Quick Answer
A combination square set is a versatile tool for mill and lathe setup, letting you check vise squareness, verify head tram, and set tool heights with confidence. For bench-top machines, a compact 6" 4R square like the Starrett 33JHC-6-4R offers the precision and portability you need.
Why a Combination Square Set Works for Setup
A combination square set gives you a square head, a center head, and a protractor head on one blade, so you can handle several setup checks without switching tools. The square head is ground for accuracy, and the blade is rigid enough for most bench-top work.
For mill and lathe setups, the compact size of a 6" junior square is a real advantage. It fits in tight spaces around the vise or chuck, and it is light enough to hold steady while you read the result. The Starrett 33JHC-6-4R has a 3/4" wide, 5/64" thick blade that is stiff without being bulky.
Step-by-Step Setup Process
- Check Vise Squareness: Clamp the square head against the fixed jaw of the vise and bring the blade close to the mill column or table edge. Adjust the vise until the blade sits flush with no gap. Common mistake: forgetting to tighten the vise before checking, which lets the jaw shift. Always snug the vise down before you trust the reading.
- Verify Head Tram: Mount the square in a tool holder or hold it against the spindle. Rotate the spindle by hand and watch the blade for any gap against the table. If you see a gap, adjust the head tilt. Common mistake: checking tram with a dirty or burred table surface. Clean the table and the square before you start.
- Set Tool Height on the Lathe: Place the square across the lathe ways and lower the tool tip until it just touches the blade. Use the square's beam as a straightedge to align the tool with the centerline. Common mistake: using the square's head as a height gauge, which can rock and give a false reading. Use the blade, not the head, for height checks.
Product Facts
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Combination Square Set, 6" 4R, Starrett: The Starrett 33JHC-6-4R is a 6" junior combination square set with a square head, center head, and protractor head, designed for mechanics, toolmakers, and patternmakers. Its compact size and light weight make it easy to maneuver around bench-top mills and lathes, and the multiple heads let you switch from squaring to centering without changing tools.
Combination Square Set, 6" 4R, Starrett