Tractor backhoe - homemade
- Thread starter BFreaky
- Start date
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Brad_Blazer
Veteran Member
It's great to see it coming together. There have been some epic build threads here on TBN but I think yours pretty much blows them all away. The closest one was probably a guy about 10 years ago who built an entire skidsteer loader from scratch.
Redneck in training
Elite Member
Thanks for your help offer. The material of pins is OK. It is a design issue.
Redneck in training
Elite Member
Because of the dipper is made of 3"x3" square tubing the joint is only3" wide. The dipper is about 3ft long. The pin is 1" diameter. Therefore if the lateral force on the dipper is 100lb the shearing force on the pin is about 2400lb. The bushing in the dipper also might be worn out making the issue worse. I will cut out all the bushings and replace them with larger in example 1.5" diameter. I might also make the joint wider to decrease the shearing force.
unclebilly
Member
If I can mahe a suggestion, try to use 420 stainless steel for your pins. You can free machine it in the annealed condition and then have it quenched and tempered at 200C (400F). This will give you nice hard pins that aren't too brittle. An alternative is 8620 carburized HRC 60 to 0.060" deep but the 420 pins will work out better.
Kyle_in_Tex
Super Star Member
I've always wondered whether it was better to have hard bushings and softer pins, so that the pins would wear and have easier replacement.
unclebilly
Member
the pins are in shear, the bushings are loaded in compression.
your shear stress is .577 X radial load (lbs) / pin cross sectional area (square inches)
you want the yield strength of whatever your pins are made from to be atleast 2 - 5 times greater than this. Because it is subject to repetitive loading (fatigue) it should be 10X or more.
your shear stress is .577 X radial load (lbs) / pin cross sectional area (square inches)
you want the yield strength of whatever your pins are made from to be atleast 2 - 5 times greater than this. Because it is subject to repetitive loading (fatigue) it should be 10X or more.
JDonly
Bronze Member
Uh, Wut?
Kyle_in_Tex
Super Star Member
The only pin I've made for my post hole digger pivot pin, was made from 17-4 Stainless, (Type 630 for you international folks). I drilled it and crossdrilled it for grease, then heat treated it to H900 fahrenheit about HRc 44 hardness. It is VERY tough stuff. But it doesn't have the super hard rockwell you guys are mentioning.
175,000 psi yield, 190,000 psi Tensile strength
It doesn't get used much, I can't put down pressure on it. It just pulls it out of the ground and hangs from it.
175,000 psi yield, 190,000 psi Tensile strength
It doesn't get used much, I can't put down pressure on it. It just pulls it out of the ground and hangs from it.
unclebilly
Member
17-4 at H900 should be around HRC 50 and about 150ksi yield off the top of my head That will be awesome, provided it s not too brittle. I work with 17-4 all the time for down hole tools.
