Monday, 11 November 2013

Back to the Merry Mixer - At last...

After a bit of a lay off it is back to the Merry Mixer. We got as far as a test assembly and discovered that it was not only unstable but the whole thing looked, well, ugly! Sue's chair spiders were great, it was the proportion of the top support arm assembly and the central column that looked wrong. Compound that with the fact I was having problems getting the lower arms rigid and the models was getting to be a problem. Deep breath, time for a rethink.

A mock-up proved it was not going to work...
It is hard to go back to the beginning but after a lot of mucking about I decided that I was not going to rectify these basic faults and out can the spanners. The central column has been dismantled as has the top support arm assembly. With help from the guys on Rust Bucket, I have managed to sort out the lower arms.

 The problem with the lower assembly was one of rigidity.  When I first conceived the design I had it in my head to just bend some strips and brace the sides of the arms. It wasn't until I came to do it I realised the holes would not align conveniently. It was suggested that I used the 5½ inch slotted strips (Part No.55), suitably formed to fit, and and make use of the slotted holes to make the fixing the the arms. Apart from the fact that we only have a few of these and that I am reluctant to bend them, it would still have meant the end holes would not align. His suggestion reminded me that the formed slotted strip (Part No.215) is, when flattened out, longer than its stated 3 inches. It fits perfectly to act as a brace.

The final bracing
The addition of that part to each of the three joints alone makes a substantial difference. However the leverage is so great that the assembly is still flexible. The addition of tension braces, suggested by another contributor to Rust Bucket, has solved the problem completely by turning the the hub into a triangular torsion 'box' The only flex now is in the length of the girders which is minimal and I think will be acceptable - time will tell.

That seems to have sorted out the lower arms, now it is back to redesigning the central column with a bit of shape and sorting out the top support arm assembly...

The Rust Bucket thread regarding the lower arm assembly can be found HERE. There are even more suggestions on the Rust Bucket thread and I my take up even more ideas if the assembly still proves problematic.


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