Tuesday, 19 May 2015

Myford Super 7

I still don't have a proper workshop but I do have a new lathe. New being a relative term of course. The Myford Super 7 that I mentioned months ago has now been completely refurbished. It's a sad and somewhat ironic fact that now that the original Myford company is no longer in business, spare parts are much easier to get hold of. Sadly, I think that this is a temporary situation as the inventory will run dry in due course. I've replaced everything that was worn. Bushes, bearings, feed screws, you name it. If it was worn I got a new one. The lathe has been dismantled into its component pieces, cleaned, painted and reassembled. The only component that didn't get taken apart was the clutch assembly as it was fine and I didn't need to touch it. The bed and slides are in very good condition. The front vertical shear being the only part that required attention. I made a jig to run up and down the bed and scrape the front shear. It was located on the two rear shears and adjusted with its own jib strip. This was very successful and has removed most of the taper. I didn't want to take too much material off but the result is very satisfactory. I had trouble with the original 0.75hp motor but I found another one and got it professionally wired to the Dewhurst switch. I'm pretty confident that I could have done it myself but knowing when to not do stuff myself is a useful skill that I'm slowly developing. I've only made a few little bits and pieces on it so far but I'm looking forward to learning the new lathe on the next project. So far I'm loving the gearbox, the higher speeds, the extra rigidity, the long cross slide, the spindle lock, the really easy back gear engagement, the 360 degree top slide, the auto eject tail stock. I could go on but you get the idea.

A long bed Super 7, this morning.

When I sold the ML7 back to Mr. Middleton I included all the original spares it came with including the chucks as they all had matching numbers and my OCD meant that they must stay together. The chucks that came with this lathe weren't good enough for my standards so I bought replacements from a supplier in the UK. They are original Bernerd chucks with almost no use. I'm keeping the old 3 jaw as a roughing chuck but I've sold the old 4 jaw. None of the numbers matched anyway. I also bought a larger 9" face plate and I treated myself to a genuine Dicksons QC tool post. I've been using one of the modern copies that are sold on any number of engineering websites. I was never happy with it, the standard of accuracy just wasn't there. Of the 16 QC tool holders I had only 3 would lock down tightly, I was unable to use the remainder. The Genuine Dicksons model is a pleasure to use and all of the tool holders can now be used for the first time. The difference in quality between the two is like night and day.

I also discovered that the Myford cabinet that the lathe came on isn't. A genuine Myford, I mean. It's far too flimsy, almost useless and it would be impossible to level. So I've cut the top off and bolted it down to my work bench instead. I like having my lathe up quite high so I don't have to bend over too much and the raising blocks have made this easy to achieve.

I've been riding a lot but not a huge amount on the facile. I do take it out occasionally but it has been having some issues. I snapped the first spoke a few months ago and I had a really hard time getting the broken thread stub out of the flange. I was concerned at the time I made the spokes that stainless steel was not a good material for this particular spoke application. The spoke had fatigued and snapped flush with the flange. I tried to cut a slot in to the stub with my Dremel and use a screw driver to extract it but it was just too tight. In the end I drilled a 1.5mm hole down the centre of the 2.4mm spoke and then filed the remaining threads away. It too me two days and I needed to completely strip the drive down and remove the front wheel to do it.

I suspect that all remaining spokes are similarly fatigued so I'm reluctant to break another. 

During the strip down I noticed wear on the bearing surfaces, particularly those in the lever pivots and the live axle. In all cases the wear appears to have started as the result of an impact that has dented the bearing surface, this has then got progressively worse. This means that the nitrided 4140 is simply not the right approach. I'm going to have to replace quite a lot of components but I'll have to do some research first. I've made a few sets of BSA cones as my first trial of new techniques to harden bearing surfaces. They are machined from 4140 but have been through hardened instead of nitrided. I'll see how they perform before I invest too much time re manufacturing lots of parts.

A pair of BSA cones in hiding. Notice the cams for chain tension adjustment.

The hub will need replacing as it has 6 bearing surfaces. Given the spoke issue, I'm going to take the opportunity to rebuild both wheels as tangentially spoked. When I first stared this project I wasn't aware that Ellis & Co. made tangentially spoked models. I've since found an excellent description from 1888 and located two surviving faciles with tangential wheels, one is geared and the other ungeared. The spokes are in a most unusual arrangement with the front hub having just 6 or 7 holes in each flange depending on the wheel size and spoke count. Each hole housing 4 spokes. I'll provide full details in due course. I was hoping to be doing my big ride about now but I'll put it off until the bike is repaired. I'm reasonably fit at the moment which is a great irony.

So the first real project on the new lathe is going to be making a rim roller. The rims currently on the bike aren't the right profile and for various other reasons I want them off my bike. I've been collecting parts for the rim roller for a little while and I hope to be able to start it soon. Both my giant son and Kung Fu Pete have expressed a desire to own a racing penny farthing so I'm going to need to be able to make some really nice, light rims in various sections. Both of them being unnecessarily tall means that I can make some huge bikes, probably 60" or so. Kung Fu Pete has also taken on the project of getting rubber tyring in various sizes made locally. I am extremely grateful for this as I simply don't have time. He's had a sample made that shows promise. We're learning all about exciting things like the shore hardness of rubber and what extruding dies look like. This will all be the topic of future blog entries.

In other news, we've had both sets of parents here over the summer. My lovely wife's parents weren't too happy when I had a 9" face plate, a Dicksons QC tool post and a pair of chucks delivered to their address in the UK to bring over for me. What's 15 kg between family members for goodness sake? My parents only left a short time ago. I needed to go out to the garage to count the Super 7 when they left as my Dad has always wanted one. Being a long bed model, he wasn't able to fit it into his hand luggage though.

In more other news, I finally got around to making a decent size trebuchet as a garden feature for the kids to play with.

Garden furniture.

We're fortunate in that we live on a hill and have a good half a kilometer of our land between us and the public road. It's a work in progress and it still needs more tuning. Adjustments to the sling length, pouch shape, counterweight, connecting rod length and the angle of the release hook all effect the trajectory of the missile. We're probably at the upper limit of what the frame will support with a 100 kg counterweight but by tuning we should be able to hurl a 1 kg rock out to 200m (~650 feet). We can reliably throw to 150 m at the moment. As my lovely wife commented though, with the tuning and the addition of weight, it's gone from a fun toy to a genuinely lethal weapon. I threw three rocks down the field this morning before work just because I can. There's something about it that I find immensely satisfying.

My giant son made a video of it in action you can see it here.