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Greg Furtman

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I was thinking not about the drilling per se, but drilling just the right size for a BT-5. Has anyone got a bit for that? Of course, one could start smaller and finish with a boring bar, but that could be a real bugger with the softness and weakness of balsa.

As for doing it my drill press, I simply didn't want to assume that Marten would want to take it on, and I could do it in the drill press, where at the moment I couldn't in my lathe.
I'd put a dowel in it. A 3/8" dowel which would be a good size.
 

Greg Furtman

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I certainly don't mind drilling the hole, and it would be nice to have hardwood at one end for the purposes of turning on a lathe.

Looks like the O.D. of the BT-5 is 0.544" or 13.8 mm. A 35/64" bit would probably be the right size, but I haven't got one of those.
Why use BT-5? Just use a 1/2" birch dowel.
 

mbeels

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Alright, a 1/2" dowel is inserted into the center of the balsa block, and I glued plywood on each end for the lathe. Also, that is a lot of fine triangular stock, so I cut off the corners to use in my airplanes.

My son is taking care of plowing the balsa dust.

PC070075.JPG PC070076.JPG
 

jqavins

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Because I expected to be drilling and inserting it myself and I have plenty of BT-5, and I thought (still think) it would do. But the dowel is a better answer. And since Marten is doing it for me, and he is using a dowel, that's that.
 

mbeels

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Well, it sure isn't perfect, but I learned much. The balsa was quite soft, but not the same density throughout. So if I sanded free hand, I got shallow divots. If I sanded with a sanding block, it wanted to bounce and I got mountains and valleys.

My cheap lathe doesn't have a live center in the tailstock, so it wanted to bounce around and shift a lot. I've got to see if I can find a live center that will fit it. I also need to learn how to properly sharpen lathe tools. They don't seem to be as simple as chisels or planes.

I noticed that when necking down the tip of the nose cone, the soft grain would shift and slip internally, and the previously straight nose cone would take on a "C" shape, so the last 1" or so of the tip was finished off the lathe.

PC070077.JPG
 

Greg Furtman

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Well, it sure isn't perfect, but I learned much. The balsa was quite soft, but not the same density throughout. So if I sanded free hand, I got shallow divots. If I sanded with a sanding block, it wanted to bounce and I got mountains and valleys.

My cheap lathe doesn't have a live center in the tailstock, so it wanted to bounce around and shift a lot. I've got to see if I can find a live center that will fit it. I also need to learn how to properly sharpen lathe tools. They don't seem to be as simple as chisels or planes.

I noticed that when necking down the tip of the nose cone, the soft grain would shift and slip internally, and the previously straight nose cone would take on a "C" shape, so the last 1" or so of the tip was finished off the lathe.

View attachment 400360
Looks good. Congrats.
 

neil_w

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Not bad for an amateur. ;)

That's a pretty significant hunk of balsa, how much does the whole thing weigh?
 

mbeels

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Exactly what I wanted. Thank you very, very much.
Sure thing, it was a fun project! The shoulder is slightly on the loose side, but a coat of sanding sealer on the balsa shoulder, or a layer of CA on the inside of the body tube will probably make it about right. And the "V" is slightly at an odd angle, but it isn't too noticeable unless you look closely.

That's a pretty significant hunk of balsa, how much does the whole thing weigh?
Ah, I didn't think to weigh it, it's boxed up already. It has a 4" length of 1/2" dowel inside (+glue), plus I left the 1/8" plywood bulkhead attached to the bottom end. Even with all that, it feels lighter than it looks. I think that the balsa block was relatively low density. At least it is weight on the "right" end.
 

jqavins

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I'll have to weigh it when it arrives to update the RS model. So I'll post the result.
 

jqavins

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I got it today. It looks just as good in person, though some fill-sand work is indicated especially in the waist section. It weighs 98½ grams, but I might carefully saw off the plywood base plate; it's served its purpose to help with the turning, and cutting it off will save some weight.

I tried to locate the CG by balancing it on a ruler, but it turns out the CG is in the waist section, so that wasn't going to work. At least I know reasonably close, since it's within a given 3/4 inch length.
 

mbeels

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Yeah, it will need some finishing work for sure. The fit of the shoulder in the body tube may be a bit looser without the plywood bulkhead, but it would reduce the weight somewhat.
 

jqavins

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The fit is too loose as is; since I've got to build that up in any case I don't think it makes a whole lot of difference
 

jqavins

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Still not dead here. This week I received a box from Apogee with, among other things, the BT-80 for this rocket.

I went ahead and cut the plywood baseplate from the nose cone which took off - well, I don't remember, but some weight. Updated the model with the reduced weight.

I updated the model also with the length of an uncut BT-80, because I'm lazy, but it really looks better cut down, and still has plenty of stability margin.

I need to get back on the stick and order the updated custom laser cut balsa bits (remember where this all started?) and start building. I'll be doing it alongside my Secret Santa gift, a LOC Park Flyer Magnum.
 

mbeels

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Alright, I was wondering about this build the other day. I forget, are you custom cutting your motor mount centering rings? Are you utilizing your local laser cutter, or sending away for them?
 

jqavins

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I'm sending away for them. This whole thing started because I told 802High that I had a project I could use some parts for (he asked for projects to practice on before going into business; see this thread) and it all took off from there. Before then this had all been in the back of my mind for several years. He cut the rings, fins, and a jig for me, then the design changed so I never took delivery. Now that the design is settled I feel morally obligated to go back to him for the revised parts and to pay for both sets.
 

mbeels

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Just curious if you got your centering rings, any progress?
 

jqavins

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No, this fell by the wayside. Ifeel a little guilty about it, after mbeals made me that nose cone.

Coincidentally, I was just thinking about it today. I have the coming week off and I'm almost finished with another rocket, so this might be the time to get back to it.
 

Greg Furtman

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No, this fell by the wayside. Ifeel a little guilty about it, after mbeals made me that nose cone.

Coincidentally, I was just thinking about it today. I have the coming week off and I'm almost finished with another rocket, so this might be the time to get back to it.
So many rockets. So little time. ;)
 

jqavins

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I redesigned the laser cutting patterns for the centering rings, fins, and fin jig yesterday. The cutter I have access to is in an area public library, and I don't know if they're open. If they are, I might actually have this ready for a naked flight at this weekend's launch.
 

jqavins

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Update: no, the library is not open. Could one cut the items I need by hand? Well, someone could, but I don't think I could to my own satisfaction regarding precise size and positioning. So progress will have to wait.
 
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