CustomPartNet
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August 7, 2026
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Updated August 7, 2026
If your part drawing calls out an angular tolerance tighter than a degree, the way a shop verifies that angle matters just as much as the machine that cuts it. Angular features like dovetails, tapered locating surfaces, and inspection fixtures often can't be checked reliably with a protractor alone. Shops rely on sine bars and gauge blocks instead, a combination that turns an angle problem into a length problem, which is much easier to measure with confidence.
Knowing how this works helps you ask better questions when you're comparing suppliers, and it's also just useful if you're setting up the work yourself. CustomPartNet's Sine Bar Calculator and Gauge Block Calculator take care of the trigonometry and block selection so you can focus on the setup itself.
A sine bar is a hardened steel bar with two precision cylinders fixed a known distance apart, most commonly 5 inches or 10 inches. Raise one end by a specific height using gauge blocks, and the top surface tilts to a specific angle relative to a flat reference surface. Since the bar length is fixed and known, the relationship between the height and the angle follows directly from basic trigonometry: height equals bar length multiplied by the sine of the desired angle.
That's a simple formula on paper, but in practice you're usually working with an angle given in degrees and minutes, and you still need to figure out which actual blocks from your set add up to that exact height. This is where the two calculators come in, one for the angle math and one for the block combination.
The Sine Bar Calculator solves the core trigonometric relationship in either direction. Enter your sine bar length and a target angle, and it returns the exact gauge block height needed to achieve that angle. Enter a height instead, and it works backward to give you the resulting angle, which is useful for checking a setup you've already built or verifying a part on the surface plate.
Because the calculator is built around the same standard block sets shops actually use, it also suggests a gauge block stack automatically, drawing from the standard 81 piece imperial set or the 87 piece metric set. That means you're not left doing the second half of the math by hand once you know the required height.
Sometimes you need more control over the block combination than a quick suggestion provides. Maybe a block from the standard combination is missing from your set, chipped, or is being used by a colleague. Maybe you want to add wear blocks to protect your precision blocks from repeated contact. This is what the dedicated Gauge Block Calculator is built for.
Enter a target height, choose imperial or metric, and the calculator finds the optimal combination of blocks from the standard set to reach that dimension. You can also mark specific blocks as unavailable if they're missing from your set, and the calculator will recalculate around them. It includes support for wear blocks, which are typically thin, hardened blocks placed on the outside of a stack to absorb wear from repeated handling, extending the life of your precision blocks underneath.
If you’re logged in, you can also save your set configuration with its specific list of unavailable blocks as a preset, allowing you to reuse the same configuration easily in the future!
Say your drawing calls for a compound angle of 22 degrees, 15 minutes, and you're setting up a 5 inch sine bar to check it.
Step 1: Find the required height. In the Sine Bar Calculator, enter a bar length of 5 inches and an angle of 22°15'. The height works out to roughly 1.893 inches, since 5 multiplied by the sine of 22.25 degrees lands right around that figure. The calculator handles the conversion from degrees and minutes automatically, so you don't need to convert the fraction by hand.
Step 2: Get a suggested block stack. Along with the height, the calculator suggests a combination from the standard 81 piece set, something like a 1.000 inch block, a 0.800 inch block, and a 0.093 inch block wrung together to total 1.893 inches.
Step 3: Adjust if needed. If your 0.093 inch block happens to be missing from your set, switch over to the Gauge Block Calculator, mark that block as unavailable, and target the same 1.893 inch height. It will find an alternate combination that avoids the missing block. If you also want to protect your stack during repeated use, add wear blocks and the calculator adjusts the interior combination to account for the added thickness on each end.
That's the full workflow: one calculator to turn the angle into a length, and one to turn that length into a real, buildable stack of blocks.
If you're evaluating machine shops or precision grinding suppliers for a part with tight angular callouts, it's worth asking how they verify those angles during inspection. A shop that references sine bar and gauge block setups as part of its quality process is telling you something specific about how it holds tolerance, not just that it "checks the angle." Comparing sample parts and inspection reports from a few suppliers, alongside their quoted lead time and pricing, gives you a much clearer picture than pricing alone.
What is a sine bar used for?
A sine bar is used to set up or verify precise angles on a part or fixture. By raising one end of the bar with gauge blocks to a calculated height, the top surface forms a known angle relative to a flat reference surface, which can then be used for machining setups or inspection.
How accurate is a sine bar setup?
Accuracy depends on the precision of the bar itself, the gauge blocks used, and the flatness of the reference surface. A well maintained sine bar and calibrated gauge block set can hold angular accuracy within seconds of arc for smaller angles, though accuracy decreases at very steep angles due to the geometry of the sine function.
What's the difference between the Sine Bar Calculator and the Gauge Block Calculator?
The Sine Bar Calculator converts between an angle and a required height for a specific sine bar length, and includes an automatic block suggestion. The Gauge Block Calculator is a more flexible tool for finding a block combination to reach any target height, with options to exclude unavailable blocks or add wear blocks.
What sine bar lengths does the calculator support?
The calculator is built around the standard 5 inch and 10 inch sine bar lengths most commonly used in machine shops, though you can enter other lengths if your setup uses a different size.
Can I use the Gauge Block Calculator for metric sets?
Yes. It supports both the standard 81 piece imperial set and the 87 piece metric set, so you can work in whichever system matches your shop's equipment.
What is a wear block and why would I use one?
A wear block is a thin, hardened block placed at the ends of a gauge block stack to absorb the wear and contact damage that comes from repeated use. Using wear blocks protects your precision blocks underneath, and the calculator adjusts the rest of the stack to account for their added thickness.
Can a sine bar measure any angle?
Sine bars work best for angles up to about 45 degrees. Beyond that range, small errors in the height measurement translate into larger angular errors, and other angle measurement methods become more practical.
Whether you need a compound angle held to a tight tolerance or a full inspection report to back it up, CustomPartNet can connect you with qualified suppliers experienced in precision machining and grinding. Register for a Free Account → to manage RFQs or browse our supplier network to compare inspection capabilities.