Sd Kfz 7 Sprocket question and partial model rebuild..

[Jerry Carducci]

I have a question regarding the sprocket for this model. It appears that the previous owner substituted screws and nuts to retain the
sprocket rollers but the problem I see is the track clearance isn't quite right and metal is being abraded from the track where the screws rub the track tooth holes. My question is this: was there any upgrade for the original pins that the original kits were equipped with? As I don't have the original pins and not certain that they're still available I'll be forced to make some new one... which I'm trying not to do.

I've read previous posts after a search on this subject but didn't really see any sure resolution I'd like to avoid breaking anything...

Jerry

[simon_manning]

Hi Jerry, put some Photo's on for us too have a look , regards simon.

[Adrian Harris]

I doubt there's any upgrade - they're one of the simplest parts of the kit.

Attached is a pic from Phil Fitzpatrick's build of the second batch, which had slightly different sprocket design, but which shows the rollers.

Adrian.

[Robert E Morey]

Looking at Simons build it looks like the rollers were held in with pins. Replacing those with screws would definately cause problems. I'm sure that is a standard size metric pin, 2-3mm dia.

download/file.php?id=27051

[Jerry Carducci]

It appears that the rollers had integral pins; they were machined that way I’d imagine. They must have just been sandwiched between the sprocket rings. Gives me an idea as to how to either modify the existing rollers or make new ones.

Thanks for that very useful information!

Jerry

[Adrian Harris]

The original release had a slightly different design:

The instructions say:

"Lightly oil the bores and place the rollers CG0325 in position between the lugs on the sprocket CG0331. Push the roller pins CG0324 in from the inside face through the lugs and rollers until they are nearly fully home. Apply a little Loctite under the head using a pin and push fully home. Allow 24 hours for the adhesive to cure and check the rollers are free to turn"

Adrian.

[Jerry Carducci]

Thanks Adrian. I was fortunate enough to receive the original booklets with the models so as I looked closer I can see the special pins that were included. I think the later design rollers with seemingly integral pins or something similar could be adapted. I suppose I may as well get cracking to make these up. Can’t really run it as is unfortunately…

I've attached a file to illustrate.

I haven't yet taken the sprockets off but by the look of things I'm suspecting they're one piece aluminum castings that were machined to
effect two separate but integrally attached tooth rings which will limit solutions to correct this.

Jerry

[Jerry Carducci]

I thought about this situation and read through the threads in the Sd Kfz7 section here everywhere I could find with references to this
sprocket. I read about several approaches to solutions regarding the rollers and pins. Likely the very best one was to replace the sprocket with a
later version that has separate steel tooth rings and rollers with integral pins. That particular approach, at least insofar as factory parts is concerned isn't an option as no further such spares exist ( although I'd happily purchase a pair should they turn up!).

The next best approach I read about was to drill and tap the rollers for a small set screw to capture the pid as part of the roller to prevent it from
coming loose. I liked this idea as simple and straight forward. However the more I thought about it the idea of these roller being made to rotate steel on aluminium and a relatively thin section of aluminium at that didn't give me warm and fuzzies...

Several other ideas came to mind. Making pins of brass to which I could solder a washer on one end after installation. Next was a 'pin with a pin' where two machined pins would be made both with flange head with one pin bored out to allow the pin with a correspondingly thinner cross section to be inserted from the opposite side. This smaller pin would then be peened on the opposite end as a rivet to securely hold the assembly together.

Lastly and the approach I decided to go with was to machine pins with a engagement groove machined on one end to accept a steel clip. This seemed to be the least time consuming approach and while the pins may still rotate in the sprocket ring hole they won't be forced to - the path of least resistance hopefully being that the roller is completely free to rotate on its pin.

I offer this up to critical review. If it's been tried already and failed miserably I'd like to know it before I proceed further. I have about an hour invested in these things, just for making the pins. The steel I used in from nails! I found that since most construction nails are imported ( what isn't?) they're
often made to metric standards and these were just shy of 4,5mm - perfect for these pins. I cleaned up the heads both front and back to eliminate the effects of how they're made although the serrations near the head remain. Th greatly thinned the heads and made them much smaller and made a tapered profile to minimize interference with the tracks. I made the end with the groove as short as I dared and also gave it a slight taper again to help it slide past the track engagement holes.The grooves themselves are about .002-006" undersized which allow the clips to rotate and move with demand. I

I've checked the clearance of the pin assemblies with respect to the track and it seems adequate with a margin of clearance on both sides but I don't know exactly how it will behave under load conditions. My guess and hope is that it should be ok. The sping clip isn't or shouldn't be subjet to direct or violent mechanical action. There is always the possibility that a clip could fail releasing the pin with what I can imagine wouldn't be pretty results!

In the meantime I'll keep an eye Out for better parts but also look to casting a sprocket body for which I could make separate steel toothed rings...

Be kind!

[Jerry Carducci]

For some reason I've been having issues with my session while updating this last post. I see a message that someone is updating my post while I am! Must be some strange ghost session cookie nonsense.

I was trying to add the line: " I realize these don't look very 'scale-like' but I was going for mechanically sound. Hopefully...

Jerry

[Jerry Carducci]

I may as well rename this thread as the sprockets are well into the rear view mirror now rightly or wrongly so.

I've got the model down to the chassis with mostly everything above the frame scattered about my workbench and shop.
I dismounted all the road wheels and the brass bushings show little wear. I might if I'm ambitious make some delrin or teflon
versions before I reassemble it although I see very little play in the wheels.

At present I'm focusing on the winch. The previous owner had made a cut of sorts on the cover so I tidied that up on my mill.
Didn't really need to I s'pose but it looks better to my eye. When I run the winch standalone using a cordless drill there's an alarming
tapping coming from the unit - it actually did the same when I test-ran it via a power supply ( It wasn't connected at all to the model's electronics- didn't appear to have ever been used) while still installed in the model only the sound used the model body as a sound box and was louder.
It seems to me that this thing needs some thrust washers. I might try making a new shaft for this thing that has a gap between the shaft and the brass plug/bearing for a thrust bearing. I can't do much for the inner end of the shaft except put in a shim washer or two. The tapping seems more pronounced
with the shaft all the way in and less so with the input power in one direction than the other. It seems to me the worm gear pair isn't happy. I cannot see
any metal being worn from any part nor is any part burnished showing wearing...

I want the winch to function flawlessly as well as without tapping sounds if possible.

The heavy aluminum parts of this model are impressive to say the least- no skimping on metal here!

I've changed out the screws on the road wheels to use a more proportional scale 3mm nut with screws inserted from the inner face of the hubs to serve as studs. Small change but looks better. I cheated and have just done the outer sets of screws- those little 3mm steel nuts are a little more difficult to get here. MVD is my friend though...

I'm eying the dashboard. Needs instruments. And the radiator... needs that Krauss-Maffei name plate!

I'm not going to go to an nth degree on this. I'm not a rivet counter by a long shot but there's some things I really like a model to have.
Plus I have a stack of Armortek kits in my garage that are begging to be started

[Jerry Carducci]

Modified the winch assembly to use thrust bearings one either side of the worm gear. Much quieter, no unusual sounds plus I'm using 'sticky' red grease for lubrication. I can actually turn the winch input power shaft by hand which I couldn't do before, just by the shaft without even the coupling for leverage.

Before I install this I'm going to bypass the set screw used to hold the worm to the shaft and use a hard pin instead. Don't want to have to take all this apart again if the screw lets go. Plus I like the 'cable keepers' several of you have made so I'll make those and a way to capture to reel end of the cable..I used 2mm very flexible braided cable before and it will be more than strong enough. What did you guys say it needs 7 meters?

I was going to post a short video of a winch test but the hand drill I used to power the thing makes a dreadful noise and you can't hear how marvelously quiet the winch itself is!

Jerry

[Jerry Carducci]

I'm just lollygagging along with the 7 project (now it's a project).

I'm spoiled in that I can look at all the work that's been done before me by the rest of you a decide which modifications I'd
like to implement. The real danger I've always been aware of with larger models is that the abstraction of detail that's generally acceptable
with smaller scales very often doesn't cut the mustard in the larger.

I always temper the desire to shoot for the stars with the sobering words of the editor of a well known modeling magazine: " you can spend years researching every minutiae for a subject model and include it your work or you can build a shelf full of models in six months that make you happy". There's room for us all...

I though when I began working on larger models my days of threading holes for tiny screws were past but nooooo.... On the winch I used 1,2mm steel hex head
screws to attach the cable keepers to the body. Rather nerve wracking using a tap the size of a needle in a thick alum part... but I made
it through 10 holes without breaking drill or tap...

Changed the bolts of the road wheels to appear as I've seen them.
Reworked the winch a bit further to include cable keepers and made a provision to anchor the cable on the reel.
Made a Krauss-Maffei badge for the radiator housing.
Hollowed out both headlights but I'm not convinced I'll use them as they appear lead. pewter?

I'm glad I was able to find an image of the badge I could manipulate and invert so I could photo etch it. I used the cheat method
to make it, I used my laser printer to print the image on glossy magazine paper. Then with a clothes iron I transferred the image to brass sheet.
Soak the print separates the paper from the toner leaving the image print properly oriented on the brass. I coated the rear of the plate to protect it. Etching was do with alternate soaks in Ferric Chloride and hydrochloric acid/Peroxide baths. It came out ok and once painted should look the part.

Going on to the side panels. The curved rub rail(?) or edging had been delaminating so I'm going to use the opportunity to give it a contour and likely solder it back on..

I'm going to examine what's going on with the steering servo; for some reason the steering works like a champ to the right but barely moves left; something is afoot there.

Jerry

[Jerry Carducci]

Continuing to poke along on this model. Took out my rotary table which I can't even remember when or even if I've used it since purchasing it from the Sears Roebuck of old. It was a time when 'Craftsman' tools were pretty good quality. It's a solid unit but since I added several indexing heads to my shop I find them of greater utility for most things I've needed to do.

The purpose for it this time was to open all the slots on the roadwheels. 14x16 = 224 slots. Mind numbing work but made less annoying by this rotary table. I did 2 the first night; 7 the second and 3 the following day and didn't get to the 4 idlers until today. Glad these are done. I use A9 cutting fluid for aluminium and it's water soluble- my goal being to not have to totally repaint everything yet. After machining a little warm soapy water took the A9 right off the parts. I'll first try touching up just the holes if possible. The wheels do appear better but I had to take frequent breaks even though I got the time down per wheel to about 20 minutes. I'd come back inside and watch an episode of "Ozark' with a glass of OJ then back out to do a few more wheels!

Now it's on to the side panels 'edging' and the dash. The KienzleTachometer looks like a challenge.....anyway I'll cross that bridge when I get to it. I need a better color printer to print the instrument dials...

One of these days I'm going to have to start on one of the Armortek kits piling up in my garage...but I really wanted an SdKfz 7....!

I've long been aware that these models are like favorite candies.... one is never enough.

[Robert E Morey]

That's a great mod to open those slots! Good use of rotary table. Your nameplate came out excellent!
Bob

[Jerry Carducci]

Plodding along. Worked over the side panels. For the edging/ side rails I searched for 2mm or 5/32" half round steel wire that wasn't hardened and when that wasn't forthcoming I switched to looking for similar brass half round but in the end decided I didn't want to put so much brass in such a prominent area for worried of scuffed or scratched paint revealing its true nature. I did find a source of 1/2 round carbon steel but never could get through to them and as I understood it I'd have to purchase 10 miles of it which was a bit much... So I decided to go with the square profile stock that had been OEM to the kit. I gave a shot to contouring the lower side of this construction knowing that after its installation access to that side would problematic.

I primed the side panels basically to keep them from rusting! The primer coat isn't definitive..

I soldered this railing on to the side panels and I was instantly reminded how much I dislike soft soldering steel; 'wetting' issues, even after rigorously cleaning and prepping the surface; instant rusting... ugh. Finally got it done after using just about every miniature 'C' clamp I own. I may, actually try to contour the upper section of the rail but there's a good chance not!

For the grab handles I took a different rout. I brazed 3mm washers to the ends as gussets but left a protrusion out that would engage the read-made holes in the side panels. I essentially made a brazing jig from one of my fire bricks by drilling 2 hols in it at the spacing of the holes on the side panels.
brazing the assembly was fairly straight forward unlike the previous soft-solder exercise. Once the handles were all assembled I serially installed them on the side panels. With part of the handles just sticking through the panel sheet I was able with the aide of a heavy steel anvil peen the handle metal into a sort of rivet head capturing it effectively. No glue. I'm sure a determined effort could pry these handles off but I believe this is mechanically sound for my purposes.

I got the bug in my bonnet that like several others I wanted functional turn signals, or at least signals that look like they should work. So I found some good steel sheet in my scrap box and had at it. I'd be lost without my Beverley B3 Shear. She's a beast and allows my to cut 1/16 sheet steel like butter.
My signals aren't as nice as some I've seen and I took some creative license but they should serve. They actually would function, or rather do function but I have no intention of connecting them to the steering of the model... The were rather fun to make but a challenge to keep together in subsequent brazing steps, a few things 'slipped' here and there but they're strong enough that I can clamp them in my milling vice to shape them further. The shape of the semaphore can be changed. It's held in place by one of my old friends.... at 1.2mm hex head screw! So even after I install them permanently I can remove the semaphores if need be.

One issue I have is that I don't know accurately how wide and tall the flanges of these turn signals are supposed to be so if someone has those measurements handy I'd appreciate that info. I'd like to finish the final dimensions before I drill them for tiny rivet holes. I suspect from what I see that I have to remove quite a bit of material...

Working next on the dashboard. My understanding is that in order to use a more scale looking version I'd need to mill out the existing part a bit. I've already used a fly cutter on the underside to level it out. I'm looking forward to making the instruments- I did a similar exercise for my 1/10 scale Kaelble trucks and they cam out quite well complete with illumination.

I'm also waiting on some 500k lenses for my headlights, also discovered that a pretty ideal size if 31.5mm and there are many different sized watch glasses on a particular auction site....I'm looking into the possibility of making masks and chemically etching the watch glasses. True there's no refracting aspect to an etched vs cut pattern however...

Jerry