Glossary
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A
B
- blade guide/guard
- Bandsaws have an upper blade guide (and another under the table). Saws built in the last 30 years have a guard built into the guide to reduce the liklihood of getting cut. The guard covers the blade from the upper blade guide to the upper wheel cover.
- built-up edge
- A small amount of material can build up at the cutting edge of a tool (lathe tool, drill, etc.). This is a desirable effect in some materials because the BUE protects the cutting edge of the tool, extending it's life.
- burrs
- The small, stray peice of material left along the edge of the part after a cut. They should be sanded off.
C
- center drill
- A very short, stiff drill used for accurately starting drilled holes.
- center finder
- A tool used to align the spindle of a machine with a center punch mark, a center drilled hole, or any other round feature smaller than about .375 inch. Not as accurate as a dial indicator.
- center punch
- A tool used for making small, conical depressions in ductile materials (doesn't work in glass, etc) to mark the location of holes. These depressions are then used by the machinist (using acenter finder) to locate the workpiece relative to the spindle of the machine.
- chuck keys
- The tool used to tighten most drill and lathe chucks. Some drill chucks are called keyless chucks because they are designed to be tightened by hand.
- compass
- A machinist's compass is used for layout work. Basically the same object as used in high school math classes.
- coolant
- Coolant is a somewhat misleading term because they are used synonymously with "cutting fluid". Coolants are used in machining processes that generate a considerable amount of heat, i.e. milling, turning, drilling, and grinding. Cutting fluids are used in processes where the primary concern is the reduction of galling (sticking) between the tool and the workpiece, i.e. tapping, reaming, and broaching.
- cutting speed
- Cutting speed is usually expressed in units of "surface feet per minute". The cutting speed of a tool is the maximum relative speed between the workpiece and the part of the tool that is in contact with the work, e.g. the circumference of a drill mesured in feet and the spindle speed measured in rpm.
D
- dial indicator
- People are sloppy with this term. A dial indicator has a rod that is displaced along its axis. The rod is connected to a gear rack on manual indicators and to who knows what on the electronic ones. The numbers on the dial measure actual displacement
- (threading) die
- A cutting tool used to form external screw threads. Not a accurate as single point turning the threads on a lathe, but much easier and quicker.
E
- edgefinder
- The tip of a mechanical edgefinder moves to indicate that the edge of the part has been located relative to the centerline of the tool. On electric edgefinders, which are becoming more common, a light goes on when the edge is located.
- feed rate
- The fundamental feed rate for lathes is expressed in thousandths
of an inch per revolution of the spindle. For example, a feed of 5
thousandths per rev when turning a part means the saddle (and tool) move
0.005" along the lathe bed with every spindle revolution. Some lathes
(Hardinge and clones) have a separate motor for moving the saddle and the
cross slide, so the feeds are in inches per minute. The operator must then
divide that number by the spindle rpm to get the true feed rate. This
system is very convenient for adjusting the feedrate, but if you take a big
enough cut to slow the spindle down, the cut gets bigger, which slows the
spindle down some more,..., untill the spindle stops. The feed, not coupled
to the spindle, tries to keep going, usually damaging the part and or the
tool - be careful.
The fundamental feed rate for milling machines is chip load per tooth, measured in thousandths of an inch per tooth. This number is multiplied by the number of teeth and the spindle rpm to get the axis feed rate in inched per minute. Unfortunately, the axis feeds used on milling machines are also implemented in 2 different ways. The common one uses separate motors (like the Hardinge lathe) so the operator needs to do all of the calculations. The cheaper feeds aren't even calibrated in inches per minute but just have a scale from 0 to 10, so if you care, you need to calibrate the feed yourself. The speed of the cheap feeds also tends to vary significantly with the load, making calibration difficult.
- feeds
- Hand feeds and power feeds are screws, driven by hand cranks or motors, that move the axes of machine tools.
- fillets
- A fillet on a machined part is at the concave transition from one surface to another, e.g. a step in a shaft. The concave transition (small diameter to shoulder) will have a fillet and the convex transition (shoulder to large diameter) may have a chamfer. The surfaces are usually, but not always perpendicular. The minimum fillet size is determined by the smallest tool tip radius that will give acceptable tool life. Often a much larger radius is used to improve the fatigue life of the part.
- flutes
- The function of flutes is the clearest on drills, but milling tools such as end mills also have flutes for the same reason. The flutes transport the chips away from the cut. Most tools have flutes of the same "hand" as the cutting edge, i.e. a right hand drill cuts when turned clockwise from the top and the flutes spiral down clockwise from the top. This geometry generates forces on the chips that tend to push them up the flutes.
G
H
I
J
K
L
- last word indicator
- Often incorrectly called dial indicators. Unlike dial indicators, last word indicators have a nonlinear relationship between the dial reading and the actual displacement. They are intended to be used in a "last word" mode, i.e. if the dial reads 3 and you move away and come back to 3, you will be back where you were. If you put it on a part in the lathe and the reading doesn't change when the chuck is spun around, the part is concentric with the spindle. This tool is useful for aligning vises, squaring up workpieces, locating round features in parts relative to the machine spindle, setting up parallel parts, and much more.
M
- material removal rate
- This is a production term usually measured in cubic inches per minute. Increasing this rate will obviously get a part done quicker, and therefore possibly for less money, but increasing the material removal rate is often accompanied by increases in tool wear, poor surface fininshes, poor tolerances, and other problems. Optimizing the machining process is a very difficult problem.
- micrometer
- A measuring tool that is shaped and functions very much like a C-clamp (but don't use them for C-clamps!) The screw in a standard machinist's inch micrometer is precision ground and has 40 threads per inch, so one revolution changes the measuring length by 0.025" A standard, good quality micrometer that is not worn is accurate to about 0.0001".
N
O
P
- parallel plates
- Parallels are precise spacers commonly used to set up small parts in the milling machine vise or larger parts on the bed of the milling machine. Spacing parts off of the bed of the mill lets you drill holes through the part, mill the sides of the part, and mill features in the face of the part in the same setup. Parallels are *matched pairs* of bars with at least one of the short dimensions identical to within 0.0002". This accurate dimension is usually guaranteed to be within about 0.001" of another parallel with the same nominal dimension.
- pilot hole
- A small hole can typically be located and drilled more accurately than a large hole, so a small pilot hole is often drilled where a larger hole is desired. The larger drill used to bring the hole to the desired diameter will then follow the pilot hole. Also, the use of a pilot hole can greatly reduce the force required to feed the large drill
- platen
- A general term for flat worksurface or reference surface. press brake
Q
- quill
- A spindle that can be moved along it's axis of rotation without moving the entire head (spindle drive system and housing). Bridgeport milling machines have a quill, which makes operations like drilling very easy. Also, on manual (non-CNC) milling machines a quill gives the operator the ability to "feel" how the drill is cutting
R
S
- scribe
- A tool used to mark parts for machining, usually by scratching the part or by scratching through a thin paint (layout fluid) that has been applied to the part.
- spindle
- A general term applied to a shaft mounted in bearings. The shaft may be used to hold tools (milling machine) or the workpiece (lathe).
- spindle speed
- The rotational speed of the spindle measured in revolutions per minute. This number is multiplied by the workpiece diameter on a lathe or the tool diameter on a milling machine to get the cutting speed in surface feet per minute (sfm)
- machinist's square
- A tool used for checking 90 degree angles or for setting up parts at 90 degree angles. Similar to a carpenter's square but much more accurate and hardened to resist nicks, scratches, and wear.
- stick wax
- The cutting speed and life of bandsaw blades is improved with proper lubrication. Stick wax is a heavy paste wax that is used on manually operated machines. The wax is heavy enough to stay on the blade and is relatively non-toxic. High production automated band saws usually use flood cooling with coolant (lubricant) similar to that used in CNC mills and lathes. Long term contact with these coolants can cause skin problems, and the parts can be difficult (and therefore dangerous) to hold by hand.
T
- T-bolts
- T-bolts are used to hold workpieces in many metalworking machines. T-bolts have a special head that allows the bolt to slide in a T-slot, but not turn. This allows the operator to install and tighten a nut on the end of the bolt without requiring wrench access to the head.
- tap
- A tool for cutting threads in a part.
- thread standards
- Thread standards are a list of specifications for thread sizes and profiles. In addition to the common diameter and pitch specifications 1/4-20 (1/4 inch diameter and 20 threads per inch), there are specifications and tolerances on the shape of the tooth.
U
V
- Vernier scale
- A great idea. For example: put 4 marks on an inch on the fixed part of a measuring tool and 5 marks on an inch of the moving part. Align the first mark on each scale and then move untill the second two marks are aligned. The distance traveled is 1/4 - 1/5 = 1/20 of an inch. This type of scale lets you resolve distances much smaller than the spacing between the marks, making high resolution scales easier to make and read. The two common scales use 25 marks in 1.25 inch and 50 marks in 2.5 inches.
W
X
Y
Z