Splitting a balsa nose cone - Semroc Hydra 7

[STRMan]

OK, after nearly a year without a build, I have started building a Semroc Hydra 7 I purchased a few years back. I've got the 7 engine tubes glued up so far.I forgot how much I love building.

I have NEVER had to split a nose cone longitudinally before. I don't have a razor saw. I do have a nice selection of X-acto knives, from small to large ones. The instructions say you can use either to accomplish the job. Before I hack this up, how has anyone done this that has built the Hydra 7?

[Doug Sams]

Before I hack this up, how has anyone done this that has built the Hydra 7?Sorta. I've split nosecones before - not for the hydra - but for the same application.

You can buy a razor saw cheap with a 40% off coupon at Hobby Lobby :) You can cut it with an eXacto knife, too. Either way, one tip I offer is to mark the line all the way around, then work your way around in multiple passes, going deeper each time around.

Keep in mind it doesn't have to be pefect. Filler will solve most problems :) Looking at the instructions (from the Semroc site), the sanding shown in step 32 on page 15 is exactly how I contoured the cone halves to the airframe.

After they're glued in place, a little FnF and a wet finger will make all your cuts perfect :)

Doug

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[stefanj]

I've split cones with hobby knives, but I would invest in a razor saw.

Suggestion:

Soak the cone(s) in wood hardener, or watered down yellow or white glue, first. Give it a nice hard surface and sub-surface.

The actual cutting will take more effort, but the cut will be more precise because you are dealing with a hard material rather than a fibrous one.

[Feyd]

I've built the Hydra VII (great rocket!).

I marked the nosecones all the way around and cut with an xacto knife as recommended above. They don't need to be perfect since they will be fit-sanded on the main body tube. It was relatively easy to cut the cones as they are not very hard (at least mine weren't).

Another tip... decide on your paint pattern early! This thing is a BEAST to paint after it's all assembled if you want to do anything fancy and not have to hand-paint.

[luke strawwalker]

Sorta. I've split nosecones before - not for the hydra - but for the same application.

You can buy a razor saw cheap with a 40% off coupon at Hobby Lobby :) You can cut it with an eXacto knife, too. Either way, one tip I offer is to mark the line all the way around, then work your way around in multiple passes, going deeper each time around.

Keep in mind it doesn't have to be pefect. Filler will solve most problems :) Looking at the instructions (from the Semroc site), the sanding shown in step 32 on page 15 is exactly how I contoured the cone halves to the airframe.

After they're glued in place, a little FnF and a wet finger will make all your cuts perfect :)

Doug

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What doug said...

Print off a 40% off coupon from HL and buy a Razor saw... you'll be glad you did.

I haven't build the Hydra 7 but the Zooch Vanguard Eagle uses the same method to build the SRB nosecones on the lower stage... Actually you have to split balsa tube couplers lengthwise into half-moon shapes, round one end over into a nosecone, and then cut three half-moon bulkheads off the back end of the nosecone, but it's the same idea...

It would have been VERY VERY TOUGH to accomplish without a good razor saw!

Later! OL JR :)

[o1d_dude]

Even at full price, the Zona razor saws don't cost more than $7 a piece. They should be available locally at pretty much any hobby store. These saws are very popular and not specific to any one particular craft.

Make sure you look at the TPI (teeth per inch) rating and choose accordingly.

[jeffyjeep]

After building for c. 40 years I bought my first razor last year. I don't know how I EVER got by without one.

[Scotty Dog]

If i understand whats beeing done here. Splitting balsa cones? I have not done this but I would make a "Miter" box for the cone.Box that the cone just fits in and maybe Ca or screw to hold it, have yo saw come down the "slots" in the box. One other way and I have done this with plastic cone. Put the cone in a tube, lay the tube against fence on table saw and run it thru. You could do this with a saber or band saw also as they would have thinner blades. Anywhoo-good luck witht he build Scotty Dog

[jharding58]

If a band saw is available then I would go that way. If not, then a razor saw is almost requried. I used a couple of BNC-5AW to create the motor fairings for an Arianne. If you are careful, and fast, then you can get through them relatively plumb. Sand them on to an appropriate sized BT with a layer of 400 grit and their undercamber will match the inner BT.

Just as a suggestion, a bench top bandsaw with a fine blade is pretty much indespensible. If you want to spoil yourself, then pick up a 10" diameter disc sander from Micro Mark as well. It costs a little more, but having the speed control to be able to sand at 280 RPM is a Godsend with balsa. Think about it when you prepare to stack sand all of those fins...

Enjoy the Hydra VII - you will really love getting all those tubes and ring support fins to align themselves. And then comes the masking. I have built one Hyrda VII and two copies of the Hydra I. I think that I am done with that particular design. :eek:

[jharding58]

After building for c. 40 years I bought my first razor last year. I don't know how I EVER got by without one.

I knew that they never shaved on pig boats, but that is a long time to go without shaving.

[STRMan]

I broke down and bought a razor saw from my local hobby shop for $5.99 today. I first traced a bisecting line all the way around the cone, and then went to work with the saw. The cuts were nearly perfect. I then wrapped some 220 grit wet/dry paper around the body tube and carefully contoured the inside radius. Took a couple of passes, and finally the main tube popped right in. Outstanding. I'm heading off to bed and plan to do my gluing tomorrow.

Thanks for all the input everyone. I'll snap a few pics and post them soon.

[jeffyjeep]

I knew that they never shaved on pig boats, but that is a long time to go without shaving.
OOPSIE! I either left out the word "saw" or I'm Billy Gibbon's understudy! No, wait. That's Billy Gibbons's understudy(?)

OK, I give up. What's the possessive form of "Gibbons"?

Aw, screw it. I'll be Dusty Hill's understudy. MARY!! More Scotch, please!

The end.

p.s. We didn't wear skivvies, either. TMI

[sandman]

I knew that they never shaved on pig boats, but that is a long time to go without shaving.

I read that book ("Pig Boat") a long time ago!

Good book! ;)

[jeffyjeep]

I read that book ("Pig Boat") a long time ago!

Good book! ;)
Yes. VERY good book. But if you want a synopsis of what I REALLY did on subs during the cold war, read "Blindman's Bluff" by Sherry Sontag and Christopher Drew. I thought this stuff was still classified. It probably is.

[Doug Sams]

Y...read "Blindman's Bluff" by Sherry Sontag and Christopher Drew. I have. Some of those sub captains had huge kahones. I don't know how they put their pants on :)

Another great submarine reading topic is Swede Momsen.

Doug

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[PaulK]

OK, after nearly a year without a build, I have started building a Semroc Hydra 7 I purchased a few years back. I've got the 7 engine tubes glued up so far.I forgot how much I love building....Its about time, Paul! A few more suggestions, if it isn't too late - 1) leave more than one engine tube open, so you've got redundant ejection charges (you'll never fly it on just one motor anyhow), put in a semroc ST-16 baffle (my kevlar burnt through after 3 or 4 flights being tied right to the motor block), and put dab of epoxy in between the NC halves, where the ST16 tube buts up to the ST7 tubes (to protect against the ejection charges).

Here's my build from 2006 (http://www.rocketryforumarchive.com/showthread.php?t=25439). So where are the pics already!? ;)