Guide
Chatter marks on machined parts: are they acceptable, and how do you control them on the drawing?
Chatter marks are the regular, wavy pattern a cutting tool leaves when it vibrates during the cut, usually because the tool, the part or the setup is not stiff enough. They are acceptable only where the drawing’s roughness, waviness, form and cosmetic requirements are all still met; on sealing, bearing and visible surfaces they are normally a reason to reject, and the drawing should say so with a waviness or form limit rather than a roughness value alone.
By Saola Manufacturing engineering team · Published · Updated
Chatter is one of the few machining defects a buyer can see from across the receiving bench: a band of evenly spaced ripples on a bore, a face or a turned diameter. The argument starts when the part measures in tolerance and the roughness reading passes. This guide explains why that happens, when chatter actually matters, and what to write on the drawing so the question is settled before the first lot. A single step or line between two cuts is a different mark, covered in the witness marks guide.
On this page
What causes chatter marks on a machined part?
Vibration between the tool and the part during the cut, most often from long tool overhang, a slender or thin-walled part, weak clamping, or cutting conditions that excite the setup.
Tool makers’ troubleshooting guidance lists the usual suspects. Sandvik Coromant links chatter marks to high radial cutting forces from the tooling or the tool mounting, typical for internal machining with boring bars, and lists remedies such as a smaller nose radius, a larger entering angle, a sufficient depth of cut, reduced overhang, the largest possible bar diameter, damped or carbide bars and longer clamping (Sandvik Coromant, troubleshooting in turning). Its guidance on long-reach tooling states that vibration starts to become an issue from a tool overhang of four times its diameter (Sandvik Coromant, long overhangs).
The part is just as often the cause. A long shaft between centers, a thin-walled sleeve or a large thin flange flexes under the cutting force and rings. Deep bores and small internal grooves force long, slender tools. These are design features, which is why chatter risk is worth discussing at drawing review rather than after the first article.
Why can a part with chatter marks still pass the Ra check?
Because chatter often has a wavelength longer than the roughness cutoff, so the filter that separates roughness from waviness removes much of it before Ra is calculated.
ASME B46.1 defines surface texture as three components: roughness, waviness and lay. Ra is a roughness parameter; it is computed after the long-wavelength component has been filtered out, as the surface roughness guide explains. A tool chattering at a frequency that leaves ripples a few millimeters apart puts most of the defect in the waviness band. The profilometer reports a good Ra; the eye, a seal lip or a bearing sees the waves.
Chatter can also show up in form measurements instead. On a turned diameter, vibration can leave a lobed section that fails roundness while every diameter reading is in tolerance. On a bored hole it can do the same to the bore. So a part can be in tolerance on size and Ra and still be functionally wrong if only those two are on the drawing.
When should chatter marks be accepted or rejected?
Judge by the surface’s function: reject chatter on dynamic seal, bearing, sliding and visible cosmetic surfaces, and accept it on non-functional, hidden surfaces where every drawing requirement is still met.
| Surface | Why chatter matters | Usual decision | What to put on the drawing |
|---|---|---|---|
| Dynamic seal surface (lip seal track, piston rod) | Waves pump fluid past the lip and wear it | Reject | Roughness range, waviness or roundness limit, lay if needed |
| Static O-ring gland face | Deep ripples can form leak paths | Reject if visible ripples cross the seal band | Roughness plus a note: no chatter in seal area |
| Bearing seat or bushing bore | Lobing loads the bearing unevenly | Reject | Circularity or cylindricity, plus roughness |
| Visible cosmetic face | Ripples show through plating and anodizing | Reject on class A surfaces | Cosmetic class note naming chatter |
| Clearance bore, hidden face | No function affected | Accept if size and Ra pass | General roughness only |
Finishes do not hide chatter. Plating, anodizing and powder coating follow the surface, and a bright finish makes ripples more visible, not less. If the part is finished after machining, judge chatter before finishing with the finished appearance in mind.
How do you control chatter marks on the drawing?
Add the control that matches the failure: a waviness limit or form tolerance on functional surfaces, and a cosmetic note that names chatter on visible ones.
- Waviness. The surface texture symbol of ASME Y14.36 can carry a waviness requirement alongside roughness. It is the direct control, but it needs a profilometer that reports waviness, so confirm the supplier can measure it.
- Form. A circularity or cylindricity tolerance on a bearing or seal diameter catches the lobing that chatter produces, and is easier for most shops to verify.
- Lay. On seal surfaces, a lay symbol or a note such as “no spiral or lead” controls the direction of the marks, a separate issue from chatter but often specified with it.
- Cosmetic note. “No visible chatter on surfaces marked A” with a viewing condition and a limit sample is the practical control for appearance.
Avoid blanket notes such as “no chatter marks” on the whole part. They turn hidden faces into inspection points, and they still do not tell anyone how visible a mark must be to count.
Which design features invite chatter, and what can the designer change?
Long reach relative to diameter, thin walls, deep narrow grooves and large unsupported faces; the cure is usually a small design change that lets the shop use a shorter, stiffer tool or support the part.
- Deep small bores and internal grooves: a deeper bore needs a longer bar. If the depth is not functional, shorten it, or allow a larger counterbore at the entry so a bigger bar fits.
- Thin-walled sleeves: allow finish machining in a supported state, or loosen form and finish on non-functional sections.
- Long slender shafts: add center holes if they are allowed to remain, so the part can be supported by a tailstock or steady rest.
- Sharp internal corners on deep features: a larger corner radius allows a stronger tool nose, although a very large nose radius on a slender bar can itself excite vibration.
What should the RFQ say about chatter, and how does Saola handle it?
Mark the functional and cosmetic surfaces, give each the control it needs, and flag deep bores or thin walls so the setup can be planned at drawing review.
Turned parts are machined at our lead CNC plant in Vietnam on CNC turning, and second operations on castings on CNC milling. The turning page states the as-machined finish expected on turned parts; anything finer, and any waviness or cosmetic requirement, should be on the drawing so it is confirmed at drawing review. The plant’s inspection equipment includes a 2D optical (vision) measuring instrument and a height gauge; tell us if you need a waviness or roundness measurement so the method can be agreed. New parts get a first-article inspection report and every lot a dimensional inspection record. Send the drawing for a quote.
Frequently asked
Can chatter marks be polished out?
Light chatter on a cosmetic face can sometimes be blended, but polishing removes material unevenly and can break form or size. On functional surfaces, re-machining with a stiffer setup is the reliable fix, if stock allows.
Is chatter the same as feed marks?
No. Feed marks are the regular helix left by the tool nose at each revolution and set the roughness. Chatter is an additional wave pattern from vibration, usually coarser and often patchy rather than uniform.
Does chatter damage the part beyond appearance?
It can. Besides leaking seals and noisy bearings, the ripples act as small notches on fatigue-loaded surfaces, and heavy chatter can tear the surface of soft or gummy materials.
Who decides if a chatter mark is acceptable?
The drawing should. If it carries only size and Ra, a supplier can reasonably ship a part with chatter that meets both. Put the waviness, form or cosmetic control on the drawing, or agree a limit sample before production.
Sources
- Troubleshooting in turning, Sandvik Coromant knowledge pages, accessed November 2026
- Machining with long overhangs, Sandvik Coromant knowledge pages, accessed November 2026
- ASME B46.1-2019, Surface Texture (Surface Roughness, Waviness, and Lay), ASME, 2019
- ASME Y14.36, Surface Texture Symbols, ASME, 2018