End mills / Drill bits for aluminium
Hello, I am new to this forum and generally to cnc machining. So I am in process of building my first cnc, and I have a question about end mills. I need to drill/plunge different size holes in 6061 aluminium, my spindle is 2.2kw Chinese water cooled, so I can go up to 24k rpm, but that's not really the case as I need to drill 8-20mm holes in 16-50mm depth. If I am not wrong these chinese spindles can go as low as 1k rpm. The idea is getting something like 8mm carbide 2 flute drill bit and drill a hole slowly (~1k rpm), then change it to 8mm carbide 2 or 3 flute end mill, that will widen the hole size up to 20mm.
Is the right approach and where to buy these end mills?
P.S. I will be drilling shit loads of holes so I need something lasting.
Thank you, any tips will be much appreciated.
Re: End mills / Drill bits for aluminium
Chinese spindles typically have a minimum rpm of 6000-8000. They won't have any torque at 1000rpm, and will die a quick death.
I've drilled 3 and 6mm holes at 5000 rpm with my SuperPID controlled router. I don't think I'd try any larger at 6000rpm. I often just drill shallow 3mm locator holes, and finish drill on the drill press.
A single flute "O" flute works very well in aluminum. For larger holes, just interpolate them with the single flute tool. 50mm deep may be an issue, though.
Re: End mills / Drill bits for aluminium
No they won't drill paper at 1000rpm and 5000Rpm is about the lowest usable speed and even then they don't drill very well.
I'm cutting and drilling Ali all the time with same spindle and Drilling aluminium with these spindles needs a few things in place, air and mist coolant then use Peck drilling. If you have these you can just about drill 8mm but I very rarely do and prefer to pilot with 5 or 6mm drill then use drill press.
Also with lots of larger holes like 20mm then I'd not bother with drill and just use pocketing and spiral down with 8-10mm end mill and open out to diameter.
So small holes drill and large holes Pocket and in all cases if doing lots of them you'll need coolant to extend tool life and stop small drills sticking and clogging.
Really only time I drill holes is when the drill size is hole size required and any hole larger than 8mm I use pocketing.
Re: End mills / Drill bits for aluminium
Thank you both for such descriptive answers. I read here that you can have your inverter "tuned" to get lower rpm, but I guess that's wrong then.
Anyway, JAZZCNC, where did you buy your end mills, and do you have any suggestion for good price-performance wise end mills for aluminium?
I guess I will need 6,8,10 mm 2 flute end mills for pocketing and something like 8mm 3-4 flute for inside-hole finish.
Thank you again!
Re: End mills / Drill bits for aluminium
People too often confuse torque and power. They are related by a simple formula, but represent completely different things. Power is torque times speed (if you use the correct units).
With the correct control (which is not necessarily easy) you can get rated torque at *any* speed from the spindle. That doesn't help you much though, as at 1000 rpm you're at 1/24th of the rated speed, so at rated torque you have 1/24th of the rated power - so less than 100W.
The problem with drilling is you generally need *more* torque, so just getting the rated torque (about 1Nm) isn't so helpful. You can use tricks like the one you linked to and exceed the ratings of the motor to get more torque (e.g. just apply a higher voltage at low speed), but I certainly wouldn't recommend it when this is something you need to do regularly. That's how I managed to drill several hundered 8.5mm holes with a carbide drill using my spindle:
Homemade CNC Router aluminium bed drilling with coolant - YouTube
I also occasionally drill aluminium with the spindle at around 4000rpm with a 4.2mm HSS drill, but I wouldn't recommend doing it regularly.
Re: End mills / Drill bits for aluminium
Quote:
Originally Posted by
ivars211
Anyway, JAZZCNC, where did you buy your end mills, and do you have any suggestion for good price-performance wise end mills for aluminium?
I guess I will need 6,8,10 mm 2 flute end mills for pocketing and something like 8mm 3-4 flute for inside-hole finish.
I buy most of my tooling from cutwell tools but I'll buy from Ebay when I see quality cutters come along at right price. Buying cheap cutters is false economy in long run because if they snap the potential for wrecking the job is high and at very best time is wasted. On some jobs this can wreck expensive material and you can bet your last penny the bastard will snap 10mins from end of 6hr job.!!
Only time I'll use cheap cutters is if they are so cheap I can afford to throw away after each job or I have lots of little jobs so can keep an eye how it's working.!
Like Jonathan says and you have seen you can tweak the VFD to give more Torque but your messing with fire and can easily fry something and will certainly shorten it's life so is it really worth the trouble.? If you need torque which you really do for drilling then really you need to look at a differant setup for the spindle. Something like Collet spindle in a housing connected to a normal motor 2 pole 3 phase motor via belt drive and gearing 3:1ratio to 1000rpm would give you the torque required.
If done correctly you could design a back plate system so they could be swapped over for when you require milling.? This is really the only way you'll get reliable drilling without getting silly on price for the correct spindle.
Re: End mills / Drill bits for aluminium
Never used them but they look ok thou I wouldn't call them overly cheap I can buy them for nearly same money from Cutwell tools and I think if you look around you'll find cheaper.
I ment to mention in last post don't buy 4 flute cutters for aluminium, single or twin flute work best, only 3 flute cutter I use are rippers thou they do shift some material thou they need a finish cut with different cutter as they are ribbed cutters.
