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Building Tips and technical articles. => Building techniques => Topic started by: Bootlegger on June 28, 2012, 10:35:59 AM
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When you hollow blocks what method do you use to hollow the inside of the block?
Tools, and what ever else you use to do this.
I am working on a Dixon Cardinal and want to hollow the top block to get it as light as possible.
I am thinking about using Forestener bits, then Xacto blades and other tools for this.
Your thoughts, and why do you use this method...
thanks,
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I've been using this tool for years. Works well. X-Acto I think? Nothing written on it. Certainly other tools can be used also.
Check out The New American build and you'll see photos of the top block hollowed with this tool.
Charles
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I've been using some gouges that I made myself, some from music wire, some from drill rod, one teeny one (my first) from a bicycle spoke.
Find a good woodworker supply and look into their carving tools -- you'll find lots of stuff, at higher quality than anything that comes from X-Acto.
But if you go that route -- sharpen often, and treat the tool with the delicacy and patience you'd give to a newborn baby. Balsa wood, particularly the nice soft stuff, wants a scary-sharp tool and wears edges down quick. So if you believe that a cutting tool is something that you let rattle around in a drawer until you need it, then you pull it out and use it, then you merrily fling it back in when you're done, stick with X-Acto. If you are willing to take the tool out, sharpen it until it slices things it hasn't touched yet, use it, sharpen it again, and gently restore it to it's place in the leather pouch -- then you're golden.
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Hi Gil,
I use the round gouges from X-Acto, especially the 1/2" one. If I need to leave a bulkhead, etc., in the block I have a tear drop bit I use in my Dremel. I finish all by final sanding with 180-220 paper taped on a piece of old Ringmaster LE. It fits well and you can easily get everything down to an even thickness. If I cannot see a light bulb shining through the block I have not gone deep enough. ;D
Bill
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I don't do anything manually if there is a power tool handy! For hollowing blocks, just a Dremel and the 80 grit sanding drum works well. Makes a bunch of sawdust, but at least you don't cut your fingers.
Floyd
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What are you trying to hollow?
For tips - I use a dremel tool bit, to bring it down far enough, then use sandpaper to adjust it further.
If your doing top block/ or bottom block; I generally dont hollow out block. Bob Hunt is one of the masters at molded shells, they are very easy to make and you will not get close to the weight with a hollow block.
Technique is fairly easy.
Take Foam put it on the plane and carve it to suit.
Seal the foam with epoxy resin.
Add a wood lower block for rigidity.
Take 1/16 wood soak it in Apple Vinegar for 15 minutes.
Mold it around your carved block
Fix it with bandage wrap
Let it dry for 24 hours.
Now you have a completed molded shell ready for Install.
Matt Newman also is a master at this technique if you look in SSW there are many threads which explain this.
Another option is to purchase the Molded shell DVD from Bob Hunt Direct, he talks and shows in detail this simple techique. Its excellent.
Al Rabe was one of the earliest people to use molded shells. Its quicker and you can replicate it time and time again.
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Why not mold it instead? Molding has several benefits:
1) The process is very simple and quick. create a buck out of pink foam, glue it on a piece of pine(to have something to hold on to and to prevent warping), soak a balsa sheet in hot water with a little bit of ammonia(my wife likes that after I'm done, the bathtub is very clean :-) ), wrap it around the buck with elastic bandage(like this one http://www.cvs.com/shop/product-detail/CVS-Elastic-Bandage-With-Clips-3-Inches?skuId=160093 ) and let it dry(can be completely dry in 1 hour if left in the sun).
2) has almost no chance for making a mistake or messing up the shape. pink foam is very easy to work with and if you mess up, it's very easy to make another one. A sheet of 2" Owens Coning pink foam board costs less than $20 and will last you for many, many years.
3) The process allows you to creat multiple exact looking parts. This comes in handy when we crash or drop a heavy tool on top of the model(done that) or when a kid wants to experiment with a saw and grabs the top block(yep, that can happen) while you are not watching.
4) the process can be used for creating many parts: top blocks, bottom blocks, wing leading edge, stab leading edge, etc
5) the process allows for creating super strong parts. Just mold two 1/32 sheets with carbon veil in between and you will know what I mean. Just mold one sheet, let it dry, add carbon veil, apply epoxy(the surface will have to look very dry. if it's shiny, you have too much epoxy), and mold the second layer on top. After epoxy dries, take it out of the mold and be prepared to be amazed!
I used to carve top blocks too. It was one of my most favorite activities during model construction. The slow, careful carving was very soothing to me but after seeing the results of molding I to switch. The only place I still get to carve is wingtips and the front part of the engine cowl(the back side is molded too)
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Steven,
Correct on all accounts.
Some scale models we would have 5 layers or more of 1/32 ply laminated for the curve of the wing tip. Golden Era airplanes. Nails in ply for placing the wood.
Mystery Ship by Fred Reese was built this way but balsa is added. .5" wide when done! Works well.
Here's 1/16" balsa done your suggested way. 72" span on this model. Vintage Tiger Shark, was R/C now being fitted for CL.
I don't know about the Epoxy use, that stuff is heavy, weight adds up?
Hey! Got any photos of your models?
Charles
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Here's the best hollowing tool I've used. Dremel ball bit. Cuts like butter.
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I been thinking on a new technique to do mouldings. Involves making a jig. Will experiment with it on next build sometime this summer, and post it when it pans outs. Will eliminate the wrapping with the ace bandage which should cut down the drying to something like 4 hours. Stay tuned.
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I been thinking on a new technique to do mouldings. Involves making a jig. Will experiment with it on next build sometime this summer, and post it when it pans outs. Will eliminate the wrapping with the ace bandage which should cut down the drying to something like 4 hours. Stay tuned.
Keep us posted. Idea of a jig is interesting. not sure about drying time. Leaving the whole thing in the sun usually gets the job done in an hour or so, depending on how hot it is.
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Keep us posted. Idea of a jig is interesting. not sure about drying time. Leaving the whole thing in the sun usually gets the job done in an hour or so, depending on how hot it is.
I've done several mouldings using Hunts ace bandage method. I thought they had to stay wrapped for at least 24 hours because it took that long to dry with the moisture trapped inside by the wrapping. If you have done some that dried in a couple of hours, then the only advantage my idea would have is it eliminates the ace bandage making it a little easier to put the balsa onto the form.
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Instead of Ace bandages, use strips cut from an old sheet. The cotton will absorb the water and let it evaporate much quicker. This is what Al Rabe does. H^^
If Rabe has done that I'm sure it works, but one of the reasons I got to thinking about another method was to eliminate the wrapping part all together because its kind of clumsy. If I was going to wrap it I would stay with the Ace bandage because they stretch and I think that makes it easier to get a better fit of the balsa sheet to the form.
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I use a Rapala fish filleting knife to hollow blocks and also to carve my cowls. Been using it for decades. Get a new knife sharpened by a pro and then make small slices until you get used to using the knife. It has a very pointy tip which helps in tight placeslike cowl openings. Once my blocks are hollowed to the thickness I desire I custom fit formers wherever required.
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I used tools I made. Brass tubing with a loop soldered on the end that is sharpened on both sides. Rough it out with that then use a ball bit in a Dremel to smooth it out. But I agree, most of the time, molded balsa is better. Depends.
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Hey Gil: These are the only pics of my hollowing tool I told you about that I was able to find in my Archives. I made these in many variations, and have better ideas for the next revision. Not sure how soon I will be doing another block hollowing but when I do I will post an update. Right now I'm working on the design for a new type of moulding jig for current project. For now these older hollowing blades will give you something to work with.
The Xacto round router blades are about as sharp as my big toenail, and not at all easy to sharpen. Solution, whats the sharpest thing you know, a razor blade. But its straight, and it's also thin which makes it easy to bend into a curve. So you just bend it, shove it into a balsa stick, couple drops of CA to lock it in place, done.
When I get ready to hollow a block I will make 3 or 4, with different shaped curves. In the pictures I used a disposable razor blade that the barbers use in their straight razor. It comes with an aluminum back (like a backsaw or a regular single edge razor blade) to make it rigid, but its easy enough to remove the backing which allows it to be bent (wear goggles in case it snaps, they are brittle). The easier way is to just get some double edge blades and snap them in half. They work just as good (might even be a little sharper and thinner) but are shorter in length. I have use both types of blades and prefer the barbers straight razors becase they are about 1/4" - 3/8" longer. I had my barber order me a box of 100 for $28. You might find them cheaper online. Or you might get you barber to sell you some to try out. Inside the 100 packaging they were in smaller packs of 5 each.
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Allan,
Interesting.
How long is that lenght of wood?
Charles