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Machining speed:

SFM: Surface Feet per Minute.

Material removal rate (MRR)

The phrase speeds and feeds or feeds and speeds refers to two separate parameters in machine tool
practice, cutting speed and feed rate. They are often considered as a pair because of their combined
effect on the cutting process. Each, however, can also be considered and analyzed in its own right.
Types of Finishing Services
At Pioneer Service, Inc., we work with trusted and reliable companies to offer a wide range of
metal part finishing and surface treatment services. These include:

Bead Blast
Bead blasting involves firing small, spherical pellets at a part’s surface to remove imperfections
from machining. Unlike traditional abrasive blasting, bead blasting typically uses a glass
medium to protect the surface while still eliminating tooling marks. The result is a smooth,
uniform surface with a matte, satiny appearance.

Black Oxide
Black oxide is a type of conversion coating, meaning that the component’s surface reacts with a
chemical bath to create a new protective layer. Black oxide is used to add a degree of corrosion
resistance to ferrous metals while also reducing light reflection. This process can also be used
for aesthetic purposes, as it yields a smooth, black surface finish.

Burnishing
Burnishing is a polishing procedure in which a ball or roller is used to smooth and shape a
component’s surface. The burnishing process creates an attractive mirror finish while also
increasing fatigue strength, adding corrosion resistance, and minimizing porosity.

Case Hardening
Case hardening adds hardness to a component’s surface while leaving its core soft. After
treatment, the component’s inner core continues to absorb stresses, but the outer surface has
greater wear resistance. Flame hardening, carburizing, and nitriding are all options for case
hardening.

Electroless Plating
Electroless plating is the process of catalyzing a reaction between the surface of a component
and a chemical bath to create a surface finish. Compared to electroplating, chemical plating
creates a more uniform surface finish for even complex surface geometries. Electroless-plated
components have improved wear resistance and corrosion resistance compared to untreated
components, so they are ideal for demanding applications.

Electroplating
Electroplating uses electrical current to create a surface coating with improved surface qualities
such as corrosion and abrasion resistance, conductivity, and reflectivity. It can also be used to
improve the appearance of the component if it will be visible after it is installed on the final
product (ie. knobs on a device). The exact characteristics depend on the component’s substrate
and the choice of plating material. Various methods of electroplating exist to accommodate
parts of different sizes and complexities, including barrel plating for smaller parts and rack
plating for larger, more complicated parts.

Electropolish
Electropolishing describes the process of applying electrical current to smooth a components
surface. In contrast to electroplating, electropolishing removes material to even the surface,
whereas electroplating adds a smooth protective coating.

Grinding
Grinding is used to improve the appearance and dimensional tolerance on the surface of a
finished component. Although various grinding processes exist, each using different abrasion
media and treating different parts of the component, all remove a precise layer of metal to yield
a more uniform finish.

Knurling
Knurling is a unique finishing process designed to indent a component to make it easier to grip.
When applied to fasteners and fittings, knurling makes a component more ergonomic and
decreases the likelihood that it will slip.

Laser Engraving
Laser engraving is a specialized finishing process that uses a laser to burn an aesthetic or
functional image onto the surface of a metal part. It is commonly used to add part numbers, or
logos onto components.

Passivating
Passivating is a conversion coating process designed to protect the substrate by making it more
inert. Typically used for ferrous materials, passivating minimizes environmental impacts on a
metal component while removing surface contamination and improving corrosion resistance.
Two types of passivation include:

 Anodizing. Anodizing is a common passivation process that generates a thicker oxide

layer on the metal’s surface. Anodizing is ideal for aluminum parts, lending them a wear-
resistant, non-conductive finish.
 Chromate Conversion. Chromate conversion is a passivating process that retains the
electrical conductivity of the metal surface. It can be used alone or as a primer for other
coating processes.

Pickling
Pickling describes an acid bath designed to remove oxide scaling from a component’s surface.
The process is usually used after heat treatment to clean the metal’s surface.

Thread Rolling
Thread rolling is used to create threaded fasteners and fittings across a range of precision
applications. Rather than machining the threads, which requires removing material from the
blank, rolling forms threads by reshaping the already-machined blank. The process creates a
more durable, wear-resistant component ideal for aerospace components..

Tumbling
In the tumbling process, a rotating barrel rolls components against abrasive tumbling media to
smooth burrs, harden surfaces, and remove tooling marks.

Vibratory Finishing
Vibratory finishing is similar to tumbling in that it involves agitating metal components against
an abrasive media to improve the machined surface finish. The difference is that tumbling
requires a rolling barrel while vibratory finishing simply requires shaking the tub. Vibratory
finishing is usually chosen over tumbling for turned components and complex precision parts.
Rough CNC Machining
Rough CNC machining is the initial stage in the CNC machining process. It focuses on removing excess
material from the workpiece quickly and efficiently. The primary objectives of rough CNC machining are:

Material Removal: The main purpose is to eliminate the bulk of the material from the workpiece, such as
excess stock or rough surfaces.

Time Efficiency: Rough machining aims to reduce the overall machining time by removing significant
amounts of material in this stage.

Tool Preservation: By removing excess material in the rough machining phase, the cutting tools used in
subsequent stages are subjected to less stress and wear.

To achieve these objectives, rough CNC machining employs larger cutting depths and higher feed rates. It
prioritizes efficient material removal over achieving intricate geometries or fine surface finishes. Robust
cutting tools capable of withstanding higher cutting forces are typically utilized in this stage.

Fine CNC Machining

Fine CNC machining follows rough CNC machining and focuses on achieving the desired precision and finish.
The primary objectives of fine CNC machining are:

Dimensional Accuracy: Fine machining ensures that the workpiece meets the required dimensional
specifications accurately.

Surface Finish: It aims to achieve smooth and precise surface finishes, eliminating any remaining
imperfections.

Tolerance Control: Fine machining allows for tighter control over dimensional tolerances, ensuring the
workpiece meets the desired precision requirements.

In fine CNC machining, smaller cutting depths and lower feed rates are employed to refine the workpiece.
Precision cutting tools specifically designed for achieving intricate geometries and superior surface finishes
are used. Attention to detail and meticulous precision are the hallmarks of fine CNC machining.

Roughing and finishing of CNC lathes

CNC lathe roughing is the process of removing a large amount of machining allowance from the workpiece.
Roughing generally uses a low-speed large pass to quickly remove excess metal material on the workpiece,
and the achieved product size is the process size of the semi-finished product rather than the process size of
the finished product. The achievable precision is lower, the CNC machined surface is rough, and the
production efficiency is higher, which is usually a preparation process for finishing. The machining accuracy of
rough machining can generally reach IT12-IT11 level, and the surface roughness Ra value can reach 50-
12.5μm.

When performing rough machining, the CNC machining speed is generally emphasized, so the cutting
amount and feed amount are relatively large, and the cutting speed is relatively small, but this will cause a lot
of vibration to the lathe, and also aggravate the various parts of the lathe. wear of components. If possible, we
can use different lathes for roughing and finishing to better protect the mechanical equipment.

The finishing of CNC lathes is also known as precision machining. There are two main ways to realize the
finishing of workpieces. One is to use high-precision CNC lathes and CNC to process workpieces with high
precision; the other is to use error compensation technology to improve CNC machining. Part accuracy. The
finishing CNC machining accuracy can reach IT8-IT6 level, and the surface roughness Ra value can reach
1.6-0.8μm, and even can reach Ra0.4μm under better conditions.

The main function of finishing is to improve the size and surface accuracy of CNC machined parts, not the
amount of cutting. Through the process of cutting a thin layer of metal material on the surface of CNC
machined parts with a high cutting speed and a small amount of cutting and feed through a high-precision and
rigid lathe and finely sharpened tools, obviously, This process is able to significantly improve the accuracy of
CNC machined parts.

The difference between roughing and finishing of CNC lathes

The difference between roughing and finishing of CNC lathes is that one is rough machining and the other is
fine machining, and the latter pays more attention to details than the former. Rough machining is for the
purpose of quickly cutting off the remaining surface of CNC machined parts, so as to achieve as much cutting
as possible in a short period of time. The dimensional accuracy and surface quality of CNC machined
parts are relatively low. The purpose of finishing is to cut thin metal materials on the surface of the workpiece
to obtain higher precision and surface quality.
 When roughing, the choice of cutting amount is generally based on improving the production efficiency of
CNC machining, followed by economy and processing cost. Therefore, when considering the cutting amount
of roughing, we should try to choose a larger cutting amount within the allowable range, followed by a larger
feed rate, and then a smaller cutting speed. When finishing machining, the choice of cutting amount is mainly
to ensure the quality of CNC machining, followed by improving production efficiency and tool life. Therefore,
when considering the cutting amount of finishing, generally choose a smaller amount of cutting tool, and then
choose a smaller feed amount, and you can choose a larger cutting speed.

What is the difference between roughing and finishing of CNC lathes? After browsing the above articles, you
can find that the difference between roughing and finishing of CNC lathes is that one is rough machining and
the other is fine machining. Rough machining removes a lot of material, feed rate and cutting knife The
amount is relatively large, the cutting speed is relatively small, and the dimensional accuracy and surface
quality of the workpiece processed by CNC are relatively low. Less material is removed by finishing, the feed
rate and cutting amount are relatively small, the cutting speed is relatively large, and the dimensional
accuracy and surface quality of the parts processed by CNC are high.

 Material Removal: Rough CNC machining focuses on efficient removal of excess material, while fine CNC
machining aims for precision and accuracy in achieving the desired dimensions.

 Cutting Parameters: Rough CNC machining utilizes larger cutting depths and higher feed rates, whereas
fine CNC machining employs smaller cutting depths and lower feed rates for more controlled and precise
cutting.

 Tool Selection: Rough machining uses robust cutting tools capable of withstanding higher cutting forces,
while fine machining employs precision tools designed for achieving intricate geometries and superior surface
finishes.

 Objectives: Rough machining primarily aims to remove excess material quickly and prepare the workpiece
for further processing, while fine machining emphasizes achieving precise dimensions, surface finishes, and
tight tolerances.
Conclusion

In conclusion, rough CNC machining and fine CNC machining are two distinct stages within the CNC
machining process. Rough machining focuses on efficient material removal, while fine machining emphasizes
precision and achieving the desired dimensions and surface finishes. Understanding the differences between
these processes is essential for optimizing CNC machining operations and producing high-quality
components with accuracy and efficiency.

The above is the summary of VMT CNC machining manufacturers. If you want to know more about the
knowledge and application of CNC machining, please contact us to discuss with me.

Difference Between Roughing and Finishing

in Machining
Machining or metal cutting is one of the secondary manufacturing processes by which excess material is gradually removed
from a preformed blank to obtain desired shape, size and finish. There exist larger number of processes to fulfil the basic
requirement of machining. Such processes can be broadly classified as conventional machining processes (turning, threading,
facing, drilling, boring, shaping, planing, milling, grooving, reaming, etc.), abrasive cutting processes (grinding, lapping, honing,
polishing, superfinishing, etc.), micro-precision machining processes (micro-milling, micro-drilling, diamond turning, etc.), and
non-traditional machining processes (ultrasonic machining, electro-discharge machining, electro-chemical machining, laser
beam machining, ion beam machining, hybrid machining, etc.).

All of these are subtractive manufacturing processes, which indicates layer by layer material is removed from a solid workpiece
to obtain desired three dimensional features; however, they follow varying principles of material removal and thereby possess
varying capability in terms of machinable materials, stock removal rate, surface quality, production rate and cost, etc. Most NTM
processes and micro-precision machining processes are not suitable for removing bulk volume of material; instead, they can
generate fine features with high accuracy. Conventional machining processes are suitable for high stock removal as well as
imparting reasonably good surface quality. However, achieving both in a single pass is not possible. Thus machining is usually
carried out in two steps with varying process parameters (cutting velocity, feed rate and depth of cut).

In first step, bulk amount of material is quickly removed from workpiece as per required feature. Higher feed rate and depth of
cut are employed for this step so that high stock removal rate is obtained. This step is called rough cut or roughing pass. It
cannot provide good surface finish and close tolerance. After rough cut, a finish cut or finishing pass is carried out to improve
surface finish, dimensional accuracy and tolerance level. Here very low feed rate and depth of cut are employed. So stock
removal rate reduces in finish pass but surface quality improves. Various differences between roughing and finishing in
conventional machining processes are given below in table format.
Table: Differences between roughing and finishing
Roughing Finishing

Objective of rough pass is to remove bulk Objective of finish pass is to improve surface
amount of excess material from workpiece in finish, dimensional accuracy and tolerance.
every pass.

Higher feed rate and depth of cut are Very low feed rate and depth of cut are
utilized. utilized.

Material removal rate (MRR) is high. MRR is comparatively low.

Surface roughness after rough pass is more; Surface roughness after finish pass is low;
thus surface finish is poor. and thus surface finish is good.

It cannot provide high dimensional accuracy It can provide high dimensional accuracy
and close tolerance. and close tolerance.

An old cutter can be utilized for roughing Sharp cutter is highly desired to achieve
pass. good finish.

It is performed prior to finish pass. It can be performed only after rough pass.

Objectives of rough cut and finish cut: Rough cut is carried out to quickly impart a basic shape according to desired feature.
Here surface roughness is not important factor; instead, removing maximum unwanted material is ultimate objective. Contrary to
this, finish pass is carried out to improve surface finish, dimensional accuracy and tolerance of the desired feature. Stock
removal rate has no importance in case of finish pass.
Process parameters and MRR: Cutting velocity (Vc), feed rate (s or f) and depth of cut (t or a) are three process parameters for
every conventional machining process. These parameters greatly influence overall machining action and capability. Higher
velocity, feed and depth of cut can increase material removal rate (MRR) but with the sacrifice of surface finish. MRR is
proportional to velocity, feed and depth of cut and thus can be mathematically expressed by the multiplication of velocity, feed
and depth of cut with a positive constant for unit conversion. During machining, velocity is normally maintained unchanged as it
is selected on the basis of work and tool material, machine tool capability, vibration level and other important factors. To fulfil the
basic objective, higher feed and depth of cut are employed in rough pass and as a consequence MRR increases. On the other
hand, low feed and depth of cut are employed in finish pass and thus MRR reduces.

Surface finish and dimensional accuracy: Presence of scallop marks or feed marks on the finished surface is inherent to
every conventional machining process due to feed velocity. Such saw-tooth alike scallop marks cause primary surface
roughness. Apart from cutting tool geometry, surface roughness directly relies on feed rate. Higher feed rate can lead to poor
surface finish. Higher depth of cut also tends to degrade surface finish and machining accuracy. In rough cut, higher feed and
depth of cut are utilized and thus poor surface finish is obtained. It also fails to provide high dimensional accuracy and close
tolerance. On the other hand, finish pass can improve finish, accuracy and tolerance as very low feed and depth of cut are
employed.

Usage of old cutter: An old cutter may have less sharp edges (i.e., higher edge radius and nose radius) as it has already worn
out during machining. Edge and nose sharpness limit the achievable surface finish in the process. A sharp edge cannot take
high chip load but is mandatory to obtain better finish and accuracy. So an old cutter can be utilized in rough pass without
noticeable problem as surface quality does not matter. However, a sharp tool should be used in finish pass so that better finish,
accuracy and tolerance is achieved. Here feed and depth of cut remain low, so chip load possesses no detectable problem in
tool breakage or edge chipping.

Scientific comparison among roughing and finishing in machining processes is presented in this article. The author also
suggests you to go through the following references for better understanding of the topic.