Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Machining deflection

Machining deflection

Machining deflection

Is anyone aware of an anayltical method to estimate tool induced deflection when turning a relatively thin walled cylinder on a vertical lathe? I'm aware I could use FEA or similar software to solve my problem for me but it seems a simple enough problem that there must be a first principles way to get a quick estimate. Roark's wasn't forthcoming with an answer
The cylinder will be ridgidly clamped on a rotary table at the bottom end and unconstrained at the top end where machining will take place. A bracing fixture is being considered to oppose any deflection but I'm not convinced, and neither are many others here, that the component will deflect significantly. However, I can't rely on such non-scientific guessing to say "it will be fine", and I don't fancy spending a chunk of cash on a fixture I might not really need.

RE: Machining deflection

I'm not sure that you will get an answer for "tool-induced deflection of part during a turning operation."

If you examine & study chip-formation theory and the equations developed from that theory which are used to analyze machining processes, you will see that tool-induced forces apply to shearing off a thin layer of material and making chips. I would think that forces are primarily used to make those chips because that is where the weakest point will be: shearing off a chip along a shear plane and not deflecting the bulk material through bending. This applies to proper machining conditions for your work (speed, feed, depth of cut). Go outside those "normal" parameters for your part and, sure, I suspect that you'll deflect the heck out of it. Wear your face-protection shield and stand back when you do because it may get momentarily exciting.

At the micro level of thought, minimal cutting conditions would (I suspect) produce some deflections in the part, but those deflections would (I suspect) be less than your measuring instrument tolerance and you'd never see them.

Blue Technik LLC
Virtuoso Robotics Engineering

RE: Machining deflection

You should be able to find some machining calculators that will give you radial force and axial force when turning. I've generally assumed both are less than about 200 lbs. maximum for the amount of material my tooling can handle.

A Google search found this:


RE: Machining deflection

So what are we talking about for dimensions and material?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Machining deflection

I believe this is where the Swiss lathe comes in. It has an opposing feature that resists the force of the cutting tool to provide greater accuracy and avoid chatter. I may be taking liberties with this description so here's another write-up:


Static deflection might not be much, but if you get a match for the natural frequency you'll make garbage out of the workpiece and maybe the cutting tool as well.

RE: Machining deflection

Brian - That Kennametal calculator is very helpful.
Ornerynorsk - 2m diameter, 2m length (ish) nickel-chromium-iron alloy with a 20mm or so wall thickness.

Parts used to be made on a horizontal borer and sagged into a slight oval under their own weight - ended up being machined in that deformed shape, recieving a circular cut and relaxing to an oval bore when stood upright again.
They are being cut vertically this time to stop that but it doesn't change the fact they are not really that rigid.

RE: Machining deflection

Rigging the support is not "routine" on a vertical mill or vertical boring machine, but ANY method of providing the equal to a lathe's mid-point support that will oppose the sideways of into EITHER inside or outside of the wall of the thin rotating part will work. Thus, take a lathe's support, weld a stiff bracket to a frame that can be bolted to the vertical mill's bed, then position the support opposite the machining tool. Done. You don't need to exactly "calculate" (really, just estimate) the force sideways invoked by the tooling, just oppose that force with something stiff enough not to move.

RE: Machining deflection

I've used cerrocast to stabilize parts for machining before, but on a part this large it becomes impractical. Clamping at the bottom end and machining at the top end may still cause the material to present like a wet noodle to the cutting tool. Tough part, fixturing may be your best answer, I personally don't think it will machine well unsupported. An ID or OD ring could help stabilize and remove some of the tendency to deflect and chatter.

I'm curious, is the machining to be done on the ID, OD, or end face, and I'm assuming it has a weld seam?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Machining deflection

I'd guess a tooltip force quite a bit greater than 200 lb to make a cut on NiCrFe.

The workpiece proportions are not a whole lot different from those of a common steel drum, but without the reinforcing ring ribs.

I submit that you may need to insert a diaphragm near the top end while machining it; I'm thinking something like the end of a whisky barrel, made from >100m thick timber, jammed in or made with some expandable features, like peripheral elements expanded by driven wedges.

You've got room to frame a big door in the diaphragm, include columns to support it while it's being tightened, and stairs down to access the faceplate inside the cylinder for securing the bottom end.

Mike Halloran
Pembroke Pines, FL, USA

RE: Machining deflection

You could finish machine the ID or OD and then lightly press fit a a reusable stiffener to the part before machining to final wall thickness.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


eBook - Functional Prototyping Using Metal 3D Printing
Functional prototypes are a key step in product development – they give engineers a chance to test new ideas and designs while also revealing how the product will stand up to real-world use. And when it comes to functional prototypes, 3D printing is rewriting the rules of what’s possible. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close