Screws and Dowels
Dowels
Dowels hold parts in perfect related alignment by absorbing side pressures and lateral thrusts.They facilitate quick disassembly and reassembly of tool elements in their exact former relationship.Dowels are precise in their accuracy and in their surface finish.They are made of alloy steels and case hardened to 58HRC.Standard dowels are available in the range of sizes from 1.5mm to 20mm dia, in various lengths.The dowels are made to IT6 grade and are finish ground.The fit between the dowel hole and dowel pin is H7/m6.The surface finish is maintained at N6.The extremely smooth finish reduces the possibility of seizing of the dowel holes.The dowels are driven inside the reamed holes or in jig ground holes.The hole sizes are maintained to H7 tolerance.
Fasteners
The main function of the fastener(sscrews)is to hold or clamp two or more tool elements together in position.The fasteners are divided into two types.
Threaded fasteners
Nonthreaded fasteners.
Threaded fasteners
These type of fasteners include different types of screws and bolts.
Socket head screws
These are used to fasten the plate elements of a press tool.
eg:Punch holder assembly to the top plate.Stripper and die assembly to bottom plate.
counter sunk screws
These are used to fasten elements like nest gauges,spacers,plate stoppers etc.
Cheesse head screws
These are used to fasten sheet metal elements like spring holders,leaf springs etc.
Set screw(grub screw)
These are used to fasten parts which are to be confined with in a hole.eg:spring.
Eye bolts
Eye bolts are used for lifting heavy die sets.It is also called carrier bolts.
Non threaded fasteners
This group includes the elements like rivets and cotter pins.
Rivets
Rivets are used to fasten the support plates of an extension table in press tool.
They are made of mild stel,aluminium,copper or brass.
Cotter pins
These are used to prevent loose parts from coming out of holes.
Screw and dowel position
The components of the tools are held together by screws and are located in position by dowels.A minimum of one screw and two dowels are necessary to position and hold a tool component in place accurately.More screws may be used depending upon the size of the tool but only two dowels should be used for positioning.The size of the screws and dowels are determined by the size the tool.Dowels should be located diagonally across from each other and as far apart as possible to increase locational accuracy.
All screws and dowels should be located from 1.5 to 2 times their diameter away from the die edge.Whereever possible screw and dowel holes should be located nearer to the outer edge of the die block.owel holes are made through holes.So that they can be easy removed.The effective depth for screws should be
- 1.5 times the screw diameter for general application.
- two times the diameter when the element is subjected to shock loads.The dowel engagement length in each plate should be of minimum two times the diameter of dowel.