Micro Mach One Build Thread - Molded Balsa Tutorial - RC Groups
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Feb 26, 2011, 04:02 PM
AndyKunz's Avatar
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Micro Mach One Build Thread - Molded Balsa Tutorial


My last build was a micro Kaos, an indoor-sized model of the famous Classic Pattern plane designed by Joe Bridi. The build thread for that is in the Classic Pattern forum.

https://www.rcgroups.com/forums/show....php?t=1380102

This time I'm building another Classic Pattern plane, the Mach One by Norm Page. This one will have similar wing area (100 sq in), similar target weight (100-120g), and similar power (UMX Beast components). I'm doing it in the Builders Workshop because the construction technique for the fuselage is one that's not regularly employed, and several of my friends have asked to see a tutorial. If that bores you, skip ahead If not, stick around and you'll learn a neat technique that's been used to build ships and airplanes (since WW1!) but not often in models.

I'm spending a huge amount of time photographing the process. That slows it down, but so far I have only about 2.5 hours into the project including photography.

Let's begin!
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Feb 26, 2011, 04:07 PM
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Feb 26, 2011, 04:20 PM
AndyKunz's Avatar
Next we cut out the center pattern. Start by cutting it oversize, then come back and cut ON the line, then sand to nice flowing lines (I used a belt sander).

In order to make this mold, we need templates for each station. I simply used the former patterns attached to 3x5 cards, then cut undersize by the thickness of the wood I'll be molding (1/32"). The mold doesn't have to be perfect, but the better it is, the better your model will turn out.

Each station is marked on the edge of the wood, along with the former number. There is also a line 1/16" from the side of the wood, running lengthwise, top and bottom. This will be the centerline of the fuselage, and serves as a reference for both the former templates and for later fitting.

Follow the photos for more info to getting yourself a squared-up rough fuselage.
Feb 26, 2011, 04:29 PM
AndyKunz's Avatar
Using the templates and the marked centerline on the balsa, create yourself a rough top-view of the model. Connect the dots with a straight-edge (it's a rough cut line).

Cut near the lines (oversize again). If you have that Wing cutter, go for it. I chose to use a long-blade X-acto to cut oversize, then trimmed down to the line on my belt sander (with vacuum operating).

Use the templates and a sharp knife to rough cut the foam at each station. I forgot to take a photo here, but I'm sure you can find more info with Google.

Using a coarse paper (I used 60 grit), WET sand the foam to get it almost perfect. I then followed up with a househeld flex sander and wet-sanded it to satisfaction.

That finishes making of the mold. It's important to note that at both ends of the fuselage I have left lots of extra length. You'll find why that's important once we start molding the balsa.

Got to go do a little more work on it now. Hopefully I'll have some more photos to post before I go to bed tonight.

Please feel free to ask any questions along the way. If you prefer, you can PM them to me and I'll cover that info in the thread, maybe keeping it a little less confusing to follow.
Feb 26, 2011, 04:32 PM
Paul Pappas,.....AMA....L42520
Pitstop000's Avatar
Iím enjoying this Andy!
Feb 26, 2011, 08:29 PM
AndyKunz's Avatar
To form the balsa, it's essential to get the water boiling, and to thoroughly soak the wood. When the compound curves are not too drastic, you can form the balsa around them. The Mach 1's nose, though, it a bit too complex, and you see "bubbles" in the bent area. That's a sign that the wood isn't going any further. Mind you, this wood was not ideal either; softer wood would have been better.

The goal is to get the hot, wet wood tight against the mold. Sometimes to you have to make a lengthwise slice (always with the grain). Only slice it once per area, don't try fitting things yet. The overlap will easily be fixed after the wood is dried.

And remember to look for all your tools before you begin. If you forget, improvise!
Feb 27, 2011, 01:54 AM
Registered User
what do you mean wait over night? You're not done yet? eek:

I would not have though about trying to form a fuse like that. looks like a great way to save weight. Looking good so far. Can't wait to seeing the finished fuse.
Feb 27, 2011, 01:34 PM
AndyKunz's Avatar
Well, the tape improv wasn't nearly as nice as the Ace bandage way. The left side still isn't fully dry, so I'm hanging it closer to the heater in my shop. I removed a few pieces of tape to allow more surface area for drying. You can use the down-time to cut out wing ribs and get started on the tail.

Molding balsa is a great way to save weight. I first learned about it from Bob Hunt; he uses it to build portions of the fuselages of his C/L Stunt ships. One of the videos he did with Bill Werwage was being filmed at the same time so I got to see an early version. (We lived about 15 minutes apart).

You can order the DVD here: http://www.airbornemedia.com/store/rv-index.htm - it's the first one on the list.

BTW, if you are thinking of becoming "a builder," order one or more of those videos. They make great Christmas and birthday gifts to yourself, and you can build up a nice library. I have the entire set I believe, which I keep in my office at work in case anybody wants to borrow one.

Perhaps a club could order a set. (Hint - they all have something to learn that can be applied to our portion of the hobby, even the one on Japanese tissue covering).

Andy
Feb 27, 2011, 03:38 PM
AndyKunz's Avatar
In order to help the wood dry, I removed a few sections of tape and hung it up closer to the furnace. After doing this several times, the wood dried.

In these photos you can see the 3 slices I made to help fit the tough compound curves of the mold, and just how well it retains its shape once dry.

Then I started on the other side. It's hanging up in front of the heater now. Tomorrow I should have more to show you. While the second side is drying, cut out the formers. They should be the same size as the templates you cut earlier.
Feb 28, 2011, 05:25 PM
KE your cub.
Curare's Avatar
Ahh the good ol' Mach none

Nice choice andy, and as for moulded parts for aircraft, I've done a few belly pans this way, as per Windy Urtnowski's style, and it's GREAT! ...although I've never done a full monocoque shell.

What are you going to do to stabilize the wood to stop it changing shape over time due to humidity. It's not going to be a valid way of building a fuse if it's straight on a dry day and a pretzel on a humid one!
Feb 28, 2011, 05:30 PM
AndyKunz's Avatar
We aren't that far along! I'm working late tonight so there won't be any time to play.

Mach None is the little foam-winged thing, not nearly as nice as the real Mach One! I have plans for both, and obviously chose the better-looking model as a starting point.

Andy
Mar 07, 2011, 09:03 PM
Registered User
No speed building this time ? Have you done anything more on the Micro Mach One?
Mar 08, 2011, 08:44 AM
AndyKunz's Avatar
No, I wish I could. I've been real busy the past few weeks.

Andy
Mar 08, 2011, 09:36 AM
Registered User
well, at least the balsa should be really dry now
Mar 08, 2011, 01:21 PM
B for Bruce
BMatthews's Avatar
Years ago in the old American Modeler magazine there was an article about molding balsa shells just exactly as you're doing. Instead of boiling water the author used high strength ammonia available from industrial cleaning supply outlets. Apparently it turns the wood fibers into something as limp as a wet dishrag but when the ammonia evaporates it leaves the lignum "glue" in the wood cells as rigid and strong as it was originally but just in the new shape. No boiling required either. But you'll definetly want a covered container to hold the wood while soaking and to do the job outdoors as the ammonia fumes are hellish.

The rather shapely sailplane fuselage he molded using the technique had a shape that was compound curved as much or more than your micro Mach None shape. You may want to try it again using ammonia.


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