ER Collets and holders....Breaking the code.

[Rbeckett]

I was having a discussion with another member recently and realized that I know nothing about the ER collet and holders systems and probably should have a discussion to help others to understand them too. So if you are well versed in the ER collet systems as well as the BAT/CAT systems please take the time to describe the difference between the different ER systems like ER25 and ER32 and enlighten the rest of us how to adapt a cat 40 holder to an MT2 taper. For the sake of the discussion lets assume that the machine in question is a vertical knee type mill with an MT2 quill and a 1.5 horse power motor. Also assume further that an individual is going to start from nothing to equip and tool up this machine in the future. So I am looking to the smart fellows on the site to help all the rest of us decide if ER systems are for us, and if so what particular system would be best to use. Thanks in advance and I am looking forward to an enlightening explanation and discussion that will demystify this subject once and for all.

Bob

 

[DMS]

ER (Extended Range) collets are steel spring collets with two tapers and a "self release" feature. The shallower taper on the back (8 degrees) fits into a holder of some sort. The taper in front mates with a special nut. Between the two tapers there is a groove that engages with a lip on the nut. This is what provides the "self release" feature; when the nut is loosened, this lip pulls the collet body out of the holder by the groove.

ER collets are nice because the have (as the name might suggest) an extended clamping range when compared to other collets (R8, MT, 5C). ER collets (except for the really tiny ones) have a grip range of 1mm (0.039 inches). Most other collets won't get you more than half that, so you need a lot more to cover the same range. The main reason for the increase range is that the collets are slit from both the front and back, and there tend to be more slits than other types (the R8 collets I have are slit in 3 places, with ER collets, it's usually around 12). Another advantage of ER collets is that the material or tool can pass all the way through assuming the collet holder has clearance.

One thing to keep in mind with ER collets is that there are a number of different ranges. Typically this is denoted by something like ER-20 or ER-32. The smaller the number, the smaller the collet, and the smaller the size of the work or tooling the collet range will accept. The number (from what I can tell) is the largest diameter in millimeters.

To use ER collets, you will need collets (of course...) and something to put them in. Some small machines like CNC gantry routers have spindle tapers that accept small ER collets. Most larger machines have some other taper like R-8, MT2, or some form of CAT/BT taper. For these, you need a collet holder, which is usually just a chunk of steel with your machine taper on one end and an ER collet taper on the other. I have both ER-20 and ER-32 collets, though I don't currently have a holder for the ER-32s. The ER-20s are used in conjunction with TTS collet holders, which I like quite a bit.

I don't know much about CAT40 holders or the like, as I don't have any machines that use those, so hopefully somebody else will throw in their 2c on the subject.

 

[stevecmo]

Hi Bob,

Good explanation from DMS. The only downside (and it's minor in my opinion but depends on what kind of work you do) is that they don't grip short pieces well. It's best if the part extends thru the collet if possible. They will work if the part is shorter - just more apt to slip.

You can make an ER collet holder fairly easily. I posted pictures of my two versions in the Shop Made Tooling section some time back. I need to make an R8 to ER-40 adaptor for my mill one of these days.

http://www.hobby-machinist.com/showthread.php/7920-ER-40-Collet-Chuck(s)

Steve

 

[Mike Cole]

Yes they work better gripping longer lengths. Unlike other collet systems the ER system was designed to hold the workpiece rather than a tool. But they still make for a good tool holder. I have a ER 40 system and have just bought a ball bearing collet nut. This is to reduce the high torque required to clamp the tool.

mike

 

[DMS]

I don't have ball-bearing nuts, but I have found that using anti-seize on the collet tapers, and nut threads, that I get much better clamping force with less torque on the wrench AND I don't bust my knuckles trying to get the nut loose.

 

[Terrywerm]

Thanks for the explanations on the ER collet system. I do have a question about the spanner wrenches used on the collet nuts, however. I have seen two types of spanner wrenches as shown below. Are there any advantages of one type versus the other?? I know that the first one would be faster and easier to use, but I suspect that the second one would grip the nut much better than the first, which might be important if they need to be quite tight. Any thoughts?

 

[kd4gij]

Thanks for the explanations on the ER collet system. I do have a question about the spanner wrenches used on the collet nuts, however. I have seen two types of spanner wrenches as shown below. Are there any advantages of one type versus the other?? I know that the first one would be faster and easier to use, but I suspect that the second one would grip the nut much better than the first, which might be important if they need to be quite tight. Any thoughts?


View attachment 63323 View attachment 63324

The first one is quicker to use put can slip out. The second one will not slip, and is better if you need something realy tight.

 

[DMS]

My ER-32 collet holder had the first type of spanner. Never had any slip issues. My TTS holder are ER-20, and the nut his hexagonal so I just use a big wrench. Never used the second type you show above.

 

[NoShopSkills]

FWIW here's the video that perked my interested in collets to begin with.

http://www.youtube.com/watch?v=smKWlrjxXag

I started a similar thread because I didn't think my questions had much to do with the ER system since I'm not so sure I am looking to embark on all that would be entailed to build an ER holder for my threaded spindle nose. It was suggested that I bring my questions (if I still had any) here. I'm still not sure how much I'd use either the MT4s I'm considering buying or a more extensive ER system, which looks like I'd have to build...

Two of the things that perturb me the most about internet forums are: 1) questions that get answered with questions and 2) accusations that "you just haven't read enough be fore you posted"... None the less I suppose that working on building an ER holder could solve my concerns of protecting my threaded spindle nose, assuming I used the spindle thread system as the mount, but then the economy of a $100 ebay purchase goes out the window.

So I'll ask a different way, does anyone have any extensive experience running an older lathe collet system with a draw bar? If so does the draw bar lock somehow? or was it's function just to pull the drawn collet tight - then relax? For that matter since I still haven't purchased my first milling machine, how do collet draws work on a milling machine like is being offered by Rbeckett? Do they maintain tension the entire time?

 

[David Kirtley]

I don't know about *extensive* use but I have one on my wood lathe that screws onto the spindle taper. I have one on my mill with a drawbar (R8) and one attached to the face of the spindle on my lathe that bolts up to the face of the spindle. Some can also be chucked up in another chuck (or vice versa - some people use a 5C that have a chuck mounted to it).

Any mounted to a spindle would need to be attached. Either threaded on or held into the spindle bore. Maybe bolted on the end of the spindle. Things not solidly attached to the spindle when turning can cause unfortunate things to happen.

The 5C have a collar that draw the collet into the spindle much like a drawbar but still need to be attached somehow to the spindle. Some pull against the outboard end of the spindle to keep it in, some attach at the nose of the spindle. There several collet systems as manufacturers love to lock people into one vendor. Some kinds have faded in use, some are going strong. Most common are the MT type, 3C (for small ones) or 5C type, and the ER series. Also some oddball types like the WW collets that watchmakers use.

I love the ER32 collet holder I have on my lathe. It was a bit pricey at LMS but I don't begrudge it a bit. They have some cheaper ones that you can order from overseas.

Many people just buy the nut and make the rest. The taper is not complicated (8 degrees.)


What lathe are you trying to get one for and what is the spindle like?

- - - Updated - - -

I just saw your other post.

Generally MT collets are used to hold tools. They don't allow work through the spindle. You would be up in the range of 5C collets for that lathe. Yes, you can get a nut to protect the threads. I just bought one for my wood lathe.

Doubleboost has a good video on youtube making an ER holder for a threaded spindle. The only complicated part is the nut and you can buy them separately. Oh, and it is I believe an 2mm thread if that is a problem.


<added>

Scratch that, it is a M40 x1.5mm thread