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Old Nov 13, 2011, 07:03 PM
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Ok put the genius at work sign up to make sure no one bothers you in the flight lab LOL Good luck
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Old Nov 14, 2011, 08:32 PM
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Well I went to Walmart and bought some foam board to build me a funbat but I am having a time cutting nice and straight like I want it. I am using a brand new blade utility knife but still no luck. I looked up online to cut it layer (card layer then foam then the other layer of card paper) but its still not working out for me. It's ripping and/or not making a nice cut. Any suggestions? I thought about removing the card paper and then cutting it out then cover it in duct tape. Would that work?
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Old Nov 14, 2011, 08:50 PM
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Joined Dec 2005
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buy real depron from RCFOAM.COM
or,
think about this ...
IF the glue that holds the paper on is even a little sticky then it will build up on the knife
and drag the foam edges away.

Not all foam formulations are the same.

I know this because I've tried cutting different types on my CNC machine.
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Old Nov 14, 2011, 08:51 PM
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Hello computerman021, if its ripping chances are you need a fresh blade. Foam and cardboad dull these blades pretty fast. I think I used two or three blades on my funBat.
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Old Nov 14, 2011, 09:07 PM
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Ok thanks I will try a different blade. But I was really having a time with the square notches near the tail because the where so small and I couldn't get the foam to be so precise. So what you think about removing the paper? Also what's the best way to get the plans on the foam board. I was having a little rough time with that as well...I printed them out cut out the boarder then taped them together. Then laid it over the foamboard and and traced.
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Old Nov 14, 2011, 10:54 PM
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Sharp Blade, or Forget it

Quote:
Originally Posted by computerman021 View Post
Well I went to Walmart and bought some foam board ... It's ripping and/or not making a nice cut. Any suggestions? I thought about removing the card paper and then cutting it out then cover it in duct tape. Would that work?
Just because the utility knife blade is new doesn't mean it is sharp enough for foam. I have an old #11 blade I use to cut foam and it works fine. The secret is knowing you can use a nail file, or sandpaper on a tongue depressor to sharpen a blade. If you are thinking a shiney, new blade is the secret to cutting foam, you are half right. What that means is about half the time the new blade will be sharp enough. What cuts foam everytime without issues is called a bur, which is a very tiny, uneven surface on the edge of a knife blade. As long as the bur remains, it cuts through the foam rather than nicks, grabs, and tears the foam. The trick to making a bur edge is to know you can make it by running a rough (100 grid or so) sand paper over one side about three times, and only twice on the other side. If you look at the edge with a high powered microscope, you see what looks like a saw edge.

If you have seen a chef sharpen a meat knife, you will notice he makes a few passes over his knife with a rounded file. It is a file that is very much like 100 grit sandpaper and his objective is to create a fine bur on the edge. It doesn't take a lot of pressure, but you do need to follow the angle of the edge well enough not to change it very much, if at all. Once you get the hang of the idea, you can make the bur without giving it a lot of thought or effort. If you have some scrap foam, get a nail file (sandpaper on wood) and practice the method. When you can make no more than three passes, two on one side, and one on the other to make a bur that cuts through the paper and foam with minimal pressure, you will be able to use the same old hobby knife blade for many years. Keep a fine oil rag in a ziplock bag and wipe it over the edge of the blade when your done cutting for the day. The next time you need to make a bur before starting the first cut, it will be a little easier. The fine oil skin seems to keep the metal in better condition for sharpening the next time, but it must be a fine machine oil, like is used on sewing machines, and not applied heavy.

I am still trying to figure out what the purpose of duct tape would be on foam. Packing tape I have heard of, but duct tape? Never heard of duct tape on foam.
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Old Nov 14, 2011, 10:54 PM
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If you're having issues with the outline you are likely to have even more of an issue with things like the wing spar bevel.
I'd consider some nicer foam, but try sharpenig your blade 1st as Tsavah has mentioned
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Old Nov 15, 2011, 12:34 AM
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Originally Posted by computerman021 View Post
Ok thanks I will try a different blade. But I was really having a time with the square notches near the tail because the where so small and I couldn't get the foam to be so precise. So what you think about removing the paper? Also what's the best way to get the plans on the foam board. I was having a little rough time with that as well...I printed them out cut out the boarder then taped them together. Then laid it over the foamboard and and traced.
Well, there's more than one way to skin a (pauses and looks at cat on lap) err, to accomplish the same thing. Someone on RC groups recommends sharpening the blade every time you pick it up and has used the same blade for years. I'm not that good but I have used the same blade for a couple of planes.

As for transferring the plans to foam, I tape the tiles together and cut out the parts. Then I put the parts on the foam and pin them down with sewing pins. Then I just draw around the templates, remove them, then cut. Cut against a straight edge on all the straight lines.

As for the material, I would recommend depron or Dollar Tree foamboard. The plane's designer used foamboard and left the paper on. I removed the paper and covered mine with packing tape. If the Walmart foamboard is heavier, you may have a tail-heavy plane that requires adding weight to the nose.

Chris
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Old Nov 15, 2011, 02:26 AM
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Yet more ideas!
I use a set of these to keep my blades in tip top condition
http://www.ebay.co.uk/itm/3PC-MINI-D...#ht_1269wt_952
but I also use the small and large snap off utility knives
http://www.ebay.co.uk/itm/8-PIECE-SN...ht_1055wt_1185. Just snap off the blunt segment and you have a nice new blade. Or just add to the used pile and reach for a new one. I can buy 10 for 1 locally.
The other essential knives are a good quality scalpel with a selection of blades. I use 10a and 11 mostly and avoid anything with a plastic blade holder. A hot scalpel is great for cutting through the film on a ARTF in those areas where you need to glue e.g vert stab but the plastic would just melt. The 11 blade can be used as a drill to open up servo and control horn holes. Just turn the blade and it will quickly enlarge the hole to the perfect snug size.
The final knife in my selection is a stanley knife http://www.ebay.co.uk/sch/i.html?_nk....c0.m270.l1313
Be especially careful with this knife as it takes no prisoners. It's a very sharp and stiff blade and you don't want that skipping off your ruler and heading towards your thumb. It is quite capable off cutting through to the bone.
There is also a technique to cutting foam. Hold the blade at 90 degrees and don't try for one cut but instead use a number of cuts until you break through. Also angle the blade back at about 30-45 degress as you pull it through. Use the correct knife for the job e.g #11 scalpel is ideal for cutting CA hinge slots, tabs and servo holes as the blade's shape lets you cut right into the corner.
Finally a selection of metal rulers and set squares are essential but I know some foam bashers who also use lengths of L shaped alloy with their digits safe behind the L.
Hope the above has helped but there are also loads of Youtube vids showing foam cutting methods
Andy
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Old Nov 15, 2011, 07:21 AM
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Quote:
Originally Posted by Tsavah View Post
Just because the utility knife blade is new doesn't mean it is sharp enough for foam. I have an old #11 blade I use to cut foam and it works fine. The secret is knowing you can use a nail file, or sandpaper on a tongue depressor to sharpen a blade. If you are thinking a shiney, new blade is the secret to cutting foam, you are half right. What that means is about half the time the new blade will be sharp enough. What cuts foam everytime without issues is called a bur, which is a very tiny, uneven surface on the edge of a knife blade. As long as the bur remains, it cuts through the foam rather than nicks, grabs, and tears the foam. The trick to making a bur edge is to know you can make it by running a rough (100 grid or so) sand paper over one side about three times, and only twice on the other side. If you look at the edge with a high powered microscope, you see what looks like a saw edge.

If you have seen a chef sharpen a meat knife, you will notice he makes a few passes over his knife with a rounded file. It is a file that is very much like 100 grit sandpaper and his objective is to create a fine bur on the edge. It doesn't take a lot of pressure, but you do need to follow the angle of the edge well enough not to change it very much, if at all. Once you get the hang of the idea, you can make the bur without giving it a lot of thought or effort. If you have some scrap foam, get a nail file (sandpaper on wood) and practice the method. When you can make no more than three passes, two on one side, and one on the other to make a bur that cuts through the paper and foam with minimal pressure, you will be able to use the same old hobby knife blade for many years. Keep a fine oil rag in a ziplock bag and wipe it over the edge of the blade when your done cutting for the day. The next time you need to make a bur before starting the first cut, it will be a little easier. The fine oil skin seems to keep the metal in better condition for sharpening the next time, but it must be a fine machine oil, like is used on sewing machines, and not applied heavy.

I am still trying to figure out what the purpose of duct tape would be on foam. Packing tape I have heard of, but duct tape? Never heard of duct tape on foam.
Ok thanks I will try that out! Also I have seen people use duct tape to design there planes (different colors) instead of painting and I figured it would be tougher than packing tape (although heavier)..so should I use packing tape if I "skin" it?
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Old Nov 15, 2011, 07:33 AM
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I hope I can get the bur down because if not I will be going through ALOT of blades. Did anyone use a Exacto on the square barbs on the plans? As mentioned I had a hard time with them and it didn't turn out good (of course now I learned I didn't have a good blade). Also what about using a butane lighter and heating up the blade? Would that work or just melt the foam to bad?
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Old Nov 15, 2011, 08:35 AM
Watt Waster
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Warming the Blade

Quote:
Originally Posted by computerman021 View Post
... Also what about using a butane lighter and heating up the blade? Would that work or just melt the foam to bad?
The Exacto series of blades are a standby for model aircraft builders, which includes the RC types like us. Utility knifes are collecting a growing number of users, especially the throw away type, some of which come with break-away blades. I have a bunch I purchased for one cent per bundle of six, which was a promotional item from Hobby King a while back. Sometimes they cut through foam fine, and other times they need a bit of work as discussed before. With all knifes it is a matter of learning how to use them since cutting foam is a little bit different. For example, you could hold the knife straight up and pull across the foam, but if you do it is more likely to snag and tear the foam. On the other hand, if you angle the cutting surface at 35-50 degrees to the foam, the foam is more likely to cut smoothly. I tend to cut with light pressure on the blade and a low angle of attack so the cut is gradual and tearing is less likely, but I will need to make many passes to complete the cut. I normally use some sort of wide guide, like a steel ruler to protect my finger tips by keeping them well away from the blade cutting path. In a sense, I am using the same cutting angle as I normally use with a wood hand saw. A bit of double sided tape on the bottom of the guide (not very sticky anymore) helps keep the cutting guide in place on those long cuts. A strip of wide, thick leather held stiff also is a good way to sharpen a razor's edge, like you see in old Western/cowboy movies before the barber starts the shave of the whisker's.

As to covering foam after the paper has been removed, packing tape comes in colors, but sometimes that means a special order off the Internet. The only other places you might find colored packing tape is during the holidays for gift wrapping, or a moving box, gift wrapping specialty store. There can be a great deal of difference between packing tapes. Some tear easily, and others don't. The better tapes tend to feel thicker and a tad heavier, yet it is hard to measure. The better tapes don't come off the foam as easy and tend to take a fuzz/skin of foam with them. A few brands hold up better in the sun, stay put even if they get warm, and if colored, hold their color longer. Once you find a good brand, stick with it. It does take a bit of practice to learn when it is the best time to apply the tape on a specific project, because if you apply the tape too soon, the part won't curve easily to mate with other parts like desired. The better tapes won't stretch much and the fiber reinforced tapes won't stretch at all. Of course there are other option, but they tend to be more expensive - Monocote, other covering films, and very thin vinyl, normally outdoor sign quality. Thin, outdoor quality vinyl comes in chrome, gold, and aluminum that shine like a mirror, as well as other colors and clear. Generally 3mm thick and a bit heavier than packing tape.

If you decide to heat a cutting blade before you attack foam board, be aware you are tempting the melt demons, as if using a hot wire cutting system. Tricky business to get just the right amount of heat since the blade tends to cool off before the cut is finished. The deal is the heat is melting the foam rather than letting the blade cut it. That is why a hot wire cutter has to be "set" by testing and practice to get the temperature of the wire just right or it might stick to the foam. Once the paper is removed and the foam is clean from paper fuzz, a simple hot wire table style jig, which can be home made very cheaply, may be just the ticket many are looking for. Plenty of "how-to-make" video on Youtube. If you later want to get into making wing cores out of block foam with a bow cutter using hot wire, plenty of how-to video on Youtube also. I recommend purchasing an adjustable transformer, but you can also use other current providing devices, and manage to a degree with where the alligator clips are placed on the cutting wire. In any case, you can also watch Youtube video about shaping and cutting foam, which is very likely going to remove the mystery of the process. Cutting angle tends to be the biggest part of the secret for the new whackers of foam.
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Old Nov 17, 2011, 08:55 PM
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Update: I stopped by Dollar Tree yesterday and picked up 5 sheets of foam and man was I happy! I was paying over $2 at Walmart and the DT foamboard worked even better! Changing blades defently helps! Thanks everyone for the help! Hope to test fly it tomorrow!
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Old Nov 17, 2011, 10:35 PM
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Fantastic! pleased its all working now.

Make sure to post up pics
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Old Nov 18, 2011, 02:34 AM
Reap the wild wind
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Joined Feb 2007
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computerman021
glad you got it all worked out. Don't forget to post pictures, maiden flight report and video if you can.
I stuffed my standard one into the cold unforgiving earth yesterday. The lipo went just as I was executing a low a level loop. It stalled and nosed in but only damage was to the firewall (again) I think I'll craft on a new nose & firewall and she will be good to go.
Gave the Funbat Maxi (39") a few flights. She is a real floater and I reckon she would slope soar in 10mph+ winds even as a powered version. It's just not as exciting as the smaller version and takes up a lot of hanger/car space. Just goes to show bigger isn't always better. I built both versions of GPW's Skyray but much preferred the 28" version.
Perhaps I still need to find the right motor for it?
Andy
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