Posilock Chuck

Morning forum,

I just learnt something this morning... after reading other threads on here.

I bought a WM14 mill, which was a bargain and very little use. It came with the drill chuck, and a "Collet" chuck set, which this morning I learnt was a posilock type. It came with a selection of end mills and slot drills, and a box of HSS endmills. I have used it - but had great issues tightening it, and now I can understand why. If I use a plain shank endmill I just couldn't tighten it up. I'm wondering if I can make a sleeve that'll drop down in the bottom (or top) of the chuck, that will lift the collet out a bit. It is impossible to tighten it onto a plain shank collet without something, or installing the collet on the screw that is supposed to stop it rotating (I'm guessing here).

Has anyone used a plain shank endmill in a posilock chuck? I'm only machining brass / alloy at the moment, and no deep cuts... perhaps .25mm each time until I get used to it.

Ta

Edited By Lainchy on 09/08/2019 11:16:47

You must use threaded shank Clarkson type cutters,the design of the chuck relies on the thread to force the internal tapers into position.

Mike

That would explain it Mike. I wonder why the Mill was sold with a mix of cutters?? No wonder the HSS didn't look like they'd had much use!

You can get screwed end carriers that fit the Clarkson / Posilock chuck for the small FC3 cutters in either 1/4 or 6 mm shank diameters Ø. Works fine with plain shank ones if you add a flat to take the side-lock screw.

Better to get either a proper collet system or Weldon style side-lock holders. Shorter than an external collet system, ER et al, which can be an advantage with smaller machines which tend to run out of vertical daylight quite quickly. Spindle native collets are the shortest system but with small work and small cutters the spindle itself can get in the way.

Nothing is perfect but on balance I'd probably start by getting Weldon / side lock holders in the sizes you need and grind flats on my cutters for the screws. Probably only two or three sizes so the versatility of proper collets isn't a great benefit.

When using the Posilock do remember that the outer collar should be lightly tightened down, hand tight is fine, and the cutter screwed out as firmly as you can by hand to bring the collet into contact with outer collar. I always give the collar a quick bump with the spanner before starting work. As Mike says the system self adjusts as the screw forces the cutter out until the collet grips preventing further rotation. Starting with the collar loose can shatter the back end of the cutter.

Clive

Edited By Clive Foster on 09/08/2019 11:40:02

Edited By Clive Foster on 09/08/2019 11:40:37

Thanks Clive. I see so much info regarding the ER system, I was thinking why is this system totally different.

Thanks for the fitting details too. I'll have a look at the selection of cutters I have, and decide if I buy more Clarkson type, or change for ER. I do have to think about the headroom though in the mill as you said. Perhaps I should grab some direct MT2 collets for the plain shank cutters I have.

Posilock and autolock and Acramill are different systems utilising threaded shank milling cutters.

Posilock is used by Osborn in their Titanic II system.

Autolock is used by Clarkson.

Acramill is another system using the same threaded cutters.

Chronos LTD sell new posilock chucks and spare collets. Their collets will fit Osborn Titanic II also, but not Clarkson or Acramill.

If you google Clarkson Autolock instructions, there are diagrams showing how to use them which also apply to the similar posilock system.

You got more than I got with my mill, I learned later that they were gong broke, and flogging off the extra bit as separate items. All i got was a Jacobs chuck and a vise. For other that screw shanked cutters I made a blank with a twenty TPI thread, a hole in the end to suit the cutter to be used and a grub screw in the side to grip on the flat on the side of (most) of the plain cutters that I have, I also made up a similar fitting to hold a counter sink bit. My set goes up to 5/8", but I made a 3/4" collet from some steel from the junk box. I have made a number of fly cutters that fit the chuck.

As things were when I first got the mill home I soon found out why you don't use a Jacobs type chuck for milling. Just about finished making a tap wrench and the chuck dropped out, it didn't do too much damage, and the tap wrench is still often used.

Ian S C

Lainchy

A minor gotcha with the ER system is that the cutter shank needs to be fully inserted over the gripping part of the collet if its to hold correctly. For smaller sizes the gripping part is always shorter than the overall collet length. If you look inside from the back its fairly easy to see where the grip part ends.

Although the larger versions of the ER series collets can go down very small for equivalent grip sizes the smaller series collets have a shorter gripping section than the larger ones. For example an ER 11 collet is about 3/4 " - 20 mm long and the largest size it can hold is 3/8" - 9.5 mm which must be inserted right to the end of the collet. An ER32 collet is about 1 1/2" - 40 mm long and also requires a 3/8" cutter to be inserted full depth. Clearly using the larger style of collet means the maximum cutting depth is around 3/4" - 20 mm less. Its (very) roughly true to say that the insertion depth for a small cutter in an ER 11 is only half that required by an ER 32

Also the ER 11 collet nut is a lot smaller diameter than the ER 32, 3/4" - 19 mm as against 2" - 50 mm for the ER 32.

As our machines and work are generally quite small its important to consider clearances and cutter stick out. Short cutter in a larger chuck can be terribly limiting. Besides a 1/16 cutter in an ER32 looks plain silly.

Side lock screw type (Weldon) holders tend to be the smallest and can often be modified to improve clearances and give greater cutter stick out. My smaller ones get operated on if need be.

Clive

Lainchy, Although not so likely on the smaller machines due to small cuts it is possible when side cutting - using the side of the milling cutter or cutting a large depth of cut for the spiral to draw the cutter out of a say an ER or similar collet, this will not happen with a screw shank cutter in a Clarkson or Posilock chuck.

This problem will usually manifest itself when using larger cutters 1/2" and above, it rarely happens with small cutters. I have both systems but mostly use my ER chuck unless it is necessary because of the operation in hand.

John

Wow, thanks guys. LOADS of info there!

I reckon, the previous owner of the mill, bought the chuck from Warco, with the mill. I suspect they ordered a set of the end mills, but the wrong type. Having gone through the cutter boxes... I have one wooden box, all plain, One box with some spot drills (plain shank again - but I'm guessing these wiil go in the Drill chuck) and a box of various threaded cutters, round nose, end and slot drills. Some are imperial, so that's a no in the metric chuck lol.... there's 2 or 3 20mm cutters, these wont fit of course - chuck only goes to 16, and one threaded 10mm slot drill.

I can use some of these in the lathe I guess, but after trying the 10mm slot drill in the chuck, and seeing how rigid it is, I ordered a set off Warco (threaded metric end mills) - I know these are likely to be the cheaper end of the scale, but will at least do me for now. Warwick is coming up in October, so I'll look then... possibly even get some direct MT2 collets for the other end mills I have.

So much info though guys - thank you so much!

It looks like Lainchy has a Warco chuck, which looks to be of the Osborn Titanic Posilock type, which only seem to work with threaded end mills.

Clarkson Autolock however come in (at least) two flavours "S" & "C" types, the former have a collar at the chuck end with a couple of spanner flats to provide the drive. This collar is grooved to signify a metric fit.
They fit into a top hat style nut and clamp the cutter into the chuck body, again they don't like plain shank cutters.

The "C" type however have a couple of driving lugs sticking out of the back of each collet. The collet fits into a separate sleeve and the pair of them clamp into the body with a separate nut. The collets are again threaded to accept normal threaded cutters, but they will also accept plain shank ones because of the way the extra sleeve and collet interact. It may not be as firm a grip as an ER or Ericsson/Acramill type but it works fine, so long as one doesn't get all gung ho.

Bill

Edited By peak4 on 11/08/2019 23:08:01

Threaded shank cutters are readily available on eBay, many at very reasonable prices. I suspect the Autolock and it’s clones are on their way to becoming obsolete but as they were so popular there is still a huge amount of chucks and cutters to be found. I don’t think I have seen carbide cutters with a screwed shank but just because I haven’t seen them doesn’t mean they don’t exist. An ER chuck is a very flexible device as it will take most cutters with some care and the collets can be used on the lathe with a suitable chuck to match the mill size chosen. I still like my Autolock as it has a very definite cutter location but I also have an ER

Mike

Mike is yours a C or S type?

If the former, it will take plain shank carbide cutters, with care and a bit of common sense.
The sleeve/collet assembly stands slightly proud of the chuck body, so still allows the nut to press on the end of the sleeve; at least it does on mine anyway.

Bill

Mine is S type and definitely needs a screw shank cutter.

Mike

Or perhaps he ordered the wrong chuck! If the unfortunate purchaser was like me, he may have researched chuck systems without quite properly understanding the limitations. Asking a naive question like 'which is best, ER32 or Posilock', might well deliver a misleading answer. A better question would be 'which chuck and collet system is best for a hobbyist just starting out', to which the answer is almost certainly 'ER32'. Although Posilock has a 'better' grip, it requires threaded cutters. ER doesn't require special cutters and can be used to grip work as well. The extra flexibility provided by the ER system has caught on big time in industry and they are certainly 'good enough' for most purposes.

Posilock isn't a major mistake though, once the limitations are understood you just have to order compatible cutters.

Dave

Tracy Tools do a good range of screwed shank cutters.
I have the Warco autolock chuck on my VMC mill

A method I used before I bought a ER 32 collet set, was to make/modify a 'Grub Screw', same size and thread as that on the appropriate threaded milling cutter. A centre hole in one end and a screwdriver slot in the other.

Screw the grub screw into the collet (from the collet nose) just far enough for the collet nut to close the collet just before reaching the end of the thread. Insert the cutter and tighten.

Not quite as secure as a threaded cutter but with care, allows the use of unthreaded cutters in an Osborne type chuck.

That's a great idea Eric! I'll look into this.