The Craftmans Shop > Radio Control Models
1/16 Scale RC Truck parts
ddmckee54:
Hmmmm...guess I didn't show what the modified axles look like.
Regarding the Sherline carriage lead-screw issue, when I started taking it apart last night I discovered that the issue went away when I took the hand-wheel off. Upon closer examination of the hand-wheel and the lead-screw shaft I found a nick on the face of the hand-wheel and a burr on the lead-screw. The burr on the lead-screw was caused by the grub screw, but I've got no idea what could have caused the nick on the hand-wheel. I stoned off the raised areas and when I reassembled things that particular problem was gone.
I've been plottin' & conivin' for a while as to how I can adapt the Frankendiff into a powered steer axle. Blender's build of a 1/14 scale TH407C telehandler on another forum gave me the idea I needed. He used Losi CVD front axles to build his steer axles. Since I've already got a butt-load of the WLToys 12428 replacement rear axles I decided to get a set of replacement front axles to see if they'd be usable. After doing a little (very rough) 3D modeling, it looks like things will work out. They both use a ball and socket joint in the knuckle, but the Losi uses a CVD joint while WLToys uses a CVA joint. A CVD joint has the ball on the axle with the socket on the half-shaft. A CVA joint flips that around and has the ball on the half-shaft with the socket on the axle. Here's a picture of the WLToys CVA joints.
At the top is the assembled CVA joint, in the middle is the axle with the socket, and on the bottom is the half-shaft. At the left is the dog-bone that would normally attach to the front diff. This 14mm section on the left is totally useless to me, I only need about the last 25mm on the right. The center section of the half-shaft currently has a 3.18mm OD. My current plan is to turn part of the center section and part of the tapered area just to the right of it down to a 3mm OD. This will then be Loctited into the outboard end of the modified donor axle, just like I did when shortening the donor axles for the rear diffs.
ddmckee54:
The Sherline bearings are supposed to be lubricated for life, but they are shielded bearings - not sealed. If they sit for several years without being used, the grease will dry out and harden. According to the part number they are standard precision bearings, not high precision. Once upon a time in the west I used to repair machine tools for a living, so swapping spindle bearings is not outside my comfort zone. At least now the parts are a LOT lighter, and they're not covered in congealed nasty smelling coolant.
Yesterday I modified the first CVA half-shaft.
The modified half-shaft is just slipped into the brass tube for now, I'm just getting started on the working 3D model that will be used to print the parts. I've got bushings and shoulder bolts on order for the knuckle pivots, so I can accurately model things now. I model things in mm because that's how most 3D printers think. I really wonder sometimes when reverse engineering this stuff, because some of the measurements make no sense. Like why is part of the half-shaft turned to 3.18mm, and why is the socket bored to 7.62mm. Earlier today it finally dawned on me, 3.18mm is 0.125", and that odd 7.62mm bore is 0.3". When I convert all the oddball Metric measurements to Imperial units they come out nice and neat.
vtsteam:
I hear you, dd, on the tediousness of units conversions, but that .3" seems unusual even for imperial, where you'd expect .3125". Wonder where that came from? :scratch:
ddmckee54:
--- Quote from: vtsteam on February 26, 2025, 06:51:08 PM ---I hear you, dd, on the tediousness of units conversions, but that .3" seems unusual even for imperial, where you'd expect .3125". Wonder where that came from? :scratch:
--- End quote ---
Who knows, maybe it's just a coincidence.
I'm brain-fried right now, for the last 5-6 hours I've been fighting with Alibre locking up. I'm trying to do the final 3D design for the powered steer diff parts. The design I showed a couple of posts ago was thrown together to see if I could even make it work. NOW I need to cross the I's and dot the T's so that it will all work together, and that means modeling all the individual parts. That's actually a good thing as I found a couple of gotchya's while doing it.
One of those gotchya's was determining how much I needed to shrink/stretch the ends of the diff front and rear housings to accommodate the single front wheel instead of the dual rear wheels, and still maintain the same wheel track. It turns out I needed to take 13.5mm off each side. I know that doesn't make sense that I need to move the end of the diff housing inboard when going from duals to singles, but I spent a couple hours convincing myself that moving things 13.5mm inboard was actually right.
The second gotchya was when I realized that the screws holding what I'm calling the diff pivot in place would be hitting the outboard bearing - that would not be good. So I had to change the design of the diff pivot, it's now about 6mm longer. THIS change interfered with the outboard screws holding the front and rear diff halves together. Since the diff pivot slides over the ends of the front and rear diff halves holding them together, those screws aren't really needed any more. Problem solved, but I did have to change the 3D models for both halves to reflect this.
The third gotchya is what does the length of the brass tubing splice need to be? My modified rear axle measures 147mm from end to end. My modified axles were 70mm nominal length, so that means the spider gears were occupying 7mm of space in the middle. My 3D printed non-powered front axle is 172mm from end to end. If I subtract the 7mm for the spider gears, and divide be 2, the stack-up for my front axle length should be 82.5mm? (Why do I feel like Rodney Dangerfield in "Back to School" right now?)
While typing this I just realized that there's nothing keeping the outboard bearing of the front axle from sliding outwards. On the rear axles the hex driver holds the bearing in place, on the front axle there's nothing but air in that location. Oh well, that's a problem for future me, right now it's time to call it a day.
Don
RussellT:
It's always puzzled me :scratch: (well since I found out about it) why Nato standard ammunition is referred to as 7.62mm when it is 0.3 inches.
Russell
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