Hey guys, Just a quick question and your thoughts on the subject. Is it OK to use a spindle extension? I have a 3.5KW spindle, and the dust boot bottoms out to the workpiece when I do profile cutting. I have just put the extension on and a test cut shows no issue as far as I can see. It's only a 40mm extension. Thoughts please!
Definate no, if its not balanced with the collet nut, you are can easily get a tonne of vibration as the weight could be slightly offset. That vibration can snap an endmill and turn it into a bullet. Rather reengineer your dust solution so it moves with the Z axis
I wouldn't say no out of hand- it's not really substantially different to using toolholders of different gauge lengths in toolchanging spindles, after all- but the balance issue is critical if you're going above 8000rpm, and doubly so over 18,000rpm. If you're using a balanced collet, collet nut, ER extension, extension collet and extension collet nut, then you should be ok, though I suspect due to the substantial stack instead of a single toolholder you'd have to go tighter across all of them than G2.5 @ 20,000rpm. Probably G1. And then you may still have to test at speed and partially rotate some of them relative to each other in order to reduce the vibration. Sandvik have an excellent page on tooling balancing, what the ratings mean and how to calculate them here: Balancing and RPM The problem isn't so much the length as that it's an ER holder going into another ER holder at high speed. ER is not a precision collet system.
