End mill holder vs collet

cmv said:
My mill has an R8 spindle. I've just been using collets to hold my end mills. It's a smaller mill - similar to a G3102. I think the benefit is that I get a little more Z axis space that way (not that I've ever needed it so far). Is there an advantage or reason to use an endmill holder like http://www.use-enco.com/CGI/INSRIT?PMAKA=KE210-0104 instead? I have had an endmill slip out of it's collet a little causing me to cut too deep (it got 'longer' so milling down until I hit the stop caused me to go too deep ruining the work). This only happened once & I could have just not snugged it enough that one time? Or that might be a common drawback of using collets to hold end mills in the spindle. Don't know so that's why I'm asking :)
Click to expand...

I had the same thing happen with an end mill pulling down out of a collet. It was a 1/2" roughing end mill. I believe it was the vibration from running a larger cutter with a greater depth of cut that caused the end mill to slip.

Walt
 
In general, runout tends to be higher on the end mill holders. That being said, the higher runout only has a major detrimental affect on smaller end mills, where the runout may be as much as the feed/tooth, potentially causing one tooth to do all the work and the other none of it. There are some things that can be done about pullout of the end mills in collets, there is a very good white paper on the subject on Tormach's website. They did pullout tests using their TTS tooling system (which fits into a special 3/4" R8 Collet) under various different scenarios. The upshot is that you should ensure that your tool shank and the inside of the collet are completely clean and dry, and use some antisieze lubricant on the outside portions of the R8 collet where it contacts the spindle as well as on the drawbar threads and thrust surfaces. I have gotten pullout when I didn't tighten the drawbar enough and I was taking heavy cuts with 1/2 inch or larger end mills. Using TTS, you can get pullout whether you use collet holders or set screw holders, as the entire holder slips out of the collet.
 
Although I've never encountered the issue of pulling endmills with my mill yet, I like to use double angle style collets. These type of collets such as ER collets grip in a parallel fashion rather than just at the nose like R8 & 5C collets.

ER collets have excellent concentricity & have a wider clamping range per collet. They work great for endmills such as slippery carbide & shanks that don't have Weldon flats. Most of my carbide endmills don't have Weldon flats & I don't use endmill holders at all.

ER collets can be torqued pretty hard, for example, ER40 which can be torqued to 130ft/lbs max under the right conditions. There's also bearing nuts that increases holding power over standard ER nuts. I use Lyndex bearing nuts but there are others who make them too. So no cranking down on the R8 drawbar needed, I never need to crank down on my drawbar more than just by hand.

I use ER16, ER40, & DA200 collets/holders. Don't have to mess with the drawbar to change collets. And the collet holders have adjustable stops inside so it makes it easy to change an endmill & put in the same location. Downside is they add overhang so you can loose rigidity if you already have an issue with that as well as Z travel.
 
I had to machine my own holders for odd end mills and I have zero runout= cause 3CH collets will bankrupt the bank.

collet.jpg
 
You must log in or register to reply here.
Back
Top