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mikes-models.com |
mikes-models.com |
When visiting Harrogate Model Engineering exhibition 2008, one of the purchases I wished to make was a pair of ER25 collet chucks. One for my variable speed Turner 280GV lathe, and the second for my Myford ML10 (or 7 if I keep it after refurbishment). The salesman suggested that making an adaptor was a more cost effecient way to go, and I thank him for being so helpful. One of the more urgents tasks I have for using the ER25 collet system, is to hone the cylinder liner for the Mills diesel engine I am building. So I decided to use the Turner first and make the adaptor later. But the best laid plans as they say, thought otherwise. I gave the saesman the dimensions as per my Chinese manual that came with the lathe. Unfortunateley these seem incorrect........and it didn't fit. So I had a choice, did I send it back and wait for a new one to arrive? Did I make the Myford adaptor first and wait for the correct on to arrive? Or because it wasn't the suppliers fault, and I needed to make an adaptor in anyhow, should I make adpators relevant to both lathes? Well I have decided I would make two adaptors and they Myford would be the first one I would do. I had a cast iron blank face plate unused foor the myford and this would save me cutting any threads so I would use this plate for a relatively easy project. My first, second and third mistakes was to think it was a simle 5 minute job and therefore no need to plan. Wrong. Common sense would have said, if I had sat down and thought about it, that the recess in the bought chuck, would mean that I would remove material from the outside to in. So what did I do? Yup, I started to machine a recess in the centre of the plate and was pleased when trial fitting a shallow cut that the fit was good. Only to realise that I was doing it the wrong way around and lost the beniefit of locating the chuck onto an outward facing raised area. So, after mucking up this attempt I did what I should have done the first time, and planned what I would do,making a drawing and a machining order. As I have quite a good stock of aluminum, I looked out a suitable piece of stock. I needed to face it off, centre drill and bore it out to size. This went well enough and I wasn't worried about cutting the threads as I have done this before with a reasonable level of success. Oh how wrong was I! I got the bore smooth and within 0.001" and when cutting a light first cut, the threads per inch (TPI) were also correct. So all that was needed was concentration and keep going. After scrapping this blank and then another because the threading was going wrong I decided to give up and review my books to see what I was doing wrong compared with the threads cut for the little Mills crankcase. The following day, after reviewing all the books there was only one thing that I did differently than the methods descibed. Because the Turner doesn't have a thread screw indicator, I used the control that decides the direction of the leadscrew to maintain the position of the tool to the thread. And in theory I can't see what is wrong with that. So as this was the only variation that I could see I decided that I would stop the lathe at the end of the run, reverse the direction of the motor, Move the topslide clear for the revesre journey, then start the motor. And that was that! Everything worked fine and the threads were formed easily and to a good fit. I wonder now, whether I could have achieved better results with the crankcase? Or whether the finer threads make a difference. One thing is certain though, using the leadscrew direction change control is not the way to go in the future. As soon as the threads were finished I tranfered the blank to the Myford so that all future machining would be concentric with the lathe itself. The only other snippet was how I trannsferred the location of the chuck's retaing screws to the new adaptor. As you can see with the gallery pictures I did a sort of brass rubbing on a piece of paper. Then cutting this paper I used it as the template, sticking it on the adaptor to help when drilling the holes on the milling machine, to ensure they ran true. So, a simple job, turned out to be a valuable learning experience. One I am sure will be of beniefit in the future. |