Grinding of Lathe Tools

Lathe tools may be ground either by hand or by machines. Hand grinding needs lot of experience and skill. Hand grinding is carried out on off-hand grinding machine. (Precision tool grinding machines are usually set in the tool room of a production machine shop where all the tools are ground on it).

Off-Hand Grinding Machine

It is general purpose grinding machine used for grinding of tools and drills by hand.  Machine is mounted on the floor or on a bench.  It consists of two wheels one coarse wheel and another fine wheel for rough and fine grinding of tools.

Procedure

Procedure of grinding various lathe tools is explained below:

(a) Knife Tool - Knife tool is used for turning and facing operations. The figure "Knife Tool" below shows a tool blank. It has 5 faces at the cutting end, but only 3 of them require grinding. The back (4) surface and bottom (5) surface can be left untouched. The remaining three faces require grinding along two axis each, however they can still be created within three grinding operations. On most tools there is also a fourth grinding operation which is a radius on the tool tip. This radius increases tool life and improves surface finish. The numbered faces in this image also indicate the order in which the three faces are cut .The following sequence of operations are to be followed for grinding knife tool.

(i) Grind the side of the tool by giving required clearance angle

(ii) Grind  the  front  portion  of  the  tool  to  give  sufficient  front clearance angle.

(iii) Grind the face of the tool by giving sufficient angle.

(iv) Give nose radius to get good finish.

(b) Parting-off Tool or Recessing Tool - These tools are used for parting off or recessing operations. Following procedure is to be adopted while grinding a parting off or recessing tool.

(i) Grind one side of the tool, reduce it to the required size, and give side clearance.

(ii) Grind the front portion of the tool to give front clearance.

(iii) Grind the top portion of the tool to provide small back rake angle to promote easy flow of the chips

(c) Forming Tool. Forming tool is used for producing any special or irregular shape on the job. These tools are to be ground as per the desired profile.

(d) Boring Tool. Boring tool is used for enlarging  a drilled hole. Following procedure is to be adopted while grinding a boring tool.

(i) Grind the tool to proper shape so that it can enter the hole easily.

(ii) Grind the front end of the tool giving front clearance angle.

(iii) Grind the tool to primary and secondary clearance angle in order to avoid tool rubbing of the internal surface of the job.

Precautions

(a) Following rules should be observed while grinding single point tools on a bench or on and off grinder.

(b) Never hold the tool unsupported in the hands. Always hold it on the rest.

(c) Do not hold the tool at one place. Move it along the wheel surface.

(d) Never work on grinding machine without goggles.

(e) Apply ample amount of coolant.

(f) The cooling should be continuous or dry for carbide and ceramic tools. Intermittent cooling should never be done because it may develop cracks in the tool bit

(g) While grinding carbide tools, traverse the tool across the wheel face so that there may not be local heating.

(h) For grinding carbide & ceramic tool tips use diamond wheels of 200- 400 grit.