drill bit or carbide insert drill?

[BigDave]

The heavy steel nose cones I want to make have about a 2 1/4" diameter hole through the middle of them. The pieces are about 8 inches long.

I am debating what to buy to drill the hole through the middle. I have seen Rutland and Enco's catalog listing a 4MT taper shank black oxide coated steel drill bit for about $70 which is cheap. However I doubt the point is split, and I am not really set up to either split a point nor resharpen such a drill other than offhand eyeballing it on a lame cheasy bench grinder.

On the other hand, I can get a 4MT taper shank straight flute drill bit that holds a carbide spade insert that will drill holes without drilling a pilot drill.

I believe both may be too large to place into a tool holder on the carriage and use the powerfeed to advance it although that would be a benefit.

The carbide spade tip and holder is about $275.

I do need something with a drilling depth of about 8"-10".

The material to be drilled is 4130 ChroMo

Ideas?

[halfnut]

I myself would go with the 2 1/4 HHS bit myself, now don't try to just drill one shot with it. You were talking about your new lathe, I hate to tell you this, you don't have the horsepower or the rigidity. A 3/4 first with a split web and it should work fine. Get a drill point gage and learn how to sharpen bits, with this 4140 you are going to have to.

Turret lathes are cheap, this is what you need for these size holes if you are making a bunch of them. I have seen a bunch of good old dogs for under $1000. I hate slugging it out all day on one, but they are work horses.

My one and only experience with a spade bit went badly, was using in 4340 at 40-45 rc , twisted the tang off on first hole, went back to a hss twist bit.

Oh yea, coolant, lots of coolant.

Another one, you might couple the tailstock to the carriage, have done and seen this many times.

[C. Tate]

I agree with halfnut hss with taper to fit directly in tailstock. I recently drilled a 2" hole with the same type you are discribing. I drilled a pilot hole which was slightly larger than the web thickness of large drill and it was not terribly difficult. One other idea is to drill pilot hole and then use a core drill with coolant holes. A core drill is used to enlarge an existing hole and the through cool will clear the chips allowing you to push longer before extracting the drill from the hole. The core drills usually have more flutes allowing lower cutting forces and faster feed rates. They will be much more sturdy than any spade drill and are more easy to sharpen than a standard two flute on a bench grinder because the lip length is shorter. The good ones will compare to the spade in price but without buying inserts.

One other thing about carbide insert anything, without mechanical control of feed rates you will run the risk of tearing up inserts. Carbide is brittle and does not respond to the uneveness of hand feeding.

[This message has been edited by C. Tate (edited 08-30-2001).]

[bdarin]

Halfnut....forgive my ignorance, but what do you mean by coupling the tailstock to the carriage?

[C. Tate]

Hey BD,

What are you building? Sounds like a backyard scud missle. I am curious don't mean to be nosey.

[BigDave]

I am making some of these, which range from 3" to 8" in diameter:

http://www.trictrenchless.com/GALLERY/SYSTEMS/IMAGES/splitting%20wedges_jpg.jpg

I noticed the discoloration on the cones, which I am sure is from heat treating. The surface receives a lot of abrasion by being hydraulically dragged slowly through clay pipe. But it can't be brittle either. The medium size cone you see which is about 6" in diameter is $4000 from the manufacturer. Pretty steep!

I hope 4130 is the right material for strength but can be heat treated for as hard a surface as possible.



[This message has been edited by BigDave (edited 08-31-2001).]

[Thrud]

Dave,

If abrasion is a problem, you could suggest to your customer to get in touch with Norton Abrasives. They have Diamond Film (the stuff babes want on their finger) plated mining gear with layers upto 4" thick. I do not know how much it costs, but with clay a thin layer should work and never wear out. Might earn you some brownie points too.

Considering how deep your hole is I would consider a 1 1/4" boring bar (with an 8:1 overhang max) with insets it should not set you back more than $100. You could then use the carriage feed to cut the hole. It should be faster and safer than drilling a big, ugly hole that deep.

[BigDave]

Thrud,

With a 2.250 hole in the middle to accept the shiny steel pulling pin, I would have to predrill it first with a long shank HSS drill in the tailstock.

I have looked at boring bars and since the 6" nose cone is about 10" long, I is going to take a fairly large boring bar.

Interesting tip about Norton diamond coating.......

[C. Tate]

B.D.,

You can build a boring bar of any size or shape to suit your needs. Just take a piece of bar machine it to the diameter you need and drill and ream a hole in the end to accept a round shank tool bit. We have done it many times in the shop when we had special needs or did not want to invest in off the shelf tooling. They work well and don't take long to build. You can even build it so that it can be bolted directy on to the carriage elminating the tool post for added rigidity.

[JIM DEWOLF]

Someone asked about coupling the tail stock to the carrage. We used to do that all the time when drilling large deep holes up to 3 inches or so. What we did was to use a chain wraped around the tail stock and hooked to the tool post. you just put enough tension on the tail stock bolt so it slides without bouncing around. Of course you need a big lathe - 16 inch or so. With the feed set at slowest rate, start drilling with lots of coolent. You may be able to speed up the feed on a trial basis. This used to save us a lot of hard work and no boring bar is needed. I would drill a 5/8 pilot hole with a long drill then watch the chips fly. If things are getting a little heavy all you do is let off the feed and re-engage it. Try it. Sounds haywire but it works. Any comments?

[halfnut]

On the subject of power feeding the tail. Bdarin asked and Jim answered, I couldn't get on net last night, server was down I guess.

I used to run this old Lodge and Shipley 18", I was cutting a lot of oilfield threads, internals and externals. Anyway there is a lot of metal to take out for the internals, smallest I was cutting, memory stay with me now, was 2 1/2 on the small end of the taper, 3 something on the large.

This machine had a 18" chuck on it, true truth in advertizing back then, so it was a rather robust machine. Well there was a drilled and tapped hole in the carriage and in the tailstock, asked Melvin what it was for, to couple the tail and the carriage he said. So I made a screw in coupler out of some scrap and a couple of bolts, made so I could drop a pin in to connect the two.

I now had power feed on the tailstock, worked the best. Saved me a lot of work.

Look on some older, bigger machines and I think you will find these tapped holes.

[Thrud]

Dave

The thought occurs to me that your steel supplier should be able to supply heavy wall seamless tubing with a hole close to what you need as a finished product - you could then finish it with a boring bar to size.

I did this when I made my Golf Ball Mortar out of 8"od 4130 seamless.

Dave Smith

[JIM DEWOLF]

Half nut has the right idea. We used a chain because there was never any time to fiddle around. The chips had to fly. I did see some carriage links but never got past the chain. Oh, it wasn't the tool post I tied to. I wraped it around the carrage somehow. This was many years ago. It was an old 16" CMC. That was a real good machine made in Canada. But you should try that system. it realy works great.

[BigDave]

I get this blank stare of silence at the other end of the phone when I previouly asked about heavy bar stock with a hole in it from several suppliers.

Then they launched into an auto-script; "uh-that's not available from out suppliers, you'll have to check around." as they wiped the drooling saliva off their chins.

I wonder how hard I can have 4130 case hardened...

[SGW]

Try asking for "Shelby tubing." See http://www.middletowntube.com/shelby/ for instance.

Dunno if you can get it in the alloy you want, though....

[This message has been edited by SGW (edited 09-05-2001).]

[This message has been edited by SGW (edited 09-05-2001).]

[C. Tate]

Tubesales in St Louis they have all kinds. Will post number if I can find it.

[Wagg]

Using a lathe with about 16" swing and 4-jaw chuck I would use mechanical tubing with a 2"ID and Min. OD.

I would cut material about 1/4" to long. Face off one end and turn to finished size. bore the ID to finished size using home made boring bar. Chamfer. Turn around stock, face off, turn taper and chamfer. Finished. If i had several to do i would do them as a group.

Mechanical Tubing is a low carbon Steel and free machining. Available in many comb. of ID's and OD's.

I would Case Harden it. This would allow abrasive resistance to the exposed areas and at the same time retain its toughness so that it won't break.

I have used the carriage feed to drill holes but using a 2 1/4' drill (which has a #5 MT) puts a helluva load on the feed sys. even with a pilot drill. Risky??????

Good Luck.

[Bats]

Maybe you should consider welding the outside with a hardening welding rod and grinding, before boring. Thats how the get abrasive life out of most HD digging equipment. Most any heavy equipment dealer would know of a welder that specializes in such. We used to routinely due this for downhole equipment in corrosive environment. I doubt you have the Hp to drill in one pass. I used a HD 1" insert(set at 45) boring bar to bore .75 to 1." at a time by dragging the tailstock. But that was on a 60" lathe with 48" 4 jaw chucks on both sides of headstock. 12" passthrough set up for threading heavy walled drillstem.

[farmwrench@aol]

Clay pipe? in the ground? Wouldn't a small rock wedge and crack the pipe? or is there lots of clearance? Clay drain tile can vary a lot, why not solve the deep hole problem with a 2pc construction to sit on the pull bolt and make a more usefull product that can fit multiple pipe sizes and then replace only the large Dia. portion when it wears out?