johnsmachines

My current project is a diversion from the triple expansion steam engine, which is about 33% completed.

I wanted to do some engraving on my CNC milling machine.  It is accurate enough in XYZ movements, but the spindle has a maximum RPM of approximately only 3000.  Engraving with a cutter with a tip of diameter 0.1 to 1 mm diameter really requires 10-20 thousand RPM.

I also have in mind making some wooden things using router bits, and they usually rotate at 12-26 thousand RPM.

I wondered about a manufacturers attachment for my mill but could find nothing.

So I decided to make my own.

I briefly considered attaching an electric  router to the mill, but since many projects require constant spindle work for several hours at a stretch, I decided that the spindle should have an inbuilt cooling system.

What I bought was a 2.2kW spindle, 3 phase, with a variable speed controller, giving an RPM range up to 24,000.  It is designed for liquid cooling, and can be used for long periods without overheating.

The spindle has an 80mm diameter, and I will attach it to the 110mm diameter quill on my milling machine.

So, I cut some holes in 16mm aluminium plate.

The aluminium plate attaches to the milling machine quill, like this.

To clamp the plates to the quill, and to the spindle, I cut some slits into the holes in the plate, and drilled and tapped some 6mm holes. (done after the above photo was taken).

My problem was that my 6mm taps were all much too short for the job.
I went to my usual industrial tool supplier to buy some long series taps, only to be informed that long series taps are not kept in stock, and would take several days to arrive on special, and very expensive order. Long series taps apparently cost at least 3 times as much as conventional length taps.

Having had success at silver soldering band saw blades, I wondered whether I could add some length to a conventional tap by silver soldering some steel rod, end to end, to the tap.  It was also quite succesful.

Here is the setup for the soldering. (Sorry Americans, what you call soddering the rest of the English speaking world calls soldering).
The angle iron is held in a vice. The tap to be lengthened rests in the angle (after thorough cleaning and application of flux), and the rod likewise (in this case, a cap screw of the same diameter as the tap). The join is silver soldered in the usual manner.

This is what the lengthened taps look like.

I wondered whether the silver soldered join would be adequately strong for the tapping. the tap was totally buried in the workpiece, and would have been irretrievable if the join had broken, and ruined the workpiece.
So I was very cautious when doing the tapping. Used a tapping oil, and backed the tap out of the workpiece every few turns for cleaning.  It worked fine.  It was a demonstration that silver solder is really very strong.

One advantage of using a cap screw for the lengthening rod was that the hex head proved ideal as an attachment for a tapping handle. The tapping handle being an Allen key.

I will post more pics of the engraving-routing spindle when it is finished.

ps. my expert friend Stuart T tells me that silver solder has a similar tensile strength to mild steel!