Under Sizes Of Reaming

 

Drill size = Reamed size - (Undersize + Oversize)

Finished size :- 

Finished size is the diameter of the reamer.

Undersize :-

Undersize is the recommended reduction in size for different ranges of drill diameter. (Table 1)

Oversize :-

It is generally considered that a twist drill will make a hole larger than its diameter. The oversize for calculation purposes is taken as 0.05 mm - for all diameters of drills.

For light metals the undersize will be chosen 50% larger.

Under Size And Over Size Of Reamer

Under Size Of Reaming
DIAMETER	UNDER SIZE
0 - 5mm	0.1 - 0.2mm
5 - 20mm	0.2 - 0.3mm
21 - 50mm	0.3 - 0.5mm
More Than 50mm	0.5 - 1mm
Twist Drill Over Size 0.05mm