What type of drill bits for lathe?

[James04]

I just purchased this set of drills http://www.mscdirect.com/IWCatProdu...53010&Keyword=Y for my lathe. They are 118 degree jober lenth HSS. Only when I attempt to use them as soon as I make contact with the work piece it wonders of center and then it chatters the whole time Im cutting with it. I was drilling a piece of 1/2 dia. aluminum that was being spun in my lathe chuck and the drill was in the tailstock. I was using a very slow feed (by hand) and I had made a centering hole before I attempted to drill. Are these the wrong type of drill bits? Is it the low quality of the bits. Or am I doing something wrong?

James

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[James04]

Here's the link.
http://www.mscdirect.com/IWCatProduc...3010&Keyword=Y

[HomeCNC]

To reduce chatter when drilling, slow down the RPM. The larger the drill is the slower the RPM needs to be.

[castguy2003]

Give me details of the rpm, grade of aluminum and approx feed rate. Are you useing a spotting drill to start or a center drill? Are you trying to drill a pilot hole? If you use a pilot hole it should NOT be bigger than the wide of the web on the larger drill.
For 6061 aluminum with a 1/2 inch drill I would run about 900 RPM with no pilot hole. My feed rate would be 4-5 inches per minute. You will have to back out to clear the flutes every 1/4 inch or so.

[James04]

castguy2003

I tried slow and moderatley fast rpm's this would include 900 rpm. I dont know the grade of aluminum cause I baught it from HomeDepot. I used a centering bit to locate the center and then whent to 5/16" drill. My main concern was how the bit imediatly wondered of center as soon as it touched the aluminum and was wondering if I was using the wrong type of bit or quality was an issue. Are these the correct style of bits and will the quality do for now as I'm just starting out with this as a hobbie?

Thanks fot the help,
James

[wms]

James,
How much material in hanging out of the chuck? You should chuck the material up close, with a minimum sticking out.
Is you tail stock in line with your spindle?
118 deg should be just fine for drilling.
A 120 degree spot drill would be best. A center bit (drill) is not really made to start hole, it's made to center the work on a center.(hence the name)
To reduce chatter, increase feed rate or reduce surface speed or increase rigidity. or all three.

[lstool]

Yup,
Drill bits you are using are fine and center drilling is fine (and center drills are not designed just for centers on a lathe) if using a jobbers length drill using a center drill first would be normal & proper proceedure to start the drill on center of the desired center location accurately(Center drill) (hence the name) so I will have to disagree with WMS on that issue.
Try this as you are drilling by hand (as I am sure you cannot establish a given feed rate unless you are a robot and can regulate you hand accurately) increase the feed by hand untill the chatter stops you need to load up the tool right away, also make sure when center drilling let the center drill establish a diameter slightly larger than the drill by at least 1/32 or so.
To advoid all this and to speed processes (Time is money) up I use cobalt stub drills 135 deg. split point. Once you start using them youll wonder "Why didn't anyone tell me about this before?" it eliminates the need to use a center drill as you do when using jobber lenghth drills to drill a hole accuratley. And that web on the tip of those drills what a pain in the neck. I remove them by hand, all of them I have a special way of grinding them out nicely.

A little shop trick... WD40 work as a great lubricant for machining alluninum, drilling & tapping

So by the way the proper speed & feed would be...1528 Rpm's feed would be .005 per rev or 7.64 in. per. min

Just a thaught
Lenny

[keithorr]

Are they split point? Do they have an "S" point to self center? I use a stub drill to make a hole 3 diameters deep, then switch to a taper length parabolic flute with a lot of coolant for stainless, or lubricant for aluminum. If you start a hole with a stub drill, the hole acts as a bushing to stop chatter.
Also consider mounting a morse taper block to your tool holder for the drill chuck so the machine can feed the drill more acurately, or get split sleeves that match the taper size and drill size.

[James04]

Ok,

Looks like I was not making the centering hole big enough. Also I was feeding too slow. I'll give it another try and let you know how I make out. I will also look into some of the other types of bits some of you guys were mentioning. Im so new at this I dont even know what part of the bit is the web. Looks like I have a lot to learn. Thanks for the replies.

Lenny,

Nice web page. Makes me wish there was more to see.


James

[Fish]

Hey, just a thought here. This may sound obvious, but, is the drill centered correctly in your tailstock? Are you holding it in a drill chuck? I would check this first if it is wandering at all. The next check would be the cutting faces of the drill bit. I have found some cheap drill bits with unequal length cutting faces, causing chatter, wander, breakage, etc. Maybe trying a good drill bit would help determine if it is setup or tooling.

As far as centre drills are concerned, in Al, geometry of the centre drill doesn't much matter, as long as it's in the centre! There is no worry about work hardening of the pilot area that you would get with other materials such as stainless. Even 7075 Al is soft enough that no matter what centre you choose, the drill bit will cut through it with ease.

I think the idea of using an open web (the spiral part of the drill bit body) is a good idea for chip evacuation. Find a good tool supplier in your area. Maybe visit a machine shop and ask the guys which suppliers they use? Oh, and the way that I learned was to read as many catalogues as possible, and try as many different tools as possible. Oh, and keep notes - the time you spend here will pay dividends in the long run.

Good luck.

Adam