To get picture-frame rails to the right length, first define which dimension matters—usually the rabbet opening that holds the artwork—then calibrate a 45° cutting setup and use a stop for repeatable cuts. WOOD Magazine’s described table-saw-sled method starts rails 1/8 inch over finished length and removes half that excess at each end. The measurement and setup both matter: a perfectly repeatable cut is still wrong if it references the wrong part of the frame.
Choose the dimension before cutting
“Frame length” can refer to the inside rabbet opening, the outside frame dimension, or a point on the miter. These are not interchangeable. For artwork fit, Fine Woodworking’s framing guide measures to the inside of the rabbet and allows a small clearance; its example adds 1/8 inch in each direction to the artwork dimensions. The guide also says to account for molding width when rough-cutting stock. See Fine Woodworking’s framing guide.
For a 45° frame profile, Fine Woodworking’s May/June 2019 calculation starts with the mat length or width, adds 1/16 inch for an easy fit, then adds twice the distance from the rabbet to the outside edge. At 45°, that rabbet-to-edge distance equals the distance from the rabbet to the miter point. This gives an outside-length calculation; it is not a substitute for deciding the intended inside opening. See Fine Woodworking’s 2019 measurement tip.
Canadian Woodworking cautions against relying only on either the long outside point or short inside point of the miter; its approach uses the middle of the rabbet as the reference. Pick a reference that corresponds to the dimension you need, mark it clearly, and use it consistently for all four rails. See Canadian Woodworking’s mitered-frame guidance.
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Set up a table-saw sled and stop
WOOD Magazine’s July 7, 2017 shop tip describes a dedicated sled for repeatable 45° picture-frame cuts. It uses a plastic 45° drafting triangle to establish the fence angle. The method below reports that source’s procedure; it is not a claim of independently tested accuracy. See WOOD Magazine’s sled method.
- Square the sled base. Align the sled base square to its guide bar before making the kerf.
- Cut a partial kerf. Run the blade about two-thirds of the way through the sled base.
- Attach a rear fence. Add a fence along the rear edge of the sled.
- Set the 45° reference. Position a plastic 45° drafting triangle so its 90° point splits the kerf, then use it to align the fence at 45°.
- Make a matching-width setup piece. Crosscut scrap stock to the same width as the frame rails; use it to position a scrapwood stop.
- Leave the rails long initially. Crosscut each rail to finished length plus 1/8 inch, the oversize allowance in WOOD Magazine’s method.
- Trim to the stop. Place the rail against the stop and make the final miter cut. The source’s procedure removes half of the 1/8-inch excess at each cut, allowing the rail to be trimmed from either side of the blade without resetting a miter saw-style stop.
The stop must locate the rail from the same chosen length reference throughout. If the rail slips, or one cut is referenced from the inside point while another is referenced from the rabbet or outside point, paired pieces can differ even when the saw angle is correct.
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Make the opposite rails match
Picture frames need two equal short rails and two equal long rails. Set the stop once for each pair, cut both pieces against that same stop, and avoid shifting the stop between members of a pair. For a setup where a stop is not practical, mark both rails from the same reference and cut them together only if the workholding and saw procedure safely allow it.
Woodcraft’s framing guidance recommends making a sample frame to check miter-saw accuracy and using a stop block for matching parts. A sample made from comparable stock reveals whether the miters close and whether the assumed dimension produces the intended opening before you commit the finished rails. See Woodcraft’s picture-frame guidance.
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If you are using a miter saw instead
A miter saw can be used for the same basic logic: verify the 45° setting with a sample, establish the chosen length reference, and use a stop block for repeated cuts. Fine Woodworking also describes calculating the outside dimension from the rabbet and frame profile, then using that length to set a table-saw stop. These are alternative setup approaches, not evidence that one saw type is universally more accurate; the sources do not report controlled comparative testing.
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- Check angle first: Cut a sample and close the corners. A gap at the heel or toe signals an angle or setup issue, not necessarily a length issue.
- Check length second: Compare the sample’s opening or outside measurement against the dimension you selected.
- Check stop consistency: Confirm the stop contacts the stock securely and the same face or edge is against the fence for every cut.
Common causes of a frame that misses its target
- Measuring the wrong boundary: Artwork size, rabbet opening, and outside profile describe different dimensions. Confirm the intended fit before setting a stop.
- Switching reference points: Using a long point for one rail and a rabbet-based reference for its mate changes the effective length.
- Assuming the saw reads exactly 45°: A sample frame checks the actual result of the saw and setup together.
- Moving the stop between matching cuts: Even a small change can make opposite sides unequal; cut pairs with one unchanged stop setting.
- Ignoring stock width and molding profile: The outside length depends on how far the rabbet sits from the outside edge, while the inside opening depends on the rabbet itself.
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