Pen Blank Cut Length Calculator from Tube Spec

Pen kit instructions tell you the tube length. They don’t tell you how long to cut the wood. That is the gap this calculator fills: give it the tube length from the kit sheet and it returns the blank length to set your saw to.

The formula.

Blank length = Tube length + (2 × tolerance)

Where tolerance is the amount of wood you leave on each end to turn down to the tube. Standard tolerance is 1.5 to 2 mm per side (about 1/16 inch), enough that you can chuck the blank in the lathe, true it up, and not run into the tube during initial turning.

Most kits have two barrels, and they are rarely the same length. A Cigar’s two tubes differ by more than 5 mm. Enter both and the calculator sizes each barrel separately and tells you how much stock the pair needs, kerf included.

Why the tolerance matters.

If you cut your blank to the exact tube length, when you chuck it between centers and start turning, you almost immediately expose the tube. The wood near the tube edge is fragile and chips out at the moment the tool touches it. Result: blowout, ruined blank, start over.

Conversely, leave too much (say 5 mm per side) and you’ve got a lot of unnecessary wood to remove during initial truing, and the heavy off-center mass causes vibration in the lathe. The blank will turn less smoothly and finishes will show chatter.

Tolerance by skill level:

Tube length for common pen kits:

Always verify against your kit’s actual instructions. Kits change without notice and the listed lengths drift. The figures here are indicative, and the kit sheet in the box wins over any table on the internet, including this one.

Cutting strategy.

The biggest source of error in barrel length is not the saw, it is where you measure from. Two pieces of advice:

1. Measure twice, mark the blank in pencil, then cut on the pencil line. Don’t try to stop at a length on the saw fence alone; align your mark with the blade.

2. Cut both ends square. A blank that’s not square at the ends won’t sit flat on the assembly press, and the resulting pen will have the cap and body slightly misaligned, which is visible immediately.

For chop saws and miter saws, sacrificial fences (a piece of MDF clamped to the fence) prevent tear-out. For band saws, slow feed rate is the key.

Drilling the blank after cutting.

Once cut, the blank is drilled to accept the tube. Drill bit size by tube outer diameter:

Drill straight. Pen-turning specific drill bits with parabolic flutes are worth the price. Use slow speeds (700-1200 rpm for hardwood, 500-800 rpm for resins and acrylics) and clear chips often.

A note on tube glue and surface prep.

The cut tube length affects glue bond. Tubes that are not deburred shed copper or brass filings into the epoxy, which weakens the bond and shows as dark specks under translucent acrylics. Run a deburring tool or even just a fine file around the tube edges before gluing. Twenty seconds per tube, much cleaner result.

For segmented work.

When you’re building a segmented blank from multiple species of wood, the tolerance budget changes. Each segment has its own kerf loss and glue line. Total stack length matters more than individual segment cuts. Tighter tolerances and a final disc-sander truing pass before drilling is the typical workflow.

Storing pre-cut blanks.

Pre-cut, pre-drilled blanks make a lathe session faster, but resin and wood move with humidity. Keep cut blanks in a sealed bin with a desiccant pack if you’re prepping ahead by more than a few days. Otherwise, expect to have to re-true them on the lathe before the tube glues in cleanly.