62 terms
Machining glossary for the person buying the part
Every term a shop is likely to use in a quote, a drawing review or an inspection report, defined without assuming you have stood in front of a machine. One sentence each, and where a term costs money the definition says so.
0-9
- 3+2 machining
- A 5-axis machine that tilts and rotates the part into position, locks the two rotary axes, then cuts in 3-axis mode. It covers most angled features and needs far less programming than full simultaneous work.
- 5-axis simultaneous
- All five axes move while the tool is cutting. Required for impellers, turbine blades and complex curved surfaces. The shop list for it is short in any country.
A
- Anodising
- An electrochemical coating for aluminium that grows an oxide layer for corrosion resistance and colour. Type II is the common decorative and protective version, Type III is thicker and harder for wear surfaces. It is an electrical insulator and it adds thickness.
B
- Bar stock
- Material supplied as round, square or hexagonal bar. Cheaper to buy and to hold than plate, and the normal starting form for turned parts.
- Bead blasting
- Propelling fine media at a surface to leave a uniform matte texture. Hides tool marks, removes light burrs and is usually done in house.
- Billet
- A solid block or bar of material that a part is machined from. Parts described as machined from billet start as solid stock rather than a casting or a forging.
- Black oxide
- A conversion coating that turns steel black with almost no dimensional change. Mildly corrosion resistant when oiled, common on tooling and fasteners.
- Blind hole
- A hole that does not pass through the part. Blind holes need room below the last thread for the tap to run out and are harder to clear chips from than through holes.
- Bore
- A precisely sized internal cylindrical feature, usually produced by boring or reaming rather than drilling alone when the tolerance is tight.
- Burr
- A raised edge left by cutting. Removing burrs is deburring, and whether edges are broken, sharp or radiused should be stated on the drawing.
C
- CAM
- Computer aided manufacturing. The software that turns a 3D model into tool paths and machine code. Programming time is a real line in a quote, especially on 5-axis work.
- Carbide
- The tool material used for most production cutting. Harder and more heat resistant than high speed steel, and the reason cutting speeds in aluminium and steel differ so much.
- Chamfer
- An angled cut on an edge, usually 45 degrees. Used to remove sharpness, help assembly and start a thread cleanly.
- Chatter
- Vibration between the tool and the part that leaves a rippled surface and shortens tool life. Caused by long tools, thin walls and poor workholding.
- CMM
- Coordinate measuring machine. A probe measures points on a part and compares them with the model or the drawing. It is what makes position, profile and flatness callouts provable.
- Concentricity
- How well two cylindrical features share the same axis. Easiest to hold when both are turned in one setup.
- Counterbore
- A flat bottomed enlargement at the top of a hole so a socket head screw sits flush or below the surface.
- Countersink
- A conical enlargement at the top of a hole for a flat head screw. Specified by included angle, commonly 82 or 90 degrees.
- CTQ
- Critical to quality. The small set of features that decide whether a part functions. Marking them on the drawing tells the shop where to spend its inspection time.
- Cycle time
- The machine time to produce one part, excluding setup. It is multiplied by the hourly rate to give the largest line in most quotes.
D
- Datum
- A reference feature that measurements are taken from. A drawing with datums that match how the part is assembled is the single cheapest improvement most drawings can get.
- Deburring
- Removing the raised edges left by machining. Assume every shop does it, and state the edge condition if it matters.
- DFM
- Design for manufacturability. Changing a design so it is faster or safer to make without changing what it does, for example opening a corner radius so a larger cutter can be used.
- Dowel pin
- A precision ground pin used to locate two parts to each other. Dowel holes are reamed, which is why splitting a part into two adds an operation.
- Drawing revision
- The version of a drawing. Quotes, first articles and inspection reports must all name the same revision, and revision mismatches cause more disputes than machining errors.
E
- Electropolishing
- An electrochemical process that smooths and brightens stainless steel and improves corrosion resistance. It removes a small amount of material, so tight tolerances have to allow for it.
F
- First article inspection
- A full measurement of the first pieces from the production process against every dimension on the drawing, reported so a buyer can approve or reject with evidence.
- Fixture
- A purpose made device that holds a part in a repeatable position. A one-off cost that lowers the unit price, which is why quantity changes the price so much.
- Flatness
- How close a surface is to a perfect plane. It applies to one surface on its own and does not reference a datum.
G
- GD and T
- Geometric dimensioning and tolerancing. A symbolic language for stating what a part has to do rather than only how big it is, using datums, position, profile, runout and form controls.
- Grinding
- Abrasive machining used to hold tolerances below about ±0.01 mm and finishes better than Ra 0.8. Slow, so it is used on selected surfaces rather than whole parts.
H
- Hard anodising
- Type III anodising. A thick hard layer for wear resistance that builds dimension noticeably and darkens the part regardless of dye.
- Heat treatment
- Controlled heating and cooling to change hardness or relieve stress. Parts usually distort during it, which is why critical surfaces are machined or ground afterwards.
- HRC
- Rockwell C hardness. The usual scale for hardened steels. Above roughly 45 HRC, conventional cutting becomes difficult and grinding or EDM takes over.
I
- Interference fit
- A fit where the shaft is larger than the hole so the parts hold by friction. Requires tight tolerances on both features and often grinding.
- ISO 2768
- A general tolerance standard used when individual dimensions are not toleranced. Classes f, m, c and v for linear dimensions, H, K and L for geometry. A title block note such as ISO 2768-mK removes a whole class of quoting questions.
L
- Lead time
- The time from an agreed starting point to parts being ready. Always ask what starts the clock: the purchase order, drawing approval or material arrival are three different dates.
- Live tooling
- Driven tools on a lathe that can drill, mill and tap while the part stays in the chuck. It turns a two machine job into one setup.
M
- Mill-turn
- A lathe with live tooling and often a second spindle, able to turn and mill a part complete. Higher rate per hour, usually lower cost per part on round parts with off-axis features.
- Milling
- Machining with a rotating cutter against a fixed part. The dominant process for prismatic parts such as brackets, plates and housings.
- MOQ
- Minimum order quantity, or in practice a minimum order value. Often the real constraint on small orders, because freight and handling do not scale down.
N
- NDA
- Non-disclosure agreement. Signed before drawings are shared, it records what was disclosed and when. It sets expectations rather than guaranteeing enforcement across borders.
P
- Passivation
- A treatment that removes free iron from a machined stainless surface so the protective oxide layer can form. Not a coating, and specified to a standard such as ASTM A967.
- Position tolerance
- A GD and T control placing a feature inside a cylindrical zone relative to datums. Easier to inspect and more forgiving than equivalent linear tolerances, especially with a material condition modifier.
- PPAP
- Production part approval process. An automotive documentation package proving a process can make the part repeatably. Far heavier than a commercial first article and priced accordingly.
- Profile tolerance
- A GD and T control that creates a tolerance band following the modelled surface. The usual control for curved and organic geometry, normally inspected on a CMM.
R
- Ra
- Arithmetic average surface roughness in micrometres. Milled surfaces come off around Ra 1.6 to 3.2, Ra 0.8 needs care and Ra 0.4 or better usually means grinding or polishing.
- Reaming
- Finishing a drilled hole to a precise size and finish with a multi-fluted tool. A reamed hole holds about ±0.01 mm without grinding.
- Recast layer
- The thin re-solidified surface left by EDM. Acceptable on most parts, and removed by polishing or a finishing pass on fatigue critical ones.
- Runout
- How much a surface wobbles relative to a datum axis as the part rotates. The right callout for bearing seats, seal faces and pulleys, and cheap to measure with an indicator.
S
- Setup
- One clamping position on a machine. Every extra setup adds fixturing, re-datuming and a tolerance stack, and setups drive price far more than axis count does.
- Soft jaws
- Machinable vice or chuck jaws cut to match a specific part so it is held repeatably without marking. A cheap alternative to a dedicated fixture at low volume.
- Stress relief
- A heat or mechanical treatment that reduces internal stress in stock so the part does not warp when material is removed. Relevant on large plates and on thin parts.
- Surface finish
- The texture of a machined surface, usually specified as an Ra value and sometimes with a lay direction. It affects sealing, friction and appearance, and it is set by the finishing pass.
T
- Tapping
- Cutting an internal thread by driving a tap into a hole. Fast on small sizes in soft material, and the main risk is a broken tap in a nearly finished part.
- Thread milling
- Producing a thread with a rotating cutter spiralling around the hole. Slower per hole than tapping, safer in hard materials and large sizes, and recoverable if something goes wrong.
- Tolerance stack
- The accumulation of tolerances across features that were produced or located in different setups. The reason a single setup is worth paying for when features must relate tightly.
- True position
- The theoretically exact location of a feature, against which a position tolerance is applied. Usually written with a diameter symbol and the datums that locate it.
- Turning
- Machining with the part rotating against a fixed tool. The fastest way to remove material on round parts and the cheapest process at volume for shafts and fittings.
U
- Undercut
- A feature that cannot be reached from the direction the tool approaches, such as an internal groove in a bore. Possible with special tooling, and often cheaper to design out or to split the part at that plane.
W
- Work hardening
- A surface becoming harder because a tool rubbed rather than cut. Common in stainless and in some nickel alloys, and it makes the next pass worse.
- Workholding
- How the part is gripped while it is cut. On thin and awkward parts it decides whether the tolerances on the drawing are achievable at all.
Missing a term?
If a word in your quote is not here, send it over and it gets added with the next update. The related pages are the tolerance reference and the GD and T guide.