Recently I found myself in need of some machined specialty parts for a rocket project that has been on my bench a little too long. My two-stage Terrier-Black Brant IX has been idle for about a year now due to other priorities at home. However, I have now blown off the dust and have started poking around figuring out where I left off last. I had two problems that I needed to solve with some machining by Front Panels Express. I pulled up Front Page Designer, the free software from Front Panels Express, which I have used in the past for similar applications per a suggestion from Vern Knowles. Within an hour I had designed three pieces, priced them, and ordered them all from the design software. Two weeks later my pieces arrived in the mail.
One of my issues has been figuring out how to connect the upper and lower stages and have good motor retention for the upper stage. I cannot use an Aeropack retainer as it would interfere with the interstage coupling. I figured out that with a couple of aluminum rings I could have my motor retainer, and a strong interstage joint. I found that they have added some additional thicknesses to their material set -- up to 10mm thickness 6061 aluminum plate can now be used (previously only up to 4mm was available). This works out perfectly as 10mm is the ideal depth for an Aerotech rear closure ring. I created two 76mm rings, one of 10mm thickness with a 57.25mm opening as a spacer in which the motor retaining ring will fit, the second of 4mm thickness as a retaining ring with a 54mm opening. The 10mm plate only comes as unfinished aluminum, or anodized with a natural finish. Not a big deal since it is just a spacer covered by the top plate. The top ring I made with a black anodized finish (same price as unfinished) and engraved my TRA and NAR numbers for an extra ~$1.50. The cost was around $40 for the spacer, and $27 for the top ring. For any additional of the same size one only has to order the top ring and just use the spacer as a generic, interchangeable part between rockets.
A second issue I had was creating endcaps for a 3" diameter avioncs bay. I wanted to use a section of aluminum tubing that I had from another project. I messed around with FPD for a while, then sent in the file to Front Panels Express to see if I got it right. Although my design would have worked, the customer service rep. tweaked my file to show me a another way to achieve the same result. The result was much cheaper as it avoided a tooling change and backside processing fees. For this part, I used a 10mm thick panel to create a disc 76mm in diameter (inner diameter of airframe tube into which the avionics bay will fit). The trick was using a circle-in-circle of outer diameter 80mm and inner diameter 74mm with a depth of 4mm overlayed onto my 76mm disc creating a lip. This endcap now fits into the 76mm aluminum tubing leaving a 6mm thick cap. I had a center hole drilled and tapped, and had two other smaller holes drilled to use as pass-throughs for the e-match wires. Each cap was approx $45. I will later post some pictures of the parts in-use once I get a little further in the construction.
