Anybody know what these are ?

Spot facers for socket head cap screws ?

I'd guess they are some sort of counter-bore tool, like a D-bit.

Ed.

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Agreed ['though more probably counterbores]

... but am I right in thinking the one at the front is made for 'reverse' rotation ?

MichaelG.

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Sorry ... I think my eyes were in backwards 

Edited By Michael Gilligan on 02/03/2017 18:50:31

Interesting suggestion

This would be a pretty deep counterbore even for cap heads.

There is a blind hole at each end which could be for a pilot drill.

Etched on them is Microtools T133945

Both the same

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Not wishing to take this too far off track ... In some situations, it is good practice to counterbore as deep as is practical [it avoids bolt stretch]

MichaelG.

mmmm counterbore is an often miss-used term. Look it up.

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To humour you ... I just did:

What point are you making ?

MichaelG.

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Quote from **LINK**

https://en.m.wikipedia.org/wiki/Counterbore

A counterbore (symbol: ⌴) is a cylindrical flat-bottomed hole that enlarges another coaxial hole, or the tool used to create that feature. A counterbore hole is typically used when a fastener, such as a socket head cap screw, is required to sit flush with or below the level of a workpiece's surface.

< etc. >

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Edit: A typical 'use case' for deep counterbores would be items like this:

https://www.thermofisher.co.nz/Uploads/file/Environmental-Industrial/Environmental-Monitoring-Safety/Environmental-Simulation/Vibration-Test-Analysis-Systems/LDS-Test/pdf/Head-Expanders-Fixtures.pdf

... not one of mine, but I have designed a couple in my time.

Edited By Michael Gilligan on 02/03/2017 21:56:10

Not sure it is a counterbore as the difference between the pilot and larger dia does not seem enough even allowing for a very large clearance hole for the bolt/screw.

Maybe just something to put a small radius around the edge of a hole?

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Yes, I did wonder about the proportions .... maybe not for capheads after all.

Perhaps Alan could tell us the diameters

... I've had no luck searching for that Microtools reference.

MichaelG.

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Edit: another possibility is that the disproportionately large pilot diameter matches a flanged insert for use in a relatively soft component.

Edited By Michael Gilligan on 03/03/2017 08:10:10

Any bolts that is tightened is going to stretch, its not avoidable.

OK it might not be a measurable amount but many fixings rely on 'prevailing torque' to stop them coming undone and bolt stretch is deliberately 'designed' in to keep the two parts being held together with the correct pressure between the faces.

Ian P

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O.K. Ian ... I should have said something like "[it reduces bolt stretch to manageable values]" ... Note: I was using "stretch" in the dynamic sense; but I hadn't made that explicit.

On a 20,000 lb thrust shaker ... I can assure you that short caphead screws, down deep counterbores, are much more effective than long ones in shallow counterbores. [see the 'head expander' that I linked.]

Feel free to continue the discussion without any further input from me.

MichaelG

Edited By Michael Gilligan on 03/03/2017 08:43:13

To return to the original photo, the counterbore on the parts is not deep - on the contrary, it is very shallow. There is little exit for the swarf, so it will completely choke up before 5mm depth is achieved. So more for shallow spot facing than a counterbore for a cap head.

But it does demonstrate a very simple way to make a custom counterbore cutter!

Martin

Edited By Martin Whittle on 03/03/2017 10:23:44

I think it's a deburing tool.

Agreed

I agree, it is for deburring holes, and putting a radius on the edge. Ian S C

Deburring is my opinion also, with the addition that the tool could produce a shallow, larger bore to allow for a dowel to be inserted leaving a relief around it's base to avoid a raised burr.

Thanks all for your thoughts.

I will store in the drawer marked 'Might be useful one Day' (which is slightly overflowing).

Alan

They could be ejector pins from an injection mould tool, or quick change punches from a press tool. The scallops could be for retaining the pins/punch in the platen/die-set. Roy M.