|Here are a few shots of the CAD models I've been making to create the various parts. What's so nice about building the model in the software first is that you can link them together in an assembly and then make sure it all fits together properly before you even make a cut. Although it takes time to build the models it saves time and materials at the machining end of the job because you know it's going to work. The software also writes most of the code to create the part, either on the 3D printer or on a milling machine or lathe. Some parts, like the tracks and sprockets can't be machined in one process but the software can be tweaked to change the way a part is machined. To the left are a couple of shots of the track links.
To the right are a couple of screen shots of the model for the track drive sprockets.
Click the images for bigger versions.
|Model of the rear sprocket.||
These images show the assembly of the drive sprocket, one set of road wheels, and the rear sprocket, aligned with the track links model. When rotated it's possible to see the alignment of the sprockets and wheels with the different parts of the track. This ensures that the finished parts will fit together.
To the right you can see the various stages of swinging arm manufacture. The top image shows the arms machined and drilled and with the machining marks still on them. The six arms on the right have been polished and shot blasted to remove machining marks and give them a nicer look. The axles were machined to fit into the holes and will be welded into position. These axles go into the axle blocks, shown on page 2 (and one on the bottom right of this image), and connect to the torsion bar suspension. The axles for the wheels go onto the other end of the swinging arm.
|OK, I've started on the drive sprockets. They are a really complicated shape if made to scale, so machining time is huge. See the CAD drawings above. Therefore I'm attempting to make the outer section in two halves, the outer spokes and then the inner cone section that fits into that. Here are the outer spokes being milled. The basic shape was turned on a CNC lathe first as it's much faster than milling. The the holes for the spokes and outer gear teeth were milled into it. Because I don't have to worry out the inner cone shape I could use a bigger cutter and go full depth through the spoke holes. That cut estimated milling time down to 3.5 hours from about 2 days !! Cheers to Steve for letting me hog a machine for half a day.||
The inner cone can be turned on a lathe and then I'm hoping to weld the two parts together to make the completed outer sprocket. The inner half of the sprocket is simpler so can be turned on a lathe, except for the teeth, they will be milled.
|Here is the finished sprocket in various orientations and also shown with the hub.
The hub was made using some of the old cast aluminium billets I used for the wheels, so it looks a bit messy, but it will be covered by an end plate, shot blasted and then painted so it won't show.
The next trick is to join the sprocket to the hub. Welding looks like it's not going to work due to the thickness of the hub compared to the spokes, so I'm going to try to use steel pins and see if they are strong enough. If that doesn't work I guess it's back to the drawing board.
|Here is the inside of the drive sprocket. In the original the drive gears fitted into a housing that was partially enclosed within the front drive sprocket, hence the large space inside it. I still need to drill the holes for the flance bolts and finsh the shape of the teeth.|
OK so after looking at the front sprocket for a while it didn't seem to look right. With the inner being too rounded. I re-measured the Tamiya kit and it looked right compared to that but didn't look the same as other models or the pictures of the full size Tiger 131 I have. The centre of this doesn't look so curved. So I decided to make another one but with a less rounded inner. This would also make it easier to machine as one piece.
|So here is the new sprocket - bolted to the original back. It needs a bit of work around the machining marks which will be filed and then filled to make them smooth but if it saves all the soldering to join the two parts together it will be worth it. This shape is also now the same as the pictures I have of 131. There is a rounded cap to go on the outside of the sprocket but this will be made seperately and bolted on. The image on the right shows how it fits onto the 3D printed tracks.|
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