Any one know how I can adjust this, slightly out (red lines) Its an old one made by Ambrose Shardlow. There is a bit that turns with a rachet in it on the end but that doesnt seem to have any effect.
Do you have the little spanner that fits the two slits between the knurled knobs?
In message , ss writes
Mine came with a little flat spanner to fit the slots in the shaft.
The ratchet gives a fixed torque setting for accurate measurement.
Not the original but I do have one that fits, I tried that but without forcing anything it just appears to rotate the thimble.
Is there a grubscrew to undo first?
Using a google diagram so I get hopefully the correct terminology: There is a grubscrew at the top of the frame that the spindle goes through This maybe a locknut of some kind. Below that there is an knurled wheel and that is connected in some way to a pin that contacts the underside of the spindle. The only other screw is on the rachet part of the thimble. I watched the video clip on how to adjust (different but similar) and they appear to slightly rotate the sleeve, it being a friction fit, with the grubscrew and the pin from the knurled wheel passing through the sleeve on my version I cant see how that would rotate for adjustment.
Well, on the other end of that spanner, is usually a "C" spanner, the pin o f which usually is fitted into a hole at the end of the barrel nearest the frame. I f no hole is visible, wind-off the thimble and remove it completely; there MIGHT be an adjusting hole under the thimble, on the sleeve. ( There is lik ely to be a ring on a thread visible, with a pin hole in it. This ring is f or adjusting for slackness, and does nothing toward adjusting the Zero erro r, so don't move it.) If there seems to be no other course, wind a rubber o r leather strap around the sleeve in the direction you need to move the sle eve, grip the strap tightly and turn it by hand. If that doesn't work, try pliers on the strap. HTH.
The "ratchet bit" is what you use to turn the stem when measuring something. It ensures you get uniform torque so that measurements taken are uniform/consistent.
We were taught "three clicks" at school. On working with experienced machinists / lab technicians in my first proper job I was surprised to find they did not do this, they did it by touch. After learning how, I discovered how to measure to two tenths or better.
Could it be some dirt on the measuring faces?
I dont really know, I wll dismantle the micrometer , clean it and re assemble and see what happens.
I don't think it's dirt on the faces. The dial has gone beyond zero; if the faces were dirty, it wouldn't have got as far as zero and would be giving a small positive reading.
+1. My bet would be wear in the threads, it does look pretty well used. Should be no problem to adjust the sleeve so that it lines up with the thimble again.
If you haven't sussed it yet, the grub screw in the top of the frame clamps the sleeve, sometimes called the stock or barrel. Loosening it should allow the sleeve to be rotated in order to move the zero line to coincide with that on the thimble when the micrometer is fully closed. Make sure the faces of the anvil and spindle are clean. Something like this
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