Model Engine Maker
Help! => Specific Engine Help => Topic started by: kev on December 23, 2015, 04:59:24 PM
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How on earth do I machine a centre hole this shape other than making a broach I cant think of a way but it must have been done a thousands of times and more
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File :)
Whats the material as a broach is not hard to make and may not even need hardening depending on what it has to cut.
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there are two parts with this hole, one is gun metal and the other cast iron. A piston rod moves is the same shape and its just to stop it rotating so maybe a file would be enough :)
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I used a file to do it, but I somehow made the flats on the cast iron section on the wrong side. I had to modify the return trip lever to fit the shaft now turned 900.
Dan
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Kev......following is an image of a model Stuart steam hammer. :hammerbash:...... is this the part in question?....
If so this builder appears to have the flats on the rod at 90 degrees to the Drawing
If you could manufacture a round broach, then machining it back to a 1/2 round profile [+ reduced width] ....assembling the components & broaching both passes in both components would be the obvious procedure
The 77733 x 7/16" image in 'special shape' format is what I was trying to explain......
Clearly the design is to achieve an anti rotation of the hammer head....so if the equivalent flat surface are is provided by one larger flat over two shorter flats could be worth considering
Certainly a high wearing component assembly :wallbang:
Derek
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Cool now I see I am not the only guy who made that part wrong..... I see that the builder did not make the lever longer to ride near the flat as I did to cover my goof.
Dan
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yes thats the part. I have been studying it more and i dont think the accuracy is so critical now as there is a large cavity that you stuff with graphite yarn so im thinking to try a simple file once the two parts are together
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I ground flats on a round file intended for a die filling machine. I now years later have a die filer so it would be a simple and quick operation.
Dan
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A broach similar to teh one I made in teh following thread may do it, just put two flats on and harden for teh iron casting
http://www.modelenginemaker.com/index.php/topic,5248.msg103906.html#msg103906
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thanks guys, I think I will try the broach first its only going from 7/16 out to 1/2 inch so there is not a lot of metal to remove