vertical grimmace

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I cut my own foam, and I also just buy them, depending on availability. It is impossible to beat a CNC bow for quality. I bought my Killer Kaos cores from Eureka aircraft. It is just easier for a one off.

Skyhawk940

Bought mine there also, but the shipping was $$$$($35.00), way too much! I could build a hot wire for about the same amount or less.

Skyhawk

vertical grimmace

My Feedback: (1)

That is a lot for shipping. I do not remember it being that high. I would not have completed the purchase if that would have been the case.

The key is to have a good power supply. I built one a few years back using a 110AC-24v DC transformer. Then I wired a dimmer switch to regulate down from 24-0 volts dc. I think I end up around 18 volts when cutting. DC is important as it does not give you a hot end of the bow.

Tapered wings are also trickier than constant chord. The best way I have found is to number the templates, and have a helper stay in the exact position with the other operator as he counts out the numbers. This way the bow enters and exits the core at exactly the same time.

Skyhawk940

Watt?! All transformers are AC. Dimmers work with AC also. Maybe you meant power supply. If that's the case what is the current output at 24VDC? I like the numbers thing.
Skyhawk

vertical grimmace

My Feedback: (1)

The transformer, transforms AC to DC. DC is what you want to power your bow. It does not create a hot end, one side of the bow hotter than the other. DC just gives a better cut. Plus it is safer. The dimmer will dim AC or DC. It is just what you use to vary the DC to exactly what you want. It really has to be right on. To hot or too cold is no Bueno!

vertical grimmace

My Feedback: (1)

Skyhawk940

Thanks, you've been a big help.

Skyhawk

vertical grimmace

My Feedback: (1)

Sure. I have been cutting foam since 1991, and this is the best power supply I have used. I recommend the light to know it is on. Other upgrades: I would and an on off switch so the position of the dimmer knob does not rotate, and I would use the type of connector that allows you to screw clamp down onto the banana plugs from your bow. (if that is what you use. My plugs seem to come out under very light pressure.

A couple of other things. Nichrome wire is touted as the best, I find it way too fragile. I use .012" steel stranded cable because I have a lot of it for 1/2 A CL flying. Otherwise you will break a lot of wires.

Build a small bow as well. Something with around a 6" opening. It comes in handy for cutting holes and carving. This bow will take about half the volts as you bigger one. The longer the wire, the more volts you will need.

Skyhawk940

Here's my new build for this winter. Follow this link for more OV-10 building. https://www.rcgroups.com/forums/showthread.php?375467-OV-10-Bronco-build/page44

Skyhawk

Skyhawk940

Sorry, photo didn't go on the last one

Skyhawk

ETpilot

Skyhawk, your Bronco is looking good.

kablake

A transformer does not convert AC to DC. A transformer converts AC to AC. AC stands for alternating current, DC stands for direct current. A transformer is basically 2 coils of wire wrapped around a core. An AC current is one that varies with time creating a magnetic field that when changes, generates a voltage in the second transformer coil. If DC is applied to a transformer nothing will be generated on the output of the transformer. With a transformer, the conversion of voltage is determined by the number of wraps in the coils. For example if the active input coil has 100 wraps and the inactive output coil has 200 wraps the voltage output of the transformer will be twice that of the input coil. But the available current will be 1/2 that of the input because the power has to be equal. The video that was presented just uses a AC voltage dimmer to vary the input voltage of the transformer, therefore varying the output voltage. But the output is still AC. In no part of that circuit is the voltage converted to DC.

Just FYI From a retired electronics engineer.. So AC seems to work fine in a cutting wire... Just a lower voltage than 120volts out of a wall socket. I thought it was quite a neat way to vary the voltage applied to the transformer. If you are interested, here is how a dimmer works..

https://home.howstuffworks.com/dimmer-switch.htm

ETpilot

Kablake what you say about transformers and AC is true. I've made a few power supplies using a rectifier bridge to produce the DC. Not an expert in electronics but I dabble in it like I do RC. I made the pictured power supply from a computer power supply so I could play and practice with making foam wings. Works good but finding time to experiment is the problem. I have s shop in town where I can get free practice foam.

ETpilot

Yesterday was an interesting day weather wise. It started out cool and rainy. Then gradually warmed up. I finally opened the shop door. Felt good. But it turned out to be very humid. After a while I noticed condensation on tools and metal in the shop. I closed the door. Today I saw the concrete back porch area was coated with water. I had to sweep it out. In the shop, some drawers were a bit open. Tools inside had condensation on them. My table saw was showing signs of rust. I had to wet sand it and recoat it with preservative. Some condensation was still around.

I've been busy with this build due to the weather. I have the tail surfaces sanded and shaped. Glued the elevator dowel in place and have all control surfaces hinged except for the elevator. Working on the fuselage I have the engine mount/ firewall in place along with some cross members. The engine area is shaped to narrow in the front while the firewall stays square with the fuselage sides. . I have the other side shaping the engine area too. The next trick is to align it all together and glue the two sides. If the two sides are mirror images it should all go together easily.

kablake

Yeah, I WAS in NO way trying to be critical. I just wanted to let those guys know that thing still put out an AC current.

Ahhh, rectifiers.. A 4 diode device that converts the positive and negative sinewave into a series of positive sinewave shaped waves, to get a nice clean DC output, filtering must be applied. Usually a coil in series and a capacitor from the output of the rectifier to ground is a basic one. Newer AC to DC converters are now specialized integrated circuits that are very small and accurate in their voltage. Take a 120V AC to 5V USB charger for instance. Years ago, 3 decades, that would have taken a box about the size that was on that video.. LOL I am amazed at the progress of electronics in the years I got interested in the technology..

I have never worked on foam for wings or anything else. But Ii do have a Sig Kit with foam wings that are already cut of course. Those will be interested in building. A wing with NO ribs!! Maybe that is why Foam is what some people use.. LOL

kablake

ETPilot, sounds like you could use a dehumidifier. You can get them fairly cheap. Although it doesn't sound like you have had this issue much in the past. If you use an airconditioner in the hot months they dehumidify. I am sure you know this info..

OHHH, one thing about one of my I have to Build Kaos 40s. I purchased a engine off of rcgroups.com. it is a NIB Rossi R40 ABC Engine with Factory Tuned Super Muffler! I was going to build one of the 60 Kaos kits I have but a 40 might be next!!! I will post that project in here..

ETpilot

Kablake, we have high humidity here in the summer. But never a shop problem. This is the first time I have seen it so bad. Lots of condensation in the shop when I opened the door yesterday. It started drying out today. Hopefully it is one time event. Looks like rain for the next week. Maybe I can be done building by the time it is all over.

Looking forward to your Kaos build when you are ready to start.

ETpilot

You need a few clamps, a few spacers, lots of weight, squares and scales to measure and align things. I have a centerline on my building board. Working off of that I align, square and clamp the sides. I mark any lines needed for applying glue. Then I take it apart, apply the glue and go thru the put together procedure again. Only the parallel sides up to the rear of the wing saddle is glued. The tail end I'll glue later. .

kablake

I see it looks like you are using wood engine mount. What engine do you have for this? And WOW, you take your construction very seriously. Maybe I should be a bit more aware and critical of the methods I use.

PS: Note to self, buy more clamps and some weights..

vertical grimmace

My Feedback: (1)

Well, whatever it is doing, it works great! I know hardly anything about electronics, and I must have misunderstood what was/is going on. The power supply shown in the video is very inexpensive, and will allow you to cut great cores.

ETpilot

Kablake see engine picture in post #1095. It is an OS GGT15 gas engine. Going to try it and see if it works. Buying clamps is always good. You need different styles and sizes. Look around your place and see if you can find material you can use for for weights. I have a few old batteries. The blue weights in my pictures are cut up mower blades wrapped in blue painters tape. I maintain 2 heavy duty mowers and have 6 blades every mowing season. I have some larger cut pieces not pictured.

The fuselage glued up good with one minor problem. The lower plywood piece aft of the clamp glued in crooked. Looking at my previous picture I forgot to add weight above the cross piece. I'll have to sand it down a bit. Right now it is lifting the left side up a bit. I'm gluing up the tail piece which will be glued at the rear and support the tail wheel assembly. Have to figure out how I will do the tail wheel. Overall looking good.

ETpilot

I'm going to try my hand at making a canopy. I made this lousy looking practice plug to see how it goes. The plug is to test the material. First a plastic bottle type then a regular vacuum formed model. I've never done it before so this will be new for me. I'm letting the plug fully dry before giving it a try.

kablake

I think I posted it before. I was in no way trying to offend anyone. Just wanted you to know what was actually happening. Yeah, as far as electronics. It takes some studying and if desired some training to really get to know a wide range of it. There is a lot of areas in electronics in areas many engineers specialize in, kind of like medicine. Digital electronics, radio frequency and antenna, audio electronics, the list goes on.. Glad that device works well for you. You are doing something with foam that I wouldn't try myself. Enjoy what you are doing...

vertical grimmace

My Feedback: (1)

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vertical grimmace

My Feedback: (1)

Here is an example of a core I cut with the hot wire and power supply explained in the video. The stack of cores there is for my 1/2A control line combat design. I kinda got mad at RC for a couple of years, and went all into competition CL combat, competing at the AMA Nats the last couple of years. The ability to cut foam is important for those events, as you need a lot of wings!

The other pics are of my Sun fli 5, which I scratch built to plans. THis is a tough one to find. It was designed in 1972, and you can clearly see the design lineage leading into the dirty birdy and the UFO. I used a slightly longer foam core, so the span on this model was 72" . I think I should have cut it down some looking back on it. The other mod I made was the larger barn door ailerons. They worked great. Not sure it was worth the effort, the airplane performed unbelievably well.

OS .65 AX engine. I flew this plane intensely dor 2-3 years until a bad Jeti radio took her away from me. The next time, I am going to build one box stock (other than I will use a foam wing) so I can experience exactly how the original performed.