Tool Changer - How?

[creative_mind]

Please, can anybody here explain to me how does a CNC tool changer function?

How is a tool removed from the spindle and is changed to a different tool. The whole process mechanically wise.

I understand how it is controlled by Gcode.

Thanks

[balsaman]

I think some use an indexer. I round thing similar to the revolver in a gun. A different tool in each section. The indexer moves around to select the tool, the machine moves to the indexer to pickup the tool. The machine has a mechanical gizmo to lock the tool in place.

I would love to build one for my machine. The trick is to automate the chuck somehow with a pnumatic cylinder or the like.

Eric

[creative_mind]

How is the tool removed from the spindle?

Does the spindle rotate to unscrew the collet? Snap off and on?

[HuFlungDung]

If your machine has a "real" machine tool spindle, it will have a taper socket for holding the tools. The rest of the spindle is hollow, or has a throuogh hole which will allow a drawbolt of some sort to pass through. This drawbolt can be actuated with an impact wrench, either electric, or air operated, to draw the tool tightly into the taper.

This is how the "Quickdraw" toolchanger works. It has a 24 tool chain carousel, with the tools standing on their threaded end in little pockets fastened to the carousel chain. This chain is indexed witha Geneva star-wheel indexing mechanism.

The electric impact wrench is run by a timer circuit which controls the on-time of the impact wrench. A short stroke air cylinder brings the impact wrench down onto the drawbolt, when the spindle is fully up at the top.

A two-finger claw arm grabs the toolholder by the flange out of the carousel, and then lifts it and swings 180 degrees to align the tool with the spindle. While the arm swings, the tool holder is also inverted so the the threaded end is up to fit into the spindle first.

It takes quite a bit of rigging to interface one of these units to your cnc controller. I've seen these units sell with old mills for $3000 or so on Ebay. I know that a factory refurbished Quickdraw can cost you $7500.00 This toolchanger is actually quite a fine piece of work. A bit dated perhaps, but it is still in use, and repairs are still available for it.

[balsaman]

I believe the tool is held in the spindle by a pnuematic cylinder. The tool goes in the indexer,is released, the indexer rotates, and the machine picks up the next tool.

Eric

[balsaman]

here is a pic I found of a indexer/changer



Eric

[balsaman]

Thanks Hu, I was hoping someone who knew what he was talikng about would step in...never mind me...

Eric

[creative_mind]

balsaman,

Thanks for the picture. I will very much appreciate if there are some more pictures in detail.

Thanks.

[balsaman]

[HuFlungDung]

I'm not sure how the real cnc's with the retention knob work. However, I would always want the tool to be retained in any event, should the power, or the air or hydraulic supply fail.

I think it most likely that the retention knob system must use some sort of a heavy spring (belleville washers) to retain the tool, and the tool change process must work against this, to release the tool.

I'd like to hear from someone who really knows, though.

[wms]

Hu,

You hit the nail on the head.

They use a "stack" of Belleville washers on the draw bar. Then there is a large piston mounted above the draw bar and when a tool change is called, (auto or manual) it energizes the piston, which presses down on the draw bar, compressing the springs to release the pull stud. The pull stud fits into a socket with small steel balls. This socket is very similar to a quick release air fitting.

Simple as hell.

[TRC1]

Long story short.....
When the spindle and head move over the chosen tool, a pneumatic cylinder actuates and opens the "fingers" in the spindle taper. The taper then drops down on the toolholder taper and when *contact* is made, the pneumatic cylinder actuates the other way and the "fingers" in the spindle taper grab the retention knob and "suck" the toolholder up into the spindle tightly. Then the tool carousel pulls the other tools away and the machine is then good to go. The whole time this is happening *most* cnc machines blow air through the spindle taper to keep chips and debris out of the spindle to keep the tolerance tight.
There is more to it than this but...
JD