Thursday, August 29, 2013

Pivots

One of the difficult tasks on my Eden iris today, fixing the pivots. These 20mm diameter tubes need to be exactly in the middle and exactly vertical, so how to do it?

At first I thought I'd drill an 18mm hole then sand around the rim, gently expanding the hole until I got a perfect tight fit. I used a blade drill, here:

I quickly discovered that these wobble and shake the wood horribly. The nice bore type thing (I think it's called a Forstner bit) was much better but I didn't have an 18mm one. Anyway, I realised that I could stop much of the vibration by drilling a big pilot hole first with the biggest drill I could find, that cleared away most of the actual solid wood, making it less effort for the blade to cut a hole.

So, I had an 18mm hole that wasn't quite in the centre (never would be it's impossible to get these things perfect). I took a cylindrical file/rasp and started to finish off the edge. After about 10 mins of mashing the chewy M.D.F. I realised that this was going to take a long time AND probably not work, the wood texture was not ideal for rasping in this way. The end result would almost certainly not be clean or vertical.

I decided a sanding drum would be better, but I didn't have one that was tall enough, so I made one from metal tubes, glueing some sanding drum bits to it...

It was good enough to work, it still rather mashed the edge a bit but was relatively clean. When I'd cleaned out the hole to make it 20mm I found that it was a worse fit than drilling a 20mm hole from the outset!

So there seemed to be no perfect way. I decided to drill a 20mm hole directly instead. There was a gap and wobble, but thought that I could glue the pivot with epoxy resin (or clay) and set it perfectly that way. But how to make sure it was vertical and central?

For centralness (is that a word) I drew rings around the 20mm guide (22mm) and used that as a guide where to place the tube. For verticality I screwed a metal collar to the pipe...

It's deep enough so that the edge of that should be at a right angle to the pipe, so I then fixed that into the hole, clamping the collar to the wood...

And there we are, one pipe that's about as vertical and central as I could get, I think. Time is short so rather than consider infinite possibilities of getting it perfect I went for the best I could think of at the time. Now I'll glue the other six. It will probably take me all day just to attach these seven tubes!

No comments :