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Post by mackintosh on Jul 30, 2007 16:14:44 GMT
Hello All I am about to make my first expansion links for my Tich. Do you have any advice on cutting / machining the slot. I have a amolco head on the Myford and a rotary table. But have also been advised to cut and file by hand. Any thoughts would be appreciated.
Bob
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Post by spurley on Jul 30, 2007 19:55:24 GMT
Hi Bob
I used my Chester mill and a rotary table to make mine, however I did have a couple of 'whoopsies' along the way! My fault in that I didn't clamp the material down rigidly enough. The other advice I'd give is to use a cutter smaller than the width of the slot and make two passes altering the cross slide setting to suit. I found high speed good too. Finish off carefully to form the square ends with Swiss files.
As LBSC advises; make the slot first, then file/machine the exterior to size and shape. Not so much work down the pan if you make a mistake. Much easier to hold down as well!
Cheers
Brian
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SteveW
Elder Statesman
Posts: 1,399
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Post by SteveW on Jul 30, 2007 21:15:16 GMT
Bob,
Bare in mind you've got to make two of them and if you go down the filing route consider making a a filing jig with the two curves (con-cave/vex) and both sides properly reference to a repeatable point and harden them.
It could be a whole lot messing about this way and a lot more controllable. Also drill the corners.
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Post by baggo on Jul 30, 2007 23:34:40 GMT
Hi Bob,
If you've got a rotary table and a way of milling the slots in the expansion links then I'd do it that way. In my opinion you'll get a more accurate result that way. I'd certainly shy away from filing the links by hand! As Brian says, use a smaller diameter cutter than the width of the slot and finish both sides separately. If you use a 3/16" cutter to cut a 3/16" slot you will end up with it being oversize and probably uneven. At the end of the day it does not matter if the width of the slot is not exactly to size as the dies are just made to suit. You can also machine these on the rotary table to get the correct radius.
John
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Post by ron on Jul 31, 2007 9:04:02 GMT
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Post by mackintosh on Jul 31, 2007 15:53:09 GMT
Thanks for all your advice. Having weighed up all the pro's and con's I am going to try the milling option. As it happens I have a 5/32" end mill, if I drill a 5/32" hole at each end of the slot I should be able to use the holes to check the setup and it will give the cutter a run off. Then I can use the 15 thou each side to clean up the slot. (sounds good typing it here anyway).
Thanks again Bob
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Post by 02jcole on Jul 31, 2007 17:17:23 GMT
Hello,
Another option is drilling a small off centre hole in each of the four corners of the expansion link, i.e right on the corner, not compensating for the size of the drill. You can then mill to size without having to worry about the corners not being 100% square, thus binding on the die block. Also you can make your die-block round instead of square, I know someone who very successfully made a round die-block out of PTFE.
Regards James.
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Myford Matt
Statesman
There are two ways to run a railway, the Great Western way, and the wrong way.
Posts: 621
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Post by Myford Matt on Jul 31, 2007 20:58:49 GMT
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Post by mackintosh on Aug 1, 2007 7:40:31 GMT
Hello MM Thanks for that link it's added some extra ideas .
Bob
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Post by ausdan on Aug 1, 2007 12:08:17 GMT
There is a large 2-6-0 7 1/4 loco running in my home state, and the gentlemen has been running a roller bearing as the die block, for quite a many miles (or KMs just dont sound right in this phrase) has not issues since installing it and has ran alot longer than the traditional guide block.
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