mineral processing thread

Good. You will see how greatly it expands what else you could consider trying. A lathe and milling machine sized to your intended projects really open doors to creativity. They enabled the Industrial Revolution, the steam engine had already been in use for ~100 years without making much difference because it remained primitive and inefficient without them.

All good work. Does anyone have any ore for antimony, then with the copper and tin you can make some Britannia metal (modern pewter), for sheet it's normally 92-6-2 tin antimony  copper.

I have an old Thumler like this whose (only) advantage is simple construction.

Since the ribs need to lift the rods more than the charge, they could be replaced by pairs of screws from outside, preferably in tapped holes. Nuts and washers on the inner end could raise the rods higher before they roll off. If screws don't work by themselves they could attach metal rib strips such as sheet metal angles trimmed and bent for best performance. This would make stirring the charge and dropping the rods easily and independently adjustable.

Screw hole locations could be marked on paper whose length equals the drum circumference. Aligning the ends of the paper positions the holes for center punching as accurately as the paper layout. You could start with one pair and observe where a rod lands when dropped from as high as practical, to space the others away from the landing area.

This gives the general idea of how to divide the length of the circumference into equal parts by angling the ruler.

I salvaged some scrapped 95-5 Sn+Sb solder from the trash at work when they rebuilt a set of heatsinks for temperature cycling GM ignition modules. It can be cast into work holding fixtures in wooden molds without charring them as lead casting does, so I made a vee block that can be drilled into. When bent it makes the "tin cry".

As I lack the experience to guess what will eventually work best I've describes a way to make the rod tumbler innards easy to modify. I've assumed that the rods will be most effective if dropped as far as possible, more stamp than ball mill. The reason for initially tapping the holes is limited wrench access inside the cylinder, they can be drilled out later.

When I plan to drill multiple copies of a hole pattern and can't mount the work on the mill I make a guide plate to clamp on and drill through. For drilling the tumbler cylinder the guide could be a bar longer enough to be supported at the ends with the cylinder clamped on and hanging underneath. This would let the job be done on a drill press with minimal fixturing, only the end support blocks. The guide can also locate the matching mounting holes in the internal ribs. The guide will stay accurate longer if used with a center or transfer punch than drilled through, which opens the holes in mild steel. Purchased drill guide bushings are hardened.

jsw

Never thought of that. Not heard of antimony in Cornwall. Can't say as I will work all night on that, but interesting thought.

I have a long long way to go along this path!

I got "accurate enough" arrangement with dividers. Was it you mentioned trammel points, which would have been better.

Methods best seen online...

Finding circular plate centre - scribed chords with rule-and-scriber then divider from each end of chord method.

All the rest I did with dividers. Sole method.

Worked well.

Then from that centre identified, with dividers mark the PCD (pitch-circle-diameter), centre-pop one starting position on it and use dividers again on PCD radius to mark off the six positions (you'll be knowing the special "law of the universe" property of a compass/dividers to create a hexagon). From the disk centre I also marked-out the as-best-measured diameter of the tube, and fiddled the position of the circular plate on the tube end to give the best averaged fit before marking-out the six "things" (block with a clearance hole for the thread) circumferential positions.

There is one "best fit", and its 180deg rotation is almost as good. Other 4 of the 6 positions - could force it, but don't. Thing is, got the job done, and the tube isn't machine-precision-round anyway.

Experience I had - do use the specific tapping-size drill. The tap "picks-up" and wants to run true to the drilled holes.

I have a long long way to go along this path!

I got "accurate enough" arrangement with dividers. Was it you mentioned trammel points, which would have been better.

Methods best seen online...

Finding circular plate centre - scribed chords with rule-and-scriber then divider from each end of chord method.

All the rest I did with dividers. Sole method.

Worked well.

Then from that centre identified, with dividers mark the PCD (pitch-circle-diameter), centre-pop one starting position on it and use dividers again on PCD radius to mark off the six positions (you'll be knowing the special "law of the universe" property of a compass/dividers to create a hexagon). From the disk centre I also marked-out the as-best-measured diameter of the tube, and fiddled the position of the circular plate on the tube end to give the best averaged fit before marking-out the six "things" (block with a clearance hole for the thread) circumferential positions.

There is one "best fit", and its 180deg rotation is almost as good. Other 4 of the 6 positions - could force it, but don't. Thing is, got the job done, and the tube isn't machine-precision-round anyway.

Experience I had - do use the specific tapping-size drill. The tap "picks-up" and wants to run true to the drilled holes.

------------------------------------------------- There are many tricks and short cuts to be learned during the apprentice phase. Until fairly recently they were passed on verbally, the way I learned accurate manual woodworking and some blacksmithing. I have collected reprints of the few books that recorded them for formal group instruction. An engineer at Segway had a good library of the originals, but no home machine shop until I directed him to one that was for sale and helped him move it.

The "best fit" orientation can be permanently marked with a center punch or chisel. Nail polish holds up well and has a brush to apply it. An inexpensive set of letter and number punches helps for more complex assemblies.

Shopping for nail polish in the bright primary colors provokes an interesting reaction from sales girls until I explain that colors code for numbers in electronics. I'd drop a "Kinky Boots" reference if those around here were more familiar with West End musicals.

When I use those 2300 year old geometric layout methods I put sticky labels on the areas of interest so I can make and correct the trial marks in pencil. Scribing on the metal with a sharp point after getting close enough on paper by trial and error is more accurate but not erasable. I first use a shop-made acutely angled "prick" punch that can track along a scribed line to an intersection by feel, then follow with the drill point shaped center punch. On a good day that's accurate to ~0.1mm.

Drilling and tapping by hand is squarer if you have a reference such as a vee block to square the tool to the work. I carried a small cabinet hinge in my pocket to use as the vee block guide. I haven't seen that idea of mine in print.

Tapping is easier and less risky with industrial cutting fluid or pipe threading oil. Kerosine works on aluminum. A tap can be sharpened by stoning the grooves. Round rods and fish hook stones may fit better.

The vee head on a combination square locates diameters.

A center in an open hole such as on a rough casting can be located and punched by fitting a wooden plug into it and then tapping on a square of sheet metal with the corners folded to stick in.

Holtzapffel wrote that prior to Ramsden's dividing engine gear tooth angles were laid out by repeatedly stepping dividers around the circle and correcting the closing error until good enough. His works are excellent descriptions of the struggles of pre-industrial "accurate" manual metalworking and how they were gradually solved. Volume 2 has hand tools.

Lindsay reprinted several tool-making instruction manuals from the late

Don't try the suggestion to straighten a bent shaft with a hammer while it's held between lathe centers, otherwise they still apply.

I've never found a piece of pipe or tubing rolled and welded from flat stock to be accurately round, especially around the weld. I use machined brass pipe fittings to center other threaded fittings in a lathe chuck. Electrical conduit may be better because the inner weld bead has been drawn smooth. jsw

I found the one about a very sharp narrow angle punch to "feel" a scribed line and its intersection with another.

Amazing tools you describe!

The "prick punch"... I found it very prone to snapping off its tip. Seems to me - tap it lightly with a hammer to leave a small prick mark, then feel a sharp centre-punch with a reasonable angle into that mark and belt it.