Cast iron cylinder in a four jaw chuck, ready to be bored

Boring the Cylinders

Cast iron cylinder mounted in a four jaw chuck ready to be bored.

Note the packing pieces, to protect the casting, from the four jaw chuck. Also the packing piece behind the casting, this is a piece of scrap steel or Aluminum bored out to be larger than the casting bore. This packing piece enables the boring bar to clear the casting, without hitting the chuck.

Line the turning tool up to the face of the casting to facilitate adjusting the four jaw chuck to make the already cored hole as central as possible

I'm using a tungsten carbide tipped tool to turn the bore. Cast Iron can have a hard skin which will wear silver steel tools very quickly, the tungsten tool overcomes this.

Once the casting is held securely, Set the lathe to a slow speed and use the boring bar to skim the face, making sure that the cut is deep enough to break through the cast iron skin.

Once the face has been skimmed, you are ready to bore the cylinder. Keep the lathe in a slow speed, take small cuts, unless you are confident , about making deeper cuts.

Tip

DONT FORGET you are using a boring bar so the cutting adjustment is toward you and not away from you.

When I'm machining holes accurately, I find, as do many others, making accurate measurements difficult.

So I usually turn a piece of scrap with the finished diameter then a couple of steps with smaller diameters, say 5 thou less and 10 thou less, so that I can try the bored hole before I make it too big.

If you do bore the hole slightly too big, or it is slightly too small, don't worry about it, you can always compensate when you turn the piston to fit.

The bored casting ready for honing

High Tech Hone, Bore Polisher

What is this funny Looking Stick?

Well it is a "High Tech", Hone, sometimes, known as a bit of broom handle and some grinding paste.

Made by taking the broom handle turning it to the bore size drilling a hole through the result, then slit with a saw and add a screw in the end.

The inner section of the Hone, where the hole is and for about an inch is tapered down lower than the working part, this is to ensure that the cylinder does not get "grabbed" by the Hone.

Slowly slide the cylinder back and fore 

You need to make a new hone, for each grade of grinding paste used, do not mix the coarse with the fine as the coarse grit will ruin the surface of a finished bore.

Use a slow speed and a light hand (only adjust the screw a small amount) Keep the cylinder moving along the hone, reversing every so often till you get the finish you are looking for.

Start with a coarse grit, you can use oil or grease as a lubricant, and to hold the grit in place. Once you have removed the turning marks move to another finer grade of grinding paste.

The casting will get hot, so let it cool from time to time.

Finished, polished Bore  

Well here is the finished article, nice and shiny.

You don't have to go to these lengths with the bores for this engine. I just like it to be nicely finished.

Some people think that too high a polish, in a bore is not a good thing, so you have to decide for yourself.

It is very satisfying to do, even if it is a bit on the slow side.

The technique can of course be used for all sorts of bores and hole finishes.

Ideal for hydraulic and pneumatic cylinders.

Rotary Table with mounted Cylinder

The Cylinders are mounted on a spigot on a rotary table then clamped solid, ready for drilling and tapping. The cylinder is mounted on a pre-made jig, or spigot.

A Dial Gauge indicator is used to center the cylinder bore under the mill spindle, (rather than centering the spigot) this means that any inaccuracies in centering the spigot are removed.

The mill table is then moved to the correct position to start drilling the holes. 1st Hole is drilled, then the rotary table is turned 72 degrees, 2nd hole drilled, table is moved 72 degree etc.

So the rotation is 0, 72, 144, 216, 288, then back to zero.

Clamp the corresponding Cylinder head and drill the same holes once again. Mark the position of the cylinder head relative to the cylinder, (They don't always line up if the two are rotated relative to each other). Remove the cylinder head.

I tap the cylinders by hand using a "Top hat" tap guide to support the tap for accuracy.

Drill the Cylinder head bolt holes out to clearance using a pillar drill, picking up on the already drilled holes.

Hold the cylinder head in a Drill Vice to do this.

Drilled and Tapped

The cylinder has been drilled and tapped ready for the head studs and the cylinder cap to be fitted.

Note

The clamps are easily made up out of strip steel and stock machine screws, I have a range of mm screws in stock, which I buy in boxes of a hundred or more for cheapness.

The two clamp sizes shown here use 6mm and 8mm machine screws, later clamps use crosshead machine screws.

The rotary table used here was picked up at a "car boot" sale in a very dilapidated state, and refurbished over time. Now works very well and is a great time saver.

Studs and Nuts in Place

The cylinder heads and bases are drilled at the same time as the cylinders, to ensure that they fit,

Each cylinder head and base are marked so that they can be matched later.

Centering the Jig on the mill

Using a Jig to mill and drill the steam passages, makes life considerably easier, and as the steam passages have to be done on both ends of the cylinder, speeds things up considerably.

The jig is quite simple, and can be made from scrap, or whatever you have to hand.

First turn up a top hat spigot, with a diameter a thou or two smaller than the cylinder bore, then drill and tap the center I use 6mm but any thread to suit the screws/bolts to hand will do.

Then take a piece of square material about 4" long drill a clearance hole at one end, and bolt on your tope hat locating spigot, leave about half an inch of thread available at the top so that you can fasten the clamping plate.

Use a dial clock gauge to centralize your spigot, before milling the steam passage slot.

Milling Jig Showing Top Clamp

Getting ready to mill the steam passage 

The top clamp for the jig consists of any thing that will do the job, in this case a failed gear blank is pressed into service.

A quick burst with a file to make the entry slot for the mill and you're ready to go.

If you are using a mill tool rather than a slotting drill, make sure that you start the mill cutting on the edge of the bore before milling the slot.

Finished steam passage ready for drilling

Steam passage milled, just needs a bit of gentle de-burring, then ready for the next stage.

There are two steam passages for each cylinder, one either end, so flip the cylinder over and mill the second, steam passage.

Repeat the exercise for the other cylinder.

Centre drilling ready to drill into steam ports

The jig is now tipped to the correct angle for drilling the hole to the steam port.

The mill table cross slide, should be kept in the same position used for milling, just adjust the longitudinal slide to position the center drill.

A little gentle pressure is all that's needed to center the hole, pushing the center drill, deep enough so that the center hole is just a little wider than the drill to be used.

Drilling final hole to steam ports

Drilling the Steam passage

The main part to be careful about when drilling down to the steam port, is to be wary about the drill snatching as it breaks into the rectangular, pre cast port.

I used the vernier, or feed wheel on the mill to complete this.

It's quite satisfying when the drill breaks through into the port, and you know, another little job is complete.

Flip the cylinder over, and drill the other side.

Finished steam ports and passage

The finished Steam Port

Well, here's the finished steam port, just needs a little de-burring, to take of the sharp edges.