|
So, it was spring 2007 and
I had been running some parts in the last weeks that
used more than one tool. With the ER16 collet spindle
it's tedious to change tools and resetting Z zero every
time. And there's no real good way to get repeatable
tool-lengths.
I started looking for a
suitable quick change system and found one from
High Tech Systems that would fit my current ER16
spindle but after careful consideration I decided to not
go that route but instead build a new spindle from
scratch.
I made some research
regarding the various toolholders available but in the
end I settled for the BT30 because it's small (-ish),
it's designed for use in CNC machines, and it's not THAT
expensive.
It took a while to collect
enough information about the dimensions of the BT30 to
just be able to start designing. I found some info
scattered on various web-pages but also ended up buying
a BT30-ER16 collet holder that I could use to double
check.
Here's the a cross-section
view of the spindle. Basicly it consists of 5 main
parts:
Housing
Spindle shaft
Drawbar tube
Drawbar assembly with
gripper (ball-type)
Bearings, seal etc
The toolholder is held in
place in the spindle by the springloaded drawbar.
There's a standard coilspring shown in the 3D-rendering
but in reality it's belleville washers providing the "pull"
114pcs of them actually. When the tool needs to be
changed a pneumatic cylinder push the drawbar down and
compresses the springs. The 4 steel balls in the gripper
now have enough room to "let go" of the toolholders
pullstud and the tool falls out.
A new holder is inserted
and the pneumatic cylinder is retracted. This makes the
springs pull the drawbar up and the chamfer at the lower
end of the drawbar assembly forces the balls in the
gripper to grab the pullstud and pull the holder up into the
spindle taper. The 114 belleville washers provide a
force of roughly 3000N when the tool is locked and it
takes around 4500N of force to push the drawbar down far
enough for the tool to drop out.
The two lower bearings are
angular contact bearings, SKF7207BEGAP to be
precise, these bearings are universally matched so by
putting 2 bearings back-to-back (DB) or front-to-front
(DO) they will provide a light preload. As you can see
mine are mounted back-to-back. The upper bearing is a
standard 6206 deep groove ballbearing.
<BACK> <NEXT>
|
