Teaching Facilities and Equipment

LESSON 04: SPIRAL GROOVE MILLING

4.1. Milling right helical groove

Time to complete: 6 sessions

Previous lesson name:

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Performed from date..................... to date ....................................

I. Teaching facilities and equipment

1.1. Teaching aids

Lesson plans, outlines, chalk, projector, drawings, ...

1.2. Equipment, tools, materials

Name and specifications of the device, tools; raw materials, consumables	Single taste	SL	Note	Additional
1	Device
	Universal milling machine 6X332B	Female	02	Continued use
	Spare parts for milling machine	Set	02	Continued use
	Universal indexing head	Female	02	Continued use
	Universal indexing head spare parts	Set	02	Continued use
2	Tool
	Dial gauge + holder	Set	02	Continued use
	Caliper 1/50, L=200	Female	10	Continued use
	Wrench set from 8÷24mm	Set	01	Continued use
	Ruler 200	Female	02	Continued use
	Universal angle gauge	Female	02	Continued use
3	Materials (for 01 student)
	Steel billet Ф26, L=200	Female	01	Cancel
	End mill Ф6	Son	01	Cancel
	HD50 Oil	Liter	01	Cancel
4	Other

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II. Lesson implementation

2.1. Lesson objectives

After completing this lesson, students will be able to:

+ About knowledge

- Calculate the basic parameters of spiral grooves

- Select the gears to install the differential

+ About skills

Fix the cutter and adjust the machine to mill spiral groove details to meet technical requirements.

+ About attitude

- Serious and self-disciplined in the learning process.

- Ensure labor safety and environmental hygiene.

2.2. Lesson content

In the mechanical field, especially the machine manufacturing industry, we encounter many parts with spiral grooves such as spiral milling cutters, spiral drills...



Figure 4.1: Detail with spiral groove

To form spiral grooves, there are many different machining methods, including spiral groove milling method.

The principle of spiral groove milling method is that when the workpiece rotates one revolution, the machine table moves an amount equal to the spiral step; that is, to create a spiral groove, the part must simultaneously perform two movements: the movement

continuous rotation and axial translation.

L
 d

Figure 4.2: Spiral groove brushing diagram

2.2.1. Technical requirements of right-handed spiral groove

- Ensure correct twist angle α ±30'

- Ensure the accuracy of groove size BxH

- Ensure groove rib roughness Ra = 2.5 mm.

- Enough grooves on the part

2.2.2. Basic parameters of right-handed helical groove

- Top diameter: D e

- Foot diameter: D i

- Average diameter: d

- Groove width: B

- Groove height: H

- Twist angle: α

- Twist length: L

2.2.3. Calculation of basic parameters of right-handed helical groove

- Average diameter: d = D e – H

- Twist length: L = п.d.cotgα

- Calculate the transmission ratio i to find the gears for the differential bridge:

i  N . T

A z 1 z 3

In which: N: universal indexing head characteristic (N=40)

T: vertical screw pitch of milling machine table (T=6)

2.2.4. Right helical groove milling procedure

Step 1: Calculate the length of the twist

L = ο.d.cotgα

Step 2: Calculate the transmission ratio i to find the gears z 1 , z 2 , z 3 , z 4 to install the gear bridge

i  N . T

A z 1 z 3

Step 3: Install the gear bridge

Gear bridge connects from universal dividing head IV shaft to the vertical lead screw shaft of the milling machine table.

Gear z 1 is tightly fitted to the lead screw shaft along the milling machine table

Gear z 4 is tightly fitted to the indexing head shaft IV (sub-shaft).

Milling the spiral groove in the right direction so we install the gear bridge as an odd bridge, meaning the number of shafts connecting from the active shaft to the passive shaft is an odd number.

Figure 4.3: Installing the spiral grooved differential gear bridge

Step 4: Mount the workpiece onto the machine

The workpiece is clamped at one end into the 3-jaw chuck of the indexing head, the other end against the tailstock center of the indexing head or both ends against the center transmitting the torque by clamping speed.

Step 5: Knife holder

- When cutting with a milling cutter, the cutter shaft should be perpendicular to the machine table.

- When cutting with a disc milling cutter on a vertical milling machine, tilt the machine head carrying the cutter at an angle equal to the required twist angle, the rotation direction of the machine head is clockwise.

- In case of cutting with a disc milling cutter on a horizontal milling machine, the machine

The milling machine must be able to rotate the machine table at an angle equal to the twist angle (for example, the 6P82 milling machine can rotate the machine table).

Step 6: Adjust the machine

Machine adjustment process for milling right helical grooves

similar to when

Figure 4.4: Gear mounting position on the differential bridge

Adjusting the machine to mill straight grooves also requires adjusting the cutter to the center of the workpiece and taking the cutting depth. The difference is that when machining a part that is both rotating and translating, the replacement gear set will rotate, so the pin that fixes the dividing disc to the head body must be loosened.

Figure 4.5: Diagram of spiral groove milling process

Figure 4.6: Rotating the machine table when milling spiral grooves on a horizontal milling machine

The graduation and the handwheel locking pin of the graduation head must be inserted into the hole of the division disc.

When milling multiple helical grooves on the same shaft, after finishing the first groove, remove the locking pin and perform normal division to mill the second groove. Do the same until all the grooves are finished (for example, when milling helical gears).

Step 7: Finish

Check all dimensions one last time then disassemble the product.

2.2.5. Types of failures, causes, and prevention

Failure mode	Reason	Prevention
1	Wrong twist direction	- Wrong gear bridge installation Incorrect axle number	- Reinstall the gear bridge
2	Incorrect twist angle	- Calculate the wrong gear ratio - Select gear with incorrect calculated number of teeth	- Recalculate - Select the correct number of teeth of the calculated gear
3	Groove side roughness not achieved	- Selecting the wrong cutting mode - Dull knife - Technology system vibration	- Reselect mode - Replace or sharpen the knife - After moving the machine table to the next tooth groove, tighten the machine table brake levers in the vertical and horizontal directions. back

2.3. Organizing skill training

1. Exercise

Milling right spiral groove on workpiece with size Ф26, L=200; α=15 0 ; B=6; H=3

Requirement: 2 students/1 product

2. Implementation sequence (implementation process table)

Steps to take	Instructions for implementation
1	Step 1: Calculate the parameters of the spiral groove	- Average diameter: d = 26 – 3 = 23 - Twist length L = п.d.cotgα L = 3.14 x 23 x cotg15 0 = 3.14 x 23 x 3.732 = 269.66
2	Step 2: Calculate the gear ratio i	i  N . T  40.6  0.89  8  100 40 L 269.66 9 50 90
3	Step 3: Install the gear bridge	- Gear z 1 = 100 is tightly mounted on the vertical lead screw shaft of the milling machine table - Gear z 4 = 90 is tightly mounted on shaft IV (sub-shaft) indexing head - Gear z2 = 50, z3 = 40 is mounted on the intermediate shaft as shown in the diagram below.
4	Step 4: Select cutting mode	- Cutting depth t = H = 3 mm - Feed rate S= 40 mm/min - Number of main shaft revolutions n=500÷600 rpm

Step 5: Mount the workpiece onto the machine

- One end of the workpiece is clamped into the 3-jaw chuck of the indexing head, the other end is against the center of the indexing head's tailstock, or both ends are against the center transmitting the torque by clamping speed.

- Check radial runout and end face runout of the workpiece

Step 6: Adjust the machine

- Adjust the tool center to coincide with the center of the workpiece as when milling a straight groove on the shaft.

- Take the cutting depth t=3mm to cut the first spiral groove, then return the knife to the original position and perform the second groove cutting division (if any) similar to cutting the first groove...

- When adjusting the spiral groove cutting machine, be careful to ensure the safety of the gear bridge and the operator.

Step 7: Finish

- Final check of dimensions

together before removing the product

2.4. Self-study

1. Calculation for milling right spiral groove on workpiece with size Ф38, L=200; α=15 0 ; B=8; H=4

2. Calculation for milling right spiral groove on workpiece with size Ф38, L=200; α=25 0 ; B=8; H=4