Having trouble turning grooves

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

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

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.

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

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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.

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...

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.

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

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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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I'm struggling to follow the logic, Frances

The toolholder is an 'aftermarket' item, so Perris and Cowells would seem to be irrelevant.

MichaelG.

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Based on the latest hyper-accurate measurements, 4-40 UNC looks a good candidate.

Edited By Michael Gilligan on 06/08/2018 18:29:10

But you could whip out one of the screws from the lathe and try it in the hole to see if it is 4BA.

From past iffy screws in far eastern items I doubt it is BA as they tend to use Whit or UNC with Whit being the more commonly used and closer to the thread angle Michael measured than UNC

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A couple of points, Jason, before I leave you to it:

1. The thread angle on the dodgy screw is probably of no consequence ... which is why I suggested checking the tapped hole.
2. I have enjoyed the exercise of trying to guess the thread, and hopefully Steve has learned a little on the journey ... His next mystery thread might be in something that is not so readily modified.

MichaelG.

I hate 4-40UNC screws! They're the standard for screwlocks on RS-232 connectors. Albeit brass, but I've lost count of the number of times I thought just a final nip up, and ping the **** screw breaks. I've had the same happen with 3/16" BSW bolts, so I'd expect 1/8" BSW to be similar. All basically too coarse a pitch for the diameter.

In my experience "professional" far eastern tooling uses metric screws, although made of cheesium and therefore need replacing. Hobby grade far eastern seems to use BSW for some reason. No idea why?

Andrew

Valiant effort Michael Thank you. Up until I started this thread, I had never even heard of the British Association thread standard! so I have learned a lot.

Posted by JasonB on 06/08/2018 18:34:38:

But you could whip out one of the screws from the lathe and try it in the hole to see if it is 4BA.

I shall definitely be investing in nut and bolts sets in every thread standard I can so I can keep on hand to test in future

Edited By Steve Sherlock on 06/08/2018 20:53:10

You'd be better off investing in taps, even if secondhand. External screws are relatively simple to identify compared to threaded holes. And taps should be more accurately made than mass produced bolts. Plus, once you've identified the thread, you can use the tap to thread more holes!

Andrew

Steve,

I've just found a set of three videos about the 90ME which you may find of interest: **LINK**

https://m.youtube.com/channel/UCf-ZiCQo0pfvubnP7M48_Fg/videos

MichaelG.

Edited By Michael Gilligan on 07/08/2018 08:19:51

I really enjoyed those Thank you Michael. Excellent viewing with a morning coffee. Being someone who spent my childhood taking everything I could get my hands on to pieces to see how it worked, I particularly loved the tear down and gave me a more intimate understanding of my machine and how it works. Invaluable. Thanks

I totally agree about 3/16 BSW, for some reason it's the tap most likely to snap. Must be to do with the thread depth/core diameter relationship. However 1/8 BSW is 40 tpi, and seems benign by comparison. All academic, I use metric for preference nowadays

Just because of the gear I had when I started this hobby, the two main threads I use are 1/8"BSW, and 3/16" UNF, although in later years I have branched out a little. One surprise I got was when making parts for a 1932 Lanz Bulldog tractor, the threads were BSW. Bulldogs built in the latter half of the 30s went metric.

Ian S C

Welcome to a hobby offering so many choices. The history of threads is fairly chaotic, which is why it's possible to bump into so many variants.

Metric fasteners are used in almost all new machines and they are easier and cheaper to source. The main exception is the USA, but even there metric threads are gradually taking over. Another exception is if your interest is in older British machines, restoring old cars or whatever. In that case BSW and BSF are your friends. US and British threads were unified in 1948, so there are at least three common variants of imperial. Another golden oldie is BA threads, which were widely used on instruments and electrical equipment.

I thought about this and, because I've no particular reason to go for an older thread, I decided to go metric. It makes life simpler! I own a box of metric nuts and bolts, metric studding, and taps, dies, and a lathe to match. I also own a small imperial capability, bought for special cases. Quite a few take the opposite line, preferring to work in Imperial, with some metric for special jobs. With a bit of cash, all combinations are possible. What suits best depends on what you do.

More good news, thread gauges are affordable. Well worth buying a few if mixed threads are a problem, for example this pair from ArcEuroTrade cover Whitworth, US and Metric for about £14.

Part of the 'fun' for beginners is discovering what's available and who sells it. I'd recommend browsing the likes of ArcEuroTrade, RDGTools, Noggin Metals and other advertisers on the forum to see what's on offer. Quite often, it's easy once you know what to look for, or how to ask the question. Also the more you explore, the more it makes sense.

Dave