M&W Straight-Edge Set

[Clive Brown 1Participant @clivebrown1]

I have an ancient boxed set of Moore & Wright Toolmakers Straight-edges. M&W part no. 315. Four steel straight-edges from about 2" to 5" in length and also a length of what looks like a piece of black glass about 5" x 1" x 0.25".

Does anyone know the purpose of this "glass"?

Clive

[Clive Brown 1Participant @clivebrown1]

[JohnFParticipant @johnf59703]

Probably an "optical flat" used as a reference for the straight edges

John

Might have an old M & W catalogue somewhere will try and find it to see if the product is in it

[LambtonParticipant @lambton]

Clive,

I have a 1965 M&W catalogue that refers to : part No 315TP as Black Glass test piece only 30/- each. (£1.50 )

I hope this is of help.

Eric

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JohnF on 22/04/2019 16:55:46:

Probably an "optical flat" used as a reference for the straight edges

John

.

That's an interesting thought, John [and I can offer nothing better at present] … but it seems rather unlikely: All the 'Optical Flats' that I have used have been transparent, so that you can see the fringes.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Lambton on 22/04/2019 17:14:34:

Clive,

I have a 1965 M&W catalogue that refers to : part No 315TP as Black Glass test piece only 30/- each. (£1.50 )

I hope this is of help.

Eric

.

Mmm … I wonder what nature of test was intended

MichaelG.

[PlasmaParticipant @plasma]

I suggest the same as when using the straight edge to check a machined surface, but the glass is as near perfect as possible I.e. stable at variable temperatures etc. Black glass so its opaque when holding it up to the light. ?

[Rod RenshawParticipant @rodrenshaw28584]

I have a set, and a M and W catalogue which lists and describes these.

The test piece is a piece of plate glass and the test is to lightly press a straight edge against the glass and hold both up the light to see if any light comes through.

I read somewhere that a gap of one tenth thou inch will shown as a coloured light (I can't remember what colour!) and a larger gap will show as white light, assuming the background light is white.

My set seem to be very good when I try this test, probably because they were well made originally and I don't use them much. I suppose a professional toolmaker using them repeatedly would need to test to be sure his set were not wearing.

Rod

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, this says it all.

Regards Nick.

P.S. I have the 6" one, which cost 11/9 = 58.75p in todays money.

Edited By Nicholas Farr on 22/04/2019 20:14:25

[Clive Brown 1Participant @clivebrown1]

Thanks for all the comments. Another minor mystery solved. My piece of glass isn't marked "test-piece" as the catalogue illustration seems to suggest.

Clive

[Clive FosterParticipant @clivefoster55965]

Clive

Its the case that is marked test piece not the glass itself. Pretty sure my personal set just has the naked glass but at least one of the guys at work had the glass in a separate case which, I think, was so marked.

Hafta say that I use mine so little that I haven't actually seen them for around 3 or 4 years! Box got moved around during a tidy up.

Clive

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Plasma on 22/04/2019 19:33:08:

I suggest the same as when using the straight edge to check a machined surface, but the glass is as near perfect as possible I.e. stable at variable temperatures etc. Black glass so its opaque when holding it up to the light. ?

.

That makes sense

… and Nick's image confirms it.

MichaelG.

Edited By Michael Gilligan on 22/04/2019 22:01:23

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