Having trouble turning grooves

[Frances IoMParticipant @francesiom58905]

Jason yes – poor memory (+ I do have thread gauges!) if metric then Screwfix + toolstation only carry M4 and above – I’d double check size as I’d expect M4 at least for that application

[SherlockParticipant @sherlock]

Posted by JasonB on 05/08/2018 15:42:55:

You can take that blade out of the holder and put it straight in the toolpost, thin strip of metal between blade and screw will help

 

 

Thanks Jason.. Do I have to Shim the side out first so it actually reaches the screws?

 

 

Posted by Michael Gilligan on 05/08/2018 16:12:11:

Going by your photo … Yes that is a metric screw: The proportions of the heads differ noticeably between Metric and Imperial.

If it's M3 then the socket should be 2.5mm a/f … So I guess you were using a 3/32" a/f wrench.

 

Yes I was indeed using a 3/32 the 2.5mm allen key definitely didn’t fit, I just double checked to make sure.

 

 

Posted by Frances IoM on 05/08/2018 16:31:00:

how on earth did you take the head off a cap head screw ? normally the thread will give way – anyway sounds as though a thread gauge can be added to your shopping list – 3mm Iso coarse are 0.6 mm thread; also suggest that if you do buy a grinder (+ safety goggles) you move away from the kitchen table to do any grinding.

 

I honestly think it was a really poor screw from looking how it broke off. It left me with a donut shaped cap with the threaded part all in one peice. Having rebuilt a lfew engines I generally have a good feel for fasteners but this was like cheese. Yes, good tip about the grinder, I would definitely get a sore ear for that on the table if nothing else!

 

Edited By Steve Sherlock on 05/08/2018 16:48:28

[Neil WyattModerator @neilwyatt]

> It left me with a donut shaped cap with the threaded part all in one peice

Sounds like the socket was too deep.

[JasonBModerator @jasonb]

The problem with going upto an M4 fixing is that the shank is only 6mm or 1/4" square so there is not a lot of metal left, having snapped two of these holders across the screw whole I should know

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Steve Sherlock on 05/08/2018 16:48:01:

Posted by Michael Gilligan on 05/08/2018 16:12:11:

Going by your photo … Yes that is a metric screw: The proportions of the heads differ noticeably between Metric and Imperial.

If it's M3 then the socket should be 2.5mm a/f … So I guess you were using a 3/32" a/f wrench.

Yes I was indeed using a 3/32 the 2.5mm allen key definitely didn’t fit, I just double checked to make sure.

.

Now I'm confused … The head-to-thread proportion of the screws in your photo definitely looks right for metric.

If they are M3, then the head diameter should be nominally 5.5mm and the socket should take a 2.5mm key

Here is a proper one: **LINK**

https://www.westfieldfasteners.co.uk/BO_ScrewBolt_Unbrako_SHCap_M3.html

If they are Imperial [probably #4] then a 3/32" key is correct, but the head should be smaller diameter

**LINK**

https://www.westfieldfasteners.co.uk/A2_ScrewBolt_SHCap_UNCoarse_0.1120.html

For the sake of my sanity, could you please check the diameter of the head ?

Thanks

MichaelG.

[SherlockParticipant @sherlock]

Posted by Michael Gilligan on 05/08/2018 18:11:18:

For the sake of my sanity, could you please check the diameter of the head ?

Thanks

MichaelG.

Just checked Michael and the head is showing 5.4mm on my callipers here are some better photos.

[duncan webster 1Participant @duncanwebster1]

On my to-do list is to make up a small version of Tubal Cain's (the English one) Gibraltar toolpost for my Perris/Cowells. Why? The top slide is always in the way unless you angle it a bit when it doesn't support the tool all that well. If I want to turn tapers I can very quickly put the topslide back on

[SherlockParticipant @sherlock]

Posted by duncan webster on 05/08/2018 18:48:48:

On my to-do list is to make up a small version of Tubal Cain's (the English one) Gibraltar toolpost for my Perris/Cowells. Why? The top slide is always in the way unless you angle it a bit when it doesn't support the tool all that well. If I want to turn tapers I can very quickly put the topslide back on

They Look Great Duncan, Never heard of them before. Thanks for that. I shall look into that a little more

I'm confused myself to be honest. I always have a hard time deciphering fasteners. The thread actual threaded part is measuring 3mm with my calipers (I should add they are not fancy mitutoyo jobbies) which i suspect is a bit big for a m3 at (2.9mm ish)?

The only thread gauge I have is a whitworth and the closest if not exact match on that is 40 / 1/8"

do they in reality come out a tad smaller like the metric versions, or does 1/8" at a nominal 3.175mm sound too big?

[JasonBModerator @jasonb]

They would usually come out a bit smaller so 1/8 x 40 whit or #5-40UNC are likely, not easy to measure thread angle at that size.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Steve Sherlock on 05/08/2018 18:38:28:

Just checked Michael and the head is showing 5.4mm on my callipers here are some better photos.

.

Thanks, Steve … That all supports my original impression

It's a rather nasty approximation of a Metric cap-head screw [*]

… relieved to see that my 'eye is still in'

MichaelG.

.

Of course, I have no idea why your 2.5mm key doesn't fit the socket.

.

[*] Edit, for Jason : Or a 5-40 with an oversized head. 

Edited By Michael Gilligan on 05/08/2018 20:35:14

[JasonBModerator @jasonb]

Posted by Michael Gilligan on 05/08/2018 20:26:20:

Of course, I have no idea why your 2.5mm key doesn't fit the socket.

Because it's more likely to be imperial at 40tpi which is a long way from the approx 51tpi of M3 and a 3/32" key fits

[Frances IoMParticipant @francesiom58905]

the toolpost on the topslide of my Perris is of course 4BA – approx pitch 0.66mm or 38.48 tpi – out dia 3.6mm – cap dia 5.56mm – the key is 3/32″

Edited By Frances IoM on 05/08/2018 20:34:30

Edited By Frances IoM on 05/08/2018 20:54:03

[Michael GilliganParticipant @michaelgilligan61133]

Rough calibration, based on Steve's 5.4mm measurement:

.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

With the eye of faith [and a large Vodka & Tonic] …

The thread angle looks more like BA than anything else.

'Mongrel' is the word that springs to mind

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Steve,

On further contemplation; I think that broken screw is the proverbial 'red herring'

May I suggest that you concentrate on identifying the tapped hole instead ?

It should be reasonably easy to screw a plastic rod of suitable diameter [maybe a knitting needle] into the hole and take an impression of the thread pitch.

MichaelG.

.

P.S. … This is a useful reference document:

https://www.socket-allied.com/files/6414/7799/4114/SAS_Technical_Guide.pdf

Edited By Michael Gilligan on 06/08/2018 09:16:45

[John Paton 1Participant @johnpaton1]

Thanks Michael – I found that inked document useful too. It can live alongside my Zeus Tables!

It amazing how often I encounter bolts with an unfamiliar thread.

John

[EmgeeParticipant @emgee]

I believe M3 can be ruled out because of the thread diameter 3.002mm shown in the drawing, the best makes are less than 3mm diam and the low cost versions can have OD less than 2.8mm.

Emgee

[SillyOldDufferModerator @sillyoldduffer]

Steve deserves a prize for finding this year's most badly made machine screw!

I wonder how things like this get made given they're mass-produced by expensive machines, not lovingly hand-made by master-craftsmen. How about:

• Buy a second-hand screw making machine
• Discover it's completely worn out and can't roll the hard steel normally used to make cap head screws. The thread rollers are out of shape too.
• Discover it will form reasonable looking screws in mild-steel or dead mild-steel.
• Produce cheap inferior screws for anyone looking for cheap screws until the machine's output is obviously unacceptable.

Cheap cap-head screws might legitimately used in non-critical fix-once applications, the danger is they're substituted for the real thing when strength matters.

An 'advantage' of a soft cap-head screw might be that the thread adapts to whatever female it's forced into. Yuk.

Dave

[Michael GilliganParticipant @michaelgilligan61133]

On the balance of evidence: My best guess, so far, is that the screw is nominally 4BA

… but has been "made" [very badly] to approximately 3mm diameter.

That would explain why head and thread diameters are out of proportion.

Dave's comment about the danger is noteworthy.

… I don't know who is selling these toolhoders; but, in my opinion, they shouldn't be !

Things might be clearer when Steve has checked the tapped thread.

MichaelG.

[SherlockParticipant @sherlock]

Thanks for all the investigation skills boys.. I've had a hell of a morning trying to take an impression of the internal threads. The day so far has consisted of turning various bits of plastic, even wood down, screwing it into the hole for it to shear flush, then spend the next 45 mins trying to drill and re-clear the hole. No Joy so far, I'm afraid.

Meantime I have ordered another holder to keep me moving. Looks like it could be the same model/manufacturer?

https://www.ebay.co.uk/itm/RDGTOOLS-MINI-LATHE-PARTING-TOOL-HOLDER-WITH-BLADE-6MM-SHANK/351151924605?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

Will let you know when it arrives!

 

 

Edited By Steve Sherlock on 06/08/2018 14:19:24

Edited By Steve Sherlock on 06/08/2018 14:38:18

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Steve Sherlock on 06/08/2018 14:18:53:

Thanks for all the investigation skills boys.. I've had a hell of a morning trying to take an impression of the internal threads. The day so far has consisted of turning various bits of plastic, even wood down, screwing it into the hole for it to shear flush, then spend the next 45 mins trying to drill and re-clear the hole. No Joy so far, I'm afraid.

.

Steve,

My apologies if I did not make this explicit, and have let you into difficulty:

Taking this impression is really only to to check the pitch of the thread, not its form. You therefore need a rod which is just big enough to need screwing into the hole … a few thou over the 'tapping-drill' size should be plenty … we only need to see a clear mark.

MichaelG.

[Frances IoMParticipant @francesiom58905]

the original Perris from which the ME90 derives used BA for most sub 0.25″ screws – usually 4BA but think there were a couple of 2BA – might be worth buying a couple of these as testing the thread per MG is a right pain – much easier to have a selection of known screws and see which fits

[SherlockParticipant @sherlock]

Posted by Michael Gilligan on 06/08/2018 16:00:28

Steve,

My apologies if I did not make this explicit, and have let you into difficulty:

Absolutely no apologies needed Steve. the problem has been not having a suitable plastic to hand that was strong enough.

I apologise in advance for this, but, when I screwed the third attempt out (maybe a turned down wooden chopstick) I was left with this which shows three threads. I know it's a terrible result and photo and wasn't going to send but just incase…

[JasonBModerator @jasonb]

Why not just drill out the thread in the tool holder say 3.0mm and use a M3 caphead right through and a nut on the bottom, nyloc would be even better. Got to be easier than trying to work out what was used, buying a replacement and hoping it will fit as the female thread could be as poor as the male screw.

[Michael GilliganParticipant @michaelgilligan61133]

O.K. this is my best estimate from your latest photo, Steve:

.

.

I think that's as near to 40tpi as you will get from measuring five threads with a chopstick.

MichaelG.

 

Edited By Michael Gilligan on 06/08/2018 18:35:03

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