Helped a friend by making a couple of pins for his excavator. He supplied the metal. He found a 7 ft bar 3 inch diameter with a bend in it at the scrap yard. Pins were to be 2.940 in diameter with a series of grease holes drilled across and a center grease nipple.. the turning went well, turned like chrome. A machinist friend said he thought it was 4140, by the way it turned. Feeling kind of smug, thinking I got this, piece of cake, let’s drill the center hole while chucked. Omg!,,,, part way in, case hardened a hole. Sucker, thought I had been going slow enough with lots of magic tap. Numerous attempts to get through the case hardened end failed with every bit buggered up. Finally got a tip to use a concrete carbides tipped bit,,,, success.... now to finish the 3 .5 inch long hole. Peck drill with a .050 depth till the end. Finished center hole,and then tapped for a grease nipple. Man this was super tough, took for ever to tap, and then I only got a 1/2 dozen turns of the nipple to thread. Off to the mill to cross drill. Same crappy performance ,till I started using a pop bottle to flood the hole with coolant. Managed to finish with great results, but sure learnt a lot about drilling. Summed up,,,,,, need to set up a flood coolant system, buy The BEST bits possible, and keep speeds low. My general ramblings here are nothing for the pros but for a hack like me there are a couple of nuggets of gold. Don’t skimp on bits, squirt bottle with coolant in a pinch, and concrete bit to punch through case hardened spot.
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Excavator pins
- Thread starter Shoprat
- Start date
Ironman
Ultra Member
Next time someone says 4140 you will remember it work hardens as bad as stainless. I have to do that aoccasionally if I can't get out of it, and I use good bits and pull out and re-sharpen, even if I think it doesn't need it.
Cross drilling excavator pins will cause them to break at the hole eventually. I prefer to drill the outer sleeve the pin works in, and if it is in the dirt at the bucket, weld a guard ring around it.
Cross drilling excavator pins will cause them to break at the hole eventually. I prefer to drill the outer sleeve the pin works in, and if it is in the dirt at the bucket, weld a guard ring around it.
I'm having trouble seeing why the pin would break at the drill hole. Unless it is pinned at both ends (which it shouldn't be) or isn't regularly greased, the drill hole transmits no forces and shouldn't fatigue the pin at the hole. I'm thinking maybe your pins are mounted differently to what I'm used to seeing.
I'm having trouble seeing why the pin would break at the drill hole. Unless it is pinned at both ends (which it shouldn't be) or isn't regularly greased the drill hole transmits no forces and shouldn't fatigue the pin at the hole. I'm thinking maybe your pins are mounted differently to what I'm used to seeing.
Ironman
Ultra Member
Like you, I have trouble seeing why, but I have made a lot of pins to replace broken ones. I have resorted to talking people into using cold rolled, as I think now that the characteristics of 4140 are to blame. Thousands will disagree, but all I have is my experiences.
The same metallurgy that causes work hardening is the culprit.
The bushings on the last Komatsu I did had 52100 steel bushings that the pin works in. Something has to be sacreficial, and changing a pin is easier than bushings. A 4140 pin may break, and sure will wear against the 52100 steel, and so will cold rolled.
Experience is what it is. Can't argue with the simple fact that it happens.
I'm still guessing somebody thought that if a retainer bolt at one end was a good idea then one at each end was better.
In my experience, the pins end up frozen from lack of regular greasing more often than any other failure mode. I hate frozen pins. I've seen more frozen pins than broken ones.
Someplace on here I have a thread about a frozen disk hinge pin.....
If you ever run into another one, I'd love to see photos before and after disassembly.
Here is a link to that pin removal from hell I mentioned above
canadianhobbymetalworkers.com
Bought a diamond in the rough mill probly
So I picked up my first mill it's a king 1050vs and for the most part seems in good condition not that old, used in low production environment and comes with dro and power feed head and table and some light abuse. Anyways long story short the gib is stuck In the knee and they broke gib lock...