Grinding 101 - Getting the Right Wheel for the Job - Gear Up with Gregg's

hey there my name is keith and i'm an

operations manager here at greg

distributors

today on gear up with greg's we're going

to discuss the basics of grinding

and how to keep yourself safe while

doing it

have been cutting and grinding metal for

more than 150 years

starting with simple sandstone and

eventually evolving into the many

options we have available today

now grinding wheels consist of two basic

elements

the abrasive and the bond

abrasives or grains should be as hard as

possible

while the size of the abrasive varies

generally speaking

the smaller and finer it is the finer

the finished surface

of the material your grinding will be

and vice versa

rougher grain is typically used for

pre-grinding like

cleaning up a messy weld bead while

finer grain

is used for finished grinding such as

smoothing the weld before paint is

applied

a bond holds the grains together in a

wheel and allows open spaces

or pores to exist between them

the bond along with the type of abrasive

determines the hardness strength and

cutting ability of a grinding wheel

while bonds started out as natural

minerals modern bonds are usually

composed of synthetic materials

such as glass

organic bonds such as resin or rubber

are generally suited for harsh grinding

conditions

that require high levels of stock

removal

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vitrified bonds or glass bond

compositions hold their form extremely

well

and produce a high ratio of material

removal

compared to the amount of abrasive wheel

used

these types of wheels are commonly used

with the medium to fine

grain grits needed for precision

grinding

resin is more common and more shock

resistant than vitrified bonds

and these wheels are generally operated

at higher speeds

they're mostly used with coarse grains

in the metal working

and metal fabrication markets

deciding which abrasive wheel is best

for your tasks comes down to several

factors

grade application

size type

material and speed

grade refers to the strength of the bond

in a grinding wheel

and is also known as a wheel's hardness

the grade ranges from a a soft bond

to zed a hard bond

grade affects almost all aspects of

grinding including wheel speed

feed rates and grinding depth

take a look at these carb random gold

aluminum oxide wheels for instance

these two discs may look similar but

this one has a24 grade

which is suitable for grinding ferrous

metals and various alloy steels

while this one has a grade of za30

which means it's ideal for grinding

stainless steel and various hard alloys

next up knowing your application is

critical to choosing the right wheel

be sure not to mix up cutting and

grinding as they are two very different

wheels

both with their own specific

applications

for cutting you need to be sure you have

a blade suited for the task

cutting wheels like these are thinner

and have a much higher risk of snapping

if you try to use them for grinding

they are normally used on angle grinders

for quick removal or trimming

on the other hand a straight grinding

wheel

is the most common style used for

cylindrical

and surface grinding operations

there are several other types of

grinding and cutting wheels so be sure

to ask your local greg's representative

to make sure you are getting the right

tool for the job

the size of the grit in a wheel is just

as important as grade or application

even though it may often be overlooked

every grinding wheel

shows a number representing grit size

which is the size of the individual

abrasive particles

lower numbers means that a wheel has a

coarse grain

coarse grains are used when speed not

precision

is key higher numbers are fine grit

wheels

used for detail finishes small areas of

contact

or with hard or brittle metals

a grinding wheels type is a number that

refers to the particular shape

and use of the wheel for instance

a type 1 grinding wheel is a flat thick

wheel

mainly used for surface grinding

operations

typically on a bench or pedestal grinder

a type 27 wheel on the other hand has a

depressed center

and is mostly used for blending

not only do the grinding wheels come in

many different shapes and sizes

they also come in many different kinds

of materials

the material or grit that a grinding

wheel is made of

is critical to finding the correct wheel

for your application

this grit is typically either aluminum

oxide

silicon carbide ceramic

or a combination of all three

aluminum oxide is the most common and is

used mainly for low to high carbon

steels

you'll notice that aluminum oxide wheels

come in a variety of colors

which indicates the wheels grinding

characteristics

gray and brown grit wheels are typically

used in

bench and production grinding they are

tough

and inexpensive the workhorse of the

grinding game

white grit is mainly used on harder

steels

that need a cooler cutting action to

avoid burning the work

piece though they run cool

they are soft wheels that break down

quickly so they are mostly used to grind

ferrous metal tools like high speed

steel

drill bits

silicon carbide is found in black or

green and is typically used as a

polishing or finishing grit

this is because the sharp grit found in

these grinding wheels

dull and create a rubbing action

especially on steel

which produces a better surface finish

black silicone carbide is used to grind

non-ferrous metals

like aluminum or brass as well as

plastics

rubber and stones such as marble or

granite

ceramic is a newer grit which doesn't

dull the same way as other wheels do

instead it will break down or fracture

into sharp corners

rather than dulling and pulling out of

the bond

this means that the wheel lasts longer

however these wheels are also expensive

typically costing two or three times as

much as aluminum oxide wheels

these wheels are not pure ceramic but

actually

a mix of aluminum oxide and ceramic

anywhere between 10 and 15 percent

zirconia alumina is tough perfect for

high pressure machining and grinding

applications

this combination of zirconium oxide and

aluminum oxide

is commonly used in general steel

fabrication shops

since they are the disk of choice for

grinding and finishing steel

and stainless steel they also have good

heat resistance

and work best between 24 and 120 grit

now if you need to remove a lot of

material

and fast stock removal speed is

something you need to keep in mind

wheels with coarser grits leave deeper

cuts while

wheels with finer grits cut faster in

harder materials

along with the grit you need to keep in

mind the usage speed

wheels with a vitrified bond are

typically used at speeds less than 6500

rpm

while organic bond wheels can be used

between

6500 and 9500 rpm

working at higher speeds usually

requires specialized wheels designed for

high speed grinding

in any case do not exceed the safe

operating speed

shown on your wheel of choice

so we know a lot about what these wheels

are made of and what they can do

but that's not the most important thing

when it comes to grinding wheels

it's about time we talked about proper

ppe and how to make sure you don't end

up with a nasty injury or worse

when grinding always be sure to wear

safety glasses with a side shield

or a full face shield keep all shields

and guards on your grinder in place

sure sometimes it might seem easier to

work on a project

if they're not there but they're in

place for a reason

those guards could be the only thing

between you and a whole lot of sharp

edge debris

if something goes wrong

when installing a wheel be sure not to

over tighten the nut

since it could crack the wheel but why

does it matter if there's a crack in the

wheel

well grinding wheels are designed to

operate at very high speeds

because of this if a wheel shatters

while in use

the fragments it creates can travel over

450 kilometers per hour

these fragments essentially become live

shrapnel and can result in material

damage

serious injury or even death

so before you mount a wheel on a grinder

you'll need to do a ring test a ring

test

assesses the sound of a wheel when it is

tapped gently

a wheel that isn't damaged will emit a

clear ringing tone

a wheel that has cracked or has other

imperfections will emit a dead sound

start by suspending the wheel from the

hole on a nail or finger

if the wheel is too heavy rest it on the

outer edge on a clean hard floor

tap the wheel gently about 45 degrees

from either side of the vertical center

line

and about 2.5 to 5 centimeters from the

outside edge

use the non-metal handle of a

screwdriver for lighter wheels

or a wood mallet for heavier wheels

listen carefully

and turn the wheel 45 degrees to the

left or right

before repeating the test

if you are suspicious of a wheel don't

use it

it's better to be safe than sorry

next inspect the grinder in wheel

position especially at the tool rest

you should never have more than an

eighth of an inch gap between the tool

rest

and the grinding wheel

otherwise tools or even fingers could

get pulled into the gap

while the wheel is running before you

start to work

turn on the grinder and stand back until

the wheel reaches its full speed

once the wheel's going at the

appropriate speed you're ready to work

overtime grinding wheels can become dull

after the grip becomes clogged by a

build up of particles

when this happens overheating is more

common and material removal is slowed

considerably

that's why wheel dressing is critical to

grinding wheel maintenance

dressing is a process to clean and

restore damaged or clogged grinding

wheels to their original state

during the process material is removed

from the wheel

including dull abrasive grains and

excess bonding material

dressing can also be used to get a

desired custom shape on a wheel face

before you start make sure you are

wearing the proper ppe

that means a face shield or adequate

safety glasses

along with a dust mask to keep the

floating debris out of your lungs

if you are wearing long sleeves get rid

of them

anything that can run the risk of

getting caught in a grinder like sleeves

gloves or loose long hair should be

avoided

roll up your sleeves or switch to a

short sleeve shirt

and pull back your hair if it is long

dressing the wheel is simple take your

tool of choice whether that's a

mechanical dresser

or a dressing stick and once the grinder

gets up to speed

hold the tool against the rotating wheel

surface

and move it back and forth

the whole process shouldn't take more

than five minutes

and when you're done you'll be left with

a grinding wheel that looks as good as

new

just remember adjust your tool rest

after you've finished dressing the wheel

since the removal of material will

likely have changed the amount of space

between the tool rest and your grinding

wheel

now i hope i didn't grind your gears too

much with all that information

but if you have any questions feel free

to leave a comment down below

or check out our website at greg

distributors.ca

again i'm keith and thank you for taking

the time to watch gear up with craigs

i hope you have a great canadian day

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you