Metric end mills

Are the threads on metric end mills metric or imperial. If they are metric, does this mean I will have to buy a metric arbour. or is there a way that I can utilise my imperial arbour.

To the best of my knowledge … all the ‘Clarkson’ threads are Whitworth-form [of whatever diameter suits the cutter] and 20tpi

MichaelG.

Edited By Michael Gilligan on 24/02/2023 10:49:01

If you are talking about the threads for tooling used in Clarkson Autolock and Vertex type Posilock then they all have the same imperial TPI but the diameter can be varied to suit either metric or imperial sized tooling. So you can have a Ø5/8" tool and a Ø16mm tool but they both have the same thread TPI. You do need collets that suit the diameter though. You should not use a Ø1/4" collet for a Ø6mm tool.

This is a Ø16mm ER11 collet chuck with the thread cut to the same TPI as a Ø5/8" or a Ø1/4" end mill.

Martin C

I seem to remember Clarkson threads being 20 tpi Whit form and whatever diameter the cutter shank is.

Well, I only have a couple of threaded metric end-mills, both of recent manufacture, and both gauge nicely as 1.25 metric pitch (about 20.32tpi)

I wouldn't be surprised to find there are different imperial and metric standards for end-mill threads. Does anyone know?

One of the benefits of ER32 is that the threads don't matter, and can be ignored!

Dave

Eric you don't need to change your whole arbor, just get a metric collet(s) to suit the size shanks you have which will have the correct thread. like this

Alternaive is to grind a flat onto the cutter and make yourself a sidelock adaptor with 1/2" screwed shank to fit your existing arbor.

Though simple option is to go for ER holder and collets as a lot of metric cutters are plain shank these days.

Edited By JasonB on 24/02/2023 11:45:12

As has been said you do need the proper metric collets on an auto lock. The thread form and TPI are the same but the diameter is different. Do be careful as one of the pairs of sizes (16mm and 5/8” I think?) are very close so the imperial will screw into the metric collet but is loose so tightening up wrecks the collet.

regards Martin

Good point, Martin

… so it’s perhaps worth mentioning that the circumferential groove on the Metric collets [see Jason’s post] is an identifying feature.

MichaelG.

When I picked up my Centec, it came with a Clarkson C type chuck and a set of imperial collets.
Until I found some metric ones second hand, I made my own set.
As far as I'm aware, all Clarkson style cutters use a 20tpi BSW thread form; The Clarkson Germany brochure claims they are made to BS122/4
http://clarkson.de/download.php?file=fraesen%2FHSS+Fr%E4ser+mit+Anzugsgewinde.pdf

Unfortunately, I've not been able to find free access to British Standards from within the GB, though it looks like readers in Northern Ireland might have access using their library cards.
Derbyshire Libraries don't seem to offer access remotely, though may do so on their own premises.
https://www.librariesni.org.uk/search/?s=LNI&q=british+standards

edit; I can't try it myself, but anyone with a Lancashire Libraries card??
https://www.lancashire.gov.uk/libraries-and-archives/libraries/access-to-british-standards-online/

Bill

Edited By peak4 on 24/02/2023 12:54:27

Thanks for the British Standard 122-4:1980 reference.

Europa Tools cross reference it to ISO1641-1 here (catalogue page 314 page 28/70 of pdf):

http://www.rsis.co.uk/downloads/136053280805_Cutting_Tools.pdf

Preview of ISO1641-1 here:

https://cdn.standards.iteh.ai/samples/65993/559a8432047445dd97cf79cd96a9130d/ISO-1641-1-2016.pdf

which refers (page 5/9) to ISO 3338-3 for threaded shank items.

Preview of ISO 3338-3 here:

https://cdn.standards.iteh.ai/samples/2689/9fb82bf3263c4617875a59cd067e4a04/ISO-3338-3-1996.pdf

and on page 4 of that document it confirms Whitworth form 20 tpi.

As Martin Kyte says, it is the diameter of the shanks, not the threads which define whether the endmills are imperial or metric. It is vital that the shanks fit the bores of the collets exactly, and a 5/8" will screw into a 16mm collet and not perform properly, so beware. There are several different types of collet, ranging from the Clarkson, the Osborn (now available as posilock) and Acramil. And the makers have changed the designs over the years, to boot. The metric posilock types which I use in the Osborn Titanic II have a band turned in the flange to denote them, the imperial ones do not, and Clarkson do that with their collets,too.

If you can read the sizes on the cutter shanks, they will be either metric decimal or imperial fractions, otherwise measuring is required.

I have also had end mills with incorrectly ground threads before now. Only a couple, clearly budget tooling but not dirt cheap. I think I had to take a touch off the crests just on the end couple of threads. If you do get that it’s worth screwing them into the collet back to front ie not inserted through the collet fingers. If it won’t screw in just using your fingers (with gloves) chuck the cutter, it’s cheaper than wrecking a collet.

I have to say I mostly use my ER collet chuck these days and tend to leave the clarkson with a large general purpose surfacing cutter in it.

regards Martin

I have a few threaded shank endmills of German origin which have carbide inlays brazed to the steel body. As I cannot sharpen the usual hss threaded shank cutters, they are only used on aluminium, and solid carbide in er collets used for steel or indexable cutters if possible. I have made a 16mm threaded arbor for small slitting saws which comes in handy.

Edited By old mart on 24/02/2023 15:52:33

Edited By old mart on 24/02/2023 15:54:43