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Delrin UCA bushing for kingpins

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I made a set of these for the NL a year or two ago. I've know that I needed to make some more for Mend. I wanted/needed something quiet to do in the early a.m. in the shop....so I out of the blue, I decided to do some measurements. I've been teaching myself CAD for several reasons. I knew I wanted to draw these up in CAD just so I'd have something nicer then scribbles to work from. Anyway......started taking dimensions off the new rubber bushings. Yep....that's the top of a dogbone cut off. I had a set that the kingpin had worn into the dogbone casting.....so they were scrap.









The rubber ones have a steel tube in the center of them to keep the bolt from completely crushing them. I had to squeeze the calipers pretty good to get a dimension off just the tube. I figured out another way right afterwards :(





The inside of the dogbone is tapered to the inside from both ends. The drill bit is a 1". It was too sloppy for me to consider that a usable dimension. I pulled out the inside gauges and got a much better reading :) Scratched down a few notes to make the drawing from.










Next thing to figure out was the angle inside the dogbone. I decided to take the reading off the new bushing. I probably should have checked the dogbone too, since I ended up having to adjust it at the lathe. Hard to tell in the pic, but the 5deg looked to be right on the money. It turned out to be a bit under 4.










Maybe I should have answered this question first......WHY make them out of delrin?? Here's why!! These were new on Paula's 521 several years ago. They've been worn out for awhile. When you would look at the truck from the front...the tires leaned in at the top. I kept fearing it was the new kingpins already warn out. It just dawned on me the other day, that it was probably the UCA bushings.....which was another reason I wanted to get these down on paper. Aside from the obvious chamber problem, it also pushes the top of the dogbone forward, which causes it to lose some or all of the caster...which means it doesn't track as nicely down the highway. The chamber lean made it harder to steer when going slow.

The pic with the jack is just to show how I unloaded the upper bolt to get it out. If you don't, the torsion bar pulls the whole assembly down against the upper limit(bump) stops and puts a lot of load on the bolt. Once you jack it up enough that the upper arms come off the stops, it's easy to work with. You guys with re-indexed torsion bars won't have this problem with the load on the bolt.

















On to the lathe. I originally set the compound slide at 5deg.....did a test cut on delrin(it's actually acetyl...delrin is a brand name that everyone is familar with) and found some wobble in the fit. So, I made it a bit shallower and as you can see from the dirt, the dogbone made contact nicely at the new angle.








If you noticed the tape/mark on the compound...here's why. I can get dead nuts with the X and Z axis', but if I use the compound, it throws those off. I want to build a hard stop for it, but for now, this worked. I set the compound where I could get the travel I needed for the taper cut. I then taped and marked that location. I took note of where the dial was on the handle. So....I'd make my cut.....run the compound back out past the mark, then turn it in(accounts for the backlash in the screw) ...as I got close, I stopped at the number on the dial that I had noted earlier. The tape/mark got me close without having to count how many times I turned the compound handle :)






I shoved the dogbone(DB) onto the taper and measured the depth from the outside edge of the DB to the end of the delrin. This told me if it was past the center or not quite there. It was past center, so I subtracted that dimension from the 1/2 DB measurement and cut that much off the end of the delrin taper. I didn't want it going past center. If anything, I wanted is just a hair short. The delrin will give a bit as I tighten the bolt.







I had planned on taking a few more pics of the lathe work for the machining thread, but I was kinda short on time and my neighbors kept coming over and chatting....I was lucky to get these done :)


Once I had the taper cut to the length I wanted, I simply had to cut the piece off at the overall length. Somewhere in there I did drill a 1/2" hole for the bolt. It fits in with no slop at all. It won't drop in, you have to push it. So here they are. They aren't perfect, but they'll do the job!!! Oh.....and the tires are back to being straight up and down!! :) That means that it will drive a lot nicer out on the highway!!







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...go figure...the last post/pic wouldn't go through ....over 30 pics!




I did the artwork in the morning before work. All the lathe work was after I got home. The dimensions aren't quite right on here, but you can see how much nicer it is than scribblings in a note book!! :)



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are you considering making and selling them? If so what would a set go for? With delrin I imagine its stiffer than the rubber, how long do you think the derlin ones will last?


oh, btw, nice work:)

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Thanks guys. I do actually plan on making them to sell. I have to see how much it will cost to have them cnc'd and compare that against how long it takes me. I won't know how much they will be until I have those two things figured out......but my hope is to keep them within the $40-60 range. Once they get over $40, I'm not sure enough will sell to make it worth it. I'll let you know :) I've got a couple of ideas about how to turn them manually and be able to make them fast enough to keep them on the cheaper side. Delrin is awesome stuff to work with.


As for how long they last...not sure. I'll have to check the ones in the NL. It doesn't have a lot of miles on it, but I'm not expecting them to show any slop or wear either.


We just took the 521 on a 340mi trip up to POTD and back. Maybe I'll jack it back up in the next couple of days and look :)

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