Four Jaw chuck

[Mike PooleParticipant @mikepoole82104]

Some of the 4 jaw chucks we use are quite light duty devices, I fully agree about giving a bit of an extra tighten to win the last gnats but don’t get too enthusiastic or you will damage something, sometimes you will have to loosen the opposite jaw. Make sure that when the job is finally running true that the job is also firmly held with both pairs of jaws. A large industrial strength 4 jaw is a different animal to the 6” light duty slim 4 jaw often used on a Myford and such lathes.

Mike

[Pete RimmerParticipant @peterimmer30576]

You can put a lot of clamping pressure with the jaws on a 4-jaw. Easy to distort the part or even the chuck if it's a lightweight model.

[Henry BrownParticipant @henrybrown95529]

I haven't seen it mentioned here but when I was on the handles we always had the clock near the place there the chuck key would be used. For example, if you use the chuck key at the top have the clock reading vertically on the top of the job. I always do this and the old skill is coming back after far too long away doing other things!

For jaws were the norm for the parts I made back then, occasionally a three jaw would be used but usually with bored soft jaws.

[HopperParticipant @hopper]

Posted by Henry Brown on 01/03/2020 21:15:13:

I haven't seen it mentioned here but when I was on the handles we always had the clock near the place there the chuck key would be used. For example, if you use the chuck key at the top have the clock reading vertically on the top of the job. I always do this and the old skill is coming back after far too long away doing other things!

For jaws were the norm for the parts I made back then, occasionally a three jaw would be used but usually with bored soft jaws.

Yes. A lot of machine shops with larger lathes that need a block and tackle to change chucks, the old timers used to just leave the four-jof aw in place permanently and could set each job up true in double quick time due to long and constant practice. A lot of the old boys did not even use a dial indicator, just a scriber block stood on the bed with the scriber point on the job. They reckoned they could get it within a couple of thou that way, as close as a three jaw might get it anyway.

[Alan Johnson 7Participant @alanjohnson7]

I use a digital DTI.

I roughly adjust job to required position, then using the DTI set it to zero at jaw 1. Rotate spindle 180 degrees (jaw 3) and the error is shown. Move job (at jaw 3 position) to half the error.

Repeat process at jaws 2 and 4. Repeat process until job is centred.

With an analogue DTI this is much harder, and requires some metal mathematics – which is harder the later it is in the day!

[Henry BrownParticipant @henrybrown95529]

Posted by Hopper on 01/03/2020 23:54:57:

A lot of the old boys did not even use a dial indicator, just a scriber block stood on the bed with the scriber point on the job. They reckoned they could get it within a couple of thou that way, as close as a three jaw might get it anyway.

Or a "sticky pin" on the tool post – woe betide you if you used a clock on a casting or bar!

Most of what we made were high speed rotating parts for large epicyclic gears so they had to be concentric for balance reasons. One exception was white metal bearings made from two halves, they were held with the joint between the jaws and roughed out, then whitemetalled and then finished. A light touch was required to avoid them springing, only achievable in a four jaw of course.

[Philip BurleyParticipant @philipburley44197]

while we are discussing 4 jaw chucks , can someone explain to me why some have numbered jaws? I assumed that it wouldn't matter where the jaws went on a 4 jaw.

[Clive FosterParticipant @clivefoster55965]

Philip

Although it theoretically doesn't matter which jaw goes where as manufacturing tolerances should be tight enough that all the jaws are, effectively, the same its best practice to put things back in the same place every time. Hence numbered jaws. Of course best practice is basically so you don't get unexpected errors due to component variations et al which shouldn't be the case with a chuck of any quality.

Self centering four jaws use a scroll for positioning, like a three jaw, so of necessity must have the jaws replaced in the correct position so they are always numbered.

Clive

Edited By Clive Foster on 02/03/2020 09:10:08

[Clive FosterParticipant @clivefoster55965]

Interesting video from Hopper showing Joe going all the way round the houses to set up a job in a four jaw whist putting an indicator at un-neccessary hazard too.

The quickest, easiest, safest way doesn't even need an indicator unless going below thou or two accuracies.

All you need is two blocks, or one block and the blunt (back) end of a lathe tool. One to register chuck rotation and one to make a solid probe. Decent resettable dials on the cross slide cuts down the maths but aren't essential.

Registration block needs to be of a suitable section to stand up on its own when it's on your lathe bed. Finish it nicely to a length such that when sat on the lathe bed with a chuck jaw resting on it the jaw is horizontal. Usually more room to put it at the back but more of a stretch. Whatever works on your machine.

Put the probe in the toolpost so its end is dead square to the work.

Put the job in the chuck and eye up relative to the rings as best you can.

Put the registration block on the bed and rotate the chuck so one jaw is resting on it.

Using the cross slide bring the probe up to touch the work, set the dial to zero and withdraw the probe

Rotate 180° so the opposite jaw is on the block and move the cross slide so the probe again touches the work. The dial reading is the total offset error (TIR).

Adjust the crosslide to halve the dial reading and adjust the opposing chuck jaws so the workpiece touches the job. Withdraw the probe and bring it up to the work again verifying the setting is in fact correct with no backlash errors.

Either adjust the error out now or just repeat the process for a fine setting. I usually don't bother to futz about on one side and just repeat, unless its a rough job, as its just about as fast to repeat. Odds are you will need a repeat anyway.

Go round a third time and verify that you have it right. If not adjust as needed before verifying again.

Now do the other pair of jaws.

I generally do the third, verification, setting on all four jaws after (hopefully) getting them all right on the first two rounds.

If it has to be dead nuts repeat using a plunger type dial gauge in place of the solid probe. Lock the cross slide and rack the saddle down the bed so the gauge is safely out of the way before turning the chuck.

Works fine with rounds too but I just use an indicator at 12 o'clock, sometimes 9 o'clock, and eyeball chuck rotation.

Clive

[Mike PooleParticipant @mikepoole82104]

As we see there is more than one way to skin a cat, it might be a worthwhile exercise to pick a method that suits you or try them all and see which you prefer. A clear idea of the process and then practise for a month by leaving the 4 jaw set up all the time might see you in the set up race against the clock.

Mike

[HopperParticipant @hopper]

Thats darn clever too, Clyde. We tend to forget we have a precision measuring device right there on the cross slide. I'll definitely be giving that one a try.

[HopperParticipant @hopper]

Thats darn clever too, Clyde. We tend to forget we have a precision measuring device right there on the cross slide. I'll definitely be giving that one a try.

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