We are nearly at the halfway point and in step fourteen it’s time to deal with the sprocket issue. As already mentioned, it has two big issues. The main one is fairly simple to remedy, if not a little time consuming. Trumpeter have not offered a left and right sprocket which had slightly forward offset rollers. The second is that the kit part contains bevelled grooves on the face. Similar marks can be seen on the face in this resto vehicle image, but they are definitely not grooved.
The grooves don’t show in the Panzer Tracts book or appear in any period reference images of the vehicle.
Some more resto vehicle sprocket face detail
Let’s look at the non-handed kit sprocket issue first. The image below shows both kit sprockets built up, and the white dotted circle clearly indicates the incorrect position of the rollers sat centrally between the track pads
The sprocket design was the same on all semi tracked vehicle design of the period and you can see in the restoration image below of the driver side sprocket of a 12-ton that the rollers are sat slightly forward of the centreline against each track pad
The image below shows a clear side view image of a driver’s side sprocket showing each track link sat slightly forward over each individual sprocket track pad.
Fixing and removing the grooved detail in the sprocket face is best attempted first as it will involves a fair degree of handling. I used Tamiya putty and you need to ensure to build up the material in stages to avoid making a mess. Sanding the dome shape back effectively when there is little room between both strengthening ribs and the central hub would be a nightmare. I added it carefully in about four coats, but it still kept shrinking!
Moving on to correcting the sprocket issue the first step is to mark each sprocket outer face parts B21 LEFT and RIGHT. Out of the kit when the sprocket parts are assembled, they are identical, but we are going to make them 'handed' as per the real thing.
This image below shows the best fitment (it can often be far worse!) you could hope for without applying the fix. Notice how the track links don’t align over each sprocket pad.
The second step is to snip off the three keyway tabs on the inner ring of the part (part B16) that fixes between the sprocket face part B21 and part B15, the rear ring which contains the rollers on. This will allow the full rotation of parts B15 & 16 around the rear of part B21 so they can be fixed to part B21 in the correct position.
Step three is to carefully remove all the square tabs (track teeth spacers) around the inner ring of the sprocket parts B15. The fix on the original PMMS site that Terry Ashley recommended instructs you to replace all these cut off tabs back onto the sprocket into their correctly orientated positions. (slightly forward of their original locations on your now left and right-handed sprockets) From experience this really is not necessary. Unless you snip everyone off with a perfect radius profile they are not going to re-attach perfectly and in all honesty this detail is difficult to see once the tracks are fitted. So, I've never bothered.
Whether you re-attach the tabs or not is up to you. All that is left then is to refit parts B15 & B16 which are now free to rotate inside the sprocket outer face part. They can now be fixed in place, so the sprocket rollers are visibly offset slightly forward on each side. This can be done by eye, but I recommend building up two lengths of track runs (ensuring they are correctly orientated for each side) and then use them to test the fitment ensuring a perfect fitment of track links around the sprocket.
The image on the right below shows the tabs re-attached
The image below shows the adjusted and now correctly oriented roller location on a drivers side sprocket. notice how the track links now fit snugly up against each track pad and the whole track run fits tightly around the whole sprocket.
I am
sure there will be some 3D printed 1/35 Sd.Kfz 7 sprocket files out there
somewhere. If you are lucky enough to own one or know somebody with a 3D printer,
then if they are made specifically to fit the Trumpeter kits and the roller
offset is correctly represented that really would be the way to go.
No comments:
Post a Comment