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View Full Version : Benifits of ER type EM holders?



Mike Hunter
06-07-2010, 01:00 PM
Looking at the ER type mill holders, and trying to understand if the benefits are worth the cost. Currently using R8s in the BP, and truthfully I can change out an end mill or collett fairly quickly. So what does the ER type em holder really buy me.

Thanks

lakeside53
06-07-2010, 01:06 PM
I have a nice ER40 set that I now use continuously. Advantages? I can mount any size drill bit (or odd-sized endmills) from tiny to 1 inch without needed 1/64 set of R8's. Large drill chucks are not a precise option and clunky for 1 inch. It is slightly easier to unscrew the end than to deal with the drawbar each time, but that's secondary.

.RC.
06-07-2010, 05:30 PM
An ER set will buy you less ridgidity as they stick out further from the spindle bearings...

Jim Shaper
06-07-2010, 05:42 PM
I think you're looking at them in the wrong application.


What you would do with an ER style holder is similar to that of a weldon shank holder in R8 - the cutter remains in the holder, the whole assembly is then removed and replaced as a single unit.

Even with a depth set screw (my rego-fix er collet chucks, and some others have this), you're still doing a lot of work to remove and replace the cutter. Unless you have a large supply of nuts, you'll have to remove and replace the cutter to get the collet out of the nut.

ER collets offer better run out, higher clamping forces, and a larger usable range than the R8 collet system, but unless you have a whole assortment of collet chucks, you'll be much faster with typical tooling. Repeatability between tool changes is also a benefit, but I'm not sure how much faith I'd put in an R8 fixed length tool's ability to seat to the same depth every time. It'd hold +/-.010 though (maybe better - I've never checked).

BobWarfield
06-07-2010, 07:22 PM
Repeatability between tool changes is also a benefit, but I'm not sure how much faith I'd put in an R8 fixed length tool's ability to seat to the same depth every time. It'd hold +/-.010 though (maybe better - I've never checked).

Even the cheap ones repeat to 3 to 5 tenths on my mill with a power drawbar. Not sure if the relatively constantly torque on the drawbar (always tightened the same with an impact wrench) contributes to repeatability or not. But, it is plenty good enough for a lot of CNC work.

Cheers,

BW

Jim Shaper
06-07-2010, 07:43 PM
Bob, have you ever checked your offsets after heavy cutting?

Even on my 40 taper spindle, the drill chuck holder is significantly harder to remove than my lighter cutting tools. That's via a spring loaded draw bar with pneumatic piston release, but you can still tell that it's pushing harder before popping the taper out with the big drills. Most notably was the 3/4" drill punching through 2" of aluminum.

Just an observation of mine. Like I said, I haven't ever measured the change in seated depth of a tool after the operation was run, nor have I trusted a Z offset for anything after a tool change on my r8 spindle.