Sorry a bit confused, are you saying I need to check the Y-Z first?

Check both X-Z and Y-Z. Only doing half the job of checking how your column lies relative to the table otherwise.

Alignments are one of those things that, to be done right, have to be done completely and in the correct order – "pick'n'mix" choosing of which bits of the alignment suite you want to check / rectify risks making other areas worse. The Schelsinger & MTB checks for machines are not just a number of checks of particluar alignments, they also specify the order in which the checks are completed. – a former colleague summed it up as "build 'em right from the base upwards".

Taken to extremes – if you use an edge finder directly mounted in a collet to set a datum on the corner of a job (head close to the table) then raise the head to get a 13mm jobber drill mounted in a keyless chuck in the spindle (say, raise the head 180mm ) would you want the tip of the drill to still be relevant to your set datum ? Your measured 0.33 / 250mm would mean that it would not be, to the tune of around 0.25mm in one plane alone – you don't know what the error is in the other plane without measuring it. Might just as well have one of the much-derided (in some quarters) un-key round column mill drills if the head alignment isn't maintained along the column traverse.

Square accuracy could be confimed by turning the square 180 degrees & re-doing the measurement – result stays the same = square OK, otherwise split the difference ? A square out by 0.33 / 250mm isn't really much of a "square" ?

The Spindle should be true to the column.

But only after the column is perpendicular to the table which, in turn, is parallel to the base.

Nigel B.

I shall clarify. The spindle should be parallel to the front face of the column as manufactured. It is irrelevant what the relationship of the column to the base is. The spindle axis should be parallel to the Z axis front plane even if the column were lying on a bench.
To do a dial gauge turn around test to check nod, the head needs to be either trimmed (set parallel to the side of the column) or a reading taken by dial gauge each side of the spindle on the table and the dial gauge set to half the difference if there is a variation. Rotating the dial gauge to read in front of the spindle will test the nod.

regards Martin

Edited By Martin Kyte on 19/03/2023 21:35:28

Bearing in mind that very often the misalignment is down to burrs on the mating faces of the base and the column.

If you do take your mill apart do a very close inspection of those faces taking special attention to the tapped and through holes where the column is bolted to the base. Also to the edges of the areas. Clean well before reassembly.

Why did you use the blocks rather than go direct on the table?

tegards Martin

Edited By Martin Kyte on 19/03/2023 23:04:59

I think you are sensible in deciding to leave it alone. Tests like this are really very sensitive and can show inaccuracies that are never apparent on your work in the general run of things.

It’s useful to know where the shortfalls are in a machine even if it’s too much bother to correct. Often you can arrange the job to minimise the shortcoming and at least you know what the limits are likely to be.

regards Martin

I'm pretty much in the same camp but, as always, it depends on the type of work being done and the personality of the operator.

Most of what I do it old-fashioned 'fitting', in which my machines and workshop skills only need to be good enough to get parts to mate. I don't expect measure to better than ±0.02mm (about a thou), and only own a basic micrometer. None of my measuring tools are calibrated. Building to plans, I approximate, and then fit critical junctions together by using the parts themselves as gauges and references. I don't own slip gauges, or anything capable of reliably reaching down to ±0.002mm. I've experimented with 'fitting' using only spring calipers and a steel-rule : works well enough, but requires time and extra care. I'm also a slob, going so far as to accept poor finish and even looking for opportunities not to machine parts at all!

My exact opposite would be a fusspot, the sort of worker who likes everything 'just so' before starting work, who wants to do the best possible job on everything. Where I'd be happy with an el-cheapo adjustable spanner, he's gpt a set of carefully researched Swiss aero-space spanners in all possible sizes. Perfectionists are much more likely to be upset by warty Far Eastern machines than slobs who just see tools as a means to an end.

The acid test is rarely applied. Ask 1000 thousand Model Engineers to make a brass rod 9.7mm diameter and 30.1mm long. Half are far eastern, half are western. The rods are sent anonymously to a third party in an envelope identifying the machine used. The third party numbers the parts randomly, mixes them together and sends the boxful on to a team of judges.

The judges only have the parts to look at. They don't know who made them, or with what. The judges list which parts they think were made by Far Eastern and which by Western. The list is returned to the third party, who compare it with the truth. A chimp choosing randomly will get about 50% right, so only a much better match is significant. The degree to which judges do better than a chimp is a measure of how possible it is to tell the difference between the two types of machine.

This type of test is designed to thwart human bias, whether conscious and unconscious. It's completely fair. When applied, it often smashes belief systems, such as wine tasting experts really can tell the difference, and old violins are better than new ones.

If no-one can tell the difference between a rod made on a Myford Connoisseur and a Mini-lathe, then the Mini-lathe ain't so bad!

Actually there is a difference. Better made machines in good order tend to be smoother in action with more trustworthy positioning. They're easier and quicker to use, which is important when the workshop has to make a profit. Much less important to a hobbyist, who has time to coddle his machines, whether they be down-to-a-price Far Eastern, or clapped out Western antiques!

I have a WM18 mill that worked straight out of the box. Not perfect but close enough. I only had to tram it after deliberately tilting the head. I can think of several improvements but so far none of them have been worth my while. Other owners might insist on stripping the whole thing down and doing a careful rebuild. They're not wrong in that I'm sure it can be improved, but what arrived on a pallet is acceptable for what I do. It's not better than a Bridgeport and certainly not a tool-room jig-borer!

Dave