Cutting slots in styrene boat tail (2.6 inch/65mm/BT-80)

SolarYellow

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I've searched and haven't found much out there.

I'm looking at doing a scratch build, converting the Apogee PNC-66A nose cone into a boat tail. Tail diameter will be whatever works with the Estes 24mm plastic motor retainer.


Will need to do TTW fins, which means cutting slots. Lots of talk about how to cut slots in straight tube. Some discussion that would be relevant to much larger, heavier boat tail parts. Not so much on the smaller & lighter side, like going through styrene. Mostly just looking at how to mark them properly straight, and how to set up a cutting guide that will go straight and not parallax off to one side as the boat tail recedes from the tube diameter.
 

bjphoenix

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Years ago I built a 2.6" V2 out of an Estes Silver Comet kit. Unfortunately I don't remember how I did the marking. Thinking about it a little bit I'll make a couple of suggestions.

1. If I was doing it, I would do some eyeballing for the layout. I do that for all of my fin alignment and they seem to come out pretty well. I would put the bt into the tube and draw line pairs down the tube to represent the fin thickness. Then I would eyeball down the tube and put marks on the back end of the bt to align with the lines. Then I would cut a tape strip the width of the space between the lines and stretch it along the bt to line up with the lines on the tube and the marks at the end of the bt. Then I would cut out the strips using a thin razor saw.

2. If you have a good fin jig, you can put the bt and airframe into it, then cut a sample fin using trial and error with a shape that just meets the airframe and the curved surface of the bt. When you have a reasonable good fit for that you can use it to draw the lines and cut the slots using a razor saw.

Some people would probably cut the slots using a cutoff disk in a Dremel. I've never tried that so I don't know how it would work by comparison.
 

Pem Tech

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Use the mold lines as an alignment guide, lay tape, trace the line and use two or three stacked cutoff disks. Works for us. In the early days before I had a dremel I would drill a line of closely spaced holes with a 1/8" bit. Clean out what is left with a razor knife or drill bit and you have slots. Have seen people use table saws, miter saws, even an ice cream scoop but we highly recommend the cutoff disks.
 
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The Dremel cutoff disks stacked is a great idea.
Only thing I would caution about is that they are thin and brittle, so keep the tool perpendicular to the cutting surface. Any twist or torque could shatter the disks.
Don't ask me how I know.
Eye protection might be a good idea.
Years ago I built a 2.6" V2 out of an Estes Silver Comet kit. Unfortunately I don't remember how I did the marking.

The plastic over the molded slots protrudes from the rest of the boat tail, IIRC.
Same tail cone as the V2.
So it's just a matter of clearing out them out with a hobby knife or cutting them off with a razor saw.
 
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SolarYellow

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Eye protection might be a good idea.

Tools don't rotate in my shop without eye protection. Period.

Since making the OP, I've purchased a CNC router. One of my intended uses is cutting clots in tail cones. Need to make some fixturing first, but it should be cool.
 

mh9162013

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Only thing I would caution about is that they are thin and brittle, so keep the tool perpendicular to the cutting surface. Any twist or torque could shatter the disks.
Don't ask me how I know.
Eye protection might be a good idea.
Those suckers shatter so often, I only use them with full face protection.
 

bjphoenix

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Tools don't rotate in my shop without eye protection. Period.
I don't do any work in my garage or household work in or out of the house without eye protection. Even if I'm working on fins or fillets I'm wearing magnifying glasses (AKA reading glasses) so I can see up close.
 

OverTheTop

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I would suggest going with a Dremel and cutoff discs if you have them.

Otherwise a very patient session with a hacksaw or some of the fancy handsaw.

Personally, I would chuck it in a rotary table on my milling machine 🙂.
 

Pem Tech

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Ever since I was 8 years old I've been wearing eye protection.
But I call them glasses.
;)

Wow.....
Can't imagine.
I made it until I was 50 and have hated them ever since. But you are right, I'll always have eye protection on since I can't see up close or read a book without them.
 

Back_at_it

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Only thing I would caution about is that they are thin and brittle, so keep the tool perpendicular to the cutting surface. Any twist or torque could shatter the disks.
Don't ask me how I know.
Eye protection might be a good idea.

Full face shield with safety glasses under it !

I had one of the "high speed" rated cutting wheels on my Dremel come apart. I was on the lowest speed setting and had just turned it on. The wheel came apart almost instantly and sliced right through a set of safety glasses I was wearing and hit my forehead just above my left eye.

I bought a face shield that evening and wear it anytime the Dremel comes out comes out and wear safety glasses under it anytime a cutting wheel is used.

As far as the question goes. Dremel cut off wheels works great. I've also used their universal cutting bit with great success but you really need to make sure the piece you're cutting is clamped down tight.
 

K'Tesh

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Here's how I did it with my downscale Binder Design Velociraptor...

 
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