FENG Xiofei，ZHENG Weigng

a．School of Energy And Power Engineering;b．Engineering Training Center，Wuhan University of Technology，Wuhan 430063，China

1.Introduction

Follow rest is one of attachments of lathe，generally fixed in the lathe saddle and moves following behind in turning tool when turning，to withstand cutting force on the workpiece［1］．As slender shaft worse stiffness，turning is more difficult，especially turning that does not allow being connected to the knife in the middle，so follow rest should be used to clamp the slender shaft［2］．If follow rest is used to support slender shaft，which can enhance its strength and rigidity，effectively prevent the bending deformation of the workpiece，and ensure the quality of the processing．Wear of supporting claw of follow rest is one of the common faults in the turner production．Follow rest usually has two types of two claws support and three-jaw support，and based on the three-jaw follow rest to put forward and improve a new follow rest to extend the life in the turner production，thereby improve economic efficiency．

2.Analysis of the present

From the principle of follow rest point of view，Just two supporting claw is ok due to total cutting force makes workpiece abutting against with two support claws on the follow rest when turning．However，in actual use，especially turning elongate shaft，the workpiece itself is with a downward gravity，while the workpiece is inevitably somewhat curved．Thus，the workpiece tends to generate vibration due to centrifugal force instantaneously left supporting pawl．If use three-jaw supporting，workpiece can not be moved up and down，left and right，in addition turn stablely and difficult to produce vibration［3］．Though threejaw follow rest supporting and turning slender shaft is an important measure，but at the same time supporting claw wear is inevitable，so it can be better used in turning operations for three-jaw follow rest for design and improvement

The material of supporting claw of three-jaw follow rest is usually ductile iron，and the material of machining shaft are usually ordinary carbon steel，high-quality carbon steel，alloy steel．As supporting pawls，ductile iron directly contact with the material，and the major axis of the processing of high-speed rotation caused severe wear of supporting pawls due to the greater coefficient of friction between the cast iron and steel，and its top end close to the conical supporting pawls before it is worn，but concave seriously after wear，as shown in Fig．1．At present in order to respond to such a support claw wear mainly continuously poured oil cooling and lubrication，and continuously adjust the position of follow rest supporting pawls to ensure the concentricity of the workpiece and avoid the generation of the shape error in the turner production ［4］ ．However，ductile iron support claws still continue to wear，which causes great inconvenience to the turner production．As can be seen in Fig．1，each supporting claw wear is different，so it is necessary to be adjusted regularly when turning，which also causes some machining accuracy of shaft parts even scrapping．

Fig．1 Wear of follow rest support claw

3.The improvement of follow rest

3.1.Improvement scheme

According to follow rest support claw wear，put forward improvement measures．In supporting claw front end features rolling bearings instead of ductile iron to contact with axial workpiece．Supporting claws and tool jointly clamp a workpiece．In order to improve stability when turning，the front end of each support claw is provided with two rolling bearing，interaction，supporting pawls after the improvement shown in Fig．2．Bracket assembly instead of the ductile iron block in supporting pawl tip，two rolling bearings 3 mounted on the bracket 1，the pin 2 passes through the bearings and gaskets 5，and the pin ensures the stability of the bearing in the longitudinal position as the gasket ensures bearing not from side to side，and then screw 4 fixed pin．

Fig．2 Diagram of support claw after improved of follow rest

3.2.Characteristics of follow rest that improved

1)Change sliding friction to rolling friction．The rolling friction is hinder that is generated when an object rolls(or scroll trend)along the other object surface against objects rolling，and rolling instead of sliding can greatly reduce the frictional resistance［5］．Rolling bearings together with the workpiece are doing rotational movement when workpiece is whirling，which changes the sliding friction to rolling friction，reduces the coefficient of friction as a result of reducing friction and wear．Besides damage to the workpiece is also smaller，thereby overcome wear problem of ductile iron block in supporting claw front end before improved．

2)Double bearings．If single bearing，the contact area is small and small pressure roles in the workpiece，and reach less than ideal results．Therefore it can increase the contact area and act the workpiece sufficient pressure to use double rolling bearings，and ensure the accuracy requirements when turning．

3)Increase the allowed speed of the workpiece and improve the processing quality．Follow rest before Improved when turning，due to the wear of supporting claws，with the result regularly adjust ductile iron block in supporting claw front end so as to guarantee a stable turning．After improved，rolling bearings together with the workpiece do rotation with minimal wear and can be allowed high-speed rotation of the workpiece，which makes it achieved to turn slender shaft parts at high-speed．

The bracket assembly that improved is mounted on the adjustable sleeve of follow rest，and the structure diagram shown in Fig．3．

Fig．3 Diagram of follow rest after improved

4.Conclusions

Improved follow rest applied to turning operations，proven，to good effect in overcoming supporting claws wear before improved while is also able to meet the accuracy requirements，improve processing efficiency．The application of this program to improvement of lathe centre rest is equally applicable．

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