I could turn cases up to 98mm and ~30" in length for you. I'll need a bit of lead time though.

Edward

Easiest case design to work with is the Kosdon and AMW style snap ring case. Also, cases must be designed to fail axially, meaning that forward or rear closures should blow out in the event of overpressure, never the case. I believe the use of steel is also banned.

You might try Vic Davis - he owns a full machine shop. However, be aware that a fully machined case requires decent tubing. The standard is drawn tubing rather than rolled/welded tubing. MUCH more expensive. Also, it is non-trivial to machine large cases. Most common engine lathes top out at 48" of workable length between centers. Vic and I discussed machining a 6" diameter case for a BALLS project and found that it would be cheaper to buy one given the length limitation of the lathes we had available and the cost of the drawn tubing.

James Russell and Ed Wranowsky probably have the most experience in the club with this sort of thing.

Ed, Warren, Thanks for the reply. Edward P.M. sent.

I am looking at making a set of 54mm cases at first as this should cover all of my needs for quite a while. 75mm would be nice in the future. I am on no time table that things have to be done by. I am happy to pay for quality materials (DOM and the like). I just figure that at the prices I'm seeing for a set of 54mm cases the machining seems to be the dominant factor. Also I just want to do it myself to the extant I can.

Thanks for the input. I am just getting started at this EX thing and appreciate any help from the guys that have done this

Tom,

You've chosen the one size that is better to buy than to have machined. 54mm tube is 2.125 x .095" wall. It used to be a standard size but is not found much outside of 5000'+ mill runs. This is how Skyripper made their 54mm motors - they had a mill run done of the tubing. You have to use 2.125 x .095" wall for standard liners to fit. If you go with 2.25 x .125 wall you can't use standard liners and you have to turn the OD to fit. Loki uses 2" SCH 80 pipe for their motors and turns the OD down. Pipe isn't held to the same tolerances so you end up making your closures and nozzles to fit your cases and hope they interchange with other 54mm hardware. AMW had a mill run of tubing done also.

In the beginning of HPR motors there was a disagreement between the people who made the paper and the people who made the motors. The paper was sized for 75mm (2.985" OD) and the motors were made out of 3" OD x .125 wall. The paper people didn't budge so the motor people turned down their casings. In the long run it would have been easier for the paper people to just upsize their tubing to fit because that is a less costly operation than machining every motor case. Sure you'd ruin some stock, but after that you'd be good.

When I do 75mm motors, I keep the OD at 3 x .125 so I don't have to turn anything down, then just use centering rings instead of a motor mount. Less weight that way also 🙂

Here is a little blurb about tubing sizes, etc.

29mm - 1.125 x .065 OR .058 wall tubing - No turning down, standard liners for .065 wall

38mm 1.5 x .083 OR .095 wall tubing - No turning down, standard paper for .083 wall (Kosdon/AMW paper for .095 wall tubing)

54mm 2.125 x .095 tubing standard size, standard liners, no turning down but very hard to find.

54mm 2" SCH 80 pipe, have to turn down OD, liners may/may not fit and interchangeability is questionable.

64mm 2.5 x .125 wall - No turning down, standard paper and liners available (but harder to find)

75mm 3 x .125 wall - have to turn down OD to 2.985, standard liners and paper available. AMW tubing is drawn to spec so you don't have to turn it down.

98mm 3.875 x .1875 wall. This starts life as 4" OD x .25 wall tube and is turned to fit. Standard paper and liner available. AMW tubing is drawn to the 3.875 so they don't have to turn it down.

After this size you don't generally turn the OD. It isn't cost effective.

Edward