40 Questions
What is the alternative method to calculate bend allowances when the Bend Allowance Chart is not available?
Using the bend allowance formula
What is the purpose of calculating the bend allowance in tube bending?
To obtain a smooth bend without flattening the tube
How is the development length calculated?
By dividing the bent object into flats and bend allowances, then adding them up
What is the minimum bend radius in tube bending?
2.5 to 3 times the OD
What is the acceptable method of bending soft, non-heat-treated aluminium tubing in an emergency?
Bending by hand to form the desired radius
What is the purpose of calculating the flat dimension?
To subtract the setback from the overall dimension
What is the formula for calculating the bend allowance?
angle of bend / 2πR
What is the result of adding up the flat dimensions and bend allowances?
The development length
What is the primary function of the handle and slide bar in the simple hand bender?
To provide mechanical advantage to bend the tubing
How is the forming die on the mechanical tube bender calibrated?
In degrees
What is the purpose of bending a replacement tubing to a specified number of degrees?
To match the original bend in the tubing
Why is a tube cutter not suitable for stainless steel tubing?
It tends to work harden the tube
What is the recommended margin of safety when cutting a new piece of tubing?
10% longer
What is the purpose of marking the tube with a felt-tip pen or scriber before cutting?
To align the cutting wheel with the cutting mark
What should be avoided when using a tube cutter to cut stainless steel tubing?
Applying too much pressure
What is the primary difference between a hand bender and a mechanically operated tube bender?
The power source used to operate the bender
What is the first step in forming a single flare?
Slip the fitting nut and sleeve onto the tube
What is the purpose of a double flare?
To form a stronger connection with small diameter soft aluminium alloys
Why is it important to check the flared end of the tube after forming a single flare?
To verify that the flared end is no larger than the largest diameter of the sleeve
What is the main advantage of using flareless fittings in high-pressure systems?
They produce leak-free attachments without flares
What is the purpose of the pre-setting tool in flareless fittings?
To create a leak-free attachment between the sleeve and the tube
What should be done to ensure a secure connection with a flareless fitting?
Select the correct size flareless fitting body
Why is it important to avoid over-tightening when forming a single flare?
It can damage the flare
What should be checked for after forming a double flare?
All of the above
What is the primary function of a mandrel in fabricating hose assemblies?
To protect sealing surfaces and support inner tubes
What is the common but dangerous method of removing skived pieces of rubber from a hose?
Taking a piece of rod or tubing and trying to poke it loose
What is the typical procedure when a failure occurs in a flexible hose equipped with swaged end fittings?
The unit is replaced without attempting a repair
What is the purpose of a protractor in fabricating hose assemblies?
To measure the angle of the fitting nipples
What is the recommended tool for cutting the hose to the required length?
Hose cut-off machine
What is the purpose of a marking pencil in fabricating hose assemblies?
To mark the hose with the correct length
What is the procedure when a failure occurs in a hose assembly equipped with reusable style end fittings?
The undamaged end fittings are removed and reused
What is the purpose of adding 5%–8% to the determined hose length?
To allow for expansion or contraction from pressure application
What is the purpose of a thickness gauge in fabricating hose assemblies?
To measure the thickness of the hose
What is the purpose of wrapping the circumference of the hose with masking or plastic electrical tape?
To prevent braid flare-out if the hose outer cover is wire braid
What should be done after cutting the hose to the required length?
The hose should be blown clean with filtered shop air
Why should a vice not be over-tightened on thin-walled lightweight fittings?
To prevent damage to the thin-walled lightweight fittings
What is the purpose of screwing the hose anti-clockwise into the socket?
To ensure a secure connection
How should the hose be turned after screwing it into the socket?
A quarter turn back to secure the connection
What is the purpose of assembling the nipple and nut?
To connect the hose to the tube or component
What is the purpose of the socket in the hose end fitting installation?
To fit over the outside diameter of the hose
Study Notes
Calculating Bend Allowances
- Use the Bend Allowance Chart if available, otherwise use the bend allowance formula: angle of bend = 2πR / 360°
- Calculate flats by subtracting the setback for each bend from the overall dimension
- Calculate overall length by dividing the bent object into flats and bend allowances, and numbering them progressively
Tube Bending
- Objective: obtain a smooth bend without flattening the tube
- Minimum bend radius: 2.5 to 3 times the OD
- Tube bending methods:
- Hand-operated tube bender
- Mechanical tube bender
- Hand bending (for soft, non-heat-treated aluminium tubing smaller than 1/4 inch in diameter)
Tube Cutting
- Cut new tubing 10% longer than the tube being replaced
- Cutting methods:
- Fine-tooth hacksaw
- Roller type tube cutter (for soft metal tubing like copper, aluminium, or aluminium alloy)
- Avoid using tube cutters on stainless steel tubing as it tends to work harden the tube
Tube Flaring
- Single flare: use a tube flare tool to form the flare
- Double flare: used with small diameter soft aluminium alloys to reinforce the flare
- Flareless fitting: used for high-pressure systems, requires pre-setting with a specialized tool
Hose Assembly Fabrication
- Basic hand tools required:
- Bench vice
- Hose cut-off machine
- Fine-tooth hacksaw
- Open-end wrench sets
- Sharp knife
- Slip-joint pliers
- Oil can
- Marking pencil
- Steel ruler
- Thickness gauge (leaf type)
- Protractor
- Recommended tools:
- Mandrel kit (protects sealing surfaces, supports inner tubes, and guides fitting nipples into hoses)
Hose Assembly Procedures
- Determine the necessary hose length from the table and diagram
- Add 5%-8% to allow for expansion or contraction from pressure application
- Wrap the circumference of the hose with masking or plastic electrical tape at the cut-off point
- Cut the hose to the required length using a cut-off machine
- Blow the hose clean with filtered shop air after cutting
- Remove the tape and clamp socket in a vice
- Install the hose end fitting, ensuring a square cut and cleanliness
- Avoid over-tightening the vice on thin-walled lightweight fittings
This quiz covers the calculation of bend allowances using the Bend Allowance Chart or formula, essential for aerospace maintenance practices.
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