drill point angle and boring

I am making a part which has multiple diameters, both outside and inside, from a piece of solid round stock. I have two questions regarding drilling/boring the inside dia.: what is the proper drill point angle for drilling in a lathe w/ bit in tailstock chuck (material is centerless ground "shaft steel"(?); don't know what grade, exactly)? I've seen 116o, 118o and some steeper; in fact, I have a heap of misc drills many of which have rather steep angles (guess: 130o). 2nd question: Am I right in my assumption that the accepted method of boring a solid is to drill it large enough for the boring bar to fit? this would mean a very large drill as my boring bar is 5/8", plus a 5/16" bit. Or should I get hold of a smaller dia one-piece boring bar (I've seen such things in Enco w/ carbide tips, but don't know how I'd mount one in a tool post, as they're pretty small dia, and round; make a bushing for the boring bar tool holder?)? Any input greatly appreciated.

I start with the center drill, then small 1/4" hole, 3/4 then 1". My boring bar fits in a 1" hole. If you need a smaller hole you will need a smaller boring bar...Bob
http://groups.yahoo.com/group/southbend10k/

Yes, drill a pilot hole w/ center drill, and follow it up incrementally w/ larger drills. Since you're on the SB forum I'll assume your lathe is most likely 9"-13",perhaps larger.

As drill diameter increases, it takes more force to turn against the drill. So the larger your hole, the smaller your drill increments will have to be. Also depends on the sharpness of your drill. It takes a lot more power to turn a dull drill. I think your machine will give you feedback if your drilling more aggressively than its capable of.

At some point, you may risk the drill spinning in the chuck, or the drill adapter spinning in the tailstock taper. Situations you want to avoid by not taking too large a drill increment.

A drill will remove metal faster than a boring bar. So keep drilling as large as possible, then go to a boring bar setup to control hole diameter and surface finish on the hole surface.

For steel, the general 118* drills will be fine. The sharper angles were most likely for something like brass or plastics that will grab the drill and pull it in too fast.

You want to be able to use the thickest boring bar you can to maximize stiffnes. This will give you better control on your hole size from pass to pass. Along with getting you a good surface finish. I think the rule of thumb for your boring bar is that its unsupported length on the cutting end should be no more than 3 or 4 times the BB's diameter.

If it chatters like crazy w/ a lousy finish something is wrong.

We all get in a jam and occaisionally use too long of a boring bar. But you'll just have to take lighter cuts, and it requires you to take a lot of spring cuts in between passes.

I'm not a seasoned journeyman by any means but I think that covers a lot of it.

Mark

Thanks for the input. I started drilling last night with a center drill, then moved to a 1/4" sharp 118o drill. was merrily drilling away, remaking to myself how well my several times resharpened drill was cutting, when the blasted thing snapped off in the hole. The part is about 3" long, and what's left of the bit is buried about 1-1/2" in it. My idea to get it out was to enlarge the hole a couple of sizes, then drill from the other side, in both cases until I got as far as the broken drill. Then use a hammer and punch to knock out/break apart the broken bit (not in the lathe, on the bench). Broken piece isn't budging, but it does break a litle bit, allowing me to drill a bit deeper. This will be a long, tedious process with a couple of serious flaws, chief among them that the work never goes back in the 3-jaw chuck exactly the same as the last time (Joe Chinaman 3-jaw is my only chuck), so the drill is always a bit off center each time I start again. I fear I'll break another bit doing this. Better ideas?

I don't know what others do, but I do almost all of my work in a 4 jaw chuck. Dialing work in with a dial indicator doesn't take too much time and avoids the errors normally involved with three jawed chucks. I simply do not have the money for a precision 3 jawed chuck, so the 4 jawed chuck and dial indicator are an adequate substitute.

Firts thing before any drilling, center drilling etc., in order to reduce deflection and wobble take a face cut off the end of the work piece to get it running perpendicular to your tools so they can get started true. Makes for easy machining, tool life, machine life etc,.

Once you master using a 4 jaw you'll never rely on a 3-jaw for precision work!

P.O.

Where's a good place to find a decent 4-jaw chuck at an affordable price? Should I haunt ebay? If there's a place to just get one i'd rather just buy it, though. What brand? Are there different varieties of 4-jaw chucks?

Chucks are like anything else. Cheap and not so cheap. You want a GOOD chuck look in the MSC cat for a Cushman or a Buck. or www.lathe.com has good ones online. I have 2 JC 4 jaws from www.jtsmach.com they are nice for some work, but i have a hard time getting ZERO because of the fits of the chuck parts. They aren't too smooth. Then theres ebay. If it were me i would spring some extra green and buy a new one from lathe .com about $200 for a 6" 4 jaw Bison...Bob

Ok, Bison. Got it. Thanks, I've heard of Bison before. Also Cushman, in fact I have a very small independant 3-jaw Cushman that came in a lot I bought. The adjusting screws are just about all damaged where the chuck key is used (either twisted from overtightening or rounded off). Any sense trying to fix these? Or maybe make new ones? They are numbered, to mtch the jaws, so I'm guessing they must be fitted and probably high precision, in which case making new would be beyond my capabilities at this point.

Suppose I found a Cushman 8-1/2" 4-jaw chuck on ebay and was able to get it pretty cheap... too big for my 10L? Description says it's 35lbs, and intended for use on 11" and up. My machine has a 3/4hp motor, right now wired for 115V, though it can be wired for 230.

In my opinion, i think a 6" is really the largest you want to go with as your primary chuck. With an 8" you may have issues with the jaws wacking the carriage and toolpost etc when you extend the jaws. Sure having an 8" on the side might be OK for that occiasional job. But I think a 5" or 6" is your best bet for your primary use chuck on a 10L.

mark

Ok, thanks. 6" it is, then. Did check out the sites mantioned above including lathe.com as well as others. $200 seems to be the price for a "semi-steel" independant 4-jaw chuck w/ solid hard jaws. Wow, are the "precision" chucks expensive!! What's "semi-steel"? Is this the ususal material? It seems to be pretty common, and the little bit of looking I did didn't turn up any "fully steel" in the same quality/price range.

leave the part in the chuck, take the whole chuck off. thats one benefit of a threaded spindle- easy to remove the chuck. you can try a prong-type tap remover to try to spring the drill bit end loose from its position, then nurse it out very carefully with a pair of forceps or longnose pliers. I say CAREFULLY so that we are aware that if it doesnt stay correctly aligned with the hole, it will quickly jam again. if the part is held on center and has to be drilled all the way thru, use the chuck to hold the part and drill down thru the chuck mounting hole with a stub drill.( be careful here- you may want to use a thread protector sleeve.) now you can tap the broken part slightly with a punch to free it and draw it out carefully.