Calculating Starting Sizes for Seamless Tubing
Most producers prefer to calculate the starting size for any seamless tubing application. But for purposes of illustration, here is a hypothetical example. In this case the finished part size is 6.500 inch outer diameter (OD) by 5.000 inch inner diameter (ID), less than 3 inches in length. Let's assume that the tubing is cold drawn and finish annealed (about 950F). In this example, the machining sequence starts with chucking on the outside.
Example IChuck OD Required: Finished part size of 6.500inch OD x 5.000inch ID, cold drawn and finish annealed seamless tubing; finish machined length less than 3 inches. Machining sequence: chuck OD, bore ID, turn OD.
Procedural Steps  Calculations 
Illustrations 

1. Determine critical machining data  L Finished machine size 

2. Determine nominal 0D  2. Maximum finished Add tolerance (6.500") Add cleanup (+ 0.023 ) allowance (+ 0.080) NominalOD (6.603") 

3. Determine intermediate tube ID (before eccentricity adjustment) 
3. Minimum finished ID = 5.000" Subtract tolerance (0.040) Intermediate = 4.960" 

4. Determine minimum wall required 
4. Nominal 00= 6.603" Subtract intermediate ID ( 4.960") = 1.643" (twice minimum wall) Divide by 2 to get minimum wall =0.822" 

5. Determine eccentricity allowance factor (F.) 
5. Applicable wall thickness tolerance = ± 7 1/2%
F_{e }= 1.00 (wall thickness tolerance) 

6. Determine nominal average wall 
6. Min. wall/F_{e } (0.822"/0.92 ) =0.888" 

7. Determine nominal tube ID (eccentricity adjustment is now included because of step 6) 
7. Nominal tube 0D = 6.603" Minus twice nominal average wall = 1.776" Nominal tube ID= 4.827" 

8. Tube size to order when machining true to OD 
Use nominal tube dimensions 

Ordering size: 6.580" 0D (+0.23"  0.000") x 0.888" average wall (±7 1/2%) 