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Drill for 6al4v manual lathe 1/2" diameter 4" deep

JCIrish

Plastic
Joined
Apr 25, 2010
Location
Michigan, USA
In need of some guidance with selecting a drill that will be the best fit for my setup:

-manual lathe (SB9 w/ 1hp and VFD), "flood" coolant from a squeeze bottle, soluble oil
-drilling through holes in 1" stock that will then be bored to just under 3/4"

I have a few questions, the more I learn about this the better as I have a fair amount of drilling in Ti to do. So far, I've had success with PTD cobalt 135 split drills, running at about 30sfm, with lots and lots of pecking. The cobalt holds up pretty well, but sometimes starts to bind in the hole after a couple inches. I have the tailstock aligned within 0.001 side-to-side and it's within 0.001 vertically (can't be sure whether it's indicator droop or actual runout), and putting some clamping pressure on the tailstock ram seems to help with alignment and reduce the rubbing of the bit in the hole. The last job I switched to a PTD HSS split point since some folks mentioned a thinner web might decrease pressure, and it did seem to be easier to push, but after about 2.5" the outside edges of the lips started to break down. This was with a 1/2" bit, the cobalt was 3/8".

So I guess I better get to my questions:

What size/type drill has worked well for you drilling 6al4v in a lathe this size? I know carbide in both solid and inserts is popular for CNC, but I don't want to risk chipping an expensive bit. I would go with an insert drill, but from what I've read it may be better to go with a good Guhring or OSG in HSS, maybe with a coating?

Should I be able to push a larger drill (say 5/8") to leave less for boring, and if so do I drill progressively or all in one shot?

I've read about grinding a back taper on the drill to minimize rubbing the walls, but I'm not in a hurry to go grinding on an expensive drill, unless it's a good idea.

Do coatings matter to me?

Any suggestions as to drill material, insert vs. solid, point, parabolic, toolholding, speeds, feeds, coolant, anything I can do to try to improve on wearing out HSS in under 3", or having to buy a 5 pack of drillbits to get through 12" of stock. I'm working on my freehand sharpening technique, but if I can buy a Guhring or OSG ex-gold and get a lot more life out of it before sharpening, I'd like to go that route. If a spade or insert drill is better, fine, although other posts seem to point more toward solid drills.



Well, I guess I just wrote a novel, but I'm hoping someone wiser than me has been down this road before on a smaller manual lathe and can point me in the right direction. Turning, boring, even threading and parting are actually fun with 6al4v, but nearly every Ti part I make has a hole through it and the drilling is slowing me down and eating my drillbits.
 
More coolant. In this case you probably need more cooling than lubricity. Minimize the pecking and maximize the coolant.

Buy a good quality drill that is marketed for Ti and you will be much better off. High quality HSS and cobalt drills have worked well for me, as well as minimizing the amount of time the cutting edges are engaged for the operation. In other words, thick chips.
 
Peck drilling with a standard tailstock is a pain. The longer it takes to get the bit in and out, the more heat you'll have to deal with.

You could think about holding your drill in your tool post and then you'll have the whole carriage to peck with. Of course this has it's own set of problems, but if it's set up right, it's quite nice for deep hole drilling. It also allows you to use power feed and get precise feed control.

It's asking a lot to drill a deep hole in Ti with your set up. No expensive drill or coating is going to make up for everything that's working against you. Whatever you can do to keep your set up cool is going to help the most. (assuming your tailstock isn't all wonky and your speeds and feeds are close)
 
Ok, so if I understand correctly that's two votes for better cooling. I was thinking about how I might mount the drill bit in a toolholder on the toolpost, not so much for feed (C model, I'm not going to sacrifice my leadscrew for drilling) as for access to the back of a coolant-thru drill. Don't laugh, but does anyone think I could rig up a squeeze bottle to the back of a drill shank and get something like continuous coolant flow to the drill tip? This idea is attractive as the only reason I peck is so that I can add coolant to the tip of the drill before it gets hot enough to break down/start a fire/bind in the hole. I just bought a coolant-thru Guhring cobalt bit you-know-where, I guess for $25 I can afford to experiment with trying to squirt coolant through the back of it. Sounds ridiculous saying it here but it might work.

Next question: how to mount the drill in a toolholder? I'm inclined to just put it in a turning/boring holder with the vee and setscrews. Otherwise I have to either make a bushing for my boring bar holder, or purchase a collet toolholder. I don't have a use for the toolholder with a drill chuck, I'd rather have a collet setup. Does anyone make ER collet toolholders for AXA size?
 
Drilling titanium with HSS can be done, but a good coolant fed carbide drill will outperform the HSS 10 to 1. A cheap 120v submersible coolant pump dropped in a 5 gal bucket would make any drill last longer than squirting coolant from a bottle.

However, using HSS drills, the best grind for titanium is a double angle point and modified cutting lip. First, the cutting lips of the drill are ground with ZERO rake and split point, then point angle is 135-140°, with the corners of the drill (about 1/4 to 1/3 of total lip length) receiving a second angle 90-100°.

Thrust required will be greater due to zero rake on cutting lips, but the drill will now cut through 100" of material before resharpening if SFM is reasonable. No peck and use the carriage to feed drill with coolant plumbed through drill.
 
The drill point sounds interesting, do you have a picture? I'm struggling with the idea of zero rake on a drill bit. I think I understand the idea of multiple point angles though. Is it kind of like the outsides of the lips are "swept" back from the point when looking from the side? I will look up zero rake for drills, I've heard of breaking the cutting edges for brass but I don't think this is what you mean. Thanks for the idea about flood coolant on the cheap, if I can rig up a collection pan under the lathe I may give it a try.

I appreciate everyone's comments, I realize I'm underpowered and working with a relatively lightweight machine, but it's what I have for now and honestly I'm continually impressed by how well my little lathe can cut when I get things right.
 
Ti is easy to work on the outside diameter. Inside work with a drill is no fun and it really gets serious when you start tapping or reaming. Main thing to remember about Ti is that you can NOT let the drill dwell or rub. That's going to work harden it and then you are screwed.

Heat is what dulls drills. Titanium is a poor conductor of heat. Any heat generated by drilling does not dissipate into the work, but instead runs back into the drill... starting at the cutting edges. If possible, slow down even further. Use a high feed rate and very low speed to prevent heat buildup. More coolant will also help. Throw a double handful of ice in your squeeze bottle or the bucket along with that coolant pump. Every little bit helps.

If your drill gets the slightest bit dull, it starts rubbing and that's when things start going south. Razor sharp tooling and low speeds are the ticket.

As for the size hole, I would not try to drill a bigger hole if you are having trouble with this size. Might not hurt to drill halfway, bore it out to 5/8, finish drilling and then bore it all out to size.
 
The drill point sounds interesting, do you have a picture? I'm struggling with the idea of zero rake on a drill bit. I think I understand the idea of multiple point angles though. Is it kind of like the outsides of the lips are "swept" back from the point when looking from the side? I will look up zero rake for drills, I've heard of breaking the cutting edges for brass but I don't think this is what you mean.

Zero rake on the lips mean the cutting edges are ground flat 90° to drill centerline axis. This can be done by grinding the chip gullet on the side of a grinding wheel to get it flat. Sharpen drill with double point with edges swept back as you envisioned.

Here is pic of a HiRoc drill with zero rake cutting lips (straight flutes). The goal is to make the TIP look like a HiRoc, but with a second angle on the outer edges. The zero rake part will only extend just past the cutting lip .050" or so, then continue back to the regular spiral drill flutes.

We have used this grind on drills ranging from 7/16 to 1.5" dia.

http://www.maford.com/Img/series/200.gif
 
Can you setup a mill to drill the 1/2" hole? (Assuming you have access to one)

It seems it would be easier to drill the part in a Bridgeport mill than with the tailstock. You'd be able to go in and out quickly, and you'd have no trouble keeping coolant in the hole...

Titanium drills just fine with sharp HSS or cobalt. More feed, less speed.
 
Thanks everyone.

I will try grinding a drill point according to the picture.

I haven't thought about using a mill, I have a Bridgeport with 1hp, I can try it out and see how it goes. It would be nice to have gravity keeping the coolant down the hole.

I tried a parabolic bit I had laying around and was surprised by how much longer I could drill before the chips packed up. I had thought for some reason that parabolic flute drills weren't appropriate for high-tensile material, but it held up fine. I will continue to slow the speed, I'm already cranking the feed pretty hard as far as I can tell. I think I may experiment with boring some clearance once I get halfway. It seems like a time-consuming solution but if it saves on drill life it may be the ticket. I'm obviously not too worried about how long it takes, as much as how often I have to re-sharpen or replace the drill bit.

I'll report back with what ends up working best for me.
 








 
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