Making Spars on the CNC Mini Mill

by John

Now that the CNC seizing serving machine is functioning properly I have turned my attention back to the CNC Mini Mill and USS Constitution model.

The masts and bowsprit are sitting in place, but not fastened, except with temporary, fine, copper wire stays so I can measure the length of shrouds and stays for the permanent standing rigging. They need to be removed again so I can apply iron hoops or facsimilies to the lower sections. Even then the masts will be removeable, in case future repairs are required.

But in a couple of sessions I used the CNC mini mill to make the spars. There are 24 of them varying in length from 60mm to 310mm, and diameters from 2mm to 7mm. They are all tapered, and 3 of them have central octagonal or hexagonal sections, so making them on the CNC mini mill seemed like the ideal tool for the job.

The home-made CNC Mini Mill.

There was some testing of the depth of cuts with a 3mm end mill in the Proxxon spindle at 16-20,000 rpm. The limiting factor was the power of the Nema 17 stepper motor rotating the headstock at about 100rpm. The steppers moving the X,Y and Z axes had no issues. The other limiting factor was the small diameter of some spars. At 1 to 2 mm diameter they sometimes flexed and started whipping, and in one case broke completely. I had to steady the workpiece sometimes using my finger as a steady, to absorb the vibrations and stop the whipping. I counted my fingers after each run, but none seemed to be missing.

Another factor to consider was the mill maximum distance between centers of 150mm. The bigger spars had to be done in 3 sections, repositioning the spar position each time. Not difficult, but increased the time taken for the job.

I was pleased with the surface finish after milling. A quick light hand sand, taking under a minute for each spar was all that was required.

The plans for the spars. Each one ticked off when made.
All of the spars. The one which I am holding is the largest, and it has a hexagonal center section. (probably should have been octagonal. Will I remake it?). Not enough dowel was supplied in the Mamoli kit, so I bought some from Bunnings. lack of 2mm dowel was a problem because the wood merchants do not carry such tiny stock. So I used some bamboo food skewers. Still had to reduce the diameter from 2.5mm, but the end result was acceptable. There might be some colour difference from the other spars, but hey, in the day I bet that frigate captains would have used whatever they could obtain when on a voyage to distant lands.

The mill worked very well. Return to dimensions was accurate, and the finish was good. It took a while to get a production run going, re- learning the commands and G codes, and the first spar took a couple of hours, but after a while I was producing one every 5-10 minutes.

Next step for the spars is to attach the footropes, blocks, and other fittings. I will lacquer them. No paint.