Day 2 of twin crayon rocket build
My day kinda got shortened by having to watch my 3 kids while the SWMBO did the grocery shopping, if not for the youngest I could have thrown the two older ones outside to play since it was 65 degrees F, the youngest is 9 weeks and taking her into the shop would get me killed by the wife. Ive set my shop up with a removable fence/barrier across the rollup door so that it can be open the the 4 and 6 year olds cant get in.
Today was assembly of the fin can/mmt that makes up the lower cap of the crayon.
For thobin here are some photos of how I'm doing the "business end"
Pic 1: Inner CR and outer Thrust plate, obviously holes line up
Pic 2: Inner CR and Thrust plate sandwich bottom of lower crayon bank cap
Pic 3: Inner CR, notice how edge is profiled for the rounded corner it fits into, all CRs are snug fit.
Pic 4: Lower cap, hole in center is not neat originally I drilled it with a hole saw but it was off center. One nice thing about the plastic these caps are made of is that they cut really easy with a sharp Xacto or Stanley Utility knife, a sharp chisel was used to remove a few distortions in the plastic.
Pic 5: Assembled nose cones and MMTs, the upper CR in the MMT is put in before the motor tube, and is wedged against the upper shoulder. All CRs in MMT are epoxied in place (if it actually sticks), all I could really do for prep was wash parts, scuff heavily with 60grit sandpaper, and then wipe with acetone followed by denatured alcohol.
The epoxy is US Composites 635 w/ Medium Hardener, thickened with milled FG.
The part I forgot to photo was the rail button block epoxied to the lowest CT, but you can see the screw on each MMT side. The top CR goes into the cardboard airframe and will be attached with Titebond II (I prefer it for Wood and Paper construction. The fin slot locations are marked, and I will cut them next session along with the fins.
Nose bulkheads are fitted snug and filleted on both sides, Scotch tape (just enough to cover tee nut holes) was used to keep epoxy out of the threads on the T-nuts.
The coin slot I covered with a piece of Scotch tape turned sticky side up and then taped in place with more Scotch tape. Thickened epoxy was then smeared into the slot and on top of that was two layers of the Bondo brand FG cloth, I have other FG cloths but decided to just use this stuff, since the weight is unknown to me, in my inventory I have .5, .75, 2, 4, 7oz cloths but I'm using the Bondo stuff in non-visual areas.
Entire Nose cone assembly weighs about 7-8 ozs. The complete bulkhead weighs about 3.3 ozs, the NC weighs about the same, plus an ounce or so of epoxy and FG cloth, and I still will have to add a fair amount of weight to the nose.
My L1/L2 project is kinda dead until these two are done, actually I'm considering doing my L1 on one of these. I was going to glass my airframes today but ran out of time.
Photos were not turned sideways by me, it happened when I uploaded them somehow.
In a few hours I will go out and pull out the all the screws so they dont get permanently epoxy threadlocked, the bottom three screw are for motor retainer clips.
One of the assembly steps for the MMT since the motor tube goes in last is that all screws are left loose until the tube has been slid into place and a motor used to line up the outer thrust plate (tube butts up to thrust plate). After everything is lined up the screws are tightened down. Once the MMT is assembled theres no going back inside without drilling at least one hole in the upper CR ( I accidently shifted the block for the rail button). A person could pre-drill some larger holes in the upper MMT CR and fiddle with stuff inside like adding additional fillets and stuff. Between the thrust plate and the upper two CRs (mmt and airframe) I dont think the motor is going any where its not supposed to, MMT tube does actually carry some of the structural strength of the MMT (I dont think its a lot though).
AFAIK, no glue I know of actually sticks to this plastic which is why I'm depending on mechanical retention methods (I don't think even the plastic welder type epoxies work on this stuff very well).