Chinese Spindles

[Jonathan]

Some things to consider...

Drilling the hole all depends on how the shaft is hardened. If you're lucky only the surface will be hardened (like with ballscrews which are induction hardened), so you could drill it with a standard drill. However the spindle is what, 200mm long(?) which is a rather deep hole to drill in any material. It's important to maintain concentricity otherwise the spindle will no longer be balanced. If you need to keep the 24,000rpm limit you may well need to rebalance the spindle after drilling - it's possible to do dynamic balancing at home and not too expensive to set up, but that's a big project in itself especially just for one item although I guess you should additionally balance the toolholders.

Drilling the shaft will weaken it and also lower the critical speed - but no point commenting on if that's an issue until we know the dimensions. What diameter drawbar will be required for instance? Will need to know the required force to hold the toolholder/collet to work that out, so need to know what toolholders (custom or otherwise) you'll be making first.... there's a lot to work out. Ideally you want to use the existing ER20 taper for the toolholders/collets so need to machine something to fit that and attach to the drawbar - again easier said than done.

It's possible to do ATC without a drawbar:

http://hightechsystemsllc.com/pt_rapid_changer.html

...but with that design I suspect the inherent imbalance of the spring will severely limit the maximum rpm, unless the holders are very small.

Something else worth considering is making some sort of contraption to imitate a manual toolchange with a standard spindle. i.e. move the spindle to rack, nut unscrewed by motor (worm drive probably to get required torque - 30-70Nm depending on collet size) then have each tool in it's own collet and collet nut, so spindle is moved above and screwed into the holder. Easiest to motorise the rack with that high a torque, so it will require an automated spindle lock mechanism and a mechanism to align the collet nut to the holder/spannery things...simples! The nice thing about this method is it can be applied to any spindle and since you're not adding bits there's no balancing issues - just might be difficult to do reliably.

[Ricardoco]

Some things to consider...

Drilling the hole all depends on how the shaft is hardened. If you're lucky only the surface will be hardened (like with ballscrews which are induction hardened), so you could drill it with a standard drill. However the spindle is what, 200mm long(?) which is a rather deep hole to drill in any material. It's important to maintain concentricity otherwise the spindle will no longer be balanced. If you need to keep the 24,000rpm limit you may well need to rebalance the spindle after drilling - it's possible to do dynamic balancing at home and not too expensive to set up, but that's a big project in itself especially just for one item although I guess you should additionally balance the toolholders..

Ive mailed the supplier i use and she has told me that some do come with hollow shafts and that she will get back to me to let me know if it is an option to stipulate although she dosnt see a problem with it. so if all goes well thats that problem solved (fingers crossed)

What diameter drawbar will be required for instance? Will need to know the required force to hold the toolholder/collet to work that out, so need to know what toolholders (custom or otherwise) you'll be making first.... there's a lot to work out. Ideally you want to use the existing ER20 taper for the toolholders/collets so need to machine something to fit that and attach to the drawbar - again easier said than done..

She is looking into the hole size of the shaft so again we will see that will be when the drawbar size will be decided, and indeed the attachment fitting and type.

It's possible to do ATC without a drawbar:

http://hightechsystemsllc.com/pt_rapid_changer.html

...but with that design I suspect the inherent imbalance of the spring will severely limit the maximum rpm, unless the holders are very small. .

yes i remember seeing these i think 10,000rpm was the max..

Something else worth considering is making some sort of contraption to imitate a manual toolchange with a standard spindle. i.e. move the spindle to rack, nut unscrewed by motor (worm drive probably to get required torque - 30-70Nm depending on collet size) then have each tool in it's own collet and collet nut, so spindle is moved above and screwed into the holder. Easiest to motorise the rack with that high a torque, so it will require an automated spindle lock mechanism and a mechanism to align the collet nut to the holder/spannery things...simples! The nice thing about this method is it can be applied to any spindle and since you're not adding bits there's no balancing issues - just might be difficult to do reliably.

I had considered this approach as a last resort if it is less work than the spindle idea....

I may just buy an ATC spindle in the end if it looks like too much of a headache.. that is if i can find anyone who sells them for less than $2000 that is ....

[JAZZCNC]

It's possible to do ATC without a drawbar:

http://hightechsystemsllc.com/pt_rapid_changer.html

...but with that design I suspect the inherent imbalance of the spring will severely limit the maximum rpm, unless the holders are very small.

Yes I seem to remember they are 10K limited.?