MMX Launch Rack

[Micromeister]

John:
Great choice for a "Stock" base building material. a little heavier then I like but easy to obtain and very much Standardized in size. Should make rack interchangability very easy. Looks like your "system" is going to be very durable and easy to mantain


Your 4 x4 x 48" model reminds me of one of my first all aluminum custom 6" x 6" x 48" 6 postion racks made for my Scout Troop in the early 80's. It was later re-wired and sold to another Space Youth Group and is still going strong today

Edit: Almost forgot! Soldering! if you'll add a bit of soldering paste "Flux" to your joints and allow both parts to come up to heat with widest part of the soldering tip in contact with the surfaces your solder will flow much better forming a great bond and smooth suface. Hope that helps a bit.

 

[JAL3]

As mentioned before, the base of my system was to be a commercially available steel sawhorse. I chose the one made by Task Force because it seemed sturdy, already had some holes drilled about where I would want them, had adjustable length legs and because it happened to be what was for sale at my local Lowes.

 

[JAL3]

The larger holes in the sawhorse turned out to be just right for 5/16" bolts. I assumed that each base would have a pair of such bolts to fasten the box above. I saw a potential problem, though of the bolt slipping out through the hole while hands were occupied handling the box. I kept asking about some fort of "retainer" to keep them from slipping out. I had just about decided to try and fit a little rubber O ring on the shance to keep it from slipping through when somebody mentioned an "E clip". That turned out to be just the ticket. The bolt was slipped through the hole and the clip was popped into place at the base. It did what I wanted and freed my hands from having to keep the bolt in place while fumbling around with the box.

 

[JAL3]

To hold the box onto the sawhorse mounted bolts, I wanted to use wingnuts that could easily be removed. I also added a fender washer to the system to spread the load out a bit if the assembly were to be picked up by the built in handle on the sawhorse. Since I was not yet ready to mount the box, I just stored the washers and wingnuts in their eventual place of residence.

 

[JAL3]

Edit: Almost forgot! Soldering! if you'll add a bit of soldering paste "Flux" to your joints and allow both parts to come up to heat with widest part of the soldering tip in contact with the surfaces your solder will flow much better forming a great bond and smooth suface. Hope that helps a bit.

I think that soldering has become a non-issue, at least as far as teh rack is concerned.

Thanks for the tip

 

[JAL3]

A day after the second coat of primer was applied, I mounted the end caps. Each one required 3 bolts I used 1/4x3/4 along with a lock washer. When in place, the caps greatly increased the rigidity of the trough.

 

[JAL3]

The bolts on the base are spaced 30" apart so I drew a light line down the centerline of the bottom of the trough and made marks for the bolt holes at that spacing, centered between the ends.

 

[JAL3]

The holes were then drilled with a 5/16 bit.

 

[JAL3]

The system was now ready for me to test fit the box on top of the support. As such, I undid the wingnuts and removed the fender washers and was pleased to see that the bolts did not then fall out. So far, so good. I set the box on top and the holes lined up the the bolts...mostly. There was a bit of tightness at one end and the box was forcing the bolt to lean. For grins, I put on the washers and wingnuts and tightened it down part of the way. I then lifted the rack by the carrying handle and it seemed the idea was sound so far but needed a little more work.

 

[JAL3]

One of the things I noticed is that the bolt stuck up farther than I liked on the inside of the box. I decided to use a 3/4" length instead of the full inch. Accordingly, I popped the e-clip off and substituted a shorter bolt. I had also noticed that the bolt tended to turn as I tried to tighten the wingnut. To remedy that I added a star lock washer under the bolt head.

 

[JAL3]

Another problem I noticed is that I must have gotten the spacing for the holes in the box just a wee bit off. On bolt was tilted to an angle when the box was put one and the nut could not be completely tightened.

 

[JAL3]

I tried to fit a nibbler into the hole but the head would not quite fit so I took a round file and opened it up a bit.

 

[JAL3]

I was then able to slip the head of the nibbler in and took a single bite out of the hole to let the bolt sit more upright.

 

[JAL3]

The box was then put back into place and this time it went down flush and the wingnut took held it flat.

 

[JAL3]

Another thing I wanted to change was the screws that held the hinged cover closed. These were simple screws that I KNEW would pop out and be lost in the field since I wanted to be able to use the box for storage. As such, I ordered some knurled headed screws from Grainger to replace them. I also ordered some split rings to keep the screws from pulling all the way out of the lid.

 

[JAL3]

When they came in, all three screws on the cover were replaced.

 

[JAL3]

I had decided that the rack would have 6 launch pads spaced 8" apart. This was tighter than I liked but I didn't want the box to be longer than 48" longs for transport. I drew a line down the center of the cover and marked 6 places evenly spaced between the 2 ends. I then drilled 5/16" holes at each station.

 

[JAL3]

The basic support of each of the heads was to consist of a 2" long, 5/16" bolt. I added a washer to distribute the force and a lock washer to keep the bolt from spinning as the exposed side is manipulated.

 

[JAL3]

To hold the bolt fast from the top side, another washer and and nut were placed and the assembly tightened down.

 

[JAL3]

A pair of nuts was then put onto the upper side and turned down approximately halfway. The purpose of the twin nuts is to be able to lock them against each other and set the height.

 

[JAL3]

Next came a pair of SAE washers and a wingnut. The washers are to sandwich the actual launch head.

 

[JAL3]

This process was repeated for all six stations.

 

[JAL3]

As the actual base and box were being built, I kept working on the design of the launch head, making some changes based upon the original prototype. On the next set of prototypes, I used plywood, a much more durable product than balsa but the trade off is that it does not whittle as easily to make adjustments. I printed up new templates for 10 heads rough cut them with a jigsaw, sanding them down to the outer profile.

 

[JAL3]

The notch for the igniters was rough cut with the same jigsaw; there was little uniformity except that I (mostly) stayed within the lines.

 

[JAL3]

Finishing down to the lines was done with a combination of X-acto, file and sanding stick and eventually, they were all pretty standard.

 

[JAL3]

An issue that had not been addressed in the previous prototype was the securing of the MMX launch rod. I wanted something more secure than just a hole drilled into the plywood. I wanted the head to retain the rod. I came up with an idea and ran it past several people with much more mechanical experience than me. The answer I kept getting was that "it might work; try it and see." That turned out to be some work and an excuse to acquire some new tools.

I bought a 3 foot length of 1/8" brass tubing to receive the rods. A cut off wheel on a Dremmel tool was used to cut 10 pieces, each an inch and a quarter long. There was some sloppiness here and some turned out longer and some shorter but, in general, their length was the same as the depth of the launch head.

 

[JAL3]

A guy at Quality Fasteners, a local screw and bolt place, gave me the idea for securing the brass tube in place. Up until now, my mind had gone off in a completely different and much more complex direction. For each piece of brass, I obtained 2 nylon harnesses that seem to be designed to retain wire. Each was sized to hold an 1/8" rod and be held in place with a #8 bolt or screw. I place them by eye and used a pen to mark the holes for drilling.

 

[JAL3]

The keepers were then bolted into place with nylon locking nuts holding them fast on the opposite side. I found that by not tightening them down all the way at first, I could slip in the brass tube and eyeball it into place. When tightened, the keepers work together to keep it straight.

 

[JAL3]

The next part was the tricky and the iffy part. I wanted a set screw that could be turned by hand that would keep the MMX rod in place. The smallest suitable screw I could find was a #2-56 which had a little head on it that I could thumb tighten. What I did not know is if I could drill the holes through the brass and have enough material to hold a thread. Added to that, I had never used a tap or die in my life.

I set up the proper drill in my Dremmel press and realized that I could much more easily keep the brass tubing straight by leaving it mounted to the launch head. Strangely enough, I managed to drill each of those little hole without having to cut any more tubing.

 

[JAL3]

Then came the moment of truth. I took out the tap and started to thread it into the hole. It seemed to bite and the threads seemed to take.