Tuesday, 18 March 2014

Levers part 2 - Beefy Bottom Mounts

Hoorah, I got the welded levers back from Pete.

As usual, he has done a brilliant job TIGing them together for me. I have some reservations about strength and the nature of welded 4130 so I'm going to get them normalised before I go too much further. If they break in use I'll have a re think about how to make them again.

This week I'm going to make these bits.

They are the bottom mounts for the con rods and are really quite beefy.

Starting with some scrap 3/4" mild steel plate, mark out and bore a counter sink at the correct depth.

Then using a series of drilled holes remove most of the excess metal from the mounts. 
Drill bits are cheap compared to milling cutters...

Then bolt directly to the bed and mill the final thicknesses of the mounts. 
The top part is just a tad thicker than the lever at 0.675" and the bottom part that the conrod bolts to is 0.375".

Next flip the mounts over and again bolt down square to the bed. Mill the sides to the correct width.

Then using these new milled surfaces as the reference, mount in the machine vice and mill the top of the mounts.

Next mill the slots for the lower con rod bolts. 
Recall that these bolts had flats machined on them. These flats locate into these slots.

Next mount at 45 degrees and mill away most of the excess of the upper thicker section...

...tidy up with files.

Then mark out the outer shape of the mounts and get busy with the hacksaw and files.

The last operation is to machine a curved slot into the upper thicker section so that the levers are wrapped by the mount, this needs to be a nice fit so that the brazed joint will be strong. Careful measuring of my Myford and the lever radius means that I can just turn these by mounting on the faceplate. It really is pushing the lathe to it's limits though. Simply bolting the mounts to the faceplate won't be rigid enough, the interrupted cut will soon knock the mounts out of alignment and make me a bit grumpier. In one of those rare moments of serendipity, I discovered that the slots in the faceplate are the same width as the slots in the mounts, This means that I can make some spacers that will rigidly locate the mounts onto the faceplate. By drilling a hole through, I can very securely bolt the mounts at the correct radial distance so that the bottom of the cut is the inner radius of the levers.

Very securely held in place, the correct radius can be adjusted by sliding in or out...

...and then bolting up.

With such a large diameter of cut, I needed to slow the lathe right down to successfully machine the groove. The interrupted cut meant that the feed in had to be very gentle.

I was also cutting almost blind, in that it was very hard to see where the tool was contacting at any time. 
I found that placing some white paper beneath the tool and viewing directly downwards with one 
eye shut wearing magnifying glasses and standing on one leg helped a lot.

Once I got close to final size and depth, I used the same trick that I used when filing the neck to fit into the backbone. The levers were coated with engineer's blue and slid around the groove, the marked high spots were then machined off and the process repeated.

I'll start on the lever pivots next week.

In other news, the strange fruit that was discovered in my garden has correctly been identified as an Akebi fruit. Thanks for that Christian. I found the vine that it grew on (we have a big garden) and discovered a few more, they don't grew on top but underneath a top layer of leaves which is why I've never seen them before. The plant, known as a chocolate vine, is classified as a noxious weed here in NZ. In the interests of scientific discovery I immediately ate one of the fruits, seeds and all. It wasn't too unpleasant, a little like melon, but had a bitter after taste. Later that evening I became slightly disorientated and nauseous. The following morning I had a mild headache and slept in a little later than usual, I seemed to be sensitive to light and loud noise. It must have been the space fruit, it couldn't possibly have anything to do with the beer I'd drunk to get rid of the bitter taste.


  1. Them akebis look like passion fruits that have been surviving on LSD water!


    1. Hi Stephen,

      Yep, my lovely wife thought they may be some kind of passion fruit. If you ever see one, I wouldn't bother eating it...