Machine Screws | Fixed Fastener Tolerance

	Fixed Fastener Tolerance
	Date:


Notes

1. The default tolerance split between the clearance and tapped holes is 50/50.
2. The threaded hole is generally considered harder to produce.
3. A 60/40 split, giving more tolerance to the threaded hole, is often used.
Thread Properties
Des			thread designation
d		mm	nominal thread diameter
p		mm	thread pitch
P_T		%	percent of positional tolerance allocated to threaded hole

Clearance Hole Properties

FIT			clearance hole fit
H_nom		mm	nominal clearance hole diameter
T_S,H		mm	clearance hole size tolerance
Results

T_P,T		mm	positional tolerance of threaded hole
T_{H,T ±}		mm	horizontal tolerance of threaded hole
T_{V,T ±}		mm	vertical tolerance of threaded hole
Results

H_MMC		mm	minimum clearance hole diameter (MMC)
P_H		%	percent of positional tolerance allocated to clearance hole
T_P,H		mm	positional tolerance of the clearance hole
T_H,H ±		mm	horizontal tolerance of the clearance hole
T_H,V ±		mm	vertical tolerance of the clearance hole

Directions

These calculators are designed to resemble spreadsheet calculators that can be printed as reports for project recordkeeping. The term project, with regards to these calculators, may refer to an engineered design, homework problem, tutorial problem, hobby design or self-study. The workflow for each calculator is from top to bottom.

Select the thread designation
If user defined, enter the nominal thread diameter and pitch
Enter the percent of tolerance allocated to the threaded hole
Select the type of fit applied to the clearance hole.
IF user defined, enter the nominal diameter and size tolerance
Press the calculate button.
Print a report for your project recordkeeping by pressing the print button.

Assumptions

Sound manufacturing practices are used to make the holes.
Mating surfaces are parallel.
Hole axes are normal to mating surfaces.

Equations

Minimum Clearnce Hole Diameter (MMC)
$$H_{MMC} = H_{nom} - T_{S,H}$$
Positional Tolerance of Threaded Hole
$$T_{P,T} = \frac{P_T\left(H_{MMC}-d\right)}{100}$$
Horizontal Tolerance of Threaded Hole
$$T_{H,T} = \frac{T_{P,T}}{2\sqrt{2}}$$
Vertical Tolerance of Threaded Hole
$$T_{V,T} = \frac{T_{P,T}}{2\sqrt{2}}$$
Percent of Positional Tolerance Allocated to Clearance Hole
$$P_H = 100-P_T$$
Positional Tolerance of Clerance Hole
$$T_{P,H} = \frac{P_H\left(H_{MMC}-d\right)}{100}$$
Horizontal Tolerance of Clerance Hole
$$T_{H,H} = \frac{T_{P,H}}{2\sqrt{2}}$$
Vertical Tolerance of Clearance Hole
$$T_{V,H} = \frac{T_{P,H}}{2\sqrt{2}}$$

Background

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