Check out this video it goes in depth of the procedures of cutting out the blanks and how the drop arm works with the bow to cut the shape of the air foil.
the drop arm is a little diffrent than mine but works on the same basic principal.

Hot Wire Foam Cutting (High Res for Broad band)
Wow! Now I can see the true potential of the bow.. Thanks for that link.... guess I have some building to do

I used some fishing leader I had for my table but now I am out... What do you use for wire? I would like to use something cheap and readily available like a guitar string or something similar.
Old Apr 14, 2012, 10:34 PM
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Wow! Now I can see the true potential of the bow.. Thanks for that link.... guess I have some building to do

I used some fishing leader I had for my table but now I am out... What do you use for wire? I would like to use something cheap and readily available like a guitar string or something similar.
If you have a harbor freight store nearby, go get a 2# spool of carbon steel welfare wire. Get the .023 diameter stuff. It's only about 6 bucks for the spool and will last forever. I've been using this lately and it is great stuff. Cheap too!
Old Apr 14, 2012, 10:36 PM
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Originally Posted by snipeworm View Post
Wow! Now I can see the true potential of the bow.. Thanks for that link.... guess I have some building to do

I used some fishing leader I had for my table but now I am out... What do you use for wire? I would like to use something cheap and readily available like a guitar string or something similar.
If you have a harbor freight store nearby, go get a 2# spool of carbon steel welders wire. Get the .023 diameter stuff. It's only about 6 bucks for the spool and will last forever. I've been using this lately and it is great stuff. Cheap too!
Old Apr 14, 2012, 11:13 PM
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Originally Posted by gmwahl View Post
If you have a harbor freight store nearby, go get a 2# spool of carbon steel welders wire. Get the .023 diameter stuff. It's only about 6 bucks for the spool and will last forever. I've been using this lately and it is great stuff. Cheap too!
I do! Thanks!
Old Apr 15, 2012, 03:31 PM
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I used a B electric guitar string
the carbon wire will work good and it takes less volts/amps to heat up the wire, lots less resistance than stainless.
stay away from Ni-chrome wire it is not worth the hassle.

a little trick is to wipe off the foam residue from the wire while the wire is still hot with a dry cotton wash cloth with every pass through a piece of foam this will make your wire last longer.
Last edited by RogueTitan; Apr 16, 2012 at 06:59 AM.
Old Apr 16, 2012, 06:01 AM
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Nice job on the drop arm !!

For wire .020 -025 stainless saftey or welding wire works pretty well. I started out with .025 welding wire back in 1978 and still use it sometimes. .020 saftey wire works a little better.

I've also use a lot of .015 music wire from LHS. This works much better on smaller panels.

My preferance is .013 Iconel wire, a bit pricey for sure , but cuts oh so nice!

But when your first starting out you can't go wrong with .020 -.025 stainless . OSH used to carry .020 in 1/4 pound spools for about $ 9 and I think you can still get 1/4 pound spools fron Aircraft Spruce for the same amount.Small 2 pound spools of .025 stainless can be had at welding suppliers pretty cheap

I think you can speed up your cutting rate just a tad! It'll still come out nice!

Blue Skies.......................Tim
Old Apr 18, 2012, 01:36 PM
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I found a couple of really good programs for designing air foils and printing out the template profiles.

profile is freeware and should do pretty much what ever I meed for constant chord wings. http://www.rc-soar.com/hardsoft/profilerev.htm

Profili-2 is an advanced program that will generate tapered chord wing profiles and generate wing rib templates for tapered wings

the program also has a very extensive air foil profile shape library for just about any air plane ever built. there is a free version but is very limited
I recommend paying the $20.20 for the license key to get the full version
http://www.profili2.com/eng/default.htm
Old Apr 25, 2012, 02:51 AM
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I made a better bow


The PVC bow just would not get the cutting wire tight enough
but this new one will get it as tight as a banjo string and is also the max length I can cut on this table

I am going to try out profili tomorrow and cut out some patterns and see what happens


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