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I actually set it up in the 4 jaw at this point. The reason was that when I set it up in the 3 jaw, I could not get the face running true AND the bore on center.
So then, on to machining.How to make a 5/8" close tolerance hole? I have seen some people stuff an undersize drill down the cast hole and then ream it, but that doesn't seem like it will guarantee a straight hole. No, I think the right approach is to bore the hole out. I do have a 5/8" reamer already, so I may well elect to bore close to size then ream to final, or I may choose to bore the thing to final dim. I don't have a powered down feed which is not necessarily an issue, just means the rate of feed is not constant.So, went to set up then remembered that while I have a perfectly serviceable boring head, I do not actually have a boring bar to fit it. So I have to procure one or make one. I may well make one to take one of my inserts. Don't know yet.In any case I decided to make something else today while I ruminate on that.So that's today's shednanigans.
Funny that Larry - I was making a revised sketch of the valve today, incorporating your threaded attachment method for easier adjustment - and as I looked at the PMR drawing I had to laugh. If I issued a drawing for a part with an OD of .624” +0 / -.001, and issued 5/8 round bar to make it, the machinist would happily come snd kick my posterior seating cushion. I’ll be starting with 3/4” to give myself a chance.