Round workholding solutions

CNC Machines Nomad
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Hey all, I’m looking for some good round workholding solutions. I’ve got some projects that will require some 2-sided machining of cylindrical stock and I’m brainstorming ways to center different size round stock on the machine repeatedly and use the Nomads center location as my zeroing point for X & Y.

After looking around it doesn’t look like there’s already a vise/chuck for this specifically, although maybe i’m not searching for the right keywords. I’m thinking of something like a lathe chuck that can be precisely mounted in the center of the nomad. Something like this but smaller and low profile enough to not take up the entire working area:
NBK10_PT8

I’ll post what I can find here. Let me know if anyone else has found any alternative solutions.

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I think you got the sticking point - low profile. Not sure what your accuracy requirements are, but a set of small V blocks in a low profile vice perhaps?

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Ya something like that could work. I ordered a super cheap mini lathe chuck to experiment with. We’ll see how it goes

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A little more information about what the size of the stock, orientation, and so on, would help.

For example, if the stock is a disk 150mm in diameter and 30mm thick, the options will be different than if it is a 5mmdia rod 20mm long being mounted axis vertically, or a 10mm dia, 100mm long rod mounted axis horizontally.

Also, the final product matters, as if there are features being machined in (or than can be machined in and further machined later) that can be used for position and alignment, that is much easier than if the stock needs to be located as a featureless, mathematical cylinder.

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I wonder if a made up set of Cole Jaws would work. You would have to work out how to attach it to the baseplate but they are a lot lower profile than a normal lathe chuck.

Another alternative would be a Longworth Chuck which you could make on the Shapeoko

Google is your friend for more info and there are plenty of DIY instructions out there

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Finally get to put my BFA in Ceramics to good use…

Look up the Giffin Grip. It’s a tool that is used to center leather hard pottery on the wheel for trimming, using the same principle as the Longworth chuck mentioned in the last replay. The product itself is way too big for a Nomad, but as you can see in this exploded parts diagram, it’s a fairly simple mechanism that could be designed & scaled down in CAD and machined with a Nomad. But, it’s very low profile and you can make the sliders whatever size or shape that fits your stock best. The Giffin Grip, as is, was not made with very tight tolerances as it was designed for a dusty, crusty working environment, but you can make your as tight as you want. Also, the Giffin Grip relies on friction and rotational inertia to stay closed. You will obviously need to have a sturdier locking mechanism than that.
giffen

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This will generally be used with cylindrical stock around 2 inched wide or less. The heights will vary, but the tricky part will be gettin precise re-alignment with double-sided machining.

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That giffin grip looks bizarre! Never seen one of those. Definitely worth looking into though. I imagine a super slim version out of metal with some tight tolerances could be fairly precise.

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(presuming that you are planning to hold the material axis vertical)

The giffin grip is pretty much a soft grip, lowish precision three jaw scroll chuck. A neat implementation.

Any three scroll chuck is going to be ok, but not great, at precise centering, and you still need to address angular alignment unless the pieces are rotationally symmetric.

The workholding here has so many options, many of which depend on the particular geometry, that it is tough to give a simple answer.

For repetative, or nearly so, work, I would make a fixture to hold the part that can be mounted to the wasteboard or to the vise alignment holes in the bedplate. Dowel pins or shoulder screws for alignment will get you within 0.01 or 0.02mm on each position. The key things is machine it on the nomad in position.

Two hard points and a screw will provide location for the part. If the work needs to flip instead of the fixture, if the fixture is machined in place alignment should be fine.

If the work has holes that can be used for alignment, that is a real good way to go. Hole in the wasteboard and a dowel pin for alignment. Again, the position will be precisely known, as it will be positioned by the machine itself.

If there is no easy way to hold the work after flip, machine a pocket (a negative of the top of the work) to seat it into for the bottom side machining. Again, this gives precise positioning with reasonable ease.

You can mount jaws to the wasteboard or bedplate several ways. Mount two bars to the bed with a small gap between them at the center of the bed. Machine the profile of the work to span them, loosen one to mount the work. If the profile is machined into the bars a little bit small, when the bars are tightened down, they will grip the work.

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Have you thought about a small set of v-blocks? These are 1", I’ve seen others. A little flat filed on the end of the stock makes for a decent flip reference with square.

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