Pre-Setting 4-Jaw Chucks Hack for Quick Centering

[dbwjbpParticipant @dbwjbp]

Hello all,

I’ve been experimenting with a method to speed up centering round stock in a standard 4-jaw independent chuck and would appreciate the collective wisdom here. The technique involves pre-setting the jaws using the job’s outer diameter, allowing the workpiece to be loaded without trial and error or rotating, and hitting a runout of 0.4–0.6 mm (checked with a dial gauge). It uses a stock manual chuck, no mods or automation, and aims to cut setup time while keeping things accessible for less experienced operators.

Has anyone here developed or come across a similar approach for pre-setting 4-jaw chucks based on workpiece diameter? If so, what’s your process—any specific measurements or tools you use to set jaw positions upfront? How long does your setup take, and what runout do you typically achieve? I’m particularly interested in methods that minimize iterative adjustments or work well in small shops with standard equipment.

I’ll keep the full details of my method under wraps for now as I explore its potential, but I’m happy to share more general info if there’s interest. Thanks for any insights or shop tricks you can share.

Cheers!!

[JasonBModerator @jasonb]

I just eyeball it by looking at the jaws. Wind two opposite jaws in until just touching the work and then look to see if one is further in than the other relative to the OD of the chuck or the concentric rings on the chucks face and adjust until that look the same. Once those two are set position the others to look like they are in the same position.

I can usually get to 0.5mm in under 60seconds depending on how far the jaws needed winding from their previous position and then get the DTI out of final clocking true

Same method works for square stock and even rectangular but you just eyeball the opposite two jaws for each opposite pair of faces

[cogdobblerParticipant @cogdobbler]

.5mm or 20 thou run-out is achievable just by using the circles engraved on the chuck.

Getting from there to 1 thou of run-out takes only a minute or two if you use the methodical approach. IE, measure run-out in line with each jaw , using dial indicator, noting max and min readings. Set the dials 0 to exactly halfway between the two. Then adjust jaws so the dial reads 0 at all four positions. You might have to go around a second time to get that last thou, taking a second minute.

If you have trouble doing this andare doing a lot of different diameters frequently, a spigot held in the tailstock chuck with a set of discs that can be slipped on can be used to set the jaws to the appropriate diameter. You will probably need to dial indicate out the last few thou of run-out.

If doing multiple pieces of the same diameter, after setting the first one true, mark 2 jaws and loosen only those when changing the workplace, and retighten only those 2. The two unmoved jaws will provide consistent location from piece to piece.

 

[Clive Brown 1Participant @clivebrown1]

A very useful aid to centre a workpiece in a 4-jaw independent chuck is a second chuck key. Easily shop-made from mild steel.

[Clive Brown 1]

On Clive Brown 1 Said:

A very useful aid to centre a workpiece in a 4-jaw independent chuck is a second chuck key. Easily shop-made from mild steel.

Even better is a pair of “twiddlers”   ie small chuck keys made from a knurled disc or knob with a piece of square bar inserted in the middle so you can simultaneously adjust 2 opposing jaws.

I have to admit my twiddlers are merely short pieces of 5/16 square key steel bent crudely in the vice at 90 degrees. Done as a “temporary” bodge some decades ago and still in use! But invaluable for quick set up as I described above.

[Neil LickfoldParticipant @neillickfold44316]

The easiest way to set a 4 jaw is having 2 keys with a little round handle. Just to move the jaws at the same time in pairs. Using a plunger type indicator mounted in the tool post can save a lot of time as well. Then when close , tighten with the chuck key for final adjustment.

I have seen in situations where they are rough castings or rough stock, where after the 1st one is set, the screws were marked with nail polish paint, so the radial position of the 2 jaws not being moved again, have a visual reference.

On large chucks, some had stops behind the jaws. The fixed jaws had the stops closed in tight, while the adjustable ones had them placed to make a gap that once opened, could allow the easy removal of the part.

I will often mark the fixed ones with a Red marker pen.

To preset the jaw position, with a rule just measure from the chuck bore, where abouts the jaw will need to be. So with a 60mm piece, and the chuck has a 1 inch bore, set with a rule at about 17.5mm or so from the edge of the inner chuck bore. Another way is to put a nominal pin in the drill chuck , like a 10mm pin, then measure off the radius required less the radius of the pin. So then would set the jaw at 25mm from the pin plus a little to get the piece in there. or look at it as the Diameter of stock -10mm(pin diameter) divided by 2 is the offset.

[Neil Lickfold]

On Neil Lickfold Said:

The easiest way to set a 4 jaw is having 2 keys with a little round handle. Just to move the jaws at the same time in pairs. Using a plunger type indicator mounted in the tool post can save a lot of time as well.

I struggled trying to centre work in a four jaw chuck until I saw a youtube video illustrating the above.  Two keys adjusting opposite jaws at the same time are essential.  With a plunger type indicator used horizontally it’s easy to adjust the front and rear keys to get a central figure on the indicator.  Turn it 90 degrees and repeat for the other two jaws gets very close, repeat again for spot on.

[Chris CrewParticipant @chriscrew66644]

Where possible, I have always opened the jaws wider than the workpiece which is centre-drilled at the axis around which it is to be turned. Then push the tailstock, with a centre in it to hold the workpiece, against the face of the chuck before closing the jaws around it. Push the tailstock clear and, if you want to be more accurate, use a wiggler in the centre-drilling before finally tightening the jaws. If the part has already been turned you can put DTI against it and adjust it to a zero run-out before the final nipping up of the jaws. If the part is too small to abut the face of the chuck place a piece flat or square stock across the face of the chuck between the jaws. You can remove it once the jaws have been tightened. Takes about a minute to do.

[BazyleParticipant @bazyle]

Several people have mentioned round knobs on their keys. I take the opposite view when adjusting things, also eg gib screws, to have an arm that I equate to a clock hand so that I turn it by ‘seven minutes’ hence with opposing jaws can understand how much I have moved one to take up on the other.

[Clive Brown 1]

On Clive Brown 1 Said:

A very useful aid to centre a workpiece in a 4-jaw independent chuck is a second chuck key. Easily shop-made from mild steel.

After seeing this method in a few videos I made a second key. As you say easily made. It did help a bit but it still seems to take me a while to centre a job! 🫤

[Nigel Graham 2Participant @nigelgraham2]

If the work-piece allows I sometimes start the process with the chuck standing vertically on the bench; using the marker-rings and a rule to centre the work as close as I can.

Then with the jaws nipped up, mount the chuck plus work for final adjustments.

……..

How fussy I am with the latter depends on the purpose.

If needing full concentricity with an existing feature such as a machined periphery or bore then I use a DTI.

If not critical, using the tip of a tool almost touching the periphery as a pointer may be close enough: the machining takes care of the important areas.

For very close accuracy on an item already machined all over but difficult to test by indicator, such as for modifying the bore of a gear, then one approach is to use a “nest” turned in a sacrificial disc secured to the faceplate. Conversely, mount the bors on a mandrel protruding through the chuck or faceplate.

…

One snag with setting larger 4-jaw chucks is that some have concave jaw faces, so as you push the work across one diameter it tries to climb the hills on the other. I am not sure of the best way here, as it seems one pair of jaws is fighting the other.

Incidentally there is an old alternative for very awkwardly-shaped work; and that is the faceplate with face-plate dogs. I have not seen much mention of these at all in modern literature, but they would seem potentially useful fittings when used appropriately. They effectively turn the faceplate into an multi-jaw chuck, but may be safer used in conjunction with intervening clamps.

On which, why not faceplates with six slots? There are many items with 3, 6 or 12 bolts-holes etc in them!

[noel shelleyParticipant @noelshelley55608]

Centre finder, scribe up, dot punch, hold on chuck face with tail stock centre, lightly hold in jaws and clock to truth. Noel.

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