johnsmachines

Today the exterior surface of the model 1779 naval cannon barrel was turned.

The piece of brass material weighed 5.1kg, was 300mm long and 50.8mm diameter.

I had used Loctite to glue a spigott in the bore, to provide a center and a driving diameter which the small CNC lathe would accept.

Although the lathe was nominally 300m between centres, the toolpost would move only about 200mm.  So the turning had to be accomplished by turning the cannon mouth end first, and then reversing the workpiece to turn the breech end.

The CNC lathe, owned by Bob Julian,  is about 30 years old, and it came out of a school.  In the course of this  job, it seemed to progressively free up, making us suspect that this is possibly the first time it has ever been seriously used.

The lathe electronics had been replaced by Stuart Tankard to use Mach3.  The G codes were generated by Stuart’s program “Ezilathe”, which is available as a free download on “CNC Zone”.   It is an excellent CNC lathe program, and I thoroughly recommend it.

I will eventually post some videos of the turning progress, but my Oz internet connection is so slow, that for the moment I will post photos only.

I started by turning a piece of rubbishy pine as a test.

That’s me, watching carefully.  Later we installed the swarf cover.

The metal turning lathe does not miss a beat chomping through wood.  These are the roughing cuts.  F300mm/min, S800/min.

The Mach3 picture of progress.

The finished distal half of the cannon barrel in pine.  If I stuff up the brass version at least I can have a wooden barrel. 

Roughing the barrel in brass.  1mm cuts, feed 100mm/min.  It took almost 50 minutes for this section, and about 15 minutes for the breech section.

The barrel mouth.  No gouging resulting from the 22 degree HSS cutter.

Finish was quite good.  Will require minimal polishing with ScotchBrite.

The workpiece was reversed in the lathe, the Z zero carefully set, the X unchanged, and the breech end turned.

The starting weight was 5.1kg.  The end weight, including the spigott was 2.9kg.  So at least 2kg of brass swarf, most of which I swept up and saved for possible future use.

Next to machine the trunions and some silver soldering.