I posted a small tip on making rings with the Punch & Die set earlier. I now use my lathe.
I use stock styrene rod from Plastruct. I drill in the rod with the correct inner diameter and use the lathe to remove enough material for the correct outer diameter (example in the image shows this in reverse). Instead of using a parting tool, I reinsert the drill and use a knife to cut the ring from the rod; the drill with catch the ring. You can make a series of rings quite quickly and collect them on the drill. Using the knife can result in some variation of the ring thickness, but the number of rejects is a lot smaller than with the punch & die set and I can now make rings of all sizes. You do need to be careful using the knife while the lathe is rotating; this is why I position the knife as in the image—cutting with and not against the direction of rotation—so that the tip of the knife can’t be hit by the jaws of the chuck and catapult into my eye.
A small how-to on cutting steel tubing at very small sizes accurately. I bought mine from Cammett Ltd. The tubing comes in a wide variety of inner and outer diameters and can be most useful for small detail work.
I start cutting of a bit of tubing and inserting it into the chuck of my drill. Both Proxxon (28941) and Dremel (4486) offer these chuck as a affordable accessory to their drills next to their range of collets. At this point I usually sand down the tube. I then use the depth probe of my caliper to insert the tube into the chuck with the to-be-cut tubing sticking out at the right distance. The drill is switched on and I use a sharp knife to cut off the tubing in a sawing movement. I do this carefully, as the part sometimes jettisons away. Don’t try to hold the part in place using a finger, you might inadvertently drill yourself. After the tube is cut, I use a precision reamer to clean the remaining tubing. I do this by hand, I lost a few reamers with the drill turned on. Positioning the reamer is probably the hardest part.
Now the small tube needs to be cleaned, but it can be very small and near-impossible to hold. I use the reamer to pick up the tube and reinsert into the chuck. I apply the reamer when the tube is again firmly in place and a drill to check if the outer diameter is larger enough after cleaning (and for drilling). Sanding down the part at this point is also possible. At the end you have small pieces of tiny tubing at a consistent size. Using the macro setting of my camera shows the edged are a bit rough, but it’s a 0.5 by 0.5 mm part.
I posted a small tip how to make rings with the punch and die set (here). I made a small refinement that allows for the punching out of holes from rod or disks. For this, I used the Waldron Sub Miniature Punch & Die set (any set will do). I would advice people who want to do scratchbuilding to buy both Waldron sets (or make their own).
1) Take a styrene strip with a hole so that it can swivel around the pin of the set. The strip should be as thin as or thinner than the working material.
2) Place the strip in the set and punch out three holes. One hole is for the working disk, the other two for positioning. Do not remove the punches until all three have been used.
3) We now have a simple template that can be repositioned using the two outer punch holes.
4) Now, drill the center hole to the exact diameter of the working material. I also added to holes at the far ends of the strip and added two disks with the same height as the disk.
5) Insert the disk into the center hole and press it so that it positioned tightly.
6) Position the styrene strip and fix it using the outer punches for the exact location
7) Gently punch out the center of the disk and remove all punches. Swivel the strip outwards and remove the ring.
8) Make many!
The advantage of this technique is that it works for all combinations of inner (depending on the punch & die set) and outer diameters. You only need to have the exact drill size ready, which is much easier than making sub punches on a lathe as with my previous tip.
Update added 18-01-09
A small refinement was added to this tip. I let the styrene strip swivel around the largest punch. The second punch is taken to set the strip into position with the third punch for the actual punching. The pic shows I use an array of holes. Top left shows the positioning with the smallest punch. At top right the holes are drilled in where the rings can be positioned. Bottom left shows a series of 10 disks in place with the result shown at bottom right. From the close-up is visible that not all rings are concentrically, so you need to throw away some of them. I also marked which side of the mould is up, as reversing it results in all rings being punched off-center.
Another small tip with a Punch & Die set. It can be used as an alternative for drilling, which is near impossible for the part below. The problem is always aligning the part with the set so that the punch is properly centered, but that can be easily solved
This series of pictures shows the in-progress platform of HMS Hood’s type 279 radar antenna. The platform is very small and is to be fitted to the mast. But as it is very small, it will show when it is off center making proper alignment more important. I use the Punch & Die set to punch off a part leaving the end of the platform circular, making it easier to position and glue to the mast. In stead of making a lot of platforms and keeping the one which worked out best, you can also first glue a disk (or rod) at the exact location where you want to punch out excess material. With styrene parts, you have some time before the glue sets and shift the disk to its proper location (top right). You can then—after the glue has set—use the disk to position the part with respect to the set simply by putting it in the correct hole. Just tap the punch gently and the part is done.
I use this trick quite often as it is easy to use and accurate. Drilling very small parts isn’t always possible, as you don’t have any space to hold them fast and they often tear when using larger drills. Very small parts can be destroyed during the punching as well, but less often than with drilling.