If you can get some 4.5 mm Silver Steel, that might be a good starting point. A 13" length may be sufficient to make what you need, presumably 0-25, 25 – 50 and 50 – 75 mm?

Once cut to a little over length, the ends can be carefully faced, with a sharp HSS tool and fine feed to the required length. The lathe should ensure that the ends are square to the axis of the rod.

You could make the required snap rings out of piano wire possibly.

You would need to grind up a tool, possibly a 90 degree Vee form, to produce the groove in the rod, unless you fancy your chances of grinding a tool with a radius small enough to match the diameter of the snap ring.

Position of the groove relative to the end of the rod may be the vital dimension, requiring some trial facing cuts. and measurement.

Howard

Gazz

As Howard says DIY should be practical with a sharp tool.

Getting them exact to length is probably impossible but the circlip style end location isn't tremendously precise so normal practice with these is to zero the display or set a fixed offset by reference to a suitable gauge block or other standard before using. Bit more faff but no great issue once you have suitable references.

The non digital breed have an adjuster on the end of the rod, usually apair of threaded rings locked together.

Clive

I don't understand the above statement, can you please explain. Thanks

Tony

If the lathe doesn't face EXACTLY square, (Many lathes face VERY slightly concave ) the out of flatness over 2.25 mm (radius of a 4.5 mm rod ) is barely going to be measureable with the kit that most hobbyists have.

So 0.0001" should be well within capability.

Within a measuring instrument containing all original parts, there will be a number of tolerances, on each component, albeit fine limit, which build up to depart from ABSOLUTE accuracy under controlled conditions.

We think of slip gauges, in good condition, as being accurate to a millionth of an inch. Stack up several slips, with the protective ones, and you can have a variation of several millionths of an inch from one box of "perfect" slips to another from the same manufacturer, even under the closely controlled conditions of temperature and humidity of a Calibration Room. .

In high volume production industry, a measuring device that is in error by 0.01 % of its operating range (SAY 0.002" in 18" ) will be condemned

And there will be very few hobbyists who work under Standards Room conditions, with measuring equipment that is calibrated on a regular basis.

Working consistently to less than 0.0001" is going to be difficult with hobby machines that are.either built down to a price or used and, therefore, worn.

In the hobby world, most of the time working to less than 0.0001" is going to stretch machine, measuring equipment and operator skill to their combined limits.

Being realistic, many of the parts in our car engines will have been made to a tolerance of 0.001". Not much requires closer than that, except some surface finishes, and fuel injection equipment which does require single micron accuracy.

Howard

The 0-25 mm rod should be 70 mm long, by my reckoning (25 + 45 mm ) judged by the 45 mm difference between the rod lengths and the measuring ranges quoted above.

So, it looks like you are almost completely set up and ready to go!

Howard