Edgar T Westbury’s Seal 15cc 4 cylinder petrol engine – update 3rd March 2009
After several weeks getting the Myford ML7 lathe refurbished I have been desperate to get back to the Seal engine build. Taking my own advice for a change, I wanted to get one of the worst (in mind at least) aspects of the build out of the way early on, that of the camshaft. I have made the fixture to turn the cams on the lathe to a design by Steve Huck’s but now comes the metal turning itself!
Looking at the plans as supplied I cannot get my head around the dimensions given regarding making the camshaft blank. Feeling a little under the weather I thought that the best way forward would be to make up a machining aide memoir (similar to the approach I used when designing and making the Chess set featured in Model Engineer, issues 4345,4346 and 4347 : 2009) and try and make sense of the drawing. Eventually I thought I was there and would check my dimensions against a broken camshaft given to me by the seller of the casting’s set.
I intend to make two camshafts initially. The first will be made from stainless steel and used to see if I can get away without hardening the shaft as recommended by one or two HMEM forum members. The second would be made from steel which I would subject to the powder hardening process. I fully intend to make other camshafts for this engine later on when trying to improve performance. I hope to learn a lot more about small/miniature cams and their performance over the coming years. Don’t ask me why but the subject does ‘rock my boat’ as they say.
Anyway I chucked a length of ½” diameter stainless steel which measures 0.499” and since I am working to a tolerance of +/- 0.001” I will not take a surface cut. Because of the tolerance limit I have set myself I thought I would take time to check that the Turner lathe I have has the tailstock in line with the chuck. You may ask why I haven’t done this before and the simple answer is lack of experience. I also believed (wrongly) that the accuracy would be as good as it got when leaving the factory so leave well alone, in case I mucked it up. Its only the rebuilding of the Myford lathe that has given me the confidence and perhaps techniques, to check something I should have done as soon as the lathe was received.
I have always suspected something could be out of line from some long cuts done earlier. When using 2 DTI’s to check alignment I couldn’t believe it was over 4 degrees out over about 7 inches! The remedy was simplicity itself, with the tailstock moved to the correct position by using the adjusters, before being locked off. I decided to run the lathe up and run the saddle up and down a couple of times and recheck, finding everything now running true. I kicked myself for not doing this earlier. If I am fortunate enough to ever buy a new milling machine I will carry out checks on everything before even switching it on! Fear of the unknown has a lot to answer for!
With the confidence that the set up of the bar was running true in the 4 jaw chuck and in line with the revolving centre in the tailstock, I set too turning down one end to the 0.250” diameter required. Steve Huck when designing the camshaft turning fixture, recommended that I should leave extra at each end of the camshaft to be removed at the end of the cam profiling. So I allowed enough to clear the centre with the turning tool and then using the DRO moved to what I thought would be the correct position to cut the gap between cams. All was going fine, if slowly until it came to cut (or in this case leave) the second inset leaving the cam blank alone. Checking before I made any cut something did not seem right. I checked the measurement and compared them the broken camshaft and whilst the width of the cam was correct, the gap between them was not.
No matter how hard I tried I kept tying myself up in knots. I got so confused that I gave up and decided to call it a day. It was only when laying down this afternoon that by using graph paper to scale, that I could work out what the dimensions should be. Blonde moment over I have made a new sheet so when I fell well enough to have another go, I should at least know where I have to cut. I don’t say I will get it right, but I know now what needs doing but I thought the same this morning so don’t get too excited! To be contd.