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Why setup tools come before more machines
A machine can have good castings, a strong motor and a fancy fence and still cut poorly if its parts do not line up. The blade must be parallel to the miter slot, the fence parallel to the blade, a jointer's tables flat and level with each other, and a bandsaw's wheels in the same plane. Few of those checks can be done by eye, and a cheap wooden or plastic ruler is not accurate enough to do them.
The tools you need are modest and last for decades. They pay back in every project because every cut starts from a better machine. They also make buying decisions better: if you can measure a used machine's table with a straightedge, you can tell a flat table from a dished one, a point the site's machine table flatness page and its fence alignment inspection page cover.
The alignments themselves, and the allowed tolerances, come from the manual for each machine. Use this guide to choose tools, not to set numbers. If a machine has no manual, look at the operator manuals page or ask the maker.
The straightedge: flatness and line-up
A straightedge is a tool used for checking straightness, as a general reference puts it, and the machining trades use it to check the flatness of machined surfaces. In a woodshop it tells you whether a table or a bed is flat along its length, whether a fence face is straight and whether two surfaces, such as a jointer's infeed and outfeed tables, line up. On a bandsaw the same reference describes laying a straightedge across the wheels to check that they are coplanar.
Buy one long enough for the work. A short rule cannot check a long jointer bed, and a long one is clumsy on a small drill press table. Because a straightedge is your reference, it has to be good. The reference notes that three straightedges can test each other, though that does not control twist, and that accurate calibration needs a surface plate, which most hobby shops do not own. In practice, compare a new straightedge with another one you trust, flip it end for end on a flat surface and watch for gaps.
A straightedge does not give a number. It shows where there is a gap, and you read the size of the gap with a feeler gauge or a thin shim. Used with a light behind it, it reveals gaps the eye would miss. See jointer knife setting jigs for a related setup tool, and the jointer size guide if you are choosing the jointer itself.
Precision straightedge
Choose a length that suits your longest table or bed, and read the stated flatness or accuracy in the listing. Used precision straightedges are common on eBay; check the edges for nicks and ask for photos of the full length.
Squares: right angles on tables, fences and blades
Squares check angles. A machinist's or engineer's square has a blade and a stock that are ground to a right angle, and it is the better tool for setting a saw blade square to the table or checking a drill press table against the quill. A combination square is more versatile for marking and depth, but is not usually accurate enough for the finest setup work.
Check any square before you rely on it. A simple check is to hold the square's stock against a straight board edge, draw a line along the blade, flip the square over and draw again, and see whether the two lines match. If they diverge, the square is out. A square that fell on the floor is worth checking again.
Use a square for blade tilt stops, fence faces and drill press tables. For the angle setting itself, many saws have a stop, but the square tells you whether the stop is right. The site's table saw rip fence not square post shows where a square fits into diagnosing fence problems.
Machinist square
Compare the stated accuracy, blade length and construction in the listing, and choose a size you can hold against the blade or the table. Solid, one-piece or hardened squares are easier to trust than light stamped ones.
The dial indicator: small differences and runout
A dial indicator turns a tiny movement into a visible needle swing. A general reference describes indicators as instruments that measure small distances and angles and amplify them so they can be seen. The probe moves along its axis, and a gear train turns the needle against a zero setting. The reference also distinguishes dial test indicators, which measure angular displacement and are affected by cosine error if the lever is not parallel to the surface.
In a woodshop, that means you can check runout on an arbor, flatness across a table, and whether a saw blade or fence sits parallel to a miter slot. It reads differences too small for a straightedge or feeler gauge. It needs a stable mount, so shops pair it with a magnetic or clamp-on base or a purpose-made jig, and with a way to turn the blade or spindle by hand with the power off.
Start with an inexpensive indicator and a sturdy base, and learn how it behaves. Read the resolution and the range in the listing; the reference gives a wide range of graduations on different models, so choose one suited to woodworking tolerances in your manual. A cheap indicator with a wobbly base will not help; a good base is half of the tool. Dust and glue shorten the life of any gauge, so store it in its case.
When you are chasing a specific problem, the indicator helps you find it. The planer snipe and bandsaw blade drift guides both start with checks that a straightedge and an indicator make easier.
Dial indicator with magnetic base
Check the stated range and graduation, and make sure the base is stable and suits the shape of your machine table. Used indicators are fine when the needle moves freely and returns to zero.
What to buy first, and how to check it
| Order | Tool | What it checks | Check the tool by |
|---|---|---|---|
| 1 | Straightedge | Flatness, table and fence line-up | Comparing against a second straightedge, flipping it |
| 2 | Machinist square | Blade and table squareness, fence faces | Drawing a line, flipping and comparing the two lines |
| 3 | Dial indicator and base | Runout, parallelism, small height differences | Checking it returns to zero and reads consistently |
| 4 | Feeler gauges | Size of gaps under a straightedge | Keeping them clean and flat |
| 5 | Combination square and rule | Marking, depth, quick checks | Occasional comparison with your best square |
Keep a note of every measurement and adjustment with the date. A simple record helps you see drift over time, and the site's equipment recordkeeping guide shows how to keep one. If an adjustment is beyond your tools or the machine's design, a technician is the next step; see when to hire a machinery technician.
The tools are the same whether you own a new saw or a vintage machine. For old iron especially, a straightedge and an indicator tell you what the machine can still do. Buy the best straightedge and square you can afford, because every other adjustment depends on them.
Frequently asked questions
What tools do I need to align a table saw?
A reliable square, a dial indicator on a stable base, a straightedge and feeler gauges cover most of it. Follow your manual for the procedure and tolerances.
Do I need a dial indicator?
Not at first. A straightedge and square handle many checks. An indicator helps when you need to measure small differences, such as runout or parallelism.
How do I check a square?
Hold its stock against a straight board edge, draw a line along the blade, flip it over and draw again. If the lines do not match, the square is not true.
How long should a straightedge be?
Long enough for the longest table or bed you check. A short one cannot judge a long jointer bed.
Can I trust the tools I buy new?
Check them before trusting them. Compare against another reference and make sure they return to the same reading.
Sources and verification
- Wikipedia: Straightedge (a general reference), for the definition, use in checking flatness of machined surfaces and the notes on checking a straightedge against others.
- Wikipedia: Dial indicator (a general reference), for how dial indicators and dial test indicators work, cosine error and the range of graduations.
- Wikipedia: Band saw (a general reference), for checking bandsaw wheels with a straightedge.
No tolerances, accuracy grades or alignment procedures are quoted. The buying order and the flip checks for squares are practical shop guidance, not a standard. Confirm every adjustment and tolerance in your machine's manual.