2-4-6 block woes

We are close to finishing the Tom Senior light vertical at the museum. There is a bit of play in the X axis which requires attention, and the Y and Z aren't great. I have been conducting tests on the spindle which runs better than expected, and is now trammed square and is also square in the fore and aft axis.

Problems started when I started checking the Z axis moving the knee up and down. A dti was fixed to the column and one of the 2-4-6 blocks was clamped square to the bed Xaxis. The knee was sloping by about 0.010" in the 6" of the block.

It turned out that the pair of 2-4-6 blocks are not dead square. They both are three dimensional parallograms. They not only lean sideways, but fore and aft also. What clinched it was putting the long MT2 test bar in an R8 holder in the spindle. Including the taper, it is 11" long. and I have it running 0.0002" tir at the top and 0.001" tir at the bottom. When I set the blocks against the test bar it was obvious that there was a problem with the blocks.

On the surface table, the lean is easy to see with my square and even more obvious when toe bottoms of the blocks touch and there is 0.020" gap at the tops.

I also have some of the cheap 1-2-3 and 1-2-4 blocks (metric), surprisingly, they are actually dead square.

If I was still working, I could have got the blocks trued up by the grinders or the toolmakers in a jiffy.

If you do not have an accurate square and have access to a lathe, you could make a cylindrical square

Paul

You could certainly have them trued up to be square. But would they still be 2-4-6? I somehow doubt it.

I don't care what size they are, I can easily measure them if I need to. Making a cylinder square is only worthwhile if you start with ground stock.

Pray tell where you get that little nugget from?

Tony

If I had a cylinder square, I would expect it to be within 0.0001" in 8" of height on the diameter, and have a perfect finish, something I could not achieve by turning.

Nothing is perfect as in finish but turning can make something good enough for your purpose.

Tony

A Gudgeon Pin from a large engine, (8 to 16 litre diesel ) will probably make a good cylindrical square.

Try your local truck repairer, they may well have a reasonable one from a scrap engine.

Howard

Hi, Wot!. Whoever would have thought of such an idea.

I've only had these about 20 years plus a few more slightly smaller.

Regards Nick.

Hi, Old Mart could possibly get several true 2-4-6 blocks with them, with a bit of precision cutting and grinding, i.e. 2mm-4mm-6mm

Probably won't be much use or what he needs.

Regards Nick.

There might be a chance for them to be trued up, as Chris, another volunteer at the museum is going to have a word with a friend of his who uses a large surface grinder at work.

Amongst the stuff I have is an Elliot shaper table which is probably pretty square, and when I used that, it would seem that the T S is not in such a bad shape as I feared.

I have a Light Vertical and have just started to overhaul an M1. I want both machines to machine accurately, but when one talks of tolerances of 0.0001" over eight inches. These types of figures do not need to be achieved in the world of model engineering lathes or milling machines. I would like to seen the original specs for a factory fresh Light Vertical.

.

But, Peter ... Would you not want the test equipment to be about ten times better than your own production expectations ?

MichaelG.

When one is slowly building a Don Young BR Standard Class 2 loco using his circa 1960 diagrams. Anything that turns or mills half square would be sufficient !!!!

As for my 2-4-6 millimetre blocks, I think they went up the hoover.

All equipment used for testing must be far more accurate than your actual product. I have micrometers in microns and tenths of a thou, but am pleased to achieve +-0.02mm or +- 0.001"

i have a set that are all over the place dimensionally making them useless as parallels , may as well use them as anvils !

Just measuring my 2-4-6 blocks fooled me into thinking they were a perfect pair, as the dimensions matched, although if I had measured several points the discrepancies would have surfaced.

If the square is good enough to show the errors on the block, can't you just use the square? Should be possible to run a DTI down the edge of the blade.

Neil

The square is a Mitutoyo combination square which might sound less than perfect, but it is very good indeed. It was the only set in the calibration system at work, and Brian who did most of the shop floor calibration was an incredibly fussy B, when he tested my Mit digital calipers, he noticed the wear at the tips, 0.0001"! I haven't tried it on its own, as it would have to be clamped down lightly, and the edge is only about 3 to 4 mm wide. I did mention getting good results with the Elliot shaper table, it is a good British make.

Edited By old mart on 10/11/2019 20:03:34