My daughter has recently become an avid knitter. She likes a 5 needle style. While most size needles are available in wood and metal, she wanted to try 9mm needles and could only find them in wood. Knowing that I enjoy a challenge, she asked for a set in metal. Aluminum was the obvious choice for the weight.
There were two ways to go: either solid aluminum rods tapered at each end or hollow aluminum tubes with cones fitted to each end. My supplier didn't have raw stock with a 9mm diameter but I was able to find tubes of perfect diameter aluminum from Tower Hobbies. They were 12" long and I chose the thick walled ones for extra strength. I wanted the needles to be 8.5" long, tip to tip, so I could cut each tube in half with the remainder of the length being the added cones.
The single most important design detail is that the needles must be very smooth with no burrs or edges to catch the yarn. A few design features take this requirement into account.
Most of the work done could be done using files and a drill or drill press but the easiest tool, by far, is a metal lathe. I suspect that aluminum could be cut freehand on a wood lathe but that was not necessary since I have access to metal lathes both at home and at my makerspace.
The dimensions in this Instructable are just a suggestion since you want to match the tubes you get, the length and tip angle wanted by your knitter.
Quick note: A rod is solid metal and a tube is hollow.
Step 1: Preparing the Tubes
I marked the midpoint of my tube and chucked it into a 3 jaw chuck since I didn't have any metric collects. I used a hacksaw and turned the tube at my lathe's lowest speed. I could have used a parting tool but for tubes I think I get a cleaner cut with the hacksaw.
I used a file and smoothed the cut edges.
I then chamfered each end of both tubes with a 60 degree countersink. This will be useful when the end cones are fitted to be sure the ends butt as closely as possible.
When using the 3 jaw chuck, wrap some paper around the tube to keep it from getting scored by the jaws. Aluminum is very soft and care must be taken to keep it from getting scratched or crushed.
Step 2: Preparing the Cones
For most of the ends, I used some 3/8" aluminum rod that I had (0.375" or 9.5mm). Since I had a 3/8" collect for my lathe, I was able to hold it securely with the length of the rod passing through my headstock. This allowed me to cut the cones off of the rod without any waste. In the photos, I used a larger diameter rod so I needed to turn it down more and use my 3 jaw chuck.
I marked the total length of the cone plus the stub that is used for gluing it in place on my rod. That would be about a 1.5" total length. For soft metals I use a cheap caliper as a marking gage (I would never do this with my good calipers but having some Harbor Freight $8 calipers has some advantages). I turned the diameter of this length down to 9mm, trying to be fairly accurate in the middle section and doing a final light pass at a slow feed rate to get as good a finish as possible.
Once this was completed, I marked the location of the stub and taper on the rod.
By the way, I am aware I am mixing units. Just pity us in the U.S., keep calm and move along.
Step 3: Cutting the Taper
Tapers can be tricky to cut on a lathe without a taper attachment. However, since the taper is very short, I used the compound to keep a regular cutting angle to make all of the end cones uniform. The easiest way to set the compound is to chuck a similar taper in the headstock with the power off and swivel the compound until the cutting tool feeds along the same angle as the chucked part. Or, if a similar part is not available, keep cutting and adjusting until the taper looks right. My choice wasn't rocket science - I just wanted a reasonable knitting needle. I ended up with an angle of 8 degrees from the centerline.
Taking repeated passes, I cut the taper until the tip had a diameter of 0.125 inches (3.18mm). Since I had marked the end of the taper previously, I knew when I was getting close.
The last pass should be a light cut with as smooth a feed as possible to make the surface smooth. This will reduce the sanding later on.
Step 4: Cutting the Stub
I then cut the stub on the other end of the part. The diameter should be a sliding fit with the inside diameter of the tube. Ideally the shoulder should be at 90 degrees to the stub but since I had the compound set for the taper, I didn't care that the shoulder was rounded. I had cut the chamfer on the end of the tube so there wouldn't be any interference.
I used a sharp tool and and a fairly high feed rate to get a rough surface. This part doesn't show and will give the glue more 'bite'.
Step 5: Shaping the Point
With the lathe turning at its slowest speed, I shaped the end of the cone freehand rounding the cylinder shape to a gentle point with a file. Once I was satisfied with the shape, I covered the bed of my lathe with a cloth (always do this when abrasives are used) and I sanded/polished the cone and tip with sandpaper, starting at 400 grit and going to 1500. I didn't worry about the straight shoulder for now since sanding that will be part of fitting the three pieces together.
I wanted a satin finish. Too well polished and I was worried the yarn would just slide off.
Step 6: Clean Up and Parting
I used my parting tool to square up the shoulder a bit and then parted the cone from the rod.
Rinse, lather and repeat. You will need 5 tubes and 10 cones. The tubes are pretty foolproof but I would suggest making a few extra cones to cover mistakes.
Step 7: Gluing Up
I switched over to my wood lathe (an old converted metal lathe) since I don't mind sanding on the wood lathe. I have a live center for my tailstock with interchangeable tips. Since I didn't want to mar the already polished ends, I turned a support that would fit into the live center and cut a dowel for my 3 jaw. I drilled a hole in each piece of wood to allow the taper to press against the edge of the hole without bottoming out.
I put the dowel in the 3 jaw and the support in the live center in my tailstock and test fitted the needle. All was well so I coated each stub with JB Weld, a metal impregnated 2 part epoxy and slid each stub into an end of the tube. I rotated the ends a bit to assure an even coating of epoxy on the inner surfaces. I placed the knitting needle between my supports, slid the tailstock over and locked it to the bed and advanced the live center until the needle was held firmly but not crushed.
I wiped off any epoxy squeeze out with a paper towel and left the needle in my lathe for 12 hours to let the epoxy harden. Once again the bed was covered to avoid getting any glue on it.
Step 8: Final Polish
Take the first needle you made (the epoxy cured the longest) and put it back between the wooden supports. Cover the lathe bed and spin it at the lathe's lowest speed. Then, step through sandpaper grits from 400 to 1500. You may find it easier to wrap the paper around a flat stick. Pay particular attention to the transition between the rod and cone. I was less worried about the aesthetics of the project than the overall smoothness so a bit of the epoxy showed but it was completely smooth and wouldn't catch on the yarn.