Questions about using plastic putty and finishing a nose cone

I have some Tamiya plastic putty which I intended to use to fill the seam on nose cones. I'm working on a rocket right now, and the seam, instead of being a lowered, divot-like area, is actually a little ridge, where the two halves of the nose don't quite meet just perfectly. I'm not sure putty is the answer for finishing this nose, since I'm dealing with a raised area.

I thought of sanding the ridge down. I tried it on the shoulder of the nose, but it seemed to scratch the plastic. However, I do have some higher grit papers - 600 and 800. I tested the 800 on the shoulder, and again, had scratches, but they seem pretty tiny, so I'm wondering if they won't show through after I prime the rocket. Then again, maybe 800 is too fine to actually take this tiny ridge off.

Anybody have any insight on this? I want this rocket to look really nice. Thanks!

lcorinth said:

I have some Tamiya plastic putty which I intended to use to fill the seam on nose cones. I'm working on a rocket right now, and the seam, instead of being a lowered, divot-like area, is actually a little ridge, where the two halves of the nose don't quite meet just perfectly. I'm not sure putty is the answer for finishing this nose, since I'm dealing with a raised area.

I thought of sanding the ridge down. I tried it on the shoulder of the nose, but it seemed to scratch the plastic. However, I do have some higher grit papers - 600 and 800. I tested the 800 on the shoulder, and again, had scratches, but they seem pretty tiny, so I'm wondering if they won't show through after I prime the rocket. Then again, maybe 800 is too fine to actually take this tiny ridge off.

Anybody have any insight on this? I want this rocket to look really nice. Thanks!

Click to expand...

Before I go any further let me say the material I'm most familiar with is Standard injection and or blow molded Styrene plastic Nosecones.
If your cone is made of something else then the following may not be as true.

Styrene parts. Cones, transitions and nozzles sand best with 240 & 320 grit sandpaper.
Most solvent based "Plastic putties" will MELT your styrene nosecone badly. I've ruined several PNC-80K Estes Nose cones trying to fill some small pits with Green and White putty.
The trick to filling such large gouges it to use medium or heavy CA to fill the holes (DO NOT use Kicker) let the CA cure in open air. Then sand with 240grit sandpaper to knock down the bump. Finish with 320 to 600 papers CA sands just like Styrene.

To Smooth out standard mold seam lines I generally do not play around with them, using a 120grit "glit-stick sanding belt and backer knock down all of the mis-match trying to round over a bit as you go. Once the ridge and/or valley have been adjusted proceed with progressively finer grit sandpapers to about 320.

Seriously: do not sand the cone completely smooth with 600 or finer papers. it is BEST for the surface of the plastic to have a bit of "Tooth" for the Primer to grab onto. After a coat or two of grey primer you can sand to about 400grit to give an very nice sheen to the primer. Your color coats (should be at least two) are then applied and AFTER they are completely (NOSE to the Surface) DRY you can polish out any dust, hairs, and other surface imperfections wet sanding with 600 to 2000grit wet/dry papers or use Perfectit-III for heavy stuff and Finessit-II to polish the finished cone, Transition and body for that matter.
Hope this helps

I'm actually planning on doing a tutorial on this, but it's a variation on how I do balsa nosecones now. Mind you, this is intended for Estes (white) Polystyrene type nosecones, and not Polyethylene nosecones. The results look good, but flat spots may occur as a result of the method I'm about to describe.

1) Take the nosecone and "paint" it with a Sharpie pen.

2) Sand the seam until the ink is gone using 220 or 320 grit wet/dry sand paper.

3) Completely sand the entire nose cone with 320 grit, until the ink is gone.

4) Prime/paint.

Results should resemble this balsa nose cone when finished:

lcorinth said:

I have some Tamiya plastic putty which I intended to use to fill the seam on nose cones. I'm working on a rocket right now, and the seam, instead of being a lowered, divot-like area, is actually a little ridge, where the two halves of the nose don't quite meet just perfectly. I'm not sure putty is the answer for finishing this nose, since I'm dealing with a raised area.

I thought of sanding the ridge down. I tried it on the shoulder of the nose, but it seemed to scratch the plastic. However, I do have some higher grit papers - 600 and 800. I tested the 800 on the shoulder, and again, had scratches, but they seem pretty tiny, so I'm wondering if they won't show through after I prime the rocket. Then again, maybe 800 is too fine to actually take this tiny ridge off.

Anybody have any insight on this? I want this rocket to look really nice. Thanks!

Click to expand...

As you've observed, most Estes style nose cones actually have a seam to sand off, not a divot to fill in a similar way to body tube spirals.

Don't worry about using coarser grits for getting rid of the spiral. I used 80 grit paper on the cone of my most recent Vagabond project to rough the surface up for the primer to adhere to, and I'm very happy with the final NC finish.

If you're using a high build formula (i like Duplicolor filler primer), you won't see any of the scratch marks after a few coats lightly sanded with 300-400.

Fine grits like 600+ are generally more useful for "finishing" work like wet sanding color/clear coats. You need some teeth to really knock down structural work like plastic seams and such.

Just my 2c. I've never used CA on a polystyrene NC.... but I'm still a first year rocketeer who's got a lot to learn.