ETpilot

I've been in need of a shop power supply for a while. I have been getting by with a battery. So I built this power supply by converting a PC power supply. Since I work with alligator clips, i used a number 10 screw for the voltage taps. I get a number of different voltages but 12V n 24 will be my primary. I have 2 LEDs. Red indicates that the PS is plugged in but not turned on. Green indicates power is on when I flip the switch. I also added a light bulb in the top rear of the cabinet. This indicates that power is on and goes off if I overload or short circuit the circuit. This light is easier to see while working rather than the small green LED. So far the PS has performed very well.

I made the unit in modular fashion so if it ever fails I can easily remove it and install another unit. I have about 5 other old PC's that I can remove the PS.


Since I have an interest in foam airplanes, I made a test short bow and then a long bow. All the short cutoff pieces in the pictures were made with the short bow. The wide flat foam piece and the thick block I made with the long bow. All the cuts came out super smooth. Next I will make a better short bow and a table so I can cut a wing planform so I can make my first wing. I have a lot of packing foam for practice n to try that first wing.

ETpilot

I finally got a chance to use this foam cutter. I am pretty pleased with the results. First time working with foam. The foam was free throw away stuff I got. I had to laminate the panels to get a thick block. I didn't have time for a good table so I worked with a Mickey Mouse set up with a few 2x4 pieces of wood. Worked pretty good. Nice straight square cuts. I was wondering how it would do with a long cut. It cut it like butter. The planform is 14"x30".

Next at will be the real test. Cutting the airfoil. So far so good.

rye

My Feedback: (10)

hi
i hear i can use a big train transformer for the train tracks

ETpilot

When I did my research, I found that some were using a train transformer for the power supply. If you have a train transformer just make up a simple bow like mine and give it a try. My bow is large but I connect the alligator clips just outside the width that I need; 30-36". Connecting the clips too close will heat the wire too much. You just need to experiment.

Propworn

My Feedback: (3)

You could use a heavy duty dimmer switch to control the power. http://www.aircraftspruce.com/catalo...clickkey=69847

ETpilot

Well cutting foam has a bit of a learning curve to it. I tried cutting my first wing core. Turned out bad. Getting the wire started was a problem for me. So the core came out with many ripples in the cut. The second core came out much better.Today I made 2 smaller practice cores and those came out really good, nice and smooth.


Some things I learned. The templet has to be super smooth. Part of my first cut problem was the wire hanging up on the templet. I was using ⅛” plywood. I resanded the templet n applied finishing wax for a slick surface. Glue, I laminated the foam panels using spray glue. I sprayed both side then joined. The glued interfered with the cut. The wire kept slowing down and I had to pull hard. Minimum amount of glue necessary is enough. Starting the cut was a problem because of my design of the templet. My templet was flush with the front edge of the foam. This made it difficult to start the cut. Having a little extension in front n behind the foam will help. Weight, you need a lot of weight to hold the foam. I was working off my table saw table which is pretty smooth. This didn't help. When the wire hit the glue I started pulling the foam core also. I then used an antiskid mat and my heavy piece of railroad track that I use in the shop.


As you can see in the photos the last 2 practice pieces came out pretty good. Super smooth with just a little sanding needed. Working with what I learned helped a lot. I did a test covering of one of the small panels. I will see how it looks in the morning when it is dry. All these cores will serve a purpose as I will practice cutting slots for spars, servo mounting holes and cutting ailerons.


Hope this may help those who may want to try a foam wing. I need to get to town to find more foam and try for a good sample of a wing.

jester_s1

The very best material for templates is formica for countertops. I got a big piece at Home Depot a few years ago really cheap by asking if there were any damaged ones they'd sell at a discount. I think it should have been around $80 but I got it for $15. If we were a bit closer together, I'd gladly share a bit with you because I have more that I'll ever use. Maybe your local home store has something like that too.

ETpilot

Thanks jester. Yes I decided formica was the way to go. I thought I had some in the shop but have not found any. I checked with Lowes yesterday. No luck. Will try Home Depot, cabinet shops and my local furniture store. I scrounge up a lot of stuff the store just throws away. It is where I got a lot of practice foam.

MTK

Formica works fine as does phenolic sheet. But these take a lot of work to finish them right with smooth edges that won't snag the wire.

My solution was to simplify templates and make them out of firm balsa. The secret is on lining the edge with sticky back Teflon tape. I get mine from McMaster Carr. Try it; it works great and it's simple to make.

On the power supply, Aircraft Spruce has a transformer intended to be used with a dimmer. Works fine. On the bows I like the idea of using a length of PVC pipe; it's light, strong and springy. I used fiberglass rod intended for yard reflectors from Home Depot. Very light, strong and springy.

Russmall

ETpilot, I don't know how close you are to Dallas but there's a company in Garland, TX that will sell you 4'x8' sheets of foam cut to any thickness you want. I usually get mine cut 3 or 4 inches thick and if you call ahead, they will have it ready for you when you arrive. Let me know if interested.

Also, your wood templates will work great if you apply a strip of foil tape to the edges. The tape is used for a/c duct work and you can get it at Home Depot.

Propworn

My Feedback: (3)

I like to make my templates out of aluminum flashing.With one inch leads in and out the thickness of the leading and trailing edges. I also drill several holes along the center line just big enough for a 2 inch finishing nail. I polish the edges of the templates so there is not hangups. A cloths pin on the lead out stops the wire from dropping off the template when the wire exits the foam.

I cut the foam the exact size and shape/length of the wing minus leading and trailing edges. I use double sided tape on the templates. Use same size wood blocks under the lead in and lead out tabs on the templates and stick to the end of the foam. Do the same to the other end and your center lines should be exactly parallel. If you need wash out then you can shim the trailing edge of the tip to suit. I have found keeping the leading edge straight works better for me. After the templates are in the correct position on the foam slide the finishing nails through the holes in the template into the foam. This will keep the templates from moving.

Dennis

jtotten

I have used a variable speed train transformer for a long time, and it works well with long or short bows. I generally recruit a fellow club member so we have a person at each end of the panel, using proportionally spaced divisions on the template. I also use a two template system - the first template has an extended trailing edge, and a 1/4 x 1/8 nipple extension at the leading edge centerline. It is attached by 5 or 6 nails driven into the edges of the foam piece. The second template is a simple rectangle that attaches thru the same nail holes. a simple vertical cut will trim the leading edge nipple and trailing edge to right length. We start the cutting process from the rear, with the person on the root chord calling the number stations. This method never has much of a problem with messed up leading edge or trailing edge. I have also used short bows to cut fuse chunks to threaded together on a straight half inch dowel , then covered with 1/16 or 3/32 balsa.

ETpilot

Thanks all for the tips on working with foam. I knew this would be a learning experience so I collected a lot of foam for practice. My shop trash can is now full of little pieces of foam. Fortunately the foam is free so no money spent there. Will have to buy foam later.

Propworn

My Feedback: (3)

So now if your foam bow is long enough to span your table to make absolute straight cuts let gravity work for you. I simply move the straight section to be cut to the edge of the table but not off the table and hang the bow so the wire is right on the line. The table has to be level of course or the bow will cut on a slight angle. Let the bow come to a complete rest (no movement), turn the power on and the weight of the bow will draw the hot wire straight down for a perfect cut. No one has mentioned it yet but your cutting heat and speed are perfect when you get little hair like strands of foam that you can brush away in the cut you made.

I also use a short bow that is bolted to the edge f the table vertically so the wire passes through a hole in the table like a scroll saw. I can tilt it on an angle and by fixing the template to the top or bottom all kinds of shapes can be cut. I do all my floats this way.
I have even made hand held small bows for freehand carving of foam.

ETpilot

Propworn, I have tried the technique you mention. For my drop down cuts I made a simple guide. It may be pictured in my first post. I used DVD jewel cases for the guide, held the bow above and let the weight drop it as it cut. Just slight pressure against the jewel cases. It made a nice straight and square cut. The foam did overhang the setup so the bow would drop out of the bottom. I am now cutting where I get the Angel hair with the cuts.

i made the bow for at least a 36" wing. It is wider than that so I can run the wire against guides for square cuts. So far it has worked pretty well.

When I have time I will make a better setup for cutting. Also will make a vertical cutter as you mention. Right now I am just learning and practicing before I try for a good wing.

Thanks.

blvdbuzzard

I have used a lot of things for templates. The easiest by far is 1/8 door skin with copper foil on the edge. You get the copper foil from a stained glass supply. Comes on a roll and pretty cheap. For one off templates that I am not going to use ever again they work great. They are good for 3 or 4 cuts before the copper stats to wear out. You can just take off the old and put on a new layer. If I am going to use the template many times, Formica or circuit board is the best. Harder to work with but has a smooth as glass edge and last for ever.

I built a feather cut and have not had a problem cutting cores. Simple and works well. It is the best one unless you want to use a CNC foam cutter.

http://www.charlesriverrc.org/articl...gmancutter.htm

http://www.amazon.com/Copper-Conduct...de+copper+foil


I have a couple power supplies right now. One is a simple door bell transformer, a variable out put power supply and a variac. For a small bow or a scroll saw type setup the door bell transformer works and they run about $12.00 and a dimmer switch is all you need.

I am working on building a new foam cutting table. The one I have is old and has seen a better day. The new one will fold up and have all the bells and whistles.


Buzz.

ETpilot

Thanks for the info. I have a door bell transformer and a 24V transformer. May have to check them out for wire cutting. A good table is what I need now. One that I can place on top of my table saw table. No drop down linkage. For now I will work with the bow I made. The cost for my set up has been zero as I had all the material on hand. The practice foam I get free in town. Lots of practice before I delve into the real wing building.

combatpigg

My Feedback: (3)

I use 5 or 6 sheet rock screws to hold formica templates.
I use a $7 dimmer switch hooked straight to 115 VAC.
Also, stainless steel aircraft safety wire, .020" to .030" diameter is the best I've found to do the cutting.
I build 6 combat planes at a time, have been doing it for over 20 years now and anything you can do to eliminate wasted effort pays dividends when your spare time is limited.