Thread: Chinese Spindles
Hi All Sorry ive not been around for so long work commitments hav had me by the throat!!!, anyhow ive seen a couple of these chinese spindles in action and for the most part im impressed, so when i got the chance to see one in bits i jumped at it. This made me ask if it was possible to drill through the spindle itself to fit a drawbar, any thoughts?? the 3hp er20 one looks like it would be worth doing. they may even be hollow in the first place, i didnt get a close enough look...Always bear in mind that your own resolution to succeed is more important than any other - Abe Lincoln
Here is a link I found some time ago where someone took apart one of the 1.5KW Chinese Spindles: http://3d.kadatka.ru/articles/shpindel/index_eng.php
It would be really intresting if a drawbar could be fitted to the 2.2KW and up Spindles."If first you don't succeed, redefine success"
Thou not sure how you'd go about drawing the ER collet.? Don't think the ER design lends it's self well to ATC thats why you don't see many, if any.!!
Last edited by Ricardoco; 24-05-2012 at 12:51 PM.Always bear in mind that your own resolution to succeed is more important than any other - Abe Lincoln
For what it is worth I think that drilling a hole down the centre may be a very bad idea. Think about it, the Chinese are very good at making things down to a price so their design is not going to be conservative, that's for sure. Therefore, the diameter of the shaft will have been minimised in diameter and material specification to do the job and no more. Removing some of this material will weaken the structure I am sure.
If you want to do it anyway and can't drill or bore it because the material is hard, you can always get is spark eroded ....maybe.
Still think it is not a good idea though.....sorry
24-05-2012 #7Always bear in mind that your own resolution to succeed is more important than any other - Abe Lincoln
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:
...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.
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 ....
The shaft is very strong on the 2.2KW spindle and would easily bore without weakening too much. Obviously it will but to be honest these spindles don't produce enough torque to get anywhere near being able to snap a shaft of this diameter.
I don't think it would be too hard to design some way to draw the ER collet but it would have to be a single large collet permantly installed.
Then separate tool holders machined to actually hold the cutting tools. Similiar to the Tormach system.
Problem with this approach, with this spindle, is both the relatively small diameter of the largest ER20 collet @ 13mm and the fact they will need to be balanced to handle the high spindle speeds.
The tormach system works by using the largest R8 collet @20mm and the tool holders shank match's . . BUT . . the main difference and the area I think will be hardest to over come is the balancing. Also because of the relatively small 13mm shank the tool holders will also need to be machined from high quality steel and hardened appropriatly.
The tormach systems highest spindle speeds are I believe 10K Max. The jump to higher speeds I think is where all the hard work will be.? Getting it wrong will shake the machine and very quickly wear the spindle bearings away, not to mention the shite cutting it will do.
It's do-able but far from simple.!! . . . . If it was simple and done cheaply our Asian cousins would have surely done it by now don't you think .??
There are several ATC spindles out there but the all cost a few 1000's not 100's.!!
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