Thursday, 14 January 2016

Alright, Chuck...

Greetings all. If you are not from the UK, and specifically from the North of England, you are going to need an explanation of this post title. "Chuck" is simply a term of endearment, which is actually a contraction of "chicken"...but enough lexicography.

I have almost finished mounting the ER32 collet chuck to the backplate (see what I did there?). All that remains now is to drill the mounting bolt holes to join the chuck and the backplate together.

After mounting the D1-3 camlock backplate, I machined a register on it that is a very good fit in the recess on the back of the collet chuck. The collet chuck was then fitted to this register, ensuring a very high degree of concentricity.

Tony at has written an excellent primer on the fitting of chucks that can be found here:- I found this to be very helpful.

Here is a photograph of the collet chuck mounted on the backplate:-

 You'll see that the chuck has three bolt holes. These are tapped for M6. I cannot put bolts through the backplate into these due to the camlock studs. So I am going to drill these out to M6 clearance and then tap the front face of the backplate. The attachment bolts will then thread into this from the front of the chuck.

Machining cast iron is a very dirty business, as you can see from this picture. The swarf takes the form of fine chippings. Needless to say these can be potentially very injurious to the lathe. I managed to minimise the amount of debris by attaching the workshop vacuum cleaner hose to the toolpost. Had I not done this, my poor machine would have ended up buried.

The purpose of the collet chuck is to hold the tubes whilst the ends are being machined, as per previous posts. With the chuck mounted on a backplate, the full length of the tube can protrude through into the spindle bore. I may need to make a push fit insert for the opposite end of the spindle to act as a guide. This will stop any tendency of the tube to whip whilst the spindle is rotating.

This is all part and parcel of making ready to trial the tubular chamber fabrication method. Once I have the chuck finished I will need to look at making a system of stops for the lathe. This will hopefully ensure that all 60 tubes end up the same, within reason. I will also need to look at a means of uniformly bending the tubes, Again, this will involve a series of stops used with the tube bender.  

All of this has to be fitted in and around normal family and work life. So progress tends to be slow, though steady. Thank you for your patience and your continued interest in my project.

Sunday, 10 January 2016

Aspiration and Inspiration

Apologies, gentle reader, for the recent dearth of posts. I have been rather busy of late with non rocket engine related activities. However, I have managed to get a few hours in the workshop here and there. 

A brief summary of practical activities that have been progressed:-

Cutting jig completed and adjusted to cut square

New ER32 collet chuck in process of being fitted to backplate

I am also in the middle of writing an article on the automated indexer for the British magazine "Model Engineer's Workshop". If you are in the UK, do look out for it.

As for the aspirational and inspirational content of this post, read on...

I expect you are probably wondering what I am going to do with all of those tubes. Well, here is the photograph that provided my original inspiration:-

This frankly beautiful little tube bundle engine was built in 1970 by Maschinenfabrik Augsburg Nurburg (MAN) of Germany. I discovered it on the website of the Deutsches Museum. Sadly, there is very little information outside of who built it and when. My best guess is that it was some sort of technology demonstrator, and is of brazed construction. There is no information regarding what the propellants were or if it was ever fired.

The next two pictures come from the Smithsonian Air and Space collection in the US:-

This experimental thrust chamber was made by Reaction Motors in the US, in about 1947. It is reckoned to be the first attempt at tube bundle construction. I like this photograph because it shows exactly what I want to do. You'll notice that the tubes have been crimped or "booked" at the throat. According to the information provided, the construction is welded stainless tube. Obviously in a device that was intended to be fired the welds would need to run the full length of the tubes to provide structural integrity. Strengthening bands would also be required, like this:-

This chamber was built by Aerojet in 1948, and apparently was arrived at in isolation from the Reaction Motor's development. It is a much more complete effort, with manifolding at the head end and strengthening banding. Just look at the tube bending that has been employed to turn the fuel back towards the head end at the exit; it is almost like basket work! Also note the booking of the tubes at this point. There are no details of construction but I suspect this is brazed. Oddly the brazing does not appear to extend to the full length of the divergent section.

I would really like to learn more about these motors. If anyone out there has any more information I'd be glad to hear from them.

Progress is slow, as always. Finding these images has spurred me on though, and when you can see your goal it is generally easier to achieve it. Keep checking in for updates, and thank you for your continued interest.