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Author Topic: Time saver/waster  (Read 849 times)
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Olbill
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« on: June 03, 2017, 03:55:33 PM »

Stan and Kurt have been using Dollartree foam board for indoor glider flaps. I got some of this material as well as some other foam board I ordered online. I don't like trying to sand foam flaps. And this material is pretty thick which means that most of it becomes dust when you make flaps from it.

I thought a workable idea would be to make a vacuum box with guide rails and use a hot wire cutter to cut tapered flaps. After about 3 days of work I finally got a couple sets of usable flaps made. Here's the gizmo I made. Maybe somebody can come up with a better way.

1. The vacuum box. The top is made from Radio Shack perf board. The top sagged when vacuum was applied so I had to install several braces inside.

2. There's a piece of foam ready to cut under the sanding bar. The sanding bar seemed to help stabilize the foam during cutting.

3. Cutting with a Proxxon foam cutter. It took all kinds of mods to keep the wire tight. A better solution would be to build a normal foam cutting bow and use the Proxxon for power or use a different kind of power supply completely. At this point I think the Proxxon was a waste of money.

4. Finish sanding after the cut was made. It only took about a minute of sanding to get a decent finish on the cut side of the flap.
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Pops
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« Reply #1 on: June 04, 2017, 05:47:56 AM »

Every solution is good, 'cept the bad ones! But this is absolutely one of the good solutions! Does it take care of some of the sanding dust as well, sucking it away from the workspace?

Personally I would also have made the rails adjustable in height for fine tuning and cutting tapers in the workpiece. A gizmo like this saves a ton of time if you plan to make several, equal pieces; once you get it tuned in you can just "slice and dice"! Smiley

Good work!
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OZPAF
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« Reply #2 on: June 04, 2017, 06:19:18 AM »

It looks like the rails are adjustable at one end as there appears to be a slot for the screw?

I agree a small homemade bow would be a good way to go and perhaps circuit board for the rails so as not to lose heat there. This would only be critical if the cut width was close to the rail spacing.

Very nifty Bill - I particularly like your idea of using vacuum to hold the foam in place.

John
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Olbill
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« Reply #3 on: June 04, 2017, 04:48:22 PM »

Yes the rails are adjustable both sides. For the first dozen or two attempts at cutting flaps I didn't see much correlation between what I planned and what came out. For the last bunch I made I found that going slow and keeping my sanding bar on top helped a lot. Then the major problem was to keep from rocking the wire up off of the rails. This always resulted in a ruined piece that sanding wouldn't fix.

So I decided to take a deeper dive and ordered some .060" perforated steel plate 6" x 24" to make a new version. When I start on that I'll make a bow that I can hold in both hands to try to keep better control of the wire - and also to put more tension on the wire.

Here's some info on foamboard:
I saw online that isopropyl alcohol sprayed on Dollartree foamboard did an excellent job of removing the backing. This worked really well. Kurt says he just pulls it off dry. I got some separation in the surface of the foam when I tried that. I measured the density of the bare foam at 1.9pcf.

I got some 11x17 x 1/8" foamboard from Foamboardsource.com. I found that if you get the backing peeled at a corner and then pour naphtha on the joint it will peel off easily. The core from this material seems to be a little stiffer and a little heavier than the Dollartree foam. I like it better. If I buy more of it I'll get a thicker size. I originally got the thinnest they had since I had planned to sand flaps from it.

I have some other foamboard around that wouldn't separate with either of the above methods. I think I had success in the past with soaking it in water for a long time.
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Olbill
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« Reply #4 on: June 05, 2017, 07:08:04 PM »

Got flaps made for my new glider on first try.
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OZPAF
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« Reply #5 on: June 06, 2017, 10:14:17 PM »

I've found that a good way to hold the wire down on the templates is to have the bow hanging under your cutting table. It would mean that you would need to cantilever a board out from your bench with clamps far enough to give you the full cut length. The bow will need to be a bit longer to fit under the assembly but the cutting section between the power connections can be adjusted to suit.

The bow then hangs on the template rails and you pull the bow only - no up or down pressure. incidentally I keep my hands and forearms almost locked and move the bow by leaning away from the bow from the waist up which tends to keep the travel constant at both ends.

Use a lot of tension - adjust when the bow is hot and pull as slow as you can and reduce the heat to suit the speed for that form. My bow is spring tensioned and this can be adjusted with a turnbuckle - I loosen it right off when not cutting. There should only be a very slight lag in the wire as you cut - too much lag means too much speed - if it is cutting do not up the heat.

I would also consider putting a small isolation switch on your bow close to one of the hand positions. you can cut the power without reaching for the main switch or the transformer.

Anyway hope all this helps.

That's a nice looking model bill. I hope to get around to building a couple of your models after my present house move is over.
John




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