R8 collets every time. I bought a set from MSC when I got my VMB and they are excellent, grip like the proverbial, don't eat daylight. I've got 2 keyless chucks, one 13mm Vertex the other 6mm Albrecht, both on standard R8 to taper arbors. I haven't measured their runout but not noticed any issues.

Martin,

I use an ER25 or ER32 collet chuck in my Warco VMC mill. When daylight under the quill is in short supply, I use R8 collets directly in the spindle, but I don't suppose I've used them more than a handful of times in my ownership of the mill, about 7 years and even then I've think I've only used one or two out of the set. I'd go for an ER collet first and buy R8 collets as dictated by the particular job requirement. I have to admit that I work to tolerances way over the NASA requirement and ER25/32 works fine for me. Never checked for run out.

John

I only use the R8 or MT3 collets when the job means I run out of head room to use ER collets. The biggest downside I find with direct collets is being able to see what you are doing or getting in close when clamps or say the spin indexer are used when using small cutters. Here is an example of a 3mm cutter in the SX2.7 held in a 6mm R8 collet.

Can't get to my R8 mounted chuck at the moment but I get 0.05mm with my MT3 one from ARC, this is a commonly quoted figure from many of the top brands but like a 3-jaw lathe chuck a drill chuck is not as accurate as collets would be and you should be able to get 0.005mm with collets as I do without splashing out.

I use R8 collets all the time, I think I may have an ER collet system also but haven't used it as yet.

Tony

Back in the 70s I worked a Bridgeport which had a small drillchuck with an R8 mount. I used to use it for co-ordinate drilling jobs amongst other things, and some of these had tight tolerances. Before I got to trust wobblers, I'd set it up against a datum edge with a .2500" dowel. My close-in eyesight was sharp then, and I think that on a good day that gave me a bit better then 0.002"/0,05mm TIR.

My guess is that APT are quoting the runout they (or their supplier) can guarantee, and most setups where careful practices are followed will give better.

Use collets where you can – the benefit of R8 collets isn't just space-saving, it's stiffening the resistance to any sidestress by shortening the leverage.

Edited By Mick B1 on 11/12/2022 11:54:55

We got a full set of R8 metric collets with the drill mill at the museum, and after several years, most of them are unused. They have little or no tolerance for missmatched diameters, I have had to buy 4 imperial ones. It would be best to only get the sizes which match the cutter shank diameters that you intend to use.

With an er collet system, either er25, (up to 16mm) or er32, (up to 20mm), it would be advantageous to have a set especially if you fancy using then on a lathe as well using a Morse Taper adaptor or a collet plate, as a set can cover every size if workpiece.

With sets of er collets, it would be better to get quality ones from Cutwel or APT, they specify the runout tolerance, I have a couple of Chinese sets which leave a lot to be desired in that respect.

Edited By old mart on 11/12/2022 14:36:04

Best of both worlds!

If you get a 12mm R8 collet then you also have the option of buying an ER11 or ER16 straight-shank chuck later (both sizes are available with a 12mm shank you see) to give you *even better* visibility when doing jobs requiring small milling cutters, the "chuck-on-a-bar" jobbies are about 15-25 quid should you find you do need that in the future.

You can extend an ER11 straight shank somewhat lower than you can buy an R8 ER16 holder, giving the best visibility.

Other than visibility there's no reason to go down to a smaller ER as you can get collets down to 2mm for ER32, so you might as well maximise the visibility you're getting in a trade off.

Straight shank collet chucks are also cheaper and more easily available than R8 ones due to widespread use in CNC machines.

On the accuracy/repeatability point.

I've previously bought 2μm TIR ER11 straight shank holders to use with bearings shrink-fitted onto the shank to make a high speed spindle for an engraver, so in a small knee mill I would consider the impact of the holder minimal.

Admittedly you would need to buy a similarly good collet to really make the best of that and you could potentially see additive effects, but even if the collet was 12μm TIR then you'd still be under 0.0005" (half a thou) which would be pretty good still.

Edited By Jelly on 13/12/2022 16:50:25

It may just be because Cutwel's site has a dreadful search facility [besides being appalling to navigate generally], but apparently there is no Cutwel R8 drill chuck for sale any longer.

Good choice when you use cutters up to 12mm. My reasoning was slightly different when I chose er25 over er32, simply the cost of cutters over 16mm gets very high. For larger sizes using R8 collets, the straight shanked 12, 14, 16 and 20mm with APHT or APMT inserts are economic to use and do not overshadow the work like a collet can. APT sell this type.

Looking at the bigger picture I use ER20 on both my R8 taper mills for cutters, although not that often. Everyday milling is done with 6mm and 10mm endmills in sidelock holders. i've never used ER collets for work holding; I use Burnerd EC collets on the lathe.

Andrew