# how do you transfer diameter from caliper to cylinder?

I'm trying to transfer a caliper diameter to the end face of a cylinder on my wood lathe. How do I determine that the caliper is centered in order for that diameter to be transferred?

For example I have a cylinder like this:

and calipers like this:

Say, hypothetically the cylinder has a diameter of 10 units. I want to mark the bounds of a smaller, 5 unit circle using the caliper. How would I do that in a way that's precisely centered?

If the question is unclear, please let me know and I can include more info

• Well you generally mark circles with a compass ;-) But because this is spindle turning you wouldn't normally mark a diameter, instead the standard practice is to turn and check, turn and check until the cylinder matches the gap in the cailpers (or anything that can hold a fixed gap and can be slipped onto the turned cylinder from the side, even an open-ended spanner can work). Jun 2, 2018 at 19:41
• @Graphus thank you so much, i really appreciate this. Yes, I understand checking the diameter periodically as Ihollow the end of the cylinder. I use the parting tool. Is there any way that I can mark the diameter witt the placement of the calliper. It would need to be centered, as with a compass. This is tricky to do since one (a human) has to rely on estimating... Any thoughts Jun 2, 2018 at 19:59
• Oh you're hollowing the end, sorry that wasn't clear. For reasonably accurate marking out you need a centre finder to locate the dowel centre (picture shows a commercial one, there are many different DIY versions of this tool that aren't difficult to make to the required accuracy), then a compass for marking the circle you want. If you don't own a compass already if necessary you can make one quite easily, but even the most basic children's compass will work fine and those can be very inexpensive. Jun 3, 2018 at 12:28

## 1 Answer

Spin the piece on the lathe and put a pencil as close to the center as you can. This should draw a small circle. Set a compass to the desired radius (half the diameter). With the piece stationary put the compass's pin in the center of the circle and draw your desired circle.