The Craftmans Shop > Radio Control Models

1/16 Scale RC Truck parts

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ddmckee54:
It's been a bit since I last updated this....

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 of the part. 

I changed the nozzle and started another print, though 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 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:
Been a while since I updated this thread, but I've been keeping busy.

The printer has been repaired and put back into operation printing out rear axle and suspension parts.  I've ordered and received a bunch of parts and materials that will be needed for the axle modifications.  Two days before Christmas my long lost axles finally showed up, turns out Customs had opened them for inspection and apparently misplaced them.  I contacted the seller, who had already refunded my money, offering to pay for the axles that I had finally received.  On Christmas Eve he told me to forget about it and have a nice Christmas. 

I found out that I am much too digitally inclined to be able to keep track of where the tool bit is on the Sherline, as opposed to where I THINK it is.  So I installed a pair of remote digital readouts on the Sherline.  Hopefully that problem is solved.

Rather than my original fairly complicated plan for shortening the axle shafts, I came up with a simpler one that should give a wannabee machinist like me a better chance of success.  I got some 5mm OD brass tubing with a 1mm wall thickness, which arrived on Saturday.  I'm going to cut a chunk out of the existing axle shafts, turn a 3mm OD stub on the pieces I'm going to reuse, use the brass tubing as a sleeve, and Loctite the parts together.  Now to get back to the axle modifications.
 
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 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 procedure 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 just not ENOUGH extra 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 - at least not 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 now 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 that's what 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

ddmckee54:
If I decide to also build a powered steer axle, I'll need to be able to take the gear off the end of the axle shaft.
 The screw holding the gear is apparently locked on there with some type of schmoo, because all I've been able to do so far is strip out the hex socket on the screw in the shaft that snapped.  Last night before I went to bed I decided that I was going to throw my remaining shortened axle into the oven for a while.  After 10 minutes at 300 degrees F, I gave it a try annddd...

We have a winner!  This should make Future Me's life a little easier.

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