Gizmo injection for fins

This weekend I'll be doing the injection. The instructions on the XL version (I have the regular Gizmo with the DD upgrade) indicates 1/4" holes evenly spaced to use to inject. That seems awfully big diameter to me.

What size holes makes the most sense? After injection I was going to use some Proline to fill the holes. Anything better than that?

The holes are sized more so you can get the tip of the syringe in there (and have some ability to aim). If you really don't want to deal with holes that big you can use a narrow-tipped syringe (or get tips to attach to your syringes, such as https://www.amazon.com/dp/B001QRZ31C/?tag=skimlinks_replacement-20 )

Just remember that epoxy is thick, and as 'hard' as it is to push out of a regular syringe tip, it's going to be that much harder to squeeze out a narrow tip. If it's too narrow you may also have issues with fillers clogging the tip.

Especially if you use a carbon mix.

Hmm. Well, I am using carbon mix. Maybe I'm not thinking of the right kind of syringe. What kind do you use/size?

Ready o drill holes Friday night. 3 upper airframe/nosecone for nylons screws. 3 for av bay bolts to attach to airfrme. 1 power switch on av bay and two vent holes. 3 nylon screw homes for lower frame to av bay. 1 vent home upper frame and one lower frame. 2 rail button holes. 12 holes for filets (4 per fin). Sound right?

I wouldnt drill holes to put fillets inside a 5" tube with a 54mm motor mount unless I had put the aft CR on (in which case, i'd ask why you did that ).

A standard 10ml syringe is easily extended with a 3mm ID (1/8th for you americans) tube, teflon works wonders as it's very easy to wash out, but anything fairly rigid works well.



Fill the syringe with your epoxy/filler, and then fill the extension tube from that - then refill the syringe and start making fillets. If you position the rocket as a Y you can do two motor mount fillets and two airframe fillets at a time (top and bottom). Constant pressure and constant retraction rate (start from as far in as possible) and you'll get a nice bead. Thicken your epoxy less than you would for external fillets and it will self-level.



4" Airframe, 3" MMT, easy internal fillets without any holes drilled.


If you've put the Aft Centring ring on... lesson learnt for next time?

build going well. Tonight fins go in. Man, not much room for drogue and recovery equipment! Plenty forward for main, aft not so much.