3 jaws are quick to set up and almost on centre. Never remove work from it until it’s finished or as you found out it won’t grip in the same position

a 4 jaw would have been much worse as gripping hexogon material in it is not easy to set true, even worse if it has to be removed and later re machined.

If your flywheel was correctly secured in the chuck, drilling. AND. Reaming the bore should leave it without wobble, but probably a faceplate job to get it really true

i can’t exactly understand why you use hexogan fir the axel , how and when does it wobble, with the hex in the lathe chuck or when the flywheel is mounted in the engine?

the axel would probably have been better turned between centres or as a minimum with a large overhang and tailstock support

do a test. Grip a bit of round stock in the 3 jaw, and use a dti to determine the runout. If it is more than sat 5 thou, remove the chuck from the backplate skim a 1/16” off the register. Re mount the chuck and tap it with a soft hammer to get the bar to run true. Mine will grip to 2 thou on all diameters after this treatment, and it’s a cheap polish chuck

But my question why are independent three jaw chucks not available

Bob

Because there's probably not much demand for them, (some-one will now post a link!).

They would be tricky to adjust as moving one jaw would release the work and also require both of the other jaws to be adjusted, and.by a different amount.

They are available Bob, just not particularly popular. Here's an example made by Bison. The type is more complicated to make and therefore pricey. I guess as most people only need them rarely they prefer to spend their cash on something else. Never seen one but I suspect they're less robust than ordinary 3-jaw types.

The old-guys had a type of chuck consisting of a tapped cylinder with three bolts that could be tightened independently to grip and centre the work inside: I imagine they would be a right pain to use. I've an idea they were called 'Bell Chucks' but can't find a reference. Easy enough to make.

Ordinary 3-jaws are usually OK provided the work isn't moved. It's difficult to reset them. I've had mild success marking the job and one jaw to recover the approximate position and turning the replaced work inside the semi-tightened jaws for minimum run-out on a DTI. Not as reliable or as easy to do as using a 4-jaw in the first place.

Recently I did some work needing a job to be moved too and fro between lathe and milling machine a few times. An ER32 collet chuck and Stephenson's Block provided good resetability, and is much faster than a 4-jaw.

Dave

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This one has eight screws [for fairly obvious reasons], but it illustrates the style nicely: **LINK**

https://mb.nawcc.org/threads/do-you-use-this-lathe-attachment-if-so-what-for.126077/

MichaelG.

When I did my apprenticeship we were only allowed to use 4 jaw chucks. You can set up a 4 jaw just as quick as a 3 jaw.

This is a most interesting post. I like that hint about skimming the backplate to improve run out. Never had to do it, but who knows, some day, perhaps?

I did buy a 4 jaw self centering chuck many moons ago thinking it would be better than my 3 jaw, but it is still in the box, never got around to making a backplate for it. Tend to use the 4 jaw independent more and more these days, quick enough to set true. I can get it near enough by eye then use my dial gauge to get it dead on.

Yes ian, it was the "what to do what to do" thread. But it was shown using a 4 jaw self centring chuck, not sure how easy to do it in and independent.

The adept came with a three jaw chuck that took a bit of setting up but could be made accurate.

As regards skimming the back plate I believe the poster was advocating take 1/16th of the register, not just facing the back plate. Then the chuck could be tapped about on its mounting holes to achieve accuracy. Not sure I'd want to ruin the register though.

Plasma