Need Help!- drilling copper

[vbundy]

Need advice drilling a 1.3mm. hole thru 1.5 inches of copper in F12 Swiss Lathe. Not experienced in copper machining. Any advice will be helpful. Using a Titex parabolic TiN coated drill and it keeps breaking.

[JimBoyce]

Unbelievable as it may seem, inexpensive black oxide stub drills have worked much better then exotic Titex or Guhring on copper parts in the past. Drill the stub as deep as possible then switch to jobber and then tapor. The drills will not last long, they will start to drill tight, but should not break.

[MadMax]

Wow that's an ugly length to diameter ratio. I'm guessing you've tried pecking cycles galore by now to clear chips. Is the bit typically breaking nearer to the shank than the tip? Are your breaks happening at a particular depth or all over?

I suspect that at some point the collective drag on the flutes is going to build up and flute scrub will be breaking the drill even with good chip clearance. At this point, I think you'll need to relieve the hole with a slightly larger diameter drill to reduce the length of engaged flute. Alternatively it might be helpful to undersize the drill behind the cutting head so you drill a slight clearance around the plunged flutes. Maybe you can try grinding the drill to a slightly smaller diameter say 1/8" behind the tip so the sides don't drag so much. I'd only take off a thou or two.

JimBoyce may have hit on something. Parabolic flute drills have good chip evacuation, but the deep flutes sacrifice drill bit strength which might be your problem. I also wonder if the Titex drill you are using may have a rake angle that is too aggressive for the soft material you're drilling. Aggressive rake angles are nice for speedy mat'l removal in soft materials, but they get grabby when your tool becomes flexible.

[wildwestpat]

Doh! One big big big problem for a 1.3 mm dia drill bit. Firstly the drill bit needs its cutting ege angle reduced with one wipe with a very fine slip stone or diamond lap. ( The lap direction is parallel with the drill shank. This also applies to most copper rich alloys. Keep new drills for steel!) The overall length of the drill will not leave much for holding in the chuck and the flutes will in all probability not be long enough to give the full depth. This means that the drill has to be withdrawn frequently from the work. With small drills complete cleaning is often necessaryto withdrawing the drill from the work to clear the chip build up. With each plunge lubricant is required to help with friction on the side wall of the hole as well as cooling the cutting edges. Suggest withdrawing the drill every few mm i.e. twenty times or more for that bepth of hole.

The frequent complete withdrawal of the drill bit from the work will test the lathe alignment as well as the persistence of the operator as I don't think this is a sensible CNC task. For CNC why can't the hole be counter bored to a much bigger diameter with the 1.3mm hole being made for the last few mm?????


Added as a last thought by edit. With small drills it is often necessary to hold the drill with just sufficient grip in the collet so that when the drill starts to labour it slips. Tighten the grip and imeadiately withdraw for clean and lubrication - slaken the collet and repeat etc - etc - etc till hole depth achieved. Relieving the the side flutes might hep but difficult of drills this small and this also increases the risk of swarf getting trapped between the drill land and the side of the hole.

Good luck.

Pat

[ctate2000]

I think some of your problem may be the coating. TiN may be causing chip welding. I would suggest a bright finish drill or TiCN coating. If your machine is tight and aligned properly carbide will be the best choice. I am a fan of OSG products, they have some excellent tools for this type of work. Look at their Atom line of cutting tools.

[wildwestpat]

Hi Ctate

That is an interesting comment about the coating. I purchased a set of coated drills when they first came out. Having broken a few of the smaller sizes 2 to 5 mm I gave them up as a lost cause and muttered about the quality of the steel as the angles all looked OK under a glass! You could have a point that the coating might cause ahesive problems at the expense of reduced tip wear. I notice that the broken drills are all little used and have broken mid way along the fluted part.

Thanks

Pat

[vbundy]

The chip is spiraling in the flutes of the drill and clogging it. The drill is breaking near the shank which has me checking the alignment of the collet to bushing.

[MadMax]

Sounds like you also need to reduce your peck depth and do full retracts once you're at full flute depth. I'm wondering if the chip could be rubbing in the hole and running up the flutes during the retract. If that's happening, you can still have the chip hit the end of the flute and bind the bit even though the flutes aren't fully packed. Are you only breaking bits once the flutes are all the way into the part?