3-Demon Fire (3D Rocketry) Build

Hi All,

A while back I purchased the new 3-Demon Fire kit from 3D Rocketry.

It's a great looking kit and it's now reached the top of my (ever growing ) build pile!



Check out those fins!

Now the work starts!!

Krusty

First step is to start work on the shock cord attachment.

The instructions call for the top CR to have a notch cut and the shock cord glued along the length of the engine tube.

I've chosen to use an eye-screw instead. I started by drilling a 2mm hole in the centering ring and screwing in the eye -


I then applied 5 minute epoxy to the inside of the hole, the exposed thread at the bottom and around the top of the eye screw.


This will allow me to add the shock cord in such a way as to make it easily changable.

The next step is to start marking the body tube. I used the included wrap -


For the fin lines, I use a solid line. For the launch lug, I use a dashed line. This will help reduce the chances of me putting a fin in the wrong spot.


More tomorrow!

Krusty

op:

On to slot cutting!

With the fin lines marked out, you need to start working out exactly where the fin will sit. The 3-Demon Fire comes with a handy-dandy fin slot template. You'll see that the bottom of the fin slot needs to be 17mm from the rear edge of the body tube.

Go mark the bottom and top of the fin slots lightly with a pencil. Once done, I block out the slot with blue tape.



I find that doing this gives me a really good outline to where the slot needs to go.

Stick a new #11 blade in your exacto and cut your slots.



Lots of light cuts makes for a better slot than trying to do it all in one go.

Krusty

Next step is to put together the motor mount. The kit ships with a 7" length of 29mm motor mount tube and two plywood centring rings. In addition to this, I purchased the Estes 29mm motor retainer from 3D Rocketry for use on this build.

You can either measure the length of the tang on the fin (the tang is the bit that extends through the wall of the body tube) or dry fit the motor mount and check it with the fin.



With the motor mount dry fitted, check to make sure that the top centring ring is located correctly - to allow the fin to fit.



Once you're happy that everything is in place and the fin will fit correctly, go ahead and glue on the top centring ring. For this, I'm using 5 minute epoxy. I have applied a little epoxy to the inside surface of the centring ring and around the top - I'm going to leave the under edge until I'm ready to glue the fins in.



Don't glue the bottom centering ring just yet.

Krusty

op:

Next up is to attach the shock cord leader.

I'm using enough kevlar to do a full loop from the eye screw to just out of the end of the body tube.

While kevlar has no give, it is fire resistant and will stand up to repeated eject charges. I've covered the knot in a short length of shrink wrap tubing.



By using a loop, should the kevlar ever need replacing, you can cut it, tie on a new bit and pull it all through the eye screw.

Krusty

Time to install the motor mount into the body tube!

Start off by wrapping two lengths of tape through the centring ring. This will allow it to be removed easily.



Now push the centring ring on the end of the engine tube.



Poke the shock cord leader through the engine tube and slide it all into the body tube. The bottom edge of the top centring should align with the top edge of the fin slot.



With the body tube upright, apply a bead of epoxy around the top edge of the centring ring. The way I do this is to attach a syringe to a length of dowel with tape. I fill the syringe with epoxy and then push the plunger down with a second length of dowel.



Once the epoxy has cured, you can go ahead and remove the rear centring ring!



And now you're set to attach the fins

Krusty

Fins are coming, but before that I'm going to attach a pair of rail buttons.

the 3-Demon Fire ships with a 1/4" launch lug, however for the launch site I frequent, buttons are better.

I've started by cutting a strip of 3mm plywood - 10mm wide by 140mm long. 10mm in from each end I've cut a 3mm hole. This will serve as the backing for the two rail buttons. I've used this as a template for marking the outside of the body tube - along the line drawn for the launch lug.



I've glued the backing strip in place with yellow wood glue and positioned it in place and the rail buttons are screwed in.



Fins!

Time to install the fins. First up, I applied a little epoxy to the inside of one fin slot - just on the top centring ring. Next I applied a bead of epoxy along the root edge of the fin and set in place. Try not to get any epoxy on the outside of the body tube.







With all the fins tacked in place, go ahead and apply internal fillets.

Krusty

Nice build!

It's been a few days since I've posted, but work has continued!

With the fins tacked in place, I set about adding internal fillets.



While the fillets were curing, I went ahead and started shaping the balsa strips that go along the root edge of each fin.



and did the first round of filling the fins. I've left a strip along the root edge free of filler - this will ensure a good bond when I glue the strips on.



I used yellow wood glue to attach the strips and held everything together with pegs until dry.





Krusty

Next step was to seal up the rear end of the rocket and attach the motor retainer.

I dabbed a little epoxy on the edges of each fin and slid the rear centering ring into place and then finished off with a fillet around the outer edge.

I roughed up the inside of the Estes 29mm motor retainer with some 160 grit sandpaper. I used JB weld to secure the retainer in place.



Now on with filling and sanding!



And the full stack Looking pretty snappy!! Should be ready to paint over the weekend.



Krusty