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  • ER collet clamping range

    I'm looking for an ER16 collet that can hold a .039 drill (and preferably some others).

    From what I read on the internet, some people have trouble with ER collets in the small end of their clamping range, while others do not. Aside from the reduced contact area from the mismatched curvature, what could cause any problems? For example, I don't see how run-out can be worsened because the "thickness" between the OD and ID of each collet segment is still the same.

    The easiest is to get a 1mm collet, but I also have a few .050 and 1/16 drills that I'd like to use.

    I got a 1/16 collet, but will probably have to return it as I think it's clamping range is only .063-.043 (instead of 1/32"). It only has 4 segments (as opposed to the usual 8) and the segments seem to touch when I squeeze on the .039 drill.

    In theory, a 1-2mm collet should work with all three drills. However, I have read a few manufacturers claim that their smaller ER16 collets have a reduced clamping range, yet I don't see a difference between the construction of theirs vs. others that claim the full 1mm range for all collet sizes.

    This is will only be used for drilling, so run-out is more important than being able to take side loads.
    Last edited by beanbag; 04-13-2013, 10:23 PM.

  • #2
    Basically any ER collet below about 2mm has a reduced holding range. There is a total collapsible range of only .5mm instead of the full 1mm for each size. So, a 1.5mm collet will only hold as small as 1.01mm. After that, a 1mm collet is needed. Same goes for the 1mm collet - only holds down to 0.51mm. That's how I read it in the catalog literature spec's.

    Beware of collets which are the same size as ER but are not actually ER. They are made to only clamp the nominal labeled diameter. The ones I am aware of are made that way to achieve extremely critical tolerances. They are not meant to collapse over a range. The Schaublin collets of this type are called "EX" and graded tolerance "UP" for ultra-precision. The Schaublin EX have only three slits originating from the front of the collet body and three originating from the back.

    Rego-Fix makes a number of ER type variants which also do not have a range. These include ER-MB (Microbore) and ER-ND (High Precision) types.
    Last edited by Arthur.Marks; 04-14-2013, 01:57 AM.

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    • #3
      I'm not sure you're going to find a collet that will fit both the 0.0625" and the 0.039" drills. Looks like the 1/16" collet clamps down to 0.0475".

      Why would you need to return the collet you have? If you have 1/16" drills, then why not use it for those and get a 1 mm or a 3/32" collet for the smaller drills?

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      • #4
        What causes the smaller collets to have a reduced clamping range? All the (metric) sizes have 8 radial cuts across the front face. Each cut is about .020 wide, for a total of .160 circumference. Divide by 3.14, and it looks like they can close about .050 before the segments touch.

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        • #5
          Originally posted by beanbag View Post
          What causes the smaller collets to have a reduced clamping range? .
          On larger collets you get a wide area between the slots, on small collets this is close to a V contact.
          You are basing your maths on the circumference when you should be basing it on the bore.
          .

          Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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          • #6
            I checked it out via CAD software, and made a 1/16 collet with 8 .020 slits in it. That left very tiny contacts, but it would squeeze in .051 on the diameter before touching. I imagine on the smaller sizes, the slits are narrower for more contact area.

            Edit: Now that I think about it, what I said two posts above is exactly correct, for all bore sizes and slit widths that still leave enough for a contact point. squeezedown = slit width * number of slits / pi.

            Still, if a collet calls itself 1-2mm, then I can assume that it really can squeeze down to 1mm, and what bad thing happens when I put a 1mm drill in it? It's like a tiny 8-jaw chuck.
            Last edited by beanbag; 04-14-2013, 09:07 AM.

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            • #7
              It's down to the stiffness of the collets. For any given type of ER collets (eg. ER32), a collet at the large end of the size range (say 19mm - 20mm) will have far less metal in it than one at the bottom. The more metal, the stiffer it is, and the more effort is needed to deform it to the lower end of its 1mm range.

              Using collet closing nuts with ball bearings helps this. Wherever possible, use the smallest bore collet that will do the job. For instance, if you have a piece of 12mm diameter rod, you could use either an 11-12mm collet, or a 12-13mm collet. Use the 11-12mm one.

              Ian
              All of the gear, no idea...

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              • #8
                I hold small drill on some jobs and use ER11 collet chucks held in larger collets.
                I use these a lot.



                Holds ER11 collets and are 16mm on the OD which fits nice into an ER32 chuck with 16mm collet.
                very handy on the CNC as by having a collar on them i can keep tool length offsets.
                .

                Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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                • #9
                  On a chit-chat note related to above...
                  There's also 'reduction adapters' that have a solid shank the shape of the ER profile. Same function as John's holder but removes one level of tolerance stacking.

                  More on topic...
                  Wouldn't the relative change in curvature be far more dramatic -- and consequential -- on the smallest collet bores? My thought is that would have a increased tendency to throw off the TIR the further the collet is collapsed. With the smallest diameters, the comparative change being much more dramatic, it may mean the limitation in range is actually due to not holding tolerance.

                  To reply directly to beanbag...
                  Yes, both the Rego Fix and Schaublin catalog specifically list the 2mm collet bore as able to be used down to 1.01mm. The 1.5mm bore collet, however, is shown with a lower range limitation of 1.01mm as well.
                  Last edited by Arthur.Marks; 04-14-2013, 11:50 AM.

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                  • #10
                    Originally posted by beanbag View Post
                    What causes the smaller collets to have a reduced clamping range? All the (metric) sizes have 8 radial cuts across the front face. Each cut is about .020 wide, for a total of .160 circumference. Divide by 3.14, and it looks like they can close about .050 before the segments touch.
                    Others have answered this question and their responses are good. But here is my slant on it. It is a question of scale. When you reduce the size of the central bore they often also reduce the width of the slots, roughly in proportion. But this simple, geometric reduction will, at some point, also result in a similar reduction in the gripping range. Although they can maintain the 1mm gripping range per collet for larger sizes, when you get down to a 1 or 2 mm collet, it breaks down. Actually, larger collets could probably be made with larger gripping ranges. As an example, a 20 mm collet could probably be easily made with a 2 mm range with wider slots.

                    Reducing the number of slots also reduces the gripping range because four slots have less total width than eight would. Note that the reduction in diameter is equivalent to a reduction in circumference via the formula C = pie d. The slot width is directly related to the possible reduction in diameter.
                    Paul A.
                    SE Texas

                    Make it fit.
                    You can't win and there is a penalty for trying!

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                    • #11
                      Originally posted by Arthur.Marks View Post
                      On a chit-chat note related to above...
                      There's also 'reduction adapters' that have a solid shank the shape of the ER profile. Same function as John's holder but removes one level of tolerance stacking.

                      .
                      On my Beaver CNC it's on INT40 tooling and had a 4,500 rev top speed [ old machine ] but at this speed it's noisy.
                      I do a lot of small hole drilling on it and really need about 9,000 revs. So I bought one of these speed increases, similar to this.



                      Mine is an older model than this one, there is a bar that fastens to the body to stop it rotating so the epicyclic gearbox comes into play. It's 4:1 incease so i run the CNC at 2,250 revs which is liveable with on the noise range.
                      Also mine has an inbuilt Clarkson chuck, something I don't like but as these are very expensive it's something I have to live with. Unfortunately the Clarkson chuck makes it even longer.

                      So by the time this is in the spindle and the littler ER11 collet chuck is fitted, then a drill, the tip of the drill is 6" out of the spindle but I'm amazed that I can detect no run out with a 0.0001" gauge
                      .

                      Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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                      • #12
                        Very nice, John. It is often surprising, isn't it, how precise a lot of items actually are regardless of the "official" tolerance levels on the package.

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