How are they made ? : Starrett 167 series Radius Gauges

In an ongoing discussion : **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=176391&p=1

John Smith 47 on 05/01/2022 08:48:34: wrote:

... that probably took about 20 seconds to be laser cut out of a sheet of metal!

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which prompted me to raise a general question for the forum:

… for anyone who actually uses laser cutting:

What size is the beam-spot ?

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The relevance of that question may have been missed; so I am repeating it here, to avoid cluttering-up the discussion on John’s thread.

Contrary to John’s opinion; my own ‘working assumption’ is that the gauges would need to be photo-etched. … I have never personally seen a laser cutter with a beam-spot sufficiently small to cut a female radius of 0.5mm.

Grateful for informed comment from those in the know !

MichaelG.

I don't know about laser cutting but I do have some experience with sheet metal. They could be made on a cnc punch machine which I have seen produce some very complex shapes.

David

Footnote:

If anyone wants drawings of the 167 series gauges; start here : **LINK**

https://www.starrett.com/searchresults?searchQuery=167

The Inch versions have 2D drawings freely downloadable as PDFs

The Metric versions have 3D drawings, but these require registration/sign-in to download

MichaelG.

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The ‘cloners’ probably did

From memory something like 0.1 mm is pretty normal. They use fibres as the light delivery system.

This might be interesting reading, although it is welding not cutting the tech is iirc the same

**LINK**

I personally doubt that small radius gages are laser cut.

Thanks, both

That’s an impressive document, Dave

MichaelG.

I have a recollection that Moore and Wright used to state that their radius gauges were machined, and hence were better than the opposition who punched them.

Andrew

The plot thickens …

I have just been comparing two of the 2D Starrett drawings:

167-010+.pdf and 167-1_8+.pdf

There are substantial differences in the level of information contained.

I suppose I better download the set, to see in any contain manufacturing instructions !

MichaelG.

Size of the laser beam..........Some twenty years ago I had some balsa wing ribs for a model aeroplane cut, approx 70 off from 1/16" thick wood and approx 140 off from 1/32" wood per aircraft set. At the extreme leading edge there to was to be a 0.8mm diameter carbon rod, which required, naturally, a 0.4mm radius cut out for about 270 degrees.

Imagine my surprise when after a very short time a parcel arrived with two sets of ribs. My major concern was the tiny cutout at the leading edge, into which the carbon rod fitted beautifully with a very satisfying "click".

I appreciate that my task involved cutting balsa wood and not tool steel or whatever, so the power of the laser could be lower and therefore presumably the beam smaller. Hopefully it gives some idea of the versatility of the process.

cheers

Bill

Wood is generally cut with a CO2 laser, métal with an ND-YAG - massive difference in power but only slight difference in wavelength IIRC - both are IR ish - so basically super hot points of light.
Other than power and wavelength I don’t think there is much difference in spot size.

Dave

I've just looked at one of the 2D diagrams, I think it was the 1/64"
I've no idea how they are currently made, but the diagram is dated 11/5/54, which rather suggests that they weren't originally laser cut.

Bill

Well-spotted, Bill

… I confess to being a little disturbed by the ‘fractional tolerance’ note at the bottom of that sheet 

MichaelG.

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P.S. I’ve just skimmed through my downloads, and found some dated ‘51

Edited By Michael Gilligan on 05/01/2022 22:58:31

Update:

This video [starting about 8 minutes in] has some reasonable images of the Starrett items.

… it looks like they are more traditionally manufactured than I thought.

MichaelG.

I think your link's dropped off.

Next time I'm in Sheffield, I see if my friend is in, and query him on the method of manufacture used by M&W etc.
I'm sure he will know.

Bill

Oops … Sorry about that, Bill

**LINK** : https://youtu.be/IR5sG1AcUVw

MichaelG.

MY COMMENT
My comments were a guess and probably rubbish (!) but in my defence they where made in the heat of the moment out of exasperation at:
- The fact that their metric radius gauges stop at 0.5mm whereas their imperial ones go down to 0.254mm
- The extreme difficulty in finding anyone who has them in stock, and able to supply the rapidly
- The lack of any keywords for which to search for a L-shaped gauge
... even if one is prepared to pay quite so much money... for what appears to be simple, easily manufactured piece of steel!

Also note that I did use the word "probably" (!)

LASER CUTTING
Re laser-cutting, I recently got some 1.4mm thick steel sheet cut for a dirt cheap price. I was told that the laser in question has a 0.3mm beam diameter, i.e. a radius of 0.15mm. They also firmly told me that "the cutting tolerances are ± 0.2mm", however this appears to be either just to cover themselves or (much like the Digital Chamfer Gauge discussions) in practice the majority of the errors in cutting are proportional to distance and so become more important for larger parts.

My parts were 32mm long and in practice the measured accuracy was +/- 0.02mm!

MY BEST GUESS
Tentatively, my best guess would be that they are cut out with CNC and then ground to exact size. But if making quite a lot of them, maybe they use a laser to do the bulk of the cutting and finish off with a CNC grinder? If making huge quantities (or if they started making them in pre laser-cutting days) maybe the punch them out and then grind them to precise size.

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John,

You are of course welcome to contribute to ‘my’ thread … but please note that I started this one with the specific intention of detaching the particular aspect that interests me from your other discussions.

… I did this as a courtesy to you; and I only referenced your remark by way of a preface to my question.

Please be assured that I neither intended, nor implied, any criticism of your ‘guess’: I mentioned it simply an introduction to my own ‘working assumption’ … at this stage, they are both just options on a much longer list of possibilities.

I am in search of knowledge, not points.

MichaelG.

OK thank you for the clarification, Michael. Good to hear.

J