1/16 Scale FrankenDiff

[ddmckee54]

The scales upgrade on the Sherline is mostly complete. Here's what things look like from the front.

As you can see, I'm no longer losing 35-40mm of carriage travel at the tailstock end due to the cross-slide scale. And the cross-slide scale is no longer a shelf where chips and dust will accumulate. That cute little 000 Phillips screwdriver on the lathe base and two extra screws came with the scales, you need it to open the battery cover.

This is what the back side of the scale install looks like - from the headstock end. The carriage scale in no longer a wide shelf that chips and dirt will land on. Both the cross-slide and the carriage scale have the actual "scale" facing away from the spindle, so they aren't directly exposed to hot chips.

That black object on the LH side of the cross-slide read-head is an end stop. Before I installed that, it wasn't uncommon for me to retract the cross-slide far enough to disengage the lead screw from the lead nut. While that wasn't a show-stopper, it was irritating. That won't happen any more.

This is the temporary location of the displays.

The brackets that came with the scales didn't work for me. They allowed you to swing the display from side to side on an arm that was 8-9" long. They did not allow any tilting of the display for a better viewing angle. I 3D printed a pair of stubby arms, about 2" long, that allow me to tilt the displays to the best angle - whether I'm standing or sitting.

There's still a few things on the To-Do list:
1) Find a more permanent home for the displays. Right now I'm leaning toward mounting them on the peg-board using some of that brown non-conductive organic material - probably about where the pin-punch set is hanging behind the 3-in-1 oil.
2) Do some cable management, not gonna get crazy with the excess cable like I did the first time. Behind the peg-board is a blocked off door that at one time went into the coal-room, for when the boiler was coal-fired. I may just let the extra cable hang in that space, it's not like I can actually use the space for any thing else.
3) I've got to find another plug and get the AC adapter modified so it will be able to power both units. Somebody might already make a Y-adapter in the right size, I'll have to check Digi-Key and Allied-Electronics to find out

Like Superfast Matt I tend to get things to the point where I can use them, then they never truly get finished. But they are good enough to use, and right now this one is "Good Enough".

I've also got the replacement spindle bearings for the Sherline, I got tapered roller bearings to replace the noisy deep-groove ball bearings, That project is on the "Someday" list too.

Don

[Zabco]

Looking good Don. Like your solution to handling the cross slide scale. Can those scales be trimmed to shorter lengths?

[ddmckee54]

Yes they can be trimmed. I cut about 3" off the original scales with a hacksaw. That got the job done, but the epoxy/glass board the actual scale's on was tough to cut. I used an angle grinder and the spinning wheel of death to cut the Igaging scales, that went MUCH easier.

I found that Igaging uses SS instead of aluminum for the scale support bar, so the cut-off wheel was probably a good choice. Because I reconfigured the cross-slide scale I was able to shorten the Igaging by about 1-1/2". But I started with a 6" Igaging scale, not an 8" like the original scales.

[Zabco]

Thanks Don. Have thought about doing similar to my lathe. Couldn't do the cross slide like you did. I bought mine set up for CNC and the servo mount prevents inserting anything into the the T-slots from the front. So can't plug up the rear access. Did come with the zero reset hand wheels which helps, don't have to remember what setting I started from.

[ddmckee54]

At one time I was considering putting the carriage and cross-slide scales parallel to each other. I was thinking of using something like a Sullivan Gold-N-Rod to link the cross-slide to the scale, to simplify making the 90 degree turn with the linkage. If I remember correctly the outer casing is only about 1/4" in diameter. Something like that might work for you.

[ddmckee54]

Further development on the steer axle is on hold for a week or so. The motor/2-speed gearbox, that I initially wanted to power the model with, uses a single 370 sized motor and has 3mm output shafts. While the 370 sized motor MIGHT have been up to the task, I don't think the 3mm output shafts would have been - since all of the differentials have 5mm input shafts.

I've got an LDRC LD1201 Unimog replacement motor/gearbox ordered. It uses a pair of 370 size motors driving a 2-speed gearbox with 5mm output shafts. One of the outputs looks to be centered, and the other appears to be offset to the side. If it is offset then I'll have to slide the pumpkin to one side on the front and rear housings for my steer axle. Unless I can find some drawings on-line, I won't be able to do any more work on the steer axle until I can get some measurements from the gearbox.

[Zabco]

Originally Posted by ddmckee54

At one time I was considering putting the carriage and cross-slide scales parallel to each other. I was thinking of using something like a Sullivan Gold-N-Rod to link the cross-slide to the scale, to simplify making the 90 degree turn with the linkage. If I remember correctly the outer casing is only about 1/4" in diameter. Something like that might work for you.

That is a very interesting idea. I've never used a Gold-N-Rod before as i've never been into airplanes but know what they are. Thanks Don, gonna have to do some thinking on this.

[ddmckee54]

No problem.

A gentleman on HMEM suggested that if I lowered the cross-slide read-head I would free up that back corner of the cross-slide for normal use. I already had everything printed by that time and didn't feel like re-designing it - AGAIN. If I ever do this again, I'll probably hang both read-heads at the level of the carriage scale with both slides parallel. Then I'll use the Gold-N-Rod trick to actuate the cross-slide scale. I just had a thought, is the "Make Flexible" check box in Alibre to simulate a connection like a flexible pushrod?

[Zabco]

I don't think the 'flexible' option would work for something like that. It only allows movement in sub-assemblies function in another assembly but only within the limits of the applied constraints. You could model and move a straight line movement like a piston rod in a cylinder because it only moves in one axis. No way that I know of for it to model movement through multiple bends. Would be kind of neat though.

I really need to have access to both T-slots in my cross slide as I usually have my cutoff tool mounted in slot closest to head stock so I can get it as close to chuck as possible. Often have to have my QCTP in back slot depending on tool holder being used so, again, I can get cut off tool as close to chuck as possible.

[ddmckee54]

It doesn't really matter about the "flexible" setting, that was just one of those wild-haired ideas that smack me in the head once in a while - kinda like Gibbs and DiNozzo.

[ddmckee54]

Wilf on MEM got a flexible pushrod to work using SolidEdge 2025. I don't think my version of Alibre has the brains, or the brawn to handle it.

Anywho...I updated the 3D model of the chassis to use the appropriate frame rail lengths, and axle spacing, for Bruder's MAN mixer. The thing's starting to look more like a truck now, I've hidden the passenger's side frame rail so things are easier to see. I've also included the motor/gearbox so I could re-design the steer axle pumpkin location.


That's done now, and we need to be verwee-verwee quiet, because we're hunting drive shafts. However, I'm having about as much luck finding one that will work as Elmer ever did getting the wabbit. I've got a couple different flavors of SCX10/TRX4 drive shafts on order, to see which will be easier to modify to fit. It would be nice if somebody made flange mount U-joints, but I don't see that happening - and I'm not building a museum scale model.

The center axle to rear axle drive shaft is the real problem. In order to be able to install that shaft WITHOUT removing an axle, that sucker needs to collapse down to under 39mm. It looks like I might as well be hunting for Unicorns. I'll probably just have to resign myself to the fact that shaft will need to be installed WITH the axle.

Don

[ddmckee54]

OK, I've found out that I'm going to have to revisit my chassis design a little. So far I've been sticking to the measurements taken off the Bruder MAN mixer, but that's gonna have to change a little. I'm going to have to modify the axle spacing/locations a little. I cannot find an off the shelf axle that will fit the existing center axle to rear axle spacing. I currently have an absolute minimum drive shaft length of 42mm. When you add in the 7mm I need to be able collapse the drive shaft to take it out. then I need a drive shaft that has a minimum length of 35mm. I was able to find drive shafts in the 30-36mm range, but they only had a 2mm ID with a 6mm OD. Nope, that ain't happenin'. I did find a Lesu drive shaft with a 5mm bore in the 45-50mm range, and have one headed my way. It costs 3 times as much as any of the other drive shafts, but none of them can be made to fit.

My current plan is to add 5mm to the spacing between the center and rear axle, and play with their locations a little so I don't mess up the drive shafts coming off the transfer case. By adding the 5mm to the axle to axle spacing, I SHOULD get into the middle of the range of motion for the Lesu drive shaft. Unfortunately it also means that the drive shaft and the axle have to be installed/removed as a unit.

[Zabco]

Well hopefully you won't have a need to remove the rear axles very often, if ever. Can't remember the last time I had to remove one of mine, or even mess with the drive shaft itself.

[Blender]

Don, in your driveshaft search did you run across any with a 4mm bore? Been looking for another project, but haven't seen much. Everything is 5mm that I found, or 4mm/3mm mismatch.

[ddmckee54]

Blender:

I sure did. Here's an Ebay listing with 5mm, 4mm, 3mm, and 2mm drive shafts - but they call them "steering shafts".
Drive shafts

The LDRC Unimog twin motor/gearbox that I'm using has 4mm output shafts, the WPL motor gearbox that I originally planed on using had 3mm output shafts. Since all of my axles have 5mm input shafts, I thought the WPL gearbox might have been a little on the wimpy side.

Don

[Blender]

That's perfect! Thanks. Even has some length options.

[ddmckee54]

One difference that I did notice between the 2 different sets of drive shafts I ordered is that one of the manufacturers wasn't particularly careful about getting the U-joints clocked properly. One of their drive shafts is OK, but the other is about 10 degrees off. I know on a full-sized vehicle, that WILL cause vibration issues. On a model that may not matter, but why chance it?

[ddmckee54]

I have found out that I needed to slightly modify my Frankendiff pinion housing design. The hole for the drive shaft's drive pin wouldn't line up with the hole in the pinion shaft. I must have fat-fingered a dimension because the outer bearing needed to be moved 1mm toward the axle shaft. I just had to decrease the extrusion that formed the nose of the pinion housing from 9mm to 8mm. While I was at it, I went back thru the design and removed anything that I'd done to optimize the design for FDM printing.

I've got a resin printer now and one of these days I gonna hafta put on my Big Boy pants and actually USE it.

[ddmckee54]

Sometimes I think Quality Control is a totally unknown concept in certain parts of the far-east. Some of the stuff is high quality, but there are a LOT of times when what you actually get is a kit of mostly usable parts. ALL of the SCX10 rear axles I ordered came from different vendors, but apparently the same supplier, and none of them were really usable when they arrived. All of them are almost impossible to turn. I chased that problem back to the fact that they arrived with an interference fit between the spider gears in the differential. I had to remove 0.3mm from the backside of each axle gear before things started to work properly. BUT, they are fixable.

I ordered some plastic bushings for the knuckle pivots on the powered steer axle I'm building. They were SUPPOSED to have a 3mm ID, it's actually under 2.8mm. Fortunately the OD is correct so they also are fixable.

I ordered drive shafts from 3 different manufacturers, 2 out of the 3 suppliers have the knuckles properly phased to minimize vibration. The third supplier... not so much. The knuckles are are least 10 degrees out of phase, and I'm not sure if there's going to be any fixing it.

And then, I've got a gotcha that's kinda my own creation. ALL of the drive shafts that I ordered are SUPPOSED to fit an SCX10, come with a 5mm bore and have drive pins that are threaded M4 on one end with the other end turned down to 2.5mm. My axles are SUPPOSED to be SCX10 replacement axles, but they all have holes for 2mm drive pins in the 5mm OD pinion shaft. I could bore the pinion shafts out to 2.5mm, since the Kong axle that I have has a 5mm pinion shaft with a 2.5mm drive pin hole. The Unimog replacement twin motor/2-speed gearbox that I got as a power unit has 4mm OD output shafts that are threaded M2.

So, here's my first dilemma, do I modify the pinion shafts? Or, do I modify the drive pins? Initially I was leaning towards modifying the drive pins, now I'm not so sure. If I modify the pinion shafts, I just punch the drive pin holes out to 2.5mm and call it a day. If I modify the drive pins by turning them down to 2mm, then I also have bush the hole in the drive shaft down to 2mm. Otherwise they'd be, to quote Wes from Watch Wes Work, "floppin' around like a hot dog in a hallway." Metal fatigue would probably cause the 2mm pin to break off in a short time. I think I just talked myself into modifying the pinion shafts.

My second dilemma is that the output shafts on the Unimog transfer case have a 4mm OD. Bushing the transfer case end of the drive shaft down to 4mm is no problem. They also have a pre-machined flat that is threaded M2. My first thought was to bore the M2 threads out to 2mm, since they are effectively that size now. I was planning on just having one drive pin that would work on either end, but that's just gonna make a lot of extra work for myself. I think what I'll do for the transfer case drive pins is cut a chunk off the 2.5mm end of the pin and turn the stub down to about 1.5mm - or whatever will fit in the M2 threads. The set screw on the flat will be the actual clamping/driving force, the little stub is just extra insurance if the set screw comes loose.

Don