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Post by ezza on Jul 23, 2009 10:56:30 GMT 10
Very good Sean. Love all the pictures. Fantastic!!
Eric
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Post by jirvin4505 on Jul 23, 2009 18:48:36 GMT 10
Sean thanks for the detailed presentation. A very tidy setup you have there. ;D ;D ;D ;D ;D few suggestions for others watching I use spring clips to hold the string on the drop bow this makes adjustment more convenient. Are you able to vary the position of the top pulleys? I find the closer they are to the width of the core the more consistent my cuts are. I use to use brads then i changed to pop rivets now I am back to brads to fasten my templates to the core. I would sometimes loose attention and allow my bow to hangup on the heads of the pop rivets. Well done... cheers jeff
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Post by jase on Jul 23, 2009 19:26:11 GMT 10
i used some nice wood screws to hold the templates to the foam. big guage so they don't slip.
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Post by Chris on Jul 23, 2009 19:49:08 GMT 10
Hey Sean, fabulous job on the cutter and fabulous results. Any chance of a parts list; like what is the ali extrusion and where to get it among other things? ? ?
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Post by sean on Jul 23, 2009 20:57:45 GMT 10
Jeff, I've had a few hangups on the rivets too, have to be very careful to put them in straight so they don't stick up in the way. Nails would be less problematic. What are brads?
My cutter is a bit of a work in progress, the clips to attach the pull cords sounds like a good idea. To move a top pulley I have to drill a new hole, which actually works surprisingly well. A better system would be good. With the short bow most of my cores are a similar span.
Chris - most of the parts are easy to source at hardware stores and hobby shops. The ali extrusion that the pulleys attach to is a tip I got from Jirvin - got it from Bunnings. The pulleys are also from Bunnings. The formica is an off-cut I got free from an office furniture factory a few years back (had to ring around to find that one). The EPP is from Wowings. Everything else should be easy to source.
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Post by chamm37 on Jul 23, 2009 23:49:12 GMT 10
I have a question. Would i be able to use my Swollow 2 charger???
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Post by jirvin4505 on Jul 24, 2009 1:20:56 GMT 10
sean.... Brads are small nails with little heads about 1.5-2cm long- I also know them as 'finishing nails' @cham ... Not sure about the swallow - I asked a similar question on rcg and couldn't get a definite answer. cheers Jeff
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Garth
> 100
wings are for wimps
Posts: 188
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Post by Garth on Jul 24, 2009 8:08:52 GMT 10
Chris why would you even risk doing damage to you smallow charger when they cost $140 and there not a power supply. Next weekend I'm getting 4 dc train transformers you can buy one of me if you want, I'm getting them for $20 each. I have found the computer ps is good for a 700mm bow but doesn't quit get the same heat for 1000mm bow.
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Post by thevon on Feb 6, 2010 22:14:17 GMT 10
Well I can revive this thread now that I've had some experience cutting Hi-Load 60 blue foam cores with a gravity drop bar cutter. But I'm not quite at the Jeff, Sean and Shane level yet. Matter of fact, I feel like chucking the whole idea as it's such a pain! But a lot of that's my own fault, as I'll explain.
I really want to be able to knock out a tough little 1.5m sloper that can perform well and withstand the beatings of a site like Shorncliffe. I want it as simple as possible, so I've been determined to cut each wing as a full 750mm panel. Sean told me very quickly that I'll have to scrap the idea as he couldn't get it to work, but being born stubborn I had to try.
The first bow has 1/4" music wire legs and used Jeff's "special" wire. I'm sure it's fine for white foam or EPP or lighter blue foam, but on the hard foam it either bows the wire too much, or makes ripples, or snaps the wire if I crank the tension up.
Determined to try anything to avoid needing a shorter bow and thus making more templates etc, I got some 3/8" spring steel. Actually Jeff very kindly picked it up for me and we got it today. After I broke a few bits of hardwood I made a new bow and strung it, but I keep breaking Jeff's wire. Next I tried some orthopaedic surgical stainless wire .025" and it seemed great, very smooth cuts, until I burnt notches in my formica templates with it and saw the amount of foam it melts. It seems to produce a lot of heat.
I pulled out some 0.016 fishing trace and I have to say it seems more durable than Jeff's wire - I've been cranking up the tension till "ping" point, but no matter what the wire still bends into an arc, which isn't good.
However after filling the bin with lots of bits of cut and re-cut foam, I got a good core and smugly though I was starting to get this baby sorted out. I quickly set up the templates on the other wing half, flicked the switch and watched it cut, realizing after 4 seconds that I had forgotten to swap the strings on the cutter so it was now cutting the short side fast and the long side slow. Next piece ... and the wire managed to hook up at the leading edge of one template, stuffing that core too. Oh, well. My personal motto is now becoming rather unwieldy ... "I might be rough, but I'm slow, and expensive, and wasteful"
Can't help wondering if I can beat the 750mm hi-load bow challenge. But I suspect I'll end up taking Sean's advice and making a shorter bow and doing the wings in 2 panels. One thing's for sure, even though I knew it before, it's been reinforced to me that it's a very fiddly process! I felt quite beaten by it but will recuperate and attack it again another day.
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Post by sean on Feb 7, 2010 0:00:29 GMT 10
I felt well and truly beaten trying to cut 750mm cores in the 60psi foam. I tried everything and wasted a lot of time and expensive foam. I don't think more wire tension is the answer. Like you I found if you tension the wire up too much you just break wires all the time and that wastes an awful lot of foam. I found that a lower temp combined with the slowest possible cutting speed (minimum weight on drop-bar) gave the best results but I still had problems - I got ripples in the middle of the core while the ends would be perfect.
I made a shorter bow and voila! Cutting cores became a joy and now 95% of the cores I cut from the 60psi foam come out good.
BTW the foam we have is not the same as Highload 60. Highload 60 is a little more crumbly and easier to crush. I don't know whether Highload 60 is easier to cut.
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Post by jirvin4505 on Feb 7, 2010 1:27:06 GMT 10
Wow Andrew you are certainly beating your own path thru the jungle!! My 'special wire' was specifically chosen after frustrations with cutting genuine HL60 with 16thou fishing trace. It has also worked well on the Rfm high density foam that Shane sourced.
I suggest the problem is not the wire. Sean has given good guidence- slow low weight cuts
I have regularly cut 900mm core Lengths in the lighter blue foam with much flimsyer bows. 3/16 music wire 16thou trace. I choose not to do the longer cores due to aerodynamic and aesthetic reasons.
There was an article floating around on the web on how to do 3' cores. NSP I think
So... Excessive wire drag is too much weight- trying to cut too fast Breaking wire.... Too much tension or heat. If you are breaking the 'special' wire then I think you are well outside operating conditions and trying the wrong solution for your difficulties.
Cheers Jeff
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Post by jirvin4505 on Feb 7, 2010 1:40:27 GMT 10
. I want it as simple as possible, so I've been determined to cut each wing as a full 750mm panel. I had to try. Can't help wondering if I can beat the 750mm hi-load bow challenge. But I suspect I'll end up taking Sean's advice and making a shorter bow and doing the wings in 2 panels. ........ one step back from making extra templates is to do the shorter more swept tip section using the vanishing wire(pivot point) technique.
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Post by graememarion on Feb 7, 2010 1:53:17 GMT 10
The easy fix for templates made out of soft material is to five minute epoxy thin wire to the edge. After the epoxy has set, clean the face of the wire with sand paper. I have successfully used thin piano wire and also copper coated electrical wire on plywood. ____________________________________________ My largest bows are made this (simple) way. My smaller bows are even simpler.
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Post by mikey100 on Feb 7, 2010 6:54:22 GMT 10
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Post by thevon on Feb 7, 2010 8:26:29 GMT 10
Aha! Brilliant Jeff. I'll have a look at the vanishing point method.
Graeme, the formica templates are fine, they don't need wire.
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