Unit 046: Advanced Milling

Spiral or Helix milling

Starter activity

Can you recall from previous lessons the four

types of indexing used with Dividing Heads?

Indexing

From the starter activity you should have:

• Simple

• Direct

• Angular

• Differential

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What is a helix

How would you describe a helix?

A curve on a cylindrical surface which would become a straight line if the surface were unrolled into a plane.

• What else can this be called?

• What else does this remind you of?

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What else could a Helix be?

5

You know this dimension as the what?

When Spiral or Helix milling, this is more accurately known as the “Lead”

What else could a Helix be?

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On a screw thread, such as the drive on a milling machine, this is also known as the “Lead”

Spiral (helix) milling

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Spiral milling

To be able to do this accurately you need to do the following:

• Turn the dividing head through 360°

and

• Move the work forward a specific amount at the same time.

To do this you use a drive chain connected to the table of the Universal Milling Machine.

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Spiral (helix) milling

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Spiral (helix) milling

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Drive gear system

Setting up the Dividing Head you need to include four drive gears and they must rotate the work a specific amount. The is a formula we use:

Lead of the machine = Gear on table lead screw

Lead of the Helix to be cut Gear on dividing head

Lead of the machine is given as = 40 x lead of the table feed screw

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Easy way to remember

There is an easy way to remember:

Driver

Driven

This means the ratio on the right hand side

• Leadscrew - Driver

• Dividing head - Driven

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Easy way to remember

There is an easy way to remember:

Driver

Driven

This means the ratio on the left hand side

• Lead of the machine - Driver

• Lead of Helix required - Driven

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Drive gear system

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Driving gear A

Driving gear B

Driven gear C

Driven gear D

Drive gear system

Lead of the machine = Gear on table lead screw

Lead of the Helix to be cut Gear on dividing head

What can you see in this formula regarding basic maths?

• Basic ratios

On the left side of the formula the Lead of the Machine is directly proportional to the Lead of the Helix.

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Drive gear system

Lead of the machine = Gear on table lead screw

Lead of the Helix to be cut Gear on dividing head

So what would this mean to the right hand side of the formula?

• Both sides of the formula should be the same ratio

On the right side of the formula the Gear on the dividing headis directly proportional to the Gear on the milling machine.

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Drive gear system

Lead of the machine = Gear on table lead screw

Lead of the Helix to be cut Gear on dividing head

An example:

The Lead of the machine is 100mm and the Lead to be cut is 25mm

100 mm = 4 = 4

25 mm 1

What should the ratio of the gears be?

–4/1 or 4 17

Drive gear system

Lead of the machine = Gear on table lead screw

Lead of the Helix to be cut Gear on dividing head

An example:

We know the ratio of the gears needs to be 4/1, we need to use four gears (A, B, C & D).

4 = A x C 4 = 40 x 10 4 = 400

1 B x D 1 10 x 10 1 100

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Drive gear system

Lead of the machine = Gear on table lead screw

Lead of the Helix to be cut Gear on dividing head

An example:

From this we can see the left hand side of the formula is exactly the same ration as the right hand side.

100 = 40 on gear A x 10 on gear C

25 10 on gear B 10 on gear D

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Ratio 4:1 Ratio 4:1

Drive gear system

Lead of the machine = Gear on table lead screw

Lead of the Helix to be cut Gear on dividing head

An example:

The Lead of the machine is 130mm and the Lead to be cut is 35mm

130 = 3.71 > 130 = A x C > 130 = (26 x 5) x (20 x 5)

35 35 B x D 35 (7 x 5) x (20 x 5)

130 x 100 > 1300 = 3.71

35 x 100 350

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Assessment for learning

You need be able to know how to describe how to set up a dividing head for spiral milling

Completing MILL WS044 will help reinforce your knowledge on the topic?