Those little screws for carbide inserts...

I'm making a holder for carbide turning bits. I have M2.5 screws for them which (if I understand the convention) should mean, in the absence of qualification, that they are coarse (0.45mm) pitch. Just wondering if anyone can confirm that before I buy a tap. The darn things are just too tiny for me to measure with my geriatric eyesight!

Robin.

Hi Robin

M2.5 coarse is 0.45mm but they may be Metric fine at 0.35mm

Emgee

Mine are definitely M2.5 x 0.45mm.

I see what you mean with trying to check it with a thread gauge!

I just removed one of the insert screws , measured the diameter (2.41mm) screwed a 2.5 x 0.45 mm tap in to the threaded hole with my fingers all he way in and it was a nice fit.

Edited By XD 351 on 22/10/2019 03:13:26

Just as a matter of interest these small torx screws can be found on ebay for a fraction of the price if bought elsewhere. I bought ten of them a while back for the price of one from "proper" supplier. The quality may not be quite as good but I have found them perfectly acceptable.

Doug

Yes agreed. I’ve not had one fail yet but the best ones seem to be those listed as “made in Taiwan”.

Standard metric coarse. I bought a 'bargain' toolholder off eBay which had a 'loose' insert. It turned out not to have the thread to full depth. Luckily I had the tap.

Probably someone bought a box of rejects.

Neil

I have a supply of these screws from 1.8mm to 3.5mm. They may not be industrial quality, but good enough for light use. They all are standard metric coarse. I overtightened one of the early CCMT 06 ones and it broke in half, now I always use the proper torx drivers with the coloured plastic end, just thumb and forefinger tightness is plenty.

 When you drill the hole, offset it about 0.002", so the screw pulls the insert tight into the holder.

Edited By old mart on 22/10/2019 12:10:22

It's only the very small ones that might break, the ones that are M3 and above should never break. My biggest problem is losing the tiny ones, they have a tendency to hide when changing inserts.

Doug

I've just realised that my last thread was ambiguous, when I said "it broke in half", I was referring to the insert, not the screw. The tendency to disappear is the reason I have a supply of all the sizes I use in a box ready.

On the subject of geriatric eyesight I found these BA thread gauges the other day. 10BA is a bit taxing eyewise .

Manufactured by J.H.Grant of Erith. Anyone heard of them?

Mike

Thanks for confirmation - I'll order up 2.5x0.45 mm taps then. Thanks also for the suggestion of eBay for the screws - £3.88 for 50 including postage from China! Not sure I'd go for that (if it seems too good to be true...) but there's a UK distributor doing them @ £4 for 10 - I imagine they're of far Eastern origin at that price, but they do at least say they're 12.9 steel which may be some sort of indication of quality. Possibly!

On taps, looking at Tracy tools they offer carbon steel at £3 or HSS at £9. My only experience of CS taps is with a Silverline set which I bought when starting out (about £30 quid for a set 2-12 mm in taper, second and plug together with dies and stocks - why pay more! ). Complete cr*p unsurprisingly, but maybe not a reflection on CS in general. Does anyone have experience of the Tracy CS offerings? I doubt that I'm going to use the tool more than half a dozen times (in mild steel).

Robin.

Personally I'd go for it unhesitatingly. I've had lots of nice hardware from eBay/China for similar low prices and free shipping. They have the volumes. And it's not like the financial risk is great anyway.

The only downside is that delivery can take a good while with free shipping ...although with small screws etc, they often pop them into a small padded envelope that arrives quite quickly.

Hi all, with regard to losing the lovely little screws securing tips in place, they are only there to stop the tip falling out if you remove the toolholder or index the turret, a well known PIA with tools with 2 inserts facing in opposite directions such as U-Drills, I always used to magnetise my Torx screwdrivers, however as dropping a titchy little screw onto a swarf conveyer at night is best avoided due to the industrial language it propogates my preferred solution was aquire one of those small buckets used by lovers of bonsai trees or windowsill gardening, around a couple of inches across hang it on the offending toolholder, problem solved, although if you are as tight as I am you can fashion one from a small baked bean tin (other vegetables are available)

Cheers Bob.

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...Really ?

I thought they were more the proverbial ‘Jesus bolt’

MichaelG.

How about being a ‘guinea pig’, buy some and report back on the quality for other’s benefit?

Regarding CS taps, I have an old set (or part-set now) and only use them for cleaning up damaged threads these days. So, good chasers, not so good for serious fresh threading is my view, but depends on what you are tapping and how many iterations, I suppose.

The forces on the insert are mostly down through the toolholder, as mentioned, the screw does not have to be super tight or strong. It is more important to ensure there is no swarf stuck between the insert and the toolholder when it is fitted. I do, however, have a Ceratizit shell mill with 5 round inserts which is rated for 11000 rpm. It stresses that if the maximum speed is used, then the screws are changed at the same time as the inserts, which can index 8 places before discarding.

Arc Euro Catalogue 10 (Out of print) lists: Torx screws for carbide tips as

060-327-02545 Sumitomo BFTX0205N as 2.5 mm x 0.45 pitch x 4.5 long T8 wrench

060-327-02555 BFTX0206N 2.5 mm x 0.45 pitch x 5.5 long T8 Wrench

060-327-04.90 BFTX0409N M4 x 0.7 pitch x 5.6 long T15 Wrench

HTH

Howard

The Arc Euro screws are top quality Sumitomo ones, but look at the price of them. Then look at the price of the wrenches ( £8.50 for one T8 wrench ) .I know I am a cheapskate but my goodness I would need to give my wallet an anaesthetic before I could make it part with that money.

Doug

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For convenience: **LINK**

https://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Lathe-Turning-Tools-Indexable/Sumitomo-Indexable-Turning-Tools/Sumitomo-Spare-Insert-Locking-Screws-and-Torx-Wrenches

MichaelG.

Robin Graham, nothing wrong with Tracy Tools carbon steel taps, I have been buying them for at least 25 years and never had a problem.