Spin the tool, or the workpiece?

All discussion about lathes including but not limited to: South Bend, Hardinge, Logan, Monarch, Clausing and other HSM lathes, including imports

Moderators: GlennW, Harold_V

Post Reply
dml66
Posts: 41
Joined: Fri Apr 29, 2022 8:21 am
Location: SW Washington State, Steelhead Country

Spin the tool, or the workpiece?

Post by dml66 »

New to the world of lathes, sorry if this is a dumb question :oops:

I'm making a simple part from aluminum round stock to start with so I can learn from my mistakes before making one out of steel.

I'm working with a mini lathe which I've equipped with an ER-32 collet chuck on the headstock, and an ER-25 collet chuck on the tailstock. The part will be 1/2" diameter, about 3" long, with a 3/8" hole center drilled on one end to depth of about 0.75". The hole needs to be concentric.

The round stock I have is about 9/16" in diameter, my plan is to the turn the 3" long piece I need down to 1/2" O.D., then part it off.

For making the hole, I'm planning to first chuck a spotting drill, then a stubby twist drill, then a boring drill, and finally a reamer, all with their appropriate, respective diameters.

My first inclination is to leave the workpiece in the headstock and chuck the cutters in the tailstock, I've seen it done that way many times on YouTube.

However, with only about 2" or so of quill travel, I'd end up having to move the tailstock to accommodate the different cutters, especially the reamer, it's close to 6" long. I suppose I could grind the reamer off to a more manageable length, but that's a one-way operation I might regret later.

So I thought, why not place the cutters in the headstock and place the workpiece in the tailstock? The headstock has ample pass-through to accommodate both short and long cutters.

And then I thought, before making a mess, why not ask some folks who actually know their way around a lathe for their thoughts?

Thank you.
User avatar
Harold_V
Posts: 20231
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Spin the tool, or the workpiece?

Post by Harold_V »

If you place the work in the tailstock, the likelihood that you'll end up with the desired concentricity isn't good. Rarely does a tailstock align with the spindle.

Turning ANY work piece that is longer than three times its diameter is going to be challenging. Taper will be a problem, as will chatter. You will have the best success turning the piece between centers, but even then you'll have to address taper, which is typically controlled by offsetting the tailstock.

Assuming you pursue that avenue, there's no guarantee that the tailstock will be in alignment with the headstock, however, so you'd still face the same problem with concentricity if you machine the work piece by holding it in the tailstock.

Shortening a reamer isn't in your best interest, as the longer the shank of a reamer, the better the chance that it will yield a round and straight hole, especially if you are turning the work piece instead of the cutting tool. By gripping the reamer very lightly on the end, it can wander in the chuck enough to self align. The reamer will still see the hole at a miniscule angle, however, as, once again, it is highly unusual for a tailstock to be in dead alignment with the spindle.

When the work piece is mounted in the spindle, the misalignment of the tailstock isn't a huge problem, as, given the opportunity, a starting drill (or center drill) will find center. That, of course, is contingent on you allowing it to do so. That isn't true of the work piece being held in the tailstock, where there is no real center (because the piece isn't rotating).

You didn't make mention of the degree of precision you hope to create. Concentricity and parallelism of the hole as it relates to the OD of the material, for example. What tolerance do you demand? What tolerance on hole size and OD of the part? How straight must it be? All of this is very much a part of solving the problem of making the part.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
User avatar
Bill Shields
Posts: 10459
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

Re: Spin the tool, or the workpiece?

Post by Bill Shields »

And then there are sliding headstock lathes (called Swiss in North America).

As Harold suggested....spin the work
Too many things going on to bother listing them.
dml66
Posts: 41
Joined: Fri Apr 29, 2022 8:21 am
Location: SW Washington State, Steelhead Country

Re: Spin the tool, or the workpiece?

Post by dml66 »

Harold_V wrote: Sat Apr 30, 2022 4:35 pm Turning ANY work piece that is longer than three times its diameter is going to be challenging. Taper will be a problem, as will chatter. You will have the best success turning the piece between centers, but even then you'll have to address taper, which is typically controlled by offsetting the tailstock.
You lost me on "offsetting the tailstock ", can you explain that procedure please?
Harold_V wrote: Sat Apr 30, 2022 4:35 pm Assuming you pursue that avenue, there's no guarantee that the tailstock will be in alignment with the headstock, however, so you'd still face the same problem with concentricity if you machine the work piece by holding it in the tailstock.
I'd planned on aligning the headstock and tailstock in advance of the activity, hence my reluctance to having to move the tailstock midstream. Since I've never actually preformed an alignment procedure, it may be more challenging than I imagine, YouTube makes it looks easy, lol.
Harold_V wrote: Sat Apr 30, 2022 4:35 pm When the work piece is mounted in the spindle, the misalignment of the tailstock isn't a huge problem, as, given the opportunity, a starting drill (or center drill) will find center. That, of course, is contingent on you allowing it to do so. That isn't true of the work piece being held in the tailstock, where there is no real center (because the piece isn't rotating).
How would I allow the center drill to find center?
Harold_V wrote: Sat Apr 30, 2022 4:35 pm You didn't make mention of the degree of precision you hope to create. Concentricity and parallelism of the hole as it relates to the OD of the material, for example. What tolerance do you demand? What tolerance on hole size and OD of the part? How straight must it be? All of this is very much a part of solving the problem of making the part.
The part I'm hoping to make is a holder for a mandrel with a 0.375" shank. The holder will be chucked in a press or lathe, not sure yet, and the idea is to have the mandrel turn at least as true as whatever is turning it's holder. Based on what I've observed so far, I should be able to achieve <0.002 TIR with a press doing the work, and maybe 0.001" TIR with the lathe turning it. Put another way, if I chuck the mandrel directly in either the press or the lathe, it's TIR is inline with the numbers above, that's academic however since the mandrel and holder is a sub-assembly. It's one of those things which I need to try to see what's possible in practice.

Thanks for your help!
Mr Ron
Posts: 2126
Joined: Tue Dec 22, 2009 12:36 pm
Location: Vancleave, Mississippi

Re: Spin the tool, or the workpiece?

Post by Mr Ron »

I think I would leave the stock 9/16" before boring the 3/8" hole. This is in case the hole does not turn out concentric with the OD. After boring, I would then mount the rod on a 3/8" mandrel and finish the OD to 1/2".
Mr.Ron from South Mississippi
User avatar
Harold_V
Posts: 20231
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Spin the tool, or the workpiece?

Post by Harold_V »

dml66 wrote: Sat Apr 30, 2022 6:57 pm You lost me on "offsetting the tailstock ", can you explain that procedure please?
Most tailstocks are made in two pieces (the housing, excluding the quill, dial and hand wheel). The base of the tailstock fits the tailstock ways, and the upper portion is generally adjustable, front to back. There is no vertical adjustment. By being able to move the tailstock towards the front of the lathe or towards the rear of the lathe, taper in the cut can be adjusted. That is done by tightening and loosening the screws found on the tailstock, front and rear, near the horizontal split in the two pieces. Note that because the vertical alignment of the tailstock is rarely on the centerline of the spindle, the center will be either forward or backwards of the centerline, which will yield a straight cut, in spite of the misalignment. I addressed that previously (see below).
Harold_V wrote: Sat Apr 30, 2022 4:35 pm Assuming you pursue that avenue, there's no guarantee that the tailstock will be in alignment with the headstock, however, so you'd still face the same problem with concentricity if you machine the work piece by holding it in the tailstock.
I'd planned on aligning the headstock and tailstock in advance of the activity, hence my reluctance to having to move the tailstock midstream.
It is common practice to move the tailstock when using it for drilling and reaming.
How would I allow the center drill to find center?
First, you should understand that it's common for a lathe to have a tailstock that is below center, although new machines may be a few tenths above. If you find yourself needing to hit absolute center, the process is to open a hole that is undersized, then bore to establish center. However, for most instances just allowing the starter/center drill to seek center works quite nicely, too. Simply grip the cutting tool short in the drill chuck, so the end is free to wander a few thou (I like to grip by ¼" or less, and hand tighten the key type drill chuck). Rotation of the work piece will drag the cutting tool to center if you don't horse the cut before it does. Simply pick up the spinning face with the cutting tool with light pressure and watch what it does. If it scribes a circle (because it isn't on center) apply a little pressure until the circle enlarges. As it does, the center (of the scribed circle) will diminish, eventually pulling the cutting tool to center. Once it's there, you can drill on location, although you likely already know that drills may or may not drill straight, round, or on location. That's their nature.

The above procedure is ultra-critical if you're using small center drills (#1 and smaller). The tips will break off readily unless you allow them time to seek center.

In regards to making the part, Mr. Ron may have offered the wisest procedure. You could achieve success by turning the piece without tailstock support, assuming you can grind a good tool. You'll get taper, but that can be polished out if you're careful. You could drill and ream the hole without concern for concentricity, which would then be established when the OD was turned. That would also address the issue with chatter.
If you pursue this approach, you'd be well served to drill 1/32" undersized, then bore the hole as deeply as you can to 1/64" undersized. Follow that with the same size drill to open the hole through. That procedure will help ensure that the hole is straight and will clean up with the reamer you'll use. Grip the reamer only by a short length, too, so it is free to find center.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
dml66
Posts: 41
Joined: Fri Apr 29, 2022 8:21 am
Location: SW Washington State, Steelhead Country

Re: Spin the tool, or the workpiece?

Post by dml66 »

Mr Ron wrote: Sat Apr 30, 2022 11:29 pm I think I would leave the stock 9/16" before boring the 3/8" hole. This is in case the hole does not turn out concentric with the OD. After boring, I would then mount the rod on a 3/8" mandrel and finish the OD to 1/2".
I thought about that approach as well, purely by accident of course :wink: .

Assuming you mean the mandrel, it does have a flat on the shank which is used to secure it in the full assembly with a setscrew. The holder itself will require an unthreaded side hole that's slightly larger in diameter than the setscrew. With the holder and mandrel installed in the assembly, the setscrew passes through the holder and rests on the mandrel's flat.

Further assuming you mean turning the rod by turning the mandrel, there's nothing to secure the mandrel to the rod. What I could possibly do is drill and tap the side hole with a small setscrew, say #6 (I think the assembly's setscrew is #10), turn the rod, then drill out the side hole to >#10. However, a centered 3/8" mandrel inside a 9/16" rod leaves just 3/32" or so for setscrew thread, I'm not sure that's enough.
dml66
Posts: 41
Joined: Fri Apr 29, 2022 8:21 am
Location: SW Washington State, Steelhead Country

Re: Spin the tool, or the workpiece?

Post by dml66 »

Well, I may be out of luck with this tailstock as it's 0.006" above the centerline of the spindle :cry:

Not sure there's anything I can do about that, so, need to apply the advice given here and work with what I have.
Post Reply