1/16 Scale FrankenDiff

[ddmckee54]

I "WAS" going to print out a new lower die for the U-bolt bender, so I could try my idea of using the brass tubing to protect the threads when bending the legs. My printer had other ideas though, I got a plugged nozzle on the 2nd or 3rd layer.

I changed the nozzle and started another print, about half way through it jammed again. This time it took out the PTFE liner. This is the second time in about a month that I've had to change that liner, and I didn't have any more spares. I ordered some more liners, and some new nozzles, and they have arrived. I'm going to just pitch the remainder of that roll of filament, It was several years old anyway. I had something similar happen a few years ago, only that was a brand new spool. When I changed the filament all the problems went away.

I've used old filament before, usually with no problems. I normally store any left-over filament in a zip-lock bag, and I'll throw a couple of desiccant pouches in with the filament. I usually don't have any problems doing this. However I have noticed that if the filament is a year or two old or more - it does tend to break in the feed tube to the extruder. Especially towards the end of the roll. It won't break while printing, but if the printer sits for a couple of days there's apparently enough stresses built up in the filament to cause it to break.

Bottom line - the plugged nozzle, the bad PTFE liner, AND the rest of that roll of filament are going to be introduced to the trash can when I put in the new parts.

Don

[ddmckee54]

Christmas miracles do still happen - sorta.

Yesterday, 12/23/24, I received an odd shaped package in the mail, in it were 6 axles for WLToys 12428/12423 1/12 cars. I ordered these axles in mid September. A few days after the delivery window had ended I contacted the seller telling him that the order hadn't arrived. According to the tracking records it was delivered into the hands of the "Final mile" shipper in mid to late October - and hadn't moved since. The seller contacted the shipper requesting them to search for the package. About a week later, with no response from the shipper, I asked the seller to refund my money - which he did on 11/19/24.

Then yesterday the axles showed up, the package had been obviously opened and resealed. The package was tagged as inspected by US Customs. I contacted the seller and told him that the axles, for which he had already refunded $87.76 to me, had finally arrived. I told him that I had received the refund in mid-November and asked him to send me an invoice for the $87.76 that had been refunded. So that I could pay him for the axles.

Today I got an e-mail from the seller thanking me for my honesty. He also told me that they couldn't access the refund from their end, so I should just forget about the money and to have a nice Christmas.

Small Christmas miracles do still happen.

Don

[ddmckee54]

Been a while since I updated this thread. The original plan for the WLToys 12428 drive axles was to shorten each 5mm OD axle about 30 mm. Turn a 13mm length of each shortened axle to a 4mm OD, thread that to M4. and then cross drill for the drive pin. Then I started wondering if it wouldn't be easier to get heavy wall tubing, use it as a sleeve, and Loctite the shortened parts back together, that was the plan anyway.

Over a month ago I ordered some 5mm OD brass tubing with a 1mm wall thickness. Today the 3mm ID x 5mm OD tubing that I ordered finally arrived.

I've got my supply of donor axles, including a few spares. It was cheaper to just get a complete axle than to get just the additional pinion and bearings that I need to build the center axle. The Sherline's been modified by adding the remote digital readouts. I guess that now I need to find out how many axles I have to trash before I get a working drive axle set.

I'm blaming Blender for throwing me down the front drive axle rabbit hole. His use of the Losi front axle shafts in his current telehandler build is what got me scratching my head and going Hmmmmm... So I ordered the replacement front axle shafts for the 12428 to check if they would be usable. They also arrived today, and it looks like a front drive axle is do-able without too much trouble.

Don

[Blender]

If I am going to have unfinished projects, everyone must. Excited to see where this goes

[Zabco]

Thought they were all unfinished projects, mine are.

[ddmckee54]

Yesterday I cleaned all of the god-awful smelling factory grease off the donor axle parts. I need to make several modifications to the axle shafts and I don't want to be smelling that crap all the time.

I know I need to find some clearance for the spider gears, but how much do I need? I knew that if I backed off the screws holding the ring gear to the spider housing the diff worked as advertised, but how to measure it? My idea was to use the M2 screws that held the spider housing to the ring gear as my indicator. If I count the number of flats as I loosen each screw until I find the sweet spot, that will tell me how far I moved the screw. Turns out that sweet spot is 1-1/2 turns out from tight. An M2 thread has a 0.4mm pitch, so 1-1/2 turns means the head of the bolt moved 0.6mm. I need to take 0.3mm off the back side of the bevel gear on each axle shaft to make things fit right. I think that's right, gonna need to try it and find out.

I also need to shorten each axle by 29-30mm. I'm not sure if that number will be affected by my fix to the spider gear clearance problem. I don't think it will but I need to try it and find out before I start whacking chunks out of the axles.

[ddmckee54]

I cut the existing axles with a hacksaw and took 0.3mm off the backside of the diff gears on the axles. I haven't spliced the axles back together yet, but I reassembled the differential to see if I have gained enough clearance. The differential now works correctly when the differential cover screws are completely tight, but it works better in one direction than the other. It turns in both directions, but in one direction it is definitely harder to turn. I also noticed that there is no noticeable end-play in the axle shafts. There is no grease in the gears right now and it is entirely possible that with proper lubrication and a little run-in time this will clear up

I'm using the Kong axle that I purchased as my benchmark so I checked to see if it had any end-play in the axles - it does. So maybe I still need to take an extra 0.1mm off the back of the gears on the axles.

[ddmckee54]

WELLLLL... things did NOT go exactly to plan, the best laid plans of mice and men - and all that crap. My very first plan was to remove the gear from the end of the axle shaft, shorten that end, cut new flats on the axle to match the gear, and cut new threads to match the screw that holds, the gear on. The only problem with that plan was that I could not get the screw to break free, I even tried heating the screw to try get whatever thread locker they had used to break free. The only thing I managed to do was to round out the hex socket in the screw. The next plan WAS that I would cut the steel axles in two, turn a stub about 10mm long on the cut ends to a 3mm OD, cut a piece of 5mm OD x 3mm ID brass tube to use as a splice, then Loctite everything back together. Easee-Peezee, right?

Things did not go well from the beginning, then went downhill rapidly after that.
Problem 1 - How do I hold these little turds to cut them? My first thought was to use my metric ER16 collets. Something like this IS after-all why I bought them and the collet chucks for the Unimat and the Sherline. So I blissfully cut the axles apart with a hacksaw, figuring that I could easily clean up the ragged ends with the lathe. Heck I could even chamfer the ends, 'cause chamfers are what separate us from the savages - right?
Problem 2 - I knew that the collet chuck for my Unimat registered on the shoulder on the spindle nose, I ASSUMED that the collet chuck for the Sherline did something similar. Imagine my surprise when I opened the box to find that the collet chuck for the Sherline registered in the spindle taper, AND uses a 1/4" bolt as a drawbar to hold it in the spindle. OK, that means that if I need to work on a longer part I'll need to work on the end hanging out in the breeze, and not work next to the chuck where there's less flex. That actually worked fine on the ends that were threaded for the wheel attachment.
Problem 3 - The other two pieces of the original axles still have the gears FIRMLY attached to them, and I need to work on the OTHER end. NO Problemo, I'll just slide the gear into the spindle bore, the bore on the Sherline is HUGE compared to the Unimat. AAWWW CRAP, there's already a drawbar there. The gear fits inside the collet chuck, maybe there will be enough room to put the part in from the back - THEN tighten the collet down? Nope, there may be a mm or two of clearance there, but there's not ENOUGH mm's. OK, lets swap out to the 3 jaw. Then the gear can just slide into the spindle bore.
Problem 4 - I got out the 3 jaw, cleaned everything up, and installed it. It has been sitting in a box for years - remember? I opened up the jaws, slid that part in, and... IT DON'T FIT!!!! WHADDAYAMEAN, it don't fit? That bore is huge, it's 10mm, and the gear is only... 10.6mm. OH Crap!
Problem 5 - I can't work on the area of the shaft I want to - where I want to work on it. But, I've got a lot of the brass tubing, I can make the splice as long as I want. I can pull the part out until it bottoms out on the back of the 3 jaw, I want to eliminate that cross drilled hole if possible. Pulling the part to the back of the 3 jaw puts the existing cross drilled hole inside the sleeve, but not by much. But, it IS inside the sleeve, so MAYBE it'll be OK?
Problem 6 - I needed to turn a 3mm OD stub on the cut end of the axle - Easee-Peezee. I figured I'd take off 1.1mm then sneak up on it - no problem. So, I made several passes taking a few tenths of a mm at a time and didn't stop to measure until I hit 1.1mm of movement. WTF, whaddayamean 2.82mm OD?? I only took off 1.1mm, but I took it off of each side didn't I. I was much more careful on the second axle. That gap is way more gap than any of the Loctite that I have is good for, but I can always use JB Weld. So I did, This is what the axles looked like at this point.

Problem 7 - I needed to shorten the brass sleeve to length. Since the gear's OD is larger than the spindle bore I had a LOT of stick-out, about 25-30mm's worth. It did not end well.
It snapped off right at the cross-drilled hole location. I think the axle would have been strong enough for the loads it will see, if only I would have just put the splice in a spot that's not close to an existing cross-drilled hole. I also found out that I need to make any axle shaft modifications starting on the outboard end, rather than the inboard end like I did this time.

The good news is that because I ordered complete extra axles, instead of just the extra pinion that I needed to make a center drive axle, I've already got spare axle shafts to work with. The extra bearings are the same size as what I would need for the front wheels if I decide to make a powered front axle.

Don

[Zabco]

Oh man, I feel your pain and aggravation. Morse taper and draw bolt is good when you want concentricity but a pain when you need length behind chuck. How were you cutting off the excess tube? Parting tool? I find that on my Sherline using their adapter to hold the parting tool cutter upside down on the back side works much better. I would really like to know how they installed those gears on the shafts. Sounded like you had a real good game plan.

[ddmckee54]

Zabco:

I was using the parting tool on the front side.

Regarding the gears, I'm seriously considering throwing the one remaining shortened shaft into the oven at 300 degrees F for 20 minutes. That SHOULD soften whatever type of schmoo they put in there, and still not destroy the die-cast gear. I need to be able to get that gear off if I want to make a serviceable powered front axle.

[ddmckee54]

After 10 minutes in the oven at 300 degrees F, and we have a winner.


Being able to do this should make things a little easier for Future Me.

[Zabco]

That's good to see. Little factoid to file away for future reference if I ever try to do the same.

I was using my cutoff tool in a QCTP for quite a while and always had issues with it. Given the thinness of the blade I even managed to shatter a couple. I read somewhere about changing to the upside down cutter from behind and gave it a try. How I've been doing it ever since.

[ddmckee54]

OK, there has been a little progress made.


I cut down the partial axle that was shown previously, and took a little more care with the diameter this time. I glued the turned stub into the brass tube using a Vee-block to align the parts as the Loctite cured. The original axle shafts were about 101.8mm, I rounded this up to 102mm. I had calculated that I needed to take 28mm out of each axle shaft. But I wanted this "practice" axle to be too long, so I added another 4mm onto my target length. I then cut the 5mm diameter end of the outboard axle stub to length and turned a 3mm OD stub 10mm long on that end. I then slipped the axle shaft together and checked the length with my trusty HF 4" caliper. After deciding it was good enough for "gubmint" work I glued the parts together, again using the Vee-block for alignment

After things had cured for a few hours I couldn't wait anymore and decided to test fit the axle in my 3D printed Frankendiff housing. I had added another 4mm onto my calculated axle length, and there's a 4mm gap between the 12mm hex driver and the outer bearing. So I've got a working procedure for narrowing my WLToys rear axles for use on my Bruder truck RC conversions.

Now I only have to do this at least 4 more times and I'll be able to get onto actually building the truck. I said at least 4, but it will probably be 6 times since I'm 99.44% sure that I'm gonna swipe Blender's idea and also build a powered steer axle.

Don

[Zabco]

Congrats on getting your process worked out. What I love about this hobby, educational opportunities just abound. Which Bruder are you going to convert first?

[ddmckee54]

Probably the MAN concrete mixer, I've already got it de-boxed and it's currently sitting on my table. The suspension parts have been designed around measurements taken from it. Although the other truck suspension parts measure close enough that I can use the Frankendiff on them too. I made sure it'd work back when I started this adventure.

That was the whole reason for this design exercise, design an appropriately sized differential for use on all my Bruder truck conversions. Educational experiences, I've been teaching myself how to use Alibre Design Pro at the same time.

[ddmckee54]

A little more progress has been made. I was able to find the broken stub that was shown in Post #68. I thought that I had pitched it, turns out I'd just misplaced it. I found it when I went to use the toaster oven to remove the gears from the next donor axle. I have enough bits and pieces that I now have the fixin's for 2 complete differentials, if I could get that M2 screw with the rounded out hex removed. While the toaster oven was hot I also took apart the axle shown in Post #73 that was 4mm too long. At some point over the last several years I had purchased the smallest Easy-Out I've ever seen. I was able to get enough purchase with it that I could back the screw out enough to grab on to it with a pair of pliers and remove it.

Today I modified the stub axles that I already had cut apart. The axle shaft from Post #73 was 74.27mm over-all in length, so I'm aiming for a 70.25mm length in my completed axles. I modified the first axle, Loctited it together, and left it clamped in the Vee-block while I modified the other axle.

One measures 70.14mm, and the other is 70.38mm. Not bad for a beginner, but I plan on doing better next time. And, the only thing that I had to scrap was that bent length of brass tubing shown in Post #68.

[ddmckee54]

Zabco:

I was using the parting tool and holder that I got with the Sherline. I was using it on the front, but it had to have a LOT of tool stick-out in order to get it on centerline. I have since switched to the 1.5mm x 6mm parting tool that I got for the Unimat, If I want to use it on the Unimat I'm probably going to have to get another one of them. I mounted it in the rocker tool-post I got with the Sherline, and that's where it will most likely stay. I put it on the back as you suggested, and things went much smoother. That could have been because there was less tool stick-out, but from now on parting off will probably be done like that.

I did have a problem when I tried to take off a 0.13mm cut like that though, it seemed like that 1.5mm blade just wanted to deflect. I got a BUTT-load of tooling with the Sherline, including a bunch of brazed carbide bits - most of them still had the wax coating on them. After trying one I understood why they were unused, straight from the factory the brazed carbide cutting edges are useless. The set I got from HF years ago were the same way, the bottom edge of the brazed carbide would hit the part before the "cutting" edge would touch the part. After touching up the relief angles on a diamond hone, so the cutting edge actually cuts instead of just rubbing the part, I have useable brazed carbide bits.

I've also got a complete prototype modified axle.

[Zabco]

Yea, with the Sherline parting tools you need to keep the blade as short as possible. Because they are so thin they can be easily deflected. And that of course will lead to problems. The other thing, if you aren't doing it, is Sherline recommends slowing your rpm speed to about half of what you used to turn the part and always use oil. I had not thought of using the Unimat cutter. I have one but would have to regrind it as I ground it to a curve to cut the grooves in a bunch of pulleys I had to make. Glad to hear its working for you. Your new axle looks real good, can't wait to see it in action.

[ddmckee54]

The axle looks good, but when I transferred the duals from the Kong axle onto my axle... the wheels sorta fell off the bus. When I tightened them down they wouldn't turn. I took things back apart and started measuring bits and pieces.

The 12mm hex driver from the Kong axles is 6.5mm thick and uses a drive pin with a 1.5mm OD. The WLToys hex driver is 5.5mm thick and uses a drive pin with a 1mm OD. I backed things off enough that the wheels turned freely and did a sanity check against the Bruder tires.

From this angle things look OK, however...

From this angle you can see they're too narrow by a couple of mm.

If I make the driver pockets 5.5mm deep instead of their current 6.5mm depth then things should be just about right. I think I'll make the pockets 5mm deep though, because a little clearance nerver hurts Clarance.

[ddmckee54]

It's been a while since I was able to update this thread. I reprinted the rear wheels fixing the hex pockets, it's shown here along with the donor axles that need to be modified for the center axle.

I finished modifying the second set of axles that will be used for the center axle, this is the modified axles.


The only difference between the center axle and the rear axle shown in the previous picture, is that the center axle uses the pinion housing for both the front and rear of the diff.


The right end of the 6" rule in the attachment shows the length of the original axle shaft. The original axle was parted off about 29mm from the inboard end of the shaft. The remaining piece of the donor axle was parted off 39mm from the outboard end of the shaft. Both the parted off ends were turned from 5mm down to 3mm. The turned stubs were about 14mm in length, this length isn't critical. What is critical is the location of the shoulder. On the inboard section this shoulder is 15mm from the inboard end, on the outboard section the shoulder is 25mm from the outboard end. These two sections are joined together with a piece of 3mm ID x 5mm OD brass tubing with a length of 30mm. These 3 parts are then glued together with the HF equivalent of red Loctite using a vee-block as an alignment jig. If I did everything right, I should end up with axles 70mm long. One measures 69.95mm, and the other is 69.97mm.

Is there an easier way to do this? You betchya! You could just cut the axle shaft with a hacksaw and glue the pieces into a piece of 5mm ID tubing, The only reason I chose the method I did is because of the way the outboard axle bearing will be installed. When I use these donor axles to build a powered steer axle, the CV joint that will be glued into the outboard end of the shaft is over 5mm in diameter. In order to install the outboard rear axle bearing it will need to be slid onto the axle shaft from the inboard end.

I've still got problems with the Sherline. First the headstock bearings are stiff and noisy. These are the original shielded bearings and I suspect that the factory grease isn't exactly greasy anymore. I've been dousing them with light oil to try to reconstitute the grease but so far without much luck. I'm thinking new bearings are probably needed.

The second problem is with the carriage lead-screw, it binds up. But only when moving the carriage toward the headstock, and only when the hand-wheel is between the 2:00 and 5:00 positions. I suspect that this is a left over boo-boo from when the Sherline took a nose-dive off the bench onto the end of the threading attachment drive dog.