Q: What is maximum material thickness that Mac Cal punch in the following materials:
Stainless Steel .074
Q: What is minimum material thickness that Mac Cal can punch in the following materials:
Stainless Steel .005
Q. What is the minimum inside bend radius?
Q: Should I include the flat pattern on the drawing?
No as your K will probably not match.
Q: What are basic tolerances:
HOLE TO HOLE ± min .005 preferred for nesting .010
BEND TO HOLE ± min .010
EDGE TO HOLE ± min .010
BEND TO BEND ± .010
BEND TO EDGE ± .010
EDGE TO EDGE ± .010
BEND ANGLE ± DEGREES.5 degree
Q: What type welding does Mac Cal perform:
Mac Cal has 14 welders certified in various materials and thicknesses. All welders are proficient in Mig and Tig welding. We also have a 200 KVA spot welder.
Q: Can 6061-T6 material be formed?
It can be formed but the material tends to crack at bend point.
Q. If a paint class is not called out, what class will Mac Cal paint to?
If there isn’t a class called out we will paint Class C internally and class B externally.
Q. What takes dimensional precedence, the drawing or the model?
The drawing takes precedence, unless otherwise specified.
Q. What is Mac Cal’s lead time for a plated sheet metal parts with no welding.
2 to 3 weeks.
Q. What Software does Mac Cal design in?
We primarily design in Solid Works but can also design in Pro-E. However, Pro-E is less cost affective to design in as it is less user friendly.
Q: Does Mac Cal have a designated Proto Area?
Yes, we have a quick turn proto area within the our Precision Sheet metal Division.
Q. What is the longest piece that Mac Cal can form?
We can form parts up to 10 feet long in our 10 Ton Press Brake which results in a uniform coin.
Common Weld Symbols and their Meanings
When welds are specified on engineering and fabrication drawings, a cryptic set of symbols is used as a sort of shorthand for describing the type of weld, its size and other processing and finishing information. Here we will introduce you to the common symbols and their meaning. The complete set of symbols is given in a standard published by the American National Standards Institute (ANSI) and the American Welding Society (AWS): ANSI/AWS A2.4, Symbols for Welding and Nondestructive Testing.
The structure of the welding symbol
The horizontal line — called the reference line — is the anchor to which all the other welding symbols are tied. The instructions for making the weld are strung along the reference line. An arrow connects the reference line to the joint that is to be welded. In the example above, the arrow is shown growing out of the right end of the reference line and heading down and to the right, but many other combinations are allowed.
Quite often, there are two sides to the joint to which the arrow points, and therefore two potential places for a weld. For example, when two steel plates are joined together into a T shape, welding may be done on either side of the stem of the T.
The weld symbol distinguishes between the two sides of a joint by using the arrow and the spaces above and below the reference line. The side of the joint to which the arrow points is known (rather prosaically) as the arrow side, and its weld is made according to the instructions given below the reference line. The other side of the joint is known (even more prosaically) as the other side, and its weld is made according to the instructions given above the reference line. The rule that below the line equals the arrow side and above the line equals the other side applies regardless of the arrow’s direction. The flag growing out of the junction of the reference line and the arrow is present if the weld is to be made in the field during erection of the structure. A weld symbol without a flag indicates that the weld is to be made in the shop. In older drawings, a field weld may be denoted by a filled black circle at the junction between the arrow and the reference line.
The open circle at the arrow/reference line junction is present if the weld is to go all around the joint, as in the example below.
The tail of the weld symbol is the place for supplementary information on the weld. It may contain a reference to the welding process, the electrode, a detail drawing or any information that aids in the making of the weld that does not have its own special place on the symbol.
Types of welds and their symbols
Each welding position has its own basic symbol, which is typically placed near the center of the reference line (and above or below it, depending on which side of the joint it’s on). The symbol is a small drawing that can usually be interpreted as a simplified cross-section of the weld. In the descriptions below, the symbol is shown in both its arrow-side and other-side positions.
Plug Welds and Slot Welds
The fillet weld (pronounced “fill-it”) is used to make lap joints, corner joints and T joints. As its symbol suggests, the fillet weld is roughly triangular in cross-section, although its shape is not always a right triangle or an isosceles triangle. Weld metal is deposited in a corner formed by the fit-up of the two members and penetrates and fuses with the base metal to form the joint. (Note: for the sake of graphical clarity, the drawings below do not show the penetration of the weld metal. Recognize, however, that the degree of penetration is important in determining the quality of the weld.)
The perpendicular leg of the triangle is always drawn on the left side of the symbol, regardless of the orientation of the weld itself. The leg size is written to the left of the weld symbol. If the two legs of the weld are to be the same size, only one dimension is given; if the weld is to have unequal legs (much less common than the equal-legged weld), both dimensions are given and there is an indication on the drawing as to which leg is longer.
The length of the weld is given to the right of the symbol.
If no length is given, then the weld is to be placed between specified dimension lines (if given) or between those points where an abrupt change in the weld direction would occur (like at the end of the plates in the example above).
For intermittent welds, the length of each portion of the weld and the spacing of the welds are separated by a dash (length first, spacing second) and placed to the right of the fillet weld symbol.
The groove weld is commonly used to make edge-to-edge joints, although it is also often used in corner joints, T joints, and joints between curved and flat pieces. As suggested by the variety of groove weld symbols, there are many ways to make a groove weld, the differences depending primarily on the geometry of the parts to be joined and the preparation of their edges. Weld metal is deposited within the groove and penetrates and fuses with the base metal to form the joint. (Note: for the sake of graphical clarity, the drawings below generally do not show the penetration of the weld metal. Recognize, however, that the degree of penetration is important in determining the quality of the weld.)
The various types of groove weld are:
Square groove welds
The groove is created by either a tight fit or a slight separation of the edges. The amount of separation, if any, is given on the weld symbol.
The edges of both pieces are chamfered, either singly or doubly, to create the groove. The angle of the V is given on the weld symbol, as is the separation at the root (if any).
If the depth of the V is not the full thickness — or half the thickness in the case of a double V — the depth is given to the left of the weld symbol.
If the penetration of the weld is to be greater than the depth of the groove, the depth of the effective throat is given in parentheses after the depth of the V.
Bevel groove welds
The edge of one of the pieces is chamfered and the other is left square. The bevel symbol’s perpendicular line is always drawn on the left side, regardless of the orientation of the weld itself. The arrow points toward the piece that is to be chamfered. This extra significance is emphasized by a break in the arrow line. (The break is not necessary if the designer has no preference as to which piece gets the edge treatment or if the piece to receive the treatment should be obvious to a qualified welder.) Angle and depth of edge treatment, effective throat and separation at the root are described using the methods discussed in the V-groove section.
The edges of both pieces are given a concave treatment. Depth of edge treatment, effective throat and separation at the root are described using the methods discussed in the V-groove section.
The edge of one of the pieces is given a concave treatment and the other is left square. It is to the U-groove weld what the bevel groove weld is to the V-groove weld. As with the bevel, the perpendicular line is always drawn on the left side and the arrow (with a break, if necessary) points to the piece that receives the edge treatment. Depth of edge treatment, effective throat and separation at the root are described using the methods discussed in the V-groove section.
Flare-V groove welds
Commonly used to join two rounded or curved parts. The intended depth of the weld itself is given to the left of the symbol, with the weld depth shown in parentheses.
Flare bevel groove weld
Commonly used to join a round or curved piece to a flat piece. As with the flare-V, the depth of the groove formed by the two curved surfaces and the intended depth of the weld itself are given to the left of the symbol, with the weld depth shown in parentheses. The symbol’s perpendicular line is always drawn on the left side, regardless of the orientation of the weld itself.
Common supplementary symbols used with groove welds are the melt-thru and backing bar symbols. Both symbols indicate that complete joint penetration is to be made with a single-sided groove weld. In the case of melt-thru, the root is to be reinforced with weld metal on the back side of the joint. The height of the reinforcement, if critical, is indicated to the left of the melt-thru symbol, which is placed across the reference line from the basic weld symbol.
When a backing bar is used to achieve complete joint penetration, its symbol is placed across the reference line from the basic weld symbol. If the bar is to be removed after the weld is complete, an “R” is placed within the backing bar symbol. The backing bar symbol has the same shape as the plug or slot weld symbol, but context should always make the symbol’s intention clear.
Plug and Slot Welds
Plug welds and slot welds are used to join overlapping members, one of which has holes (round for plug welds, elongated for slot welds) in it. Weld metal is deposited in the holes and penetrates and fuses with the base metal of the two members to form the joint. (Note: for the sake of graphical clarity, the drawings below do not show the penetration of the weld metal. Recognize, however, that the degree of penetration is important in determining the quality of the weld.) For plug welds, the diameter of each plug is given to the left of the symbol and the plug-to-plug spacing (pitch) is given to the right. For slot welds, the width of each slot is given to the left of the symbol, the length and pitch (separated by a dash) are given to the right of the symbol, and a detail drawing is referenced in the tail. The number of plugs or slots is given in parentheses above or below the weld symbol. The arrow-side and other-side designations indicate which piece contains the hole(s). If the hole is not to be completely filled with weld metal, the depth to which it is to be filled is given within the weld symbol.
Following are some of the 14 primary symbols used in GD&T:
Profile of a line
Milling holes and cavities/pockets
- Two-axis ramping linear
- Circular ramping
- Widening a hole
- Circular external milling or ramping
- Plunge milling
- Peck milling
- Slicing methods
- Closed pockets or angles
Hole milling: creating openings
- Creating openings in a solid workpiece
- Widening a hole or a cavity
- Opening up / widening a cavity or pocket
Creating openings in a solid workpiece
Opening a slot
When milling a hole, linear ramping (2 axes simultaneously) is always preferred to peck milling.
Peck milling is an alternative hole milling method, but it often produces long chips and generates undesirable cutting forces on the cutter.
Opening a hole or a cavity
Ramping a cavity
Drilling is the traditional and fastest method for producing a hole, but chip breaking can be a challenge in some materials. It also lacks the flexibility to produce varying diameters and non-round shapes.
Circular ramping (3 axes simultaneously) is a less productive method than drilling a hole, but can be a good alternative in cases of:
- Large diameter holes when machine power is limited
- Smaller series production. A rule of thumb for diameters larger than 25 mm: milling is cost-efficient up to a series of approx. 500 holes
- When a range of hole sizes are to be machined
- Limited tool magazine space to store many drill sizes
- Production of blind holes, when a flat bottom is required
- Non-rigid, thin walled components
- Interrupted cuts
- Materials that are difficult to drill due to chip breaking and chip evacuation
- No cutting fluid is available
- When milling cavities/pockets (“non-round holes”)
Choice of method – example
Opening up a cavity/pocket
Drilling and circular milling
+ High material removal for non-round holes
+ First choice in aerospace frame titanium structural parts
– Requires a stable machine
– Chip evacuation – horizontal machine
– Careful programming required
Drilling and plunge milling
+ Problem solver in long overhang applications
+ Simple programming suitable for older/multi-spindle machines
– Low material removal
Drilling and plunge milling
+ Fewer tools (no drill needed)
+ Flexible (produces a wide range of sizes)
+ No cutting fluid required = good for open machines
+ Suitable for all machine concepts and configurations
– Less productive for large cavities
Widening a hole or a cavity
Widening a hole
Boring is normally the fastest method, for the same reasons as drilling, but hole milling is sometimes a good alternative. Two alternate milling methods can be used: circular ramping (3-axis) or circular milling (2-axis). Circular ramping is preferred when the hole is deeper than ap max or in vibration-sensitive applications. In addition, the roundness/concentricity of the hole becomes better when ramping, especially with long overhangs. Roundness will be improved if the workpiece is rotated instead of moving the milling cutter in a circular path in both circular ramping and milling operations.
Widening a cavity
Internal shoulder milling and plunge milling require a starting hole and should be compared to ramping a cavity directly into a solid block.
- Ramping (3-axis) is advantageous because it only requires one tool and can produce 3D shapes, making it suitable for profile milling. If applied with high feed techniques (light and fast), the cutting forces will be directed in a favorable manner that minimizes vibration problems
- Plunge milling often solves problems with long overhangs and/or deep cavities
- Internal shoulder milling requires more programming than plunge milling, but it is faster
Internal shoulder milling
Rest (remaining stock) milling
When the roughing of a cavity is completed, stock often remains, especially in corners. Plunge milling with a smaller cutter is one method for coming closer to the finished shape. Slicing (light and fast) is another technique often used in corner milling. Trochoidal milling is one type of slicing technique that is also used for milling slots, pockets etc.
Plunging in corners
Slicing technique – light and fast
Slicing in corners
How to open up / widen a cavity or pocket
There are two clear strategies:
1. Circular ramping (3-axis) – small ap
Use a cutter with a small entering angle. A round insert cutter is another alternative.
This “light and fast” technique provides an excellent metal removal rate and is the First choice for less stable machines (according to ISO 40) and when the cavity has a profiled shape, i.e. die and mold.
Note: Avoid machining all the way against a 90° shoulder, because the effect of a low approach angle will be lost, i.e. the depth of cut increases dramatically.
- Maximum cutter diameter = 1.5 x component corner radius
- Circular ramp to depth – counterclockwise
- Roll into the next cut
- Radial cut – max. ae = 70% DC
- Axial cut for round insert cutter 25% iC
- Tool path radius in the corner = DC
- Reduce corner feed
2. Circular milling (2-axis) – large ap
Drill a hole, then change to a shoulder end mill or a long edge cutter. A typical application area is found in aerospace framing – titanium machining.
Ensure good chip evacuation to prevent re-cutting of chips / chip jamming:
- A horizontal spindle (ISO 50) is preferred
- High pressure coolant or compressed air with through tool coolant
- DC should be no greater than 75% of hole dia. Use a large axial cut – maximum ae = 2 x DC
The drilled hole should be entered in a circular path:
- Control radial engagement, maximum ae = 30% of DC
Control radial engagement to minimize vibration in corners and to maximize productivity:
- Use the largest radius possible in the corners, spiral morph programming
- Use the largest DC possible and complete rest milling separately at no greater than 1.5 x the corner radius
Small corner radius
Spiral morph programming
Profile milling is a common milling operation. Round inserts and concepts with radius are milling cutters used for roughing and semi-roughing while ball nose end mills are milling cutters used for finishing and super-finishing.
Profile milling process
Profile milling covers the multi-axis milling of convex and concave shapes in two and three dimensions. The larger the component and the more complicated the configuration of the machine, the more important the planning of the profile milling process becomes.
The machining process should be divided into at least three operation types:
Super-finishing, often performed using high-speed machining techniques, is sometimes required. The milling of remaining stock, called rest milling, is included in semi-finishing and finishing operations. For best accuracy and productivity, it is recommended that roughing and finishing are performed in separate machines, and optimized cutting tools are used for each operation.
The finishing operation should be carried out in a 4/5-axis machine tool with advanced software and programming techniques. This can considerably reduce or even completely eliminate time-consuming manual completion work. The final result will be a product with better geometrical accuracy and a higher surface structure quality.
Choice of tools
Optimized cutting tools for roughing and semi-roughing:
round inserts and concepts with radius.
Optimized cutting tools for finishing and super-finishing:
ball nose end mill and concept with radius.
Application checklist for profile milling
The profile of the component should be studied carefully in order to select the right tools and find the best-suited machining method:
- Define minimum radii and maximum cavity depth
- Estimate the amount of material to be removed
- Consider tool setup and clamping the workpiece in order to avoid vibrations. All machining should be performed on optimized machines to achieve good geometrical accuracy on the profile
- By using separate, accurate machine tools for finishing and super-finishing operations, the need for time-consuming manual polishing can be reduced, or in some cases eliminated
- Some advanced programming may be necessary to obtain large savings. Use a solid carbide end mill with high-speed technique to machine near-net shapes and achieve the best possible finish
- Roughing and semi-finishing of large components are, as a rule, most productively done with conventional methods and tooling. An exception is aluminum, for which high cutting speeds are also used for roughing
How to reduce vibrations
Vibration is an obstacle in milling deep profiles using long overhangs. Common methods to overcome this problem are to reduce depth of cut, speed or feed.
- Use stiff modular tools with good run-out accuracy
- Modular tools increase the flexibility and possible number of combinations
- Use damped tools or extension bars when total tool length, from the gauge line to the lowest point of cutting edge, exceeds 4−5 times the diameter at the gauge line
- Use extensions made of heavy metal, if bending stiffness must be radically increased
- Use balanced cutting and holding tools for spindle speeds over 20,000 rpm
- Choose the largest possible diameter on the extensions and adapters relative to the cutter diameter
- 1 mm (0.039 inch) in radial difference between the holding and the cutting tool is enough. Use oversized cutters
- Plunge milling is an alternative method for milling with extra-long tools
Extend tool length gradually
To maintain maximum productivity in roughing operations where the final pass is located deep in the component, it is important to work with a series of extensions for the cutter.
- Start with the shortest extension, as longer extensions limit productivity and tend to generate vibration
- Change to extended tools at predetermined positions in the program. The geometry of the cavity determines the point of change
- Adapt cutting data to each tool length to maintain maximum productivity
True cutting speed
If using a nominal diameter value of the tool when calculating the cutting speed of a ball nose or round insert cutter, the true cutting speed, vc, will be much lower if the depth of cut, ap, is shallow. Table feed and productivity will be severely hampered.
Base calculations for cutting speed based on true or effective diameter in cut, Dcap.
Shoulder end mill
Ball nose cutter
Round insert cutter
Point milling – tilted cutter
When using a ball nose end mill, the most critical area of the cutting edge is the tool center, where the cutting speed is close to zero, which is unfavorable for the cutting process. Chip evacuation at the tool center is critical, due to the narrow space at the chisel edge.
Therefore, tilting the spindle or the workpiece 10 to 15 degrees is recommended, which moves the cutting zone away from the tool center.
- The minimum cutting speed will be higher
- Improved tool life and chip formation
- Better surface finish
Example of center cutting cutters
Central part, z = 2
Peripheral part, z = 4
Z = 2
Z = 4
When using a round insert or a ball nose cutter at a lower depth of cut, the cutting speed, vc, can be increased due to the short engagement time for the cutting edge. The time for heat propagation in the cutting zone becomes shorter, i.e. the cutting edge and the workpiece temperature are both kept low. Also, the feed/tooth, fz, can be increased, due to the chip-thinning effect.
Example shallow cut, non-tilted versus tilted cutter
This example shows the possibilities for increasing the cutting speed when the ae/ap is small, as well as the advantages of using a tilted cutter.
Ball nose solid carbide
Dc = 10 mm, grade GC 1610.
Material: Steel, 400 HB
Cutting data recommendation for a deep cut ap – Dc/2:
vc = 170 m/min
fz = 0.08 mm/r = hex
Productivity in profile milling: constant stock
C: Finishing and super-finishing
A constant stock is one of the truly basic criteria for high and constant productivity in profile milling, especially when using high speeds.
- To reach maximum productivity in these operations, common in die- and mold-making, it is important to adapt the size of the milling cutters to specific operations
- The primary goal is to create an evenly-distributed working allowance, or stock, to obtain few changes in work load and direction for each tool used
It is often more favorable to de-escalate the sizes on different cutters, from bigger to smaller, especially in light roughing and semi-finishing, instead of using only one diameter throughout each operation.
- The best quality in finishing is achieved when preceding operations leave as little and as constant amount of stock as possible
- The goal should always be to come as close as possible to the requirements specified for the final shape
- Safe cutting process
Benefits with a constant stock
- Some semi-finishing and practically all finishing operations can be performed partially manned, or even sometimes unmanned
- Impact on the machine tool guide ways, ball screws and spindle bearings will be less negative
Opening up from a solid workpiece
- When opening up a cavity, it is important to choose a method that minimizes ap, and also leaves a constant stock for the subsequent profile milling operation
- Shoulder face/end mills or long-edge cutters will leave a staircase stock that has to be removed. This generates varying cutting forces and tool deflections. The result is an uneven stock for finishing, which will influence the geometrical accuracy of the final shape
- Use of round insert cutters will generate smooth transitions between the passes and leave less stock in more even quantities for the profiling operation, resulting in better component quality
- A third alternative is to use a high-feed cutter to open the cavity. This will also result in a small and even, constant stock, due to the small depth of cut, i.e. small staircase steps
Square shoulder cutter,
larger and uneven stock remaining
Round insert cutter,
small stock remaining
High cutter feed,
small stock remaining
The traditional and easiest method for programming tool paths for a cavity is to use the normal copy milling technique, with many entrances and exits into the material. However, this means that powerful software programs, machines and cutting tools are used in a very limited way. It is preferable to use a machine with software that has look-ahead functions, to avoid tool path deviations.
An open-minded approach to the choice of methods, tool paths, milling and holding tools is essential.
− Heavy load on the insert center point
− Reduced feed rates
− Reduced tool life
− Mechanical impact
− Form errors
− Longer programs and cutting time
A copy milling tool path is often a combination of up- and down-milling, and requires a lot of unfavorable engagements and disengagements in the cut. Each entrance and exit means that the tool will deflect, leaving an elevated mark on the surface. The cutting forces and the bending of the tool will then decrease, and there will be a slight undercutting of material in the exit area.
- Copy milling along steep walls should be avoided as much as possible. When plunging, the chip thickness is large and cutting speed should be low
- There is a risk of edge frittering at the tool center, especially when the cutter hits the bottom area
- Use a feed speed control with a look-ahead function. Otherwise, the deceleration will not be fast enough to avoid damages to the tool center
- There will be a large contact length when the cutter hits the wall, with risk for deflection, vibration or tool breakage
- When using ball nose end mills, the most critical area is at the tool center, since the cutting speed is zero. Avoid using the tool center area and apply point milling by tilting the spindle or the workpiece to improve the conditions
- It is somewhat better for the cutting process to perform up-copying along steep walls, as the chip thickness has its maximum at a more favorable cutting speed
Risk for gouging
Maximum chip thickness at recommended vc.
At bottom of cavity:
Risk of frittering at tool center.
Form errors are common, especially when using a high-speed machining technique.
Large chip thickness at very low vc.
Feed reduction to avoid shortened tool life
Reversed up- and down-milling will expose the tool to alternating deflection and cutting forces. By reducing the feed rate in the critical sections of the tool path, the risk for edge frittering is reduced, and a safer cutting process with longer tool life is achieved.
Instead of using programming techniques that are limited to “slicing off” material at a constant Z-value, it is highly advantageous to use contouring tool paths in combination with down-milling. The results include:
+ A considerably shorter machining time
+ Better machine and tool utilization
+ Improved geometrical quality of the machined shape
+ Less time-consuming finishing and manual polishing work
+ Cutting speed control – ve
+ Enabling HSM
+ High feed rates
+ Long insert life
The initial programming work is more difficult and will take somewhat longer; however, this is quickly recouped as the machine cost per hour is normally triple that of a workstation. It is preferable to use a machine with software that has look-ahead functions, to avoid tool path deviations.
- Use a contouring type of tool path, such as “Waterline milling”, as the best method to ensure down milling
- Contouring with the periphery of the milling cutter often results in higher productivity, as more teeth are effectively in the cut on a larger tool diameter
- If the spindle speed is limited in the machine, contouring will help maintain and control the cutting speed
- Contouring also creates fewer quick changes in the work load and direction. In high-speed and feed milling, and in hardened materials, this is of specific importance, as the cutting edge and the process are more vulnerable to any changes that can create differences in deflection or create vibration
- For good tool life, stay in the cut continuously, and for as long as possible
Note! Avoid cutting with the center of the tool when cutting speed is zero.
Tool path strategy
Z – constant contouring, two axes. Roughing to finishing
Waterline milling Z – constant contouring
- Common when CAM-controlled maximum scallop function is available
- Smooth engagement and retraction
- Easy programming
- Wide tool choice
Helical contouring, three to five axes. Finishing
Contouring in a ramping tool path
- Smooth changes of direction
- Good form accuracy and surface finish
- Controlled scallop height
- Constant engagement
- Short programs
- Short tool
Generation of sculptured surfaces
Down milling with a cutter tilted approx. 10° in two directions ensures a good surface finish and reliable performance. A ball nose cutter or a radius-shaped cutting edge will form a surface with a certain cusp height, h, depending on:
- Width, ae, of cut
- Feed per tooth, fz
Other important factors are the depth of cut, ap, which influences the cutting forces and the tool indicator reading of the run-out – TIR. For best results:
- Use high-precision hydraulic chuck with Coromant Capto®
- Minimize tool overhang
Roughing and semi-roughing
If the feed per tooth is much smaller than the width and depth of cut, the surface generated will have a much smaller cusp height in the feed direction.
Finishing and super-finishing
It is beneficial to achieve a smooth, symmetrical surface texture in all directions, which can be easily polished afterwards, regardless of the polishing method selected.
This is obtained when fz ≈ ae.
Always use a tilted, two-tooth cutter in super-finishing to achieve the best surface texture.
Semi-roughing with fz much smaller than ae
Super-finishing with a tilted cutter and fz equal to ae
Groove or slot milling
Groove or slot milling is an operation in which side and face milling is often preferred to end milling.
- Slots or grooves can be short or long, closed or open, straight or non-straight, deep or shallow, wide or narrow
- Tool selection is normally determined by the width and depth of the groove and, to some extent, length
- Available machine type and frequency of operation determine whether an end mill, long-edge cutter or side and face milling cutter should be used
- Side and face cutters offer the most efficient method for milling large volumes of long, deep grooves, particularly when horizontal milling machines are used. The growth in vertical milling machines and machining centers, however, means that end mills and long-edge cutters are also frequently used in a variety of groove milling operations
Comparison of cutter concepts
Side and face milling
+ Open slots
+ Deep slots
+ Adjustable widths/tolerances
+ Gang milling
+ Cutting off
+ Large product range for different widths/depths
– Closed slots
– Linear grooving only
– Chip evacuation
+ Closed slots
+ Shallow slots
+ Non-linear slots
+ Versatility (additional methods):
- Trochoidal slot milling for difficult materials (hard steels, HRSA, etc.)
- Plunge milling as a problem solver for long tool overhangs
- Additional semi-finishing/finishing operations can be added easily
- An endmill can be used for operations other than slot milling
– Deep slots
– High forces
– Vibration sensitive if deflected
Side and face milling
Side and face milling cutters can more efficiently handle long, deep, open slots, and provide the best stability and productivity for this type of milling. They can also be built into a “gang”, to machine more than one surface in the same plane at the same time.
How to apply
- Choose cutter size, pitch and position so that at least one edge is in the cut at all times
- Check chip thickness to achieve the optimum feed per tooth
- In demanding milling, check the requirements for power and torque. Stiff arbors and overhang are very important in applications in which arbors have a free end
- Fixture and arbor support must be strong to handle up-milling cutting forces
- First Choice method
- Use a firm stop in the direction of tangential cutting forces to prevent them from forcing the workpiece down against the table. The feed direction corresponds with the cutting forces, which means that rigidity and eliminating backlash are also important, since the cutter has a tendency to climb
- Alternative in applications where problems arise due to insufficient rigidity, or when working on exotic materials
- Solves problems generated by weak setups and chip jamming in deeper grooves
- Good complement for weak setups and when available power and torque are low
- Position the flywheel as close to the tool as possible
- Strengthening the workpiece mounting is always a good investment
Milling open slots using side and face milling cutters
Calculating feed per tooth
A critical factor in peripheral milling using side and face milling cutters is achieving a suitable feed per tooth, fz. Insufficient values cause serious disadvantages, so extra care should always be taken during calculation.
The feed per tooth, fz, should be decreased for deeper slots and increased for shallower ones, in order to maintain the recommended maximum chip thickness. For example, when full slotting with geometry M30, the starting value for maximum chip thickness should be 0.12 mm (0.005 inch).
Note: Because two inserts work together to cut the full slot width, feed is calculated using half the number of inserts zn.
|ae / Dcap (%)||fz (mm/tooth)||hex (mm)|
Depth of cut
For deeper slots, a special cutter can be ordered. If deeper slots are to be machined, feed per tooth should be decreased. If the slot is shallower, increase feed.
Note: The depth of a slot can be limited by the diameter of the arbor boss, the deformation strength of the driving keys and the capacity of the chip pockets.
Flywheel – on horizontal machines
Only a few teeth are engaged at any one time in side and face milling operations, which can generate heavy torsional vibrations due to intermittent machining. This is detrimental to the machining result and to productivity.
- Employing a flywheel is often a good solution for reducing these vibrations. Problems caused by insufficient power, torque and stability in the machine are often solved by the correct use of flywheels
- The need for a flywheel is greater in a small machine with low power, or in a machine with greater wear, than in a larger, more stable and powerful machine
- Position the flywheel as close to the tool as possible.
- Using a flywheel results in smoother machining, which in turn leads to a reduction in noise and vibration, and longer tool life
- In addition to up-milling, a flywheel can be fitted to the arbor on which the milling cutter is set up
- In order to further improve stability when side and face milling, use the largest possible flywheel that the application permits
- Combining a number of round carbon steel discs, each with a center hole and key groove to fit the arbor, remains the best method for constructing a flywheel
Gang milling using cutters mounted in a staggered pattern
Cutters that have bore mounting with 2 keyways can be arranged in a staggered pattern for milling more than one slot at the same time. Displacing the cutters in relation to each other assists in avoiding vibration. This also reduces the need for flywheels.
Milling of narrow and shallow slots and grooves
Versatile cutters have multiple edge inserts that are available in shapes to fit most types of small grooves. Common applications include the machining of internal circlip and seal ring grooves and of small straight or circular external grooves, particularly on components that cannot be rotated.
- A smooth entrance should be programmed when using circular milling.
- Consider the relationship between the cutter diameter and the hole diameter, Dc/Dw. The smaller the relationship, the larger the engagement will be.
End milling of slots
End milling is selected for shorter, shallower slots, especially closed grooves and pockets, and for milling keyways. End mills are the only tools that can mill closed slots that are:
- Straight, curved, or angled
- Wider than tool diameter, designated pockets
Heavier slotting operations are often performed using long-edge milling cutters.
Choice of tools
End milling and long-edge cutters
How to apply
- Use light-cutting end mills with a long, predictable tool life, mounted in high-performance chucks
- Minimize the distance from the tool chuck to the cutting edge to achieve the shortest possible overhang
- Consider feed per edge to produce satisfactory chip thickness. Use coarse pitch cutters to avoid thin chips, which can cause vibrations, bad surfaces and burr formation
- Use the largest possible tool size to achieve the best diameter/length relationship for stability
- Use down-milling as often as possible to achieve the most favorable cutting action
- Make sure to evacuate chips out of the groove. Use compressed air to avoid chip congestion
- Use Coromant Capto® coupling for best stability and support for the spindle
Grooving using end-milling cutters
Machining a groove or slot, often called full slotting, involves three machined faces:
- Slots closed at both ends are pockets, requiring end mills that can work in the axial direction
- Full slotting with an end mill is a demanding operation. The axial cutting depth should be generally reduced to around 70% of the edge length. Machine rigidity and chip evacuation should also be considered in determining the best method for the operation
- End mills are sensitive to the effects of cutting forces. Deflection and vibration may be limiting factors, especially at high machining rates and with long overhangs
This operation requires some specific guidance, in addition to the general recommendations for milling of straight surfaces and grooving. A slot milled in a single step will not have a perfectly square form due to the direction of the cutting forces and the tendency of the tool to bend. The best accuracy and productivity will be achieved if the operation employs an undersized end mill, and is divided into two steps:
- Keyslot milling – roughing of full slot
- Side milling – finishing all around the slot, using up-milling to create true square corners
The radial depth of cut should be kept low in finishing operations to avoid deflection of the cutter, which is a major cause of bad surface finish and/or deviation from a true 90° shoulder.
Keyslot milling in two steps
Methods for opening up a closed slot or pocket in a solid blank
In preparation for milling long, narrow, full-width slots, linear ramping is the most common method (after drilling) for opening up a pocket.
For shallow slots, peck milling can also be an alternative. Circular ramping is used for milling wider slots and pockets.
Comparison of three different methods
Conventional slot milling
+ Conventional 3-axis machines can be used
+ High removal rates under stable conditions
+ Simple programming
+ Wide choice of tools
– Generates high radial cutting forces
– Vibration sensitive
– Deep slots require repeated passes
+ Generates low radial cutting forces – less vibration sensitivity
+ Minimal deflection when milling deep slots
+ A productive method for:
- machining hard steels and HRSA (ISO H and S)
- vibration-sensitive applications
+ The cutter diameter should be maximum 70% of the slot width
+ Good chip evacuation
+ Low heat generation
– More programming is required
+ A problem solver in vibration-sensitive applications:
- with long tool overhangs
- in deep slotting
- with weak machines or setups
– Low productivity under stable conditions
– Requires a rest milling/finishing operation
– End cutting might obstruct chip evacuation
– Limited choice of tools
Rough slotting with long-edge milling cutter
- Cutters with large metal removal capacities are generally used for rough machining
- Shorter versions may produce slots up to a depth equal to the diameter in stable and powerful milling machines
- Use stable ISO 50 spindles, as these cutters are more likely to accommodate considerable radial forces
- Check power and torque requirements, as these are often limiting factors for optimum results
- Consider the optimal pitch for each type of operation
Longer designs are primarily intended for edging operations.
Restriction of Hazardous Substances
Taken from the European Commission guidelines,
“EU legislation restricting the use of hazardous substances in electrical and electronic equipment (RoHS Directive 2002/95/EC) and promoting the collection and recycling of such equipment (WEEE Directive 2002/96/EC) has been in force since February 2003. The legislation provides for the creation of collection schemes where consumers return their used e-waste free of charge. The objective of these schemes is to increase the recycling and/or re-use of such products. It also requires heavy metals such as lead, mercury, cadmium, and hexavalent chromium and flame retardants such as polybrominated biphenyls (PBB) or polybrominated diphenyl ethers (PBDE) to be substituted by safer alternatives.”
“Inadequately treated e-waste poses environmental and health risks. In December 2008, the European Commission therefore proposed to revise the directives on electrical and electronic equipment in order to tackle the fast increasing waste stream of such products. The aim is to increase the amount of e-waste that is appropriately treated and to reduce the volume that goes to disposal.”
For the current Candidate List of substances of very high concern for Authorisation, please click here: https://echa.europa.eu/