Stage 3: Wheels

"Now we're wheely moving"

Stage 3 consists of Packs 10-14 to build the steering, track, idler and drive wheels

Pack 10

Pack 10 is for the front steering wheels (including tyres) and steering linkages. The steering link arms (the bent bits with flat ends) look a bit flimsy, but they can be discarded for the replacement parts that can be found in the Amendments Pack. The photo here shows the original parts because I forgot to dig out the new ones. Subsequent photos show the much more solid replacements.
These parts are a simple fit. The exploded-view diagram in the manual implies that the central hub fits into the rim from 'behind', but it actually fits from the front (side with lugs). While this two-part construction is faithful to the original, the model is somewhat simplified, as can be seen in the 'Sd.Kfz.7 in detail' book (e.g. pages 46-47). At this stage, nothing is solidly set in place, as fine adjustments need to be made to the angle of the steering link arms and the lengths of the track and steering rods, and this is best carried out on the model.
In this photo, the steering system is installed on the model and the adjustments made so that the rods are the right length and the arms at an optimum angle so as not to foul the main front axle. These were set in place with a drop or two of runny superglue into the threads and allowed to set in position overnight The assembly was then removed and partially dismantled (wheels off the stub axles, rods disconnected) for painting. The steering rod is shown here as running beneath the yoke, which appears to be the position in the manual. The Sd.Kf.7 book clearly shows it to be above, and the track arms have a better angle and don't rub against the main axle, so I've since moved it.
The manual implies that the tyres are a simple push fit over the rims, but they're quite solid and there's just not enough flexibility for that. I hear claims that they can be softened by boiling them for a few minutes, and they'll then go on. Club mate Jim says he tried this method and it helped, but it was still a difficult job, and they aren't going to come off again, so the instructions to smear the rims with epoxy probably isn't necessary. I'll leave my attempt to the weekend... OK, so time to attempt the difficult bit. IMPORTANT! if you are going to use a kitchen pan to boil tyres in, first get written clearance from 'Er Indoors!! (Unless you want to boil your head after she finds out.) Secondly, use thick gloves - those tyres will be hot. Don't complain to me about blistered fingers.
So, giving the first tyre about 10 minutes on a low simmer, turning occasionally, hook out and stick the wheel rim at an angle as far as possible into the centre of the tyre. Next, use all your skill, cunning, dexterity, a bicycle tyre lever and a large wooden mallet to prise and wallop the tyre into place. The boiling does indeed soften the rubber to give enough stretch to accomplish this feat. Second tyre treated likewise, and with experience comes The Knack, and this one went on much more easily. Once on and cooled, these tyres are solidly in place, so no glue of any sort is needed.
The wheels can now be fixed to the stub axles. At this point the steering servo from OP1 was mounted in place and all the linkages connected. The montage here shows (a) the steering system from underneath, (b) the steering servo arm being adjusted so that the wheels point straight ahead with the transmitter stick at neutral and (c) a close-up of the servo and steering links.

Pack 11

Not a lot of progress to report on over the last 3 weeks. There's been a spell of weather too cold for successful spray painting and epoxy setting, and other interests have kept me out of the workshop (i.e. chilly garage!). But nevertheless, progress has been made to the point of having something to update this blog.

Pack 11 is the set of track (road) wheels Type 'A'. These are the outer wheels of the two overlapping types.

The identical pairs of wheels are bolted to the central axle with 7 bolts per wheel. It should be noted
that the bolts protrude 1-2mm above the inner flange. Following a warning from Jim, I dry-fitted an assembled Type 'A' wheel with a pair of Type 'B' wheels (from Pack 12) with tyres on the rims. The 'B' tyres do indeed rub against these protruding bolts. So nothing for it than to use a junior hacksaw to chop off the excess and file flush to the flange.

Apart that 'adjustment', removing some minor moulding flash on a couple of wheels, and bit of filing to get all the bolt holes in the wheels cleanly lined up with those in the axle flange, the actual build is really not a lot or work - just the bolting together (84 in total!) and glueing the (identical) brass bearings in place. Rather a production line with 6 pairs to make.

The wheels were painted before attaching the tyres. A strip of masking tape was first put around the centre of the wheel rims (leaving about 1mm from edges) to leave bare metal. For each wheel in turn, this area was given a very thin smear of quick-set 2-part epoxy (the 10-minute 'Araldite' variety) and the the tyre popped in place. I don't know about you, but I can't ever use epoxy without getting some on my fingers which always transfers to the most visible places on the work piece and which can nevermore be got off! In this case, finger marks only seemed to appear on the tyres when the epoxy had set, showing up shiny against the duller rubber (Oh, I forgot to mention that I 'distressed' the tyres first, by buffing with coarse sand-paper - whoever saw shiny tyres on a tank or lorry?) Fortunately the stuff comes off by carefully scraping with a blunt scalpel blade. Don't forget to paint the hub caps too. I did, which is why they don't appear in the above (right) photo of the finished items!

Put the finished wheels to one side for now. No point in attaching to the model at this stage, as they will only have to be (partially) taken off their axles in order to get the Type 'B' wheels on the companion axle in between the individual Type 'A' wheels. For the next time...

Pack 12

Pack 12 is the set of track (road) wheels Type 'B'. These are the inner wheels of the two overlapping types.

No bolts here - pairs of Type 'B' wheels are loose on their axles. The only thing to note is that the inner and outer brass bushes are different - the outer is the shorter one. Otherwise the preparation, painting and tyre fitting is identical to the Type 'A' wheels. I remembered to paint the hub caps at the same time, but then left them out of the photo... I also managed to get the epoxy mainly where it's supposed to go too!

At this time of year, spray painting outdoors is a non-starter, so it's been done on the workbench in the garage. (see Start page). After a while though, 'Er Indoors complains about the smell permeating the lounge, so for a trial period, this activity has moved to 'PaintStation-2' at the door end of the garage. With the door partly open, and on not-too windy days, the complaints have subsided, though the location is limited - see what I have to put up with?

Pack 13

Pack 13 is the set of idler wheels and adjuster mechanism.

These wheels are almost identical to the Type 'B' road wheels except they have a larger hub and take 'proper' sealed bearings and not the simple brass inserts of the road wheels.

The photo shows all the parts (left), the assembled adjuster (centre - before and after painting) and the completed idler wheels.

Pack 14

Pack 14 is the pair of drive wheels. Construction is straightforward with a dash of superglue holding the roller pins in place and making sure the rollers rotate freely. Painting and attaching the tyres is exactly the same as all the other wheels.

What is completely different is the method of attaching the wheels to the drive shafts, since unlike the other wheels, these are not supposed to freely spin on the axles! With Pack 14 are two taper 'bearings'. The manual says to follow the installation instructions to be found in the pots in which these bearing arrive, but neither pot had any such, so I had to follow common sense (!!) and suck-it-and-see methods.

It's actually not difficult - a square section bar (which needed a little grinding to fit) slips into a channel in both hub and bearing to absolutely prevent any rotational slippage. There are two large grub screws which fit the tapped half-holes in the hub (and not the tapped half-hole in the bearing). These, when tightened, squeeze the bearing onto the shaft, preventing any movement along the shaft. The manual gives instructions on setting the position on the shaft to line up with the other wheels.

Finally, each large 'hub cap' is fitted onto the end of the shaft with a M5x10 counter-sunk socket screw. Unfortunately, I couldn't find anything in the fastenings packs that fitted this description, so I'm using the only two M5, slot-head bolts I could find in my bits-box., cut down to 10mm long.

The photo (bottom left) shows the left sidedrive wheel fitted, but without the hub cap, to reveal the bearing.

Stage 3 completed

The axle pairs can be rotated sufficiently so that each pair of Type 'A' and 'B' wheels can be eased onto their axles (after a drop of light '3-in-1' oil). The 'A' wheel needs to be slid half onto its axle first, then each of the two 'B's fitted (back-to-back) and all three pushed home. The wheels are secured to their axles with a countersunk hex screw, which is then covered by the hub-cap. Ensure that all wheels rotate freely - I found I had to strip the paint off the bosses where the two 'B' wheels contact, it's that close a tolerance.

Actually, I've left the final fixing of the wheel screws and hubcaps for the moment, just in case some adjustment is needed in fitting the tracks.

Apart from the hubcaps, this completes the by-the-book build of Stage 3.

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Battery tray

Before we go on to Stage 4 (tracks) , recalling that on the Prep. page some half-track builders have mounted their batteries under the bonnet, I decided to at least retain the flexibility to do the same by installing a platform in that location.

I had planned re-deploy a couple of 12V, 7Ah sealed cell batteries used for a large boat model that hasn't been in the water for over four years, but despite occasional charging, it seems my charger had partially failed and one battery was beyond redemption having failed to get above 8V after a week of trickle-charging with a new 3-stage charger.

One of our club members, Marc, was able to source me a pair of 12V 10Ah cells which are only 1cm taller than the old batteries, bur otherwise the same size. These fit nicely under the bonnet.

Firstly, a length of 1x1cm mild steel angle was bolted to the chassis, as shown in the upper left of the photo. A length of 1x4cm aluminium 'L' bracket formed the cross-members, with other pieces bolted to them to form a tray with two divisions to the exact dimensions of the batteries, plus 1mm for slack space (bottom left of photo). When painted, the trays and battery bottoms will have some self-stick Velcro, plus some stretchy Velcro straps to keep everything in place (right of photo).

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Here endeth the third stage.

Total elapsed time from the boxes arriving: 19 weeks

Total model attention time: approx 50 hours

Total build time: approx 30 hours

Now we can make tracks...

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