Design of Flat Form Tool

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What is form tool?Form tools are intended for producing the desired contour on a work piece by means of a turning operation.

The form tool is used for production work on capstan and automatic lathes in order to ensure

• (a) High production rate.

• (b) Uniform cut shapes on all the parts,

• (c) Accuracy in work piece shape and dimensions.

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Form Tool Materials

Mostly form tools are made up of

high-speed steel, but now, carbide-forming tools are also gaining popularity, owing to productivity being raised by 30-40%.

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Types of Form Tools(a) Circular form tool (b) Flat form tool

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Types of Form Tools continued..(C) Dovetail form tool

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Types of Form Tools continued..

(C) A Radially fed form tool

(d) A Tangentially fed form tool

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Form Tool Geometry

• A form tool should have the proper rake and relief angles so that the metal is cut under sufficiently advantageous conditions.

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Rake angles () are listed below for the form turning of various

materials. Material Hardness (BHN) Rake angle (Deg.)

()

Mild steel Up to 150 25

Hard steel 235-290 12 - 20

Soft cast iron Upto 150 15

Hard cast iron 150-200 12

Aluminum, copper - 20 - 25

Bronze, leaded brass - 0 - 5

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Design of a Flat Form Tool (Using Graphical Method)

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The profile of the work piece is drawn in two views, i.e. the front view and the top view.The basic points of the work piece profile with dimensions L1 and L2 are projected on the axis I-I drawn perpendicular to the work piece axis. The projected points are1’,2’,3’. From point 01 as the center draw circles corresponding to work piece radii r1, r2 and r3.

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Apex of the cutting tool ‘1’ should lie on the work piece axis. From point 1 (the apex) draw the line representing the tool face (F) at the angle =200 and the line of the tool flank (K) at the angle =120.

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From points 1, 2 and 3 draw lines parallel to the

tool flank, (K).

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To construct the cross section of the tool perpendicular to the flank, K (section N – N), draw line L L (perpendicular to the flank, K. From line L L lay off the lengths since the dimensions of the tool profilemeasured along the work piece are equal to the corresponding axial dimensions of the work piece. At lengths draw lines parallel to L.L.Denote by 2” and 3” the points of intersection of these lines with the lines drawn from points 2 and 3 parallel to the tool flank, K.Points 1” , 2” and 3” are the points of the profile of the flat form tool in section N – N.

Design of Flat Form Tool using Analytical Method

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Draw perpendicular from point 2 and 3 on face K of the tool so as to form right angle triangles 1A2 and 1B3

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It will be sufficient to determine the dimensions denoted by P2 and P3 in this figure

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If the dimensions C2 and C3 are known ,dimensions P2 and P3 can be readily determined since they are sides of the right angle triangles.

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Following relations are used to solve right angle triangles:

P2= C2.COS

P3= C3.COS

Dimensions P2 AND P3 should be calculated to an accuracy within 0.001 mm.