Boring out a lathe spindle

Job Shopper TN · Sep 9, 2017

Hello gents.

I have a task at hand and need help figuring out how to do it. We have a Haas TL-2 lathe. For a reason that escapes me, Haas manufactures these machines with a spindle bore of exactly 3.000" - or perhaps even a thousandth or two under. We all know the old adage, a half-inch pin won't fit in a half-inch hole... well, that applies a lot more when you have a 3" bar and a supposed 3" spindle bore.

Long story short, I attempted to make and use a 2.5" diameter boring bar to skim the spindle bore to around 3.060" or so. Enough that a slightly bent or slightly oversize 3" bar goes thru, as it should have been made in my opinion... well, all I got was a lot of rubbing, endless chatter. No good. I believe I may have made the bore smaller in spots due to all the chatter ridges... heh...

So, back to the drawing board. Any bright ideas on how to open this up?

I have looked at a few technical drawings and the spindle appears to be thick enough that this modification would cause no issue. From front to back, with the chuck and end cap removed, the bore is basically 22" deep, if I recall correctly. The spindle I.D. seems to be slightly hard - maybe in the 30s Rc, based off of cutting it only about 3" deep with a short bar.

The obvious answer to me may be, remove the spindle from the machine (if that can be done without damage), set up in a lathe and bore halfway from one side, halfway from the other. But, we will never have time for all of that work, even if it is possible, even if it will aid us greatly on many, many thousand-dollar shafts we have coming up!

So - any thoughts, please let me know.

ewlsey · Sep 9, 2017

The spindle is likely made from a forging and hard as a coffin nail. It was bored and sized before heat treat. Maybe some kind of reamer or piloted tool that would follow the existing bore.

Milland · Sep 9, 2017

I don't recommend this (you're on your own), but if I *really* wanted to do this I'd set up a cylinder hone with coarse stones driven by a good corded drill, mount the drill to the carriage so I can stoke in Z, then arrange a Little Giant pump (or similar) with some shields and ducts to convey honing oil (and keep grit out of the lathe).

Shoot for ~.030 over, I don't think I'd want .060. If there's stresses still in the spindle you might relieve them and introduce a warp. Cut once, measure dozens of times to check for taper or other abnormalities. Watch the stones, if they glaze replace them.

If you try this (don't) let us know if it worked.

Marcuschrist · Sep 9, 2017

ewlsey said:
The spindle is likely made from a forging and hard as a coffin nail. It was bored and sized before heat treat. Maybe some kind of reamer or piloted tool that would follow the existing bore.

This sounds like your best option, how bad is the chatter and how deep?

Job Shopper TN · Sep 9, 2017

Marcuschrist said:
This sounds like your best option, how bad is the chatter and how deep?

It isn't horrible, not like threads or anything. I'd say .005 to .010 deep. I have only cut on the rear 6" or so of the spindle, didn't want to chance taking it thru.

I pondered on a piloted bar or reamer-esque tool. If I made such a tool, I suppose it would essentially be a boring bar, but with a brass or bronze sleeve behind the tool made to a... slip fit?... for the spindle I.D.. Over that length, I would think said bar would be flexible enough to account for any slight deviation in straightness. Obviously it would need to be very close...

I may be waaay off track though, haha.

I do like the idea of a cylinder hone as well. I've seen but never used those. That may be a good way to at least open it up a smidgeon.

ewlsey · Sep 9, 2017

The thing is that often the spindle bore is pretty rough and out of round. They are drilled out before heat treat and once quenched could be pretty far out of straightness and roundness. On a real CNC lathe, there would be a drawtube for the chuck made from DOM tube, so it's not an issue for them.

Marcuschrist · Sep 9, 2017

ewlsey said:
On a real CNC lathe

That's some absolute fire banter Ewlsey, I had a good chuckle.

adama · Sep 10, 2017

Simple steady behind the lathe a sutable bar could slide through and it's a simple line boring exercise the lathe can self perform. Inssert choice is everything, you want a small a tip radius and as free a cutting geometry as the material hardness allows.

A typical negative geometry insert like most 2" boring bars have - use is the absolute worse thing if you want to go deep, you want a lovely free cutting CCMT or similar and probaly only take out 10 thou a pass.

Me i would use a shorter bar and open up what i easily could then go after the far end bit separately. At thoes diameters, sorting the first 10"+ should be easy.

kalim · Sep 10, 2017

adama said:
Simple steady behind the lathe

another one in front of the chuck and a long bar sliding through both should allow turning the entire length

this is inspired from broaching machines

set up the insert with a dial indicator

adama · Sep 10, 2017

^ he wants a bore to clear 3" no need for a steady or DTi in front of the chuck, just use the tool post and saddle, circa 2" bar or a little more, a simple cross hole and a ccmt 05 boring bar cut of and held in the hole with a grub screw. CCMT06 bars are less than £10 each from our chinese friends, hell some of them i have more tied financially up in the insert than i do the bar!

Haveing already bored out the first 10+ inches easily with a std bar you should be able to easily do the boring of the last bit with less than 30" of unsupported span, on a double supported boring bar thats plenty rigid for doing that kinda cut in a few passes. Far support need not be anything cleaver, hell clamping the bar to a forklift (mast side not TINE!!) and letting the lathe saddle push it back as it advances the cut is plenty good enough for a clearance hole.

This is not a line boring setup job, you just want a bar going through the spindle with the cutter mounted mid way such that your supporting the cut from both sides.

kalim · Sep 10, 2017

i agree that suporting from both sides may seem too much, but is faster than taking the spindle down, and it will deliver good cylindricity

boring the 1st half should be easy, while boring the 2nd half is tricky

using a forklift is an idea, may deliver a cone instead of a cilinder, which may be acceptable, but he said that he encountered chatter with a 2.5 boring bar, so there should be no difference if same tool is used

kalim · Sep 10, 2017

pushing through the hole a hss reamer or a face mill or something, without letting it to rotate ? this tool will fall down after exiting ; sounds risky, but it may work

only 2 long flutes should deliver the cutt, but better have 4 flutes

cwtoyota · Sep 10, 2017

I don't think I would bore any of my spindles, but if I had to do it I think I would approach the problem like this:

Machine a couple caps that fit on the ends of the spindle.
Make the back end-cap first and attach it to the spindle with four grub-screws. These will allow you to dial it in radially.
Bore each cap, and press-fit a 2" bronze bushing. Bore the bushings to size to support a a long piece of bar.

Make your boring bar extra long and use a standard CCMT (or similar free-cutting insert) boring tool as suggested above.

The 2" bar-stock is supported radially by the two end-caps which are dialed in to zero radial run-out.
To adjust boring diameter, use a 3"-4" micrometer across the 2" bar to measure how far out the CCMT holder is protruding.

dcsipo · Sep 11, 2017

Job Shopper TN said:
Hello gents.

I have a task at hand and need help figuring out how to do it. We have a Haas TL-2 lathe. For a reason that escapes me, Haas manufactures these machines with a spindle bore of exactly 3.000" - or perhaps even a thousandth or two under. We all know the old adage, a half-inch pin won't fit in a half-inch hole... well, that applies a lot more when you have a 3" bar and a supposed 3" spindle bore.

Long story short, I attempted to make and use a 2.5" diameter boring bar to skim the spindle bore to around 3.060" or so. Enough that a slightly bent or slightly oversize 3" bar goes thru, as it should have been made in my opinion... well, all I got was a lot of rubbing, endless chatter. No good. I believe I may have made the bore smaller in spots due to all the chatter ridges... heh...

So, back to the drawing board. Any bright ideas on how to open this up?

I have looked at a few technical drawings and the spindle appears to be thick enough that this modification would cause no issue. From front to back, with the chuck and end cap removed, the bore is basically 22" deep, if I recall correctly. The spindle I.D. seems to be slightly hard - maybe in the 30s Rc, based off of cutting it only about 3" deep with a short bar.

The obvious answer to me may be, remove the spindle from the machine (if that can be done without damage), set up in a lathe and bore halfway from one side, halfway from the other. But, we will never have time for all of that work, even if it is possible, even if it will aid us greatly on many, many thousand-dollar shafts we have coming up!

So - any thoughts, please let me know.

I am glad i do not have this problem, but if i had it....
The spindle on the back end of the Haas TL2 stick out about an 1" or more.

https://i0.wp.com/cncmachines.net/wp-content/uploads/2017/09/IMG_7902-resized.jpg?fit=600,800&ssl=1

Make a fixture that goes over the spindle, like an end cap. Use grub screws to fasten and center it to the outside of the spindle, make sure the bottom of the cup is at least 4 or 5" past the end of the spindle. Drill the bottom of the cup and insert a 2.5" bronze bushing into the hole. Get a 30" or longer 2.5" drill rod and make a boring bar out of it. center your boring bar holder on your carriage on the spindle center and. put a bit into your boring bar and line bore the spindle. Little fidgety but you have a bar supported on both ends. There was another suggestion that said use a plug on both ends...may be easier that way, or just chuck in another 2.5" bushing in the 3 jaw to center your bar in the spindle.

dee
;-D

machtool · Sep 11, 2017

I think you going to end up with a bent spindle.

Regards Phil.

SeaMoss · Sep 11, 2017

Hand-held hone. You'll be done with the job before you can even set up for these other ways. Plus you won't have to go to the gym that day.

(You don't need to go to the extent Milland describes. Just stroke the thing manually. Kinda hard work but will do the job quickly and easily. Have done some 2' long pieces of tubing this way, it's not very difficult.

Move a little faster at the ends of the stroke as you will be there longer, that's about the only trick to it. And use coarse stones, you're not trying to get a ground finish

Squirt gun will put enough oil in to do the job, I like the black sulfur stuff but opinions vary. Honing puts the least amount of stress into a part of any machining process, and it follows the hole so what you'll get will be as good as what you started with. In fact, they hone H-13 piston pins to remove stress. Should work tits.)

adama · Sep 11, 2017

^ Your going to take out 60 thou from a 3" dia 20+" long bore with a hand hone faster than it can be bored after a simple 30 minute setup, would like to see that!

SeaMoss · Sep 11, 2017

adama said:
^ Your going to take out 60 thou from a 3" dia 20+" long bore with a hand hone faster than it can be bored after a simple 30 minute setup, would like to see that!

Why would he take 60 ? he only needs 5.

Besides that, I seriously doubt he'd be cutting that spindle within 30 minutes. I had a shop, too. More like four hours in real life. Honing with coarse stones is pretty fast - especially if the initial surface is rough (I bet it is) and you're just hitting peaks.

But hey, it's his lathe so he can decide

machtool · Sep 11, 2017

SeaMoss said:
Why would he take 60 ? he only needs 5.

OP at post # 1 claims a need of 3.060" Once upon a time that was on or about 1/16"

Long story short, I attempted to make and use a 2.5" diameter boring bar to skim the spindle bore to around 3.060" or so.

machtool · Sep 11, 2017

I maintain, this bloke will fuck up his spindle, the bore is gun drilled and bored, pre- heat treat, short of grinding the nose internal taper, post heat treat, the rest of the bore is as heat treated.

Very easy to check, stick a long stylus D.T.I onto a non ground internal journal. Don't be surprised if you see 3 -5 thou T.I.R. That's because it was finished pre heat treat.

No matter how it was heat treated, your ripping the "skin" off.

I'm known to rebuild the odd spindle, When a bearing has spun and chewed up the fit. We'll rip it down 10 thou a side for hard chrome.

When your watching it with tenth or better clocks, they still walk.That's between centres on a grinder, the shaft will bow. Just taking 0.020" off the external bearing journals.

Good luck, blindly mongrel boring out the guts.

Regards Phil.

Boring out a lathe spindle

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