Pin Offset Calculator
Convert rectangular, polar, or bolt-circle pin layouts into drill coordinates, fit-adjusted hole size, edge margin, and angular tolerance for jigs, fixtures, plates, and locating pins.
⚙Job Presets
Load a real shop scenario, then adjust the fields for your plate, pin, fit, and tolerance.
📏Pin Layout Inputs
Pin Offset Results
🧱Selected Material Specs
📚Pin Fit Allowance Reference
| Fit Class | Imperial Hole Change | Metric Hole Change | Typical Fixture Use |
|---|---|---|---|
| Press fit fixed pin | -0.0005 to -0.0002 in | -0.013 to -0.005 mm | Permanent dowel in steel or tool plate |
| Transition fit | -0.0001 to +0.0002 in | -0.003 to +0.005 mm | Accurate locator with light seating force |
| Slip fit locator | +0.0004 to +0.0010 in | +0.010 to +0.025 mm | Removable pin, repeatable fixture setup |
| Loose removable pin | +0.0015 to +0.0030 in | +0.038 to +0.076 mm | Hand templates, rough alignment, dusty work |
🔧Common Pin Size and Layout Guide
| Pin Size | Usual Prep | Good Edge Minimum | Common Application |
|---|---|---|---|
| 1/8 in or 3 mm | Spot, drill, ream | 0.25 in / 6 mm | Small templates, PCB tooling, light stops |
| 1/4 in or 6 mm | Drill 0.010 in under, ream | 0.45 in / 12 mm | Fixture stops and small locating nests |
| 3/8 in or 10 mm | Bore or ream after drilling | 0.70 in / 18 mm | General jig plates and dowel pairs |
| 1/2 in or 12 mm | Rigid setup, pilot, ream | 0.90 in / 24 mm | Heavy fixture plates and repeat locators |
📐Offset Mode Comparison
| Layout Mode | Formula Used | Best When | Shop Check |
|---|---|---|---|
| Rectangular XY | R = sqrt(X² + Y²) | Working from a DRO or plate edges | Verify diagonal center distance |
| Polar radius | X = R cos A, Y = R sin A | Pin is called out by radius and angle | Check quadrant and angle zero |
| Bolt circle | A = start + index x 360 / count | Equal index pins around a rotary plate | Confirm index starts at zero or one |
| Edge datum | Abs X = datum X + offset X | Final coordinates are drilled from edges | Measure edge margin before clamping |
⚒Material and Spec Comparison Grid
| Material | Edge Factor | Drill Stock Before Ream | Pin Layout Note |
|---|---|---|---|
| Aluminum fixture plate | 1.75 x pin diameter | 0.003 in / 0.08 mm | Deburr both faces; avoid raised lips at pin seats |
| Mild steel plate | 2.00 x pin diameter | 0.004 in / 0.10 mm | Good press-fit support when reamed straight |
| Stainless steel plate | 2.25 x pin diameter | 0.005 in / 0.13 mm | Use rigid workholding to avoid work hardening drift |
| Acrylic or wood template | 2.50 x pin diameter | 0.006 in / 0.15 mm | Leave extra edge margin for cracking or grain movement |
💡Shop Calculation Tips
Pin offset are used in the creation of jigs and fixtures. Pin offset describes the distance between a reference point and a target point for the pins that will be placed on a fixture. In creating a jig, determining the exact placement of the locating pins are essential.
If you place the pins incorrect, then the jig will either not be able to be assembled correctly or will allow the workpieces to move within the jig. Pin offset is therefore an essential parameter in the creation of jigs and fixtures in order to ensure that the points of the jig will connect with the workpiece correct. It is essential to understand that pin offset is not the distance from the edge of the fixture to the point of interest.
How to Set Pin Offset for a Jig
Instead, pin offset is the distance between two datum. Many engineering drawings will use polar coordinates to describe the placement of points of interest. However, most milling machine use X and Y coordinates.
It is essential to be able to accurately translate these polar coordinate into X and Y coordinates. If the machine dont translate these coordinates correctly, then the pins will be placed into incorrect location on the jig. The method for calculating the pin offset will depend on the application for the jig or fixture.
Rectangular offset are often used due to the rectangular movement of the machine table. However, if the machine will place components within rotary plate, then the operator will use polar coordinates to calculate the offset for the pins. For instance, if the pins are to be placed within a bolt circle, then the angle and radius for the circle can be calculated with a calculator to ensure that the angles is correct and the workpiece will be correctly positioned within the jig.
One of the last steps is to determine the fit class for the pin and the hole. There are two different type of fits for pins and holes. For instance, a press-fit can be used where the hole is slightly smaller than the pin and the two components are forced together.
A press fit is often a permanent connection between two components. In contrast, a slip fit allow the pin to move within the hole and allows for the pin to be removed for maintenance. A slip fit is often used in jigs when it is necessary to allow the jig to be removed from the workpiece.
Another consideration in the pin offset calculation is the material of the plate. For instance, aluminum plate are often easy to ream but can deform under heavy pressure. In contrast, tool steel will last a long time but will require a rigid machine setup because the tool steel can cause the drill to wander from the cutting path.
Additionally, you should take care in the edge margin of the plate. If a pin is placed too close to the edge of the plate, the plate may bulge or crack. The correct amount of material are necessary to ensure the structural integrity of the jigs.
Lastly, a twist drill should not be used to cut the final dimension of the pin hole. A twist drill is a good tool for drilling holes in the workpiece but is not good at creating a precise cut. Instead, an undersized hole can be drilled and a reamer or a boring head can be used to cut the final dimension of the pin hole.
This tool will allow the cutter to reach the final dimension of the pin and will ensure that the dimension of the hole is perfect round. Using these two tools will ensure that the size of the pin hole match the calculated pin offset for the jig. Finally, another consideration is the resolution of the measuring equipment for the jig.
If the measuring equipment cannot measure the dimension with the necessary precision, then it is impossible to cut and measure the necessary components for the jig. In this case, a safety factor can be added to the tolerance to allow for a margin of error. Adding a safety factor to the tolerance will ensure that the jig component are able to account for potential error.
By following this process, the pin offset for the jig will be accurate.
