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| jcs0001:
Onward we go: I roughly centred the 6 in. blank in my 4 jaw (since I only need 5 in. diameter eventually) and centre drilled it then step drilled up to a 1 in. hole right through. I have nothing bigger than that in drills and besides my lathe wouldn't be happy pushing a bigger bit I expect. So then it was off to the boring bar. Only I have a hodge podge of boring bars and of course the bigger one was just a little too big and the smaller one just long enough to go through. I have one other smaller one but it takes a 1/8 in. toolbit on either end and of course I can't get them locally. Just ordered a couple of hss 1/8 in. blanks but it may be a week or more to get them. Anyway I'd better get at making a couple of boring bars as I'm sadly lacking different sizes. Using the smaller boring bar I was able to work the hole up to a size large enough for my bigger boring bar. Now I need to bore it to size. The shoulder is to be 1.811 in. in diameter and the bored portion for the threads will be "about" 1.583 in. The reason I say about is that the measured distance across the internal threads on my faceplate is 1.583. If I do the calculations for thread depth based on a 1.75 in. x 8 tpi spindle thread then the bored diameter before threading will be 1.615 in. and if I do the calculation based upon a 75% thread I get 1.635 in. (formula for thread depth - 0.6134/8 tpi formula for bore = 1.75 - (1.0825/8tpi) formula for 75% thread = 1.75 - (2 x depth x 75%)/100) I got these out of Screwcutting in the lathe by Martin Cleeve. I am inclined to go with the smallest number - ie the measured one on the faceplate. Any other suggestions would be appreciated. Ralph: Thanks for the suggestion about soldering a ring on and turning it down again. I will keep it in mind. Lots of ways to "skin a cat". Yes it is a large chunk of steel - they showed some 5 in. in inventory but couldn't find it so I ended up with the 6 in. piece. He had a great deal on a 6 in. piece that was just over double the thickness but I couldn't see splitting it with my equipment so I passed on it. John. |
| John Rudd:
Get some thread gauges...Least then you can tell if the thread is the correct depth on the male portion..Once that is correct you can use it to gauge the fit in the female part...( Even though you could try and use the existing backplate as a gauge for your male test piece, it gets you into the practise of precision rather than best fit....) If you go the soft solder route make sure you use coolant or dont overdo the cutting...Generating heat will soften the solder and dislocate the ring... Just my 2 cents... |
| jcs0001:
John Rudd - thanks for mentioning the concern about soft solder and heat from turning. I didn't end up using that method but will keep it in mind for future. I did use a thread guage on the male portion and the threads were good. After a number of hours of mostly turning, I have the new back plate made and mounted on the chuck. The back portion needs to be thinned out but it is functional as is. There are 4 bolts holding the back plate to the chuck and using a pointed transfer screw I was able to line the holes up perfectly with the threaded holes in the chuck. No need to drill them slightly oversize - :D It took a long time to turn the 6 in. plug of ductile iron down to approx. 5 in. in diameter and would have been easier had I been able to get a chunk of 5 in. diameter material. John. |
| John Rudd:
Very good...Glad you managed to resolve any issues you had... I have two new CI blanks that need the same treatment...although my Chester has an M49*4 thread.... |
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