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Thread: Replaceable shear pins
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28th Dec 2017, 10:32 PM #31Senior Member
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Steve, do you need all the 7 adjustment positions? Leaving the original pin and broken pin as is, you could drill and set a new pin to engage the next hole in the arc. You would only lose the extreme adjustment position. Trying to remove the pins seems pretty difficult.
Pete, I often machine “dowell” features from solid to locate parts in assemblies. It is a quick, accurate, economical procedure. By my reckoning the entire round pin “Mr” could be machined in about 5 minutes, pins and all, plus a little extra to face the underside and cut the stepped keyway. Provided the parent material had the right shear strength, I see no problem.
The only puzzle to me is why $600
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29th Dec 2017, 12:07 AM #32Most Valued Member
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G'day Neil, yes you're absolutely correct, and that's the way the original is designed. However it's wasteful on material and it seems by the change the manufacturer agreed, as they changed the design.
To be absolutely clear however, my criticism wasn't of machining it in one piece, it was machining THAT particular part in one piece. I could see the shape of the pins and the chamfer, just to name two features I can think of without going back to look for possibly more, would make THAT part somewhat difficult to machine. The one with the integrated pins had different shaped pins (not round) and the chamfer didn't interfere. It may seem like trivial points, right up to the stage where you need to out them in and go ... "ah, that ain't gunna work"
Why $600? Because they can.
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29th Dec 2017, 10:10 AM #33Diamond Member
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20th Jan 2018, 04:02 PM #34Diamond Member
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Well the second pin failed yesterday( I felt this one ) so now I have refitted my original bushing with one pin left....
I also managed to carefully drill out the stubs of the pins ( without damaging the bushing, and also drilled a smaller hole through, so I can drift out all future broken pis...lol
I have ordered some 2.5mm pins, but I suspect the original pins were 2.80mm ( difficult to measure accurately )with 3.00 holes. Will see if they work. A bit difficult to machine 3.00 mm down to 2.80 mm on my lathe....
Thinking of using an 'adjustment' thread lock compound to hold pins in so I can still force them out when required.
If this repair works, I will move on to the bushing I'm using now. See if I can get a spare ready.
Steve
20180120_124932 (Medium).jpg20180120_124940 (Medium).jpg
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20th Jan 2018, 10:46 PM #35Most Valued Member
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I didn't get why you can't measure the diameter of the remaining pin?
Thread lock will release with heat, just avoid specific high temperature versions to make it easier. Heat the bushing up and drive the remainder of the pin out.
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21st Jan 2018, 11:34 AM #36Diamond Member
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The problem was getting an accurate indication of the original pin size. Due to wear on the pin, at every point of rotation, I was getting a different reading.
I had no idea what the original clearance tolerance the manufacturer was using. I guess I am being as careful as I can.
It sounds silly when you say it like that....lol
I'll do some digging on thread lock compounds.....ta.
Steve
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21st Jan 2018, 01:18 PM #37Most Valued Member
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It probably doesn't matter what the original was, if the hole it's registering in is also warn, you simply put in a pin to fit the hole. Given you've already drilled the hole you've pretty much determined the size of the pin you're using. Thread locking or other anaerobic fixing adhesives work in the absence of oxygen. The upshot of that is they won't cure correctly with a large gap, nor are they meant to be mechanically sound. They will somewhat gap fill, but are really there to hold the part in place. It's a bit like dropping an M8 bolt in an M10 threaded hole and wondering why it drops on the floor Each thread is mechanically sound, but they require a fit close enough to engage and work.
Ideally you would now ream both holes to suit a pin (probably 3 mm), insert the pin in one side with thread locker, and call the job done.
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