Sharing our best non-standard practices.

[edholly]

I hope this thread develops where simple practices we all stumble across, by necessity or otherwise, are listed for others to consider.

Hopefully the posts will be brief, maybe just a couple of paragraphs at most - and one post dedicated per practice. Please make the posts in a colour, so that they can be distinguished from any comments that they entice which can then be in black.

Apologies to all those that may use these processes all the time, but for the amateur like me, some of these processes have made my machining life a lot easier and wanted to share them, hopefully inspiring others to do the same.

I'll start off with a few of mine.

 

[edholly]

When finding the centre of something on the mill with DRO - I always move the spindle through 180 degrees from one side to the other. This then does not matter if there is an error anywhere in the devices, it simply cancels the error by doing this. Similarly - if finding an edge, I always double take it with the spindle 180 degrees rotated and move the bed to the centre of the 2 readings, averaging it out again cancels any error.

Since doing this have found that the centre or edge is absolutely perfect, even with a device that is not.

 

[edholly]

To get a really nice point or a very nice radius on the end of a wire say for a needle valve, or a nice radius on the end of a gudgeon pin, put the piece in the end of a drill and spin it up against a linishing belt which is also turning.

The point or radius comes out very nicely plumb in the middle of the piece.

 

[edholly]

Rather than use a dial gauge, you can check the run-out of a piece in the lathe by using the cross slide. Bring the cross slide with whatever tool it has gently up to the piece for each of the 3 (or 4) jaws and note the reading.

When the reading is the same for all 3 (or 4) jaws, the piece is running true.

 

[edholly]

Often a taper is required in a piece, sometimes just a thou or two like in a contra piston. You can check this BEFORE MACHINING by moving the compound slide the length of the cut and gently bringing the cross slide against the piece. The difference in the measurements is the taper.

Since using this process, the scrap bin for contra's is empty.

 

[spacy]

To centre a square bar in a 4 jaw dial in a round bar of the same diameter as the across flats of the square then release 2 jaws and replace with the square.

 

[spacy]

To centre a rotating table with a chuck, first face some scrap in the lathe, blue it then aligning each jaw against the tool scribe a line across the face with the tool, 3 times for a 3 jaw. Move the chuck to the rotating table and find the centre with your normal method (I use a needle). Replace the scrap with your workpiece which is now on centre.

 

[edholly]

Since using this process I have been able to size a cast iron piston diameter exact to less than a tenth of a thou. Found this process simpler and even more accurate than lapping.

Bring the diameter down to 2 to 3 thou oversize with normal machining. Cut a couple of strips of wet and dry (or similar) paper about 5mm wider than the piston length - a course one and a fine one. Get a steel ruler the width of which needs to be wider than the piston length. Place the course paper against the ruler and bring the paper backed by the ruler square up to the work spinning (I use around 770rpm). You will see the cast iron abrading, bring it down to within a half thou with the course paper then use the fine paper.

You can take the piston diameter down by just microns this way and with careful holding of the ruler under the paper, no barreling or taper will occur.

 

[edholly]

One of the nicest ways to make an exhaust port in the side of a cylinder is to use a simple slitting saw. You can buy them in various thicknesses and diameters. It is simple to make a mandrel to hold them. Be just a bit careful as the swarf will look like it hasn't broken through as it gets pushed away into the cylinder and looks like it is still meat, but I can assure you sometimes it isn't and I almost sawed the top off a lot of work first time I did this.

 

[Hopefuldave]

Very much a cheat, worms for some DP pitches are surprisingly close to metric threads, for Module pitches surprisingly close to tpi...

An example, for 16 DP the correct pitch in mm is pi * 25.4 / 16, giving 4.987 mm - so 5mm pitch can be close enough...
For 2 module, correct pitch in inches is 2 * pi / 25.4. 0.2474, so 4 tpi will be good enough for government work