Power Saws and Grinders Flashcards
What type of power saw is in the image?
A power hacksaw.
How is the speed of a power hacksaw measured?
Strokes per minute (spm).
How are power hacksaw blades different from hand hacksaw blades?
They are wider, thicker, and longer.
What are fully-hardened hacksaw blades good for?
- Long life over a wide range of materials, including stainless steel.
- They withstand heavy feed pressures for faster cutting.
How are bimetal hacksaw blades constructed?
They have a high speed steel tooth edge with a tough alloy steel back. The tough alloy back resists breakage better and handles irregular cuts.
What is blade rake angle?
Rake angle is the angle of the cutting face relative to the workpiece.
What type of power saw is in the image?
Horizontal band saw.
What are some of the advantages of a horizontal band saw?
- Continuous steel blade.
- Greater cutting efficiency.
- Variable speed drives.
When cutting a long piece of stock on a cut off saw what must be done?
Support the piece with a stand with a roller.
What should be done when cutting a short piece on a cut off saw?
Place a similar piece at the back of the jaws before clamping, otherwise the jaws tend to distort.
What is the contour band saw used for?
Shaping metal, rather than cutting lengths of stock.
What are the major sections of a contour band saw?
- The base.
- The column.
- The head.
How is capacity of contour band saws measured?
By the throat distance and the max work height.
Throat distance is the distance between the blade and the column.
Work height is the distance between the table and head.
On a contour band saw what is the work holding jaw?
It supports the work while it feeds into the blade and keeps your hands to the side of the blade.
On a contour band saw what is a power feeding table?
A chain holds the workpiece in place and a hydraulic system moves the table at a set feed rate.
On a contour band saw what is the gravity feeding attachment?
On smaller machines, the feed mechanism uses gravity with cables, pulleys, and weights or air pressure.
On a contour band saw what is the ripping fence?
A flat bar to guide the piece for rip cuts.
What are the three types of band saw blade materials?
- High carbon steel.
- Bimetal.
- Tungsten carbide.
What types of material are high carbon steel blades suited for?
Mild steel, brass, and copper.
What are some advantages of bimetal blades to high carbon steel blades?
- Greater wear resistance.
- Greater heat resistance.
- Faster cutting speeds.
- Better durability.
What are the three tooth forms found on band saw blades?
- Standard tooth.
- Hook tooth.
- Skip tooth.
What is the standard tooth blade used for?
Has evenly spaced teeth with a 0-degree rake angle.
Used for general purpose cutting of most metals.
What is the hook tooth blade used for?
Has a positive rake angle.
Has faster cutting rates and uses less feed pressure.
Good for soft metals, wood, and plastics.
What is the skip tooth blade used for?
Has a 0-degree rake but with wider teeth spacing.
The large gullet provides more chip space.
Ideal for soft materials or workpieces with a thick cross-section.
What are the three main sets of band saw blades?
- Raker set.
- Wavy set.
- Straight or alternate set.
What is the raker set used for?
General purpose cutting because it cuts quickly and leaves a good surface finish.
What is the wavy set used for?
Good for thin workpieces and workpieces with a change in cross-section like tubing.
What is the straight or alternate set used for?
Cuts fast, making it good for rough fast cuts.
What attachment do a lot of contour blade saws have to make new blades?
A blade welding unit.
Where should you place the weld when welding band saw blades?
The weld should be placed at the bottom of the gullet.
How do you calculate blade length when making a new blade for a band saw?
Blade length = pi x (diameter of one pulley/2) x center distance
What must be done to the newly welded blade before using.
The weld must be annealed so the blade does not break.
If a file slides over the weld without biting in, then the weld is too hard.
What is friction sawing and what type of blade is used?
Friction sawing cuts at 50 to 100 times the normal cutting speed and softens the steel ahead of the cut, allowing the teeth to cut.
A silcon-carbide blade that is thicker and with a wider set is used.
What type of saw is in the image?
Abrasive cut-off saw.
For what size material are abrasive cut-off saws most efficient?
For cross-sections less than 2-inches.
What are the three types of abrasive grit used for a cut-off wheel?
- Aluminum oxide.
- Silicon-carbide.
- Diamond.
What is each type of cut-off wheel used for: aluminum oxide, silicon-carbide, and diamond?
Aluminum oxide is used for steel and most other metals.
Silicon-carbide is used for non-ferrous materials.
Diamond is used for cutting ceramic, sone and brick.
What should be worn for eye protection when using an offhand grinder?
Eye protection and a face shield.
How are the wheel nuts on an offhand grinder tightened?
The nut on the right-hand side has a right-hand thread.
The nut on the left-hand side has a left hand thread.
the grinding force helps tighten the nuts.
Why should you only grind on the face of a grinding wheel.
Side pressure on the wheel can cause it to explode.
Side wheel grinders are designed for this purpose.
How do you stop tools from overheating when grinding?
Apply light pressure and cool in a bath as needed.
What are the two main types of abrasives used on grinding wheels?
Aluminum oxide and silicon-carbide.
What metals is aluminum oxide suitable for grinding?
All steels and most high tensile ferrous metals except cast iron.
What materials is silicon-carbide used to grind?
- High density materials such as cemented carbides, ceramics and stone.
- Low tensile materials such as cast iron, non-ferrous metals, and non-metals.
What is the ability of a material to fracture under stress along certain cleavage lines so that as the cutting edge becomes dull, part of the grain breaks off and presents new cutting edges?
Friability.
How are abrasives grains cleaned and sized?
Grains are passed over screens that have different mesh sizes. The smaller the number, the larger the grit size. The larger the number, the smaller the grit size.
What are the three most common types of bonds in grinding wheels and what are their letter designations?
- Vitrified - V
- Resinoid - B
- Rubber - R
The grade of a grinding wheel indicates the strength of the bond and the hardness of the wheel. How is it designated?
Grade is indicated by a letter:
A is the softest wheel,
Z is the hardest (strongest bond).
The structure of the grinding wheel indicates the density of the wheel (the space between grains). The primary function of the space is to provide chip clearance for the metal removed by a grain. How is this designated?
The structure is graded on a scale of 1 to 15.
1 is a dense structure,
15 is an open structure.
The grinding wheel marking are located on the blotter on the side of the wheel. What does each position represent?
Position 1 is the abrasive type.
Position 2 is the grain size (grit).
Position 3 is the grade (hardness).
Position 4 is the structure.
Position 5 is the bond type.
Position 6 is the manufacturer’s record.
Why should you never stand in front of the grinder when starting it?
If the wheel is damaged, it will fly apart as soon as the grinder is started.
How long should you let a grinder run after installing a new grinding wheel?
Let it run for 1 minute before approaching to ensure it won’t fly apart.
The tool rest supports the workpiece. If this gap gets too large the workpiece and the operator’s fingers can get drawn into the wheel. What is the correct gap between the wheel and the tool rest?
The gap must be set at 1/16-inch and never exceed 1/8-inch.
The spark guard protects the operator’s hands from sparks. What must the gap between the spark guard and the edge of the wheel be set to?
Should be between 1/16-inch to 1/4-inch.
Why should the grinding wheel not exceed the speed (rpm) it is rated for?
The force of inertia will tear the wheel apart.
Cracks in a grinding wheel are hard to see. the ring test helps test for this. How is the ring test performed?
- Remove the wheel from its flange.
- Suspend the wheel by its bore.
- Tap the wheel lightly in several places with a non-metallic object. The wheel will ring if not cracked.
When abrasive particles on a wheel become dull and the wheel takes on a shiny appearance. What has happened to the wheel?
It has become glazed and stops cutting.
When the spaces between the particles on a wheel become jammed with the material being ground, the wheel takes on the colour of that material. What has happened to the wheel?
It has become loaded and stops cutting.
How do you mechanically dress a grinding wheel?
- Place the head of the dresser on the work rest with the lugs down.
- Press the tool firmly against the grinding wheel and feed the tool back and forth across the face of the wheel.
- Continue until all evidence of glazing or loading is gone.
How should a wheel be dressed by a diamond dresser?
The tool should be held at 15-degrees drag angle and 30-degrees lead angle to reduce chatter and keep the tool sharp. The depth of cut should be light (0.001 inch).
Over time the face of a wheel wears unevenly. What is the process to restore the shape of the wheel and make its outer surface concentric with the bore?
Truing a wheel.
This follows the same procedure as dressing a wheel.
What should be done when a wheel goes out of balance?
- Dressing may restore its balance.
- If the vibration persists, check the shaft for runout and check the bearing condition.
What size should grinder flanges be relative to the size of the grinder wheel?
At least 1/3 the diameter of the wheel.
