help to bore to 3.500 x 24.000 on lathe

delverth · Sep 26, 2012

somebody give me some fresh ideas, i'd try to bore from 2 3/4 ID, to 3.500 x 24.000 deep with 45 degrees at bottom to 3.000, every single tool chatter, with low or high speed or feed, i'm running out of ideas, even i home made a custom bar to reduce the vibration with no success, any help ???

delverth · Sep 26, 2012

the material is 4140 an

Limy Sami · Sep 26, 2012

What machine are you trying to do this job on?

How big is the spindle bore?

3 jaw or 4 jaw chuck?

Fixed steady rest?

What's the OD of the part?

How many have you to make?

We need a LOT more information.

Forrest Addy · Sep 26, 2012

Drill etc to hog out waste, leaving 1/8 stock.

Bore first couple inches to size of packed bit (steel shanked boring tool with fitted wood wear plates.) Grind double ended to-size boring tool whose chip-load is equal and balanced. Bore remainder in one cut using 10 GPM oil coolant flwo to flush chips. Hint: grind tool to make short chips. The initial bore if straight and true will guide the bit and the subsequent bore will be round. clean, chatter free and to size - if all goes well .

If good a finish is requipred use a Sunnen portable hone.

KB3AHE · Sep 26, 2012

Sounds more like a job for a boring mill than a lathe.

24" hanging out of the chuck is a lot of real estate. I hope you are using a good steady rest. A boring bar long enough to bore 24" would have to have a lot of flex. You would probably have to make a boring bar close to the diameter of the 3 1/2" hole you are boring to be ridgid enough not to chatter.

Make sure you have very sharp tool bits. If it is chattering real bad, you are probably work hardening the 4140.
Also keep in mind that 4140 is happier when you take bigger cuts with a really sharp toolbit or a new insert.
with any of those alloys if the tool is flaxing aray from the bit, the bit will just rub the metal and work harden it.
On the next pass, you have to cut all of the way through the work hardened material to start getting descent cuts again.

Just my $.02 worth

Frank

JRIowa · Sep 26, 2012

Nope, sound like a job for a 5A
JR

Ox · Sep 26, 2012

How close doo you need to hold the bore?

What finish?

You could build a 3 (?) tooth tool by slotting the end of a 2.5" bar in a fashion that you could slip some cut down turning tools into, and set-screw into place.

???

I would try tools with 15* or more back taper, and neg inserts.

You may need to have a starting bore for it to pilot into?

I would think that you could run a copper line for coolant down the edge and hose cramp it in place?

You may have to git creative on the 45* taper in the bottom, but maybe this could at least git your bore in there for you?

-----------------

I am Ox and I approve this h'yah post!

TDegenhart · Sep 26, 2012

A lathe is not built to have that much overhang from the tool post. If you have room for it, I would consider a steady rest on the tailstock side and an extra long boring bar to help with deflection and vibration.

Tom

lbhsbz · Sep 26, 2012

The part already has as 2 3/4" bore through it right?....use that to pilot your cutter. I'm picturing a 1" diameter bar with a big pilot on the end that has a relief in it....The pilot will support the tool. Blow air through the relief to evacuate chips towards the tailstock. If the taper is fairly close to the other end, it may be easier to flip the part in the chuck after boring to an appropriate depth and go at it from the small end.

delverth · Sep 26, 2012

this is a weiler lathe e90, 4 jaws, with 10.00" bore through, od of the part is 4.000, tolerance is +.010 -.00 finish of 125, thanks guys, what can i say? U definetely know what u doing, i'll try all those tricks and let u know later,

S_W_Bausch · Sep 26, 2012

When we attempt to send non-trivial amounts of torque down a long shaft, the torque reactions are non-trivial.

We may have experience with long "aircraft" twist drills of 1/4 inch or 3/8 inch driven by a hand-held drill. There were torque reactions, but we lived with it.

I have experience of using a Milwaukee HoleHawg drill, which can drive a 4 5/8 inch Forstner bit into the wooden stud/joist of your choosing. You will (hopefully) be able to brace yourself, and it goes without much problem.

However, if you decide to add a 24 inch extension and find yourself attempting to send all that torque reaction through your arms, down your trunk, down your legs, through your feet, and into the floor, well, Not So Much.

Photo of twisted extension available on request

Same here, but it sounds as if the workpiece itself is having difficulty with torque reactions.

Good Luck
Steve

On edit: Nice lathe. What you are doing is perhaps closer to trepanning, inasmuch as you want to take a solid bar and make a pipe out of it. You are in Oil-Country, and trepanning is a well-known process. The tooling is basically a hole saw on steroids, which cuts out a core, which gets stacked in a pile, somewhere...

Specialized machinery and tooling, but it's not prone to torque reaction, so it works, even over 50-60 feet of workpiece.

http://www.todaysmachiningworld.com/how-it-works-–-drilling-deep/

Nick Mueller · Sep 26, 2012

However, if you decide to add a 24 inch extension and find yourself attempting to send ...

The length of the extension makes no difference in the torque.
The only difference you get is more torsional twist (-> risk of chatter).

The gun-drill approach (or its variants with a pilot) seem the most promising to me.

A boring bar might work, but the leverage at the X-way will be a show stopper I guess. I think you will have most part of the deflection there.

Nick

Cole2534 · Sep 26, 2012

Nick Mueller said:
The length of the extension makes no difference in the torque.

snip

I disagree. A boring bar that long may turn into a torsion spring and give a horribly erratic cutting action. Smooth like violin.

Mike C. · Sep 26, 2012

I'm with KB3AHE, save money by sending this to somebody with a HBM. If it's a home project, you might want to worry on through it, but that's 8 diameters, even using a 3' boring bar. You can probably slow down enough and take fine enough bites to keep chatter to a minimum, but you'll be making about three passes per day. Max depth will probably be .020 without it squalling on you. You can maybe let it chatter and hog out the worst of it, but you are still looking at a bunch of finish passes to clean it up.

Tonytn36 · Sep 26, 2012

You need a padded bar for that. Longitudinal polished carbide pads brazed into the boring bar a few microns under your bore size and pilot bore the shaft to get the pads engaged. Pads support the bar while it's cutting. That bar you have now is just a long spring and is bending and twisting under cutting load.

Nick Mueller · Sep 26, 2012

I disagree. A boring bar that long may turn into a torsion spring

It looks like you did not understand my first sentence that you quoted and ignored my second sentence.
I repeat: The torque stays the same, the twist increases with length.

Nick

Perry Harrington · Sep 26, 2012

You could make a large pilot for an APT spade drill insert. The insert is $50 and gives balanced drilling force, just set it on center to the bore and use a pilot to guide it on center.

3-1/2 EB112 HSS M/TL BLADE :: "E" Series Standard Duty Blades | Travers Tool

lowCountryCamo · Sep 26, 2012

I recently had to bore a 3" hole only 6" deep and I made a 2" bar from cold rolled pictured below and used a sharp tool bit, small radius for low tool pressure. Milled dovetails to mount directly to tool post. I like Forrest's idea of 2 cutting sides and a drill bushing.

gbent · Sep 26, 2012

Look up APT Multitool. That is what Perry was trying to lead you to. Its a flat bottomed blade with a pilot for the existing hole. (By the way, this system is the best way I have ever found for making large holes on a Bridgeport that are to deep for an annular cutter) When you get to the depth of the full diameter, you can grind your 45 degree in the bit and finish to depth.

I highly doubt this will give the surface finish you require so you will need to finish with a packed bit like Forrest suggested, Tony had the same suggestion with the carbide pads.

In the alternative, get a piece of the correctly sized tubing, then shrink fit and weld a plug in the bottom. Even thread, o-ring, and pin. Lots of methods will be easier than boring a 3 1/2 diameter hole 24 deep.

drewboyer · Sep 26, 2012

find somebody that will let you use a long 2.5 sandvik devibe bar. the long ones are usually good for 10x the diameter. the short ones are only rated for 7x. run some air though the bar to blow out the shavings and you should be able to hold that finish. a good devibe bar always saved the day for me.

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