Wood lathe chuck size template

This is for @geek2nurse and any other woodturners out there.

When preparing a tenon or mortise to mount a workpiece onto a chuck, the best possible fit is when the chuck jaws are nearly closed. This is the only point at which the chuck jaws form a perfect circle. Since the mortise or tenon on the blank is also a perfect circle, the wider the jaws go, the smaller the area of contact between the jaws and the wood. More surface contact == more safety so you don’t want to eyeball these. Or at least not until you have enough experience that eyeballing doesn’t put you at risk or waste your money. Which is why a template comes in handy. Fast. Accurate. Safe. Repeatable.

The chuck can compress onto a tenon or expand into a mortise and this template accounts for both. The template also provides Min/Max versions because a little wiggle room is very handy. Make the tenon oversized and sneak down until the template fits, or make the recess undersize and sneak up. You can’t run the lathe in reverse and put wood back on, after all.

I have Nova chucks so this is sized according to the Nova Accessory Jaws manual recommendations for minimum mortise and tenon sizes with the standard 50mm jaws supplied with most packages.

If using with any other chuck or jaws, please be sure the sizes are within spec for those specific jaws!

Please do not use while workpiece is spinning! If tempted to use the pointy bits to mark the mortise, it tends to melt the acrylic. And measuring while spinning is just asking for trouble.

The template has a hole so it can be hung on the lathe. I buy net release magnets and toss out the lanyards. That leaves two magnets with split rings you can attach to templates, hex wrenches, etc. to stick 'em right to the lathe. As a rule I avoid lanyards, cords, wires, or anything like that around the lathe and the net release magnets without the lanyard are perfect for this.


Also, try painting the text with a contrasting color before removing the backing paper.

If this is useful, I have 100mm and 130mm versions I can post. For folks with other size jaws I’d be happy to make templates in other sizes.

Sizing in this template
Mortise: 51.25 min - 56.25 max (Manual says 50mm - 60 mm)
Tenon: 45mm min - 50mm max (Manual says 45mm - 65 mm)

Score lines for Hershey text are black.
Cut lines are red and blue so you can turn off the blue if you don’t need the hole.

50mm Chuck Template


Huh this an interesting design. I think I see what you’re doing here, but it would be cool to see the tool in action. Got any pics of it in use?


Nice tool, thanks!!!


No but I might be able to illustrate. Here’s a platter I just finished. I used Nova Titan jaws which are larger than the template I’m showing in the photo, but I don’t have a template for those yet.

But you should be able to see in the photo how the mortise (the recessed hole in the center) sizes up to the template. If I were using the 130mm jaws I’d want those size guides to be a snug fit. The chuck jaws seat into the bottom of the recess then expand into it to hold the workpiece.

Sometimes you want a tenon which is the opposite of a of a mortise. The tenon sticks out and the jaws seat onto a shoulder around the tenon then contract onto it. After the piece is shaped and finished inside and out the tenon is removed. That’s whats happening in the photo below. I used a tenon because the wood was punky and soft and expanding into a recess would likely have split it.

When I made that bowl I used the concave part of the template to gauge the size of the tenon. That’s sized for the small jaws and I would have used the template posted at the top of this thread to measure it.

And in case anyone was wondering, here’s how I use the net release magnets. The two yellow magnets attached to the hex wrench and the template are the A and B sides of a single net release magnet set.


Thank you. I just got my husband his lathe a couple of weeks ago. He’s learning and i will show him this. I ended up getting him the JET 1221. The bowls he’s made so far look great, each one looking better. Yesterday made one of mulberry that was beautiful. We live out in the country so getting wood is NOT an issue:-) Burn wood for heat so he’s even used some of his wood pile to make one. So far has made one of walnut, 2 cedar and 1 mulberry.
If anyone wants to share what they like to turn, I’m sure he’d love to know. There’s someone local who does some turning and he’s going to try to watch him.


As of today, yes! I was making a bowl and when I grabbed the template I thought of you and took some new pics. The first two are when I’m making the mortise and the bowl is mounted with the foot out. The last one is after the bowl is turned around and mounted on the chuck using the mortise from the first two pix.

Also, the pic shows why I recommend painting the template before taking the masking paper off. I didn’t paint this one but the lettering started showing up better once it got sawdust in the grooves.