Machining Tolerances

This application help designers and engineers while designing the parts for any type of mechanical device.
The application will give you a tolerance range, equal bilateral, for a especific manufacturing process selected. Turning, Grinding, Broaching, Reaming... up to 12 different types.

  Machining Tolerances.

As a designer of mechanical components, here are a couple of recommendations I do always consider when assigning tolerances:

• It's very important to define a correct dimension composition in your drawing. Avoid having accumulation of lineal dimensions. They will only add variation in your part and in your assembly.
• Tolerance values below ±0.013 are difficult to maintain under regular conditions, even when talking about bearing bores or bearing supports, requesting values below those 0.013 mm tends to be a problem for manufacturing and quality. If you can live with something avove it, your supplier or manufacturing collegue will appreciate it.
• Face to face location in case of bearings supports (shafts or pinion gears) could be in values around ±0.05 mm. 
• Think always in those features that would need to be machined after heat treatment. In general, it is common to use a grinding operation to compensate deformation and to obtain the desired roughness. Depending on the size of the feature, values below ±0.013 can be achieved adding more cost to the part.(again, cpk requirements could be an issue for quality and for the supplier)
• Try to not assign geometric tolerance values lager than feature tolerances, so think twice about the values you define in your parts.
• Use equal bilateral tolerances in your drawings. It will help you with your stackup calculations (comming soon application) and if you are using 3D models, and your manufacturing does also, your parts will be machined centered always.
• Cost of the tolerances:

• General Tolerance values: This this the tolerance table intended to simplify drawing indications and specifies general tolerances in four tolerance classes. It applies to the dimensions of work pieces that are produced by metal removal or are formed from sheet metal. It contains three tables and an informative annex with regard to concepts behind general tolerancing of dimensions. 

         General tolerances for linear measures according to DIN ISO 2768-1

         Table one - Permissible deviations for linear dimensions except for broken    

         edges (external radius and chamfer heights) 

Designation	Description	Permissible deviations for basic size range in mm
		from 0.5# upto 3	Over 3 upto 6	over 6 upto 30	over 30 upto 120	over 120 upto 400	over 400 upto 1000	over 1000 upto 2000	over 2000 upto 4000
f	fine	±0,05	±0,05	±0,10	±0,15	±0,20	±0,30	±0,50	Nil
m	medium	±0,10	±0,10	±0,20	±0,30	±0,50	±0,80	±1.20	±2.00
c	coarse	±0,20	±0,30	±0,50	±0,80	±1.20	±2.00	±3.00	±4.00
v	very coarse	Nil	±0,50	±1.00	±1.50	±2.50	±4.00	±6.00	±8.00

Table two - Permissible deviations for broken edges (external radius and chamfer heights)

		Permissible deviations for basic size range in mm
Designation	Description	from 0.5# upto 3	over 3 upto 6		over 6
f	fine	±0,20	±0,50		±1.00
m	medium
c	coarse	±0,40	±1.00		±2.00
v	very coarse

Table three - Permissible deviations for angular dimensions

		Permissible deviations for ranges of Lengths in mm of shorter side of the angle concerned
Designation	Description	upto 10	over 10 upto 50	over 50 upto 120	over 120 upto 400	over 400
f	fine	±1.00°	±0.500°	±0.333°	±0.166°	±0.083°
m	medium
c	coarse	±1.500°	±1.000°	±0.500°	±0.250°	±0.166°
v	very coarse	±3.00°	±2.000°	±1.000°	±0.500°	±0.333

General tolerances for form and position DIN ISO 2768-2 is for simplifying drawing and fixes general tolerances in three tolerance classes for form and position. By choosing a special tolerance class exactly the precision level common in workshops should be taken into account.

General tolerances for straightness and evenness in mm

		Permissible deviations for basic size range in mm
Designation	Description	upto 10	over 10 upto 30	over 30 upto 100	over 100 upto 300	over 300 upto 1000	over 1000 upto 3000
H		0.02	0.05	0.10	0.20	0.30	0.40
K		0.05	0.10	0.20	0.40	0.60	0.80
L		0.10	0.20	0.40	0.80	1.20	1.60

General tolerances for straightness and evenness in mm

		Permissible deviations for basic size range in mm
Designation	Description	upto 100	over 100 upto 300	over 300 upto 1000	over 1000 upto 3000
H		0.20	0.30	0.40	0.50
K		0.40	0.60	0.80	1.00
L		0.60	1.00	1.50	2.00

General tolerances for symmetry

		Permissible deviations for basic size range in mm
Designation	Description	upto 100	over 100 upto 300	over 300 upto 1000	over 1000 upto 3000
H		0.50
K		0.6-		0.80	1.00
L		0.60	1.00	1.50	2.00

Source : www.huaxing.com
Links to Information:

•  Typical Tolerances
•  Machining Tolerances
•  Cost of Tolerances