Calipers have many uses in pen turning. They are an important tool.
Many pencrafters would not consider turning pens without them.
One may not use them to measure blanks as they are turned, but they are used for measuring:
- tubes, inside and out, and length.
- bushings, to make sure they are the right order, and match kit properly.
- kit fittings, to verify they are what size you just picked the bushing for.
- drill bits, there are times when you want to know exactly what size it is.
- length of finished blanks, or trimmed blanks, to see if you made it too short for the parts to work right.
- measuring all the small things in your shop that you never knew just what size they were.
- saw blade width
- thickness of an accent strip
- size of a kerf from your saw
- dowel rods
- pen blank thickness / squareness
For some pen crafters, a backup pair is a good idea. If a caliper is dropped, the backup can be uses to carry on until the first is replaced.
Micrometers are more metalworking related. A good dial/digital caliper is usually good for +/- .001 accuracy, check the manufacturer's specifications on this.
AVOID the plastic framed calipers like the plague, accuracy varies, but average is +/- .005-.015 range.
Also, for anyone's calipers out there, if they have not been calibrated and verified to be accurate still, don't bet that they are. A drop in the floor or good flip on the workbench can work ruin.
One advantage of the digital caliper is setting the zero point to the size of the fitting. During turning, the caliper will read the amount of material you have to remove to match the fitting. Place the fitting in the jaws of the caliper and press the "Zero" button. The reading should change to zero. This takes a bit of coordination. Now place the caliper on the barrel. The reading shows how much you have to remove. eg. A reading of .050" means your barrel is .050" larger than the fitting. Make sure the caliper is perpendicular to the barrel where it will read the lowest number.
Also, keeping the little teeth clean, or sliding area can be a factor in accuracy. Burrs on the jaws are a killer. If a caliper is dropped hard, a burr is very likely to occur. Burrs can be gently stoned off, but it is a delicate thing.
Keep a few batteries in stock for the digital calipers - some of the less expensive models do not have a true 'Off' setting and bleed the batteries down continually.
(By Johnny CNC - Edited by Hilltopper46)