Using Chalk to Centre a 4-Jaw?

[SillyOldDufferModerator @sillyoldduffer]

Reading an old ME I saw mention of "the well known method of centreing work in a 4-jaw chuck". Chalk's come up on the forum a couple of times but I've never seen a full explanation anywhere. The method certainly isn't "well known" to me!

Recently I've been using my 4-jaw a lot and I'm tempted to stay with it rather than continually swapping the 3-jaw in and out. The downside is the time taken to adjust a 4-jaw accurately but perhaps high accuracy isn't always necessary?

In the hope that it's quick and unskilled how does the chalk in the hand method work and how accurate is it?

Thanks,

Dave

[SillyOldDufferModerator @sillyoldduffer]

[Dod MoleParticipant @georgeclarihew]

Hold the chalk on a steady point and slowly move it by hand in till the chalk touches the work, the chalk will leave a mark on the nearest point thus showing the off centre position so one tightens and/or loosens the relevant jaws to bring part to centralness (new technical term), repeat as necessary.

Dead accurate when you are finished.

[Andy MurrayParticipant @andymurray87642]

Instead of using chalk why not use the tip of the knife tool to tell the concentricity of the work piece or better still use a DTI, practice makes you quicker.

[NJHParticipant @njh]

I have a QCTP and have a dti permantly fitted in one holder – very useful for setting work in a 4-jaw.

[Chris TriceParticipant @christrice43267]

Same as NJH for me too.

[thaiguzziParticipant @thaiguzzi]

Same as Chris T for me too.

[Thor 🇳🇴Participant @thor]

I use a DTI with a magnetic base that clamps to the top slide or cross slide. As you say Dave, takes a bit longer with the 4-jaw but its more accurate than my chinese 3-jaws.

Thor

[Eric ArthrellParticipant @ericarthrell78468]

chalk was the preferred method of the turners and borers in the boiler shop when I was a lad 50 odd years ago. can't remember seeing a DTI much outside the tool room .

quick and accurate enough for what was needed no need to chase the last thou on some jobs.

Eric

[not done it yetParticipant @notdoneityet]

As Eric, truing up to the odd thou is often just as good as using a three jaw chuck. It is only if needing to re-chuck an item that a dti is required.

Does it really matter – if the starting stock is not exactly round, anyway?

[SillyOldDufferModerator @sillyoldduffer]

Thanks George and Eric. That's enough information for me to give chalk a try. On the downside I shall have to develop a steady hand!

My current, rather slow, method takes three stages and is in line with Thor and Andy's advice:

• Step 1: Centre the work roughly using the jaw markings
• Step 2: Centre more accurately by turning the work relative to the tip of a knife tool. I do this first by eye – closing the gap and then check with the cross-slide graduations
• Step 3: Adjust with a DTI mounted on a magnetic stand on the cross-slide as per Thor. With patience I can reduce run-out to zero (within the limitations of my 'inexpensive' 0.01mm DTI)

Get thee behind me NJH, Chris and Thaiguzzi! I am tempted. The longer I spend in my workshop the more I want a QCTP. I hadn't thought of a Quick Change DTI but now you mention it the advantage is obvious. And xmas is coming.

Apart from the time taken to centre my 4-jaw chuck, its main shortcoming is that it won't grip anything less than about 3mm diameter. Which leads me to my other desire – a collet chuck.

I'll report back later how well I get on with chalk.

Many thanks,

Dave

[Jon GibbsParticipant @jongibbs59756]

I take the point that chalk is "close-enough" for some jobs but surely the advantage of the DTI is that you can determine, based upon the job in-hand, when you get "close-enough". Just because you can measure to within a thou, doesn't mean you can't stop adjusting when you get within 10 thou.

MrPete222 posted this in the last few days for a really snazzy DTI holder **LINK**

Mine uses the stem to mount the DTI which has the advantage that if I have a lot to do and can be bothered I can switch it round and check the face too with this type of holder.

[MalcBParticipant @malcb52554]

Chalk method is good as above

DTI's can be over sensitive when setting things like irregular castings initially and you may well need one with a lot of travel at first but they good as you close in to final true.

Another method is to have a decent plate that you sit on your bed and which extends back out toward the operator ( also used for sitting a mag base and clock on ) onto which you just use a scribing block at first to get the high points closed in. You can get pretty close just using it like this before final clocking if at all needed.

And for anybody reading this new to lathe work, where the material is of a pretty regular profile you can get the work relatively true to start with, just by using the machined grooves in the 4 jaw chuck face to position the jaws as either equal as needed, or offset to suit the outer profile by using as steel rule to measure positioning.

[Ady1Participant @ady1]

I just use the tool tip for a decent adjustment then go to a DTI if serious accuracy is required

[roy entwistleParticipant @royentwistle24699]

You will find it quicker if you use two chuck keys on opposite jaws

Roy

[larry PhelanParticipant @larryphelan54019]

Hi Dave,

I came across that chalk method in Sparey,s book when I bought my lathe,tried it,and was surprised how accurate it was.You might be surprised how quickly you can center stock. Although I have a DTI,most times I find the chalk just as quick and good enough for most jobs. But then,having seen my Mag stand,you will see that I am easy to please ! Anyway,the method does work and it,s worth the try,just to get your eye used to centering .

You must remember DTI,s were not always affordable to small operators but chalk was !

[egaParticipant @ega]

I understand that chalk was part of the normal equipment of oldtime turners; they used it to mark change wheels for screwcutting and to mark leadscrew bosses which lacked micrometer dials.

Someone truing a cycle wheel with limited facilities might well resort to chalkmarking.

[larry PhelanParticipant @larryphelan54019]

Truing a cycle wheel ! Ah,happy days,now gone for ever !

[Mick B1Participant @mickb1]

Posted by Ady1 on 29/11/2017 09:13:45:

I just use the tool tip for a decent adjustment then go to a DTI if serious accuracy is required

Me too. I keep the clock on a handy flat steel mount to clamp in the toolpost when needed.

[Clive FosterParticipant @clivefoster55965]

A quick and dirty method is to mount a solid block in the tool post and use the cross slide dial to measure the error when it comes up against the job. The morse taper drill holder out of my Dickson collection does the solid block bit just fine. Its never used for its intended purpose so its nice to find job for it.

Set one jaw horizontal, butt the block gently up to the job and set the dial to zero. Spin 180°, bring the block up to the work again and read the error off the cross slide dial. Set cross slide to halve the error and adjust appropriate jaw until the workpiece contacts the block. You may need to spin back 180° to find clear air for the workpiece move. Repeat with the other two jaws. Check and re-adjust if needed but you ought to be within maybe a couple of thou TIR first time round. Under a thou? Call it good and don't waste money on a lottery ticket this week.

Block is better the a tool tip because it doesn't mark the work and always contacts on a diameter so the "measured" jaw pair offset errors are independent.

DTI on a mag base is my most used method, primarily because nearly everything I haul out the four jaw for has to be tenths accurate.

If your chuck guard is of the type that mounts to a rod running parallel to and above the bed an indicator can quite effectively be fixed to that rod. My SouthBend Heavy 10 had that type of chuck guard. I made a double pivoting clamp to fit the fine adjustment arm out of an economy mag base set and mounted a lever indicator off that. Worked OK but it may be instructive to note that the Smart & Brown 1024 that repaced the Heavy 10 has the same style of chuck guard yet I never bothered to make the minor modifications needed for the transfer. Primarily because the 1024 has plenty of nice flat cross slide area to hold a mag base whilst all the convenient location on the Heavy 10 were sufficiently curved to seriously weaken the grip of a mag base.

Clive.

[not done it yetParticipant @notdoneityet]

One advantage of using chalk is that it may help the learner to realise they have gone too far withthe adjustment of one pair of jaws – the opposite side of the workn would be chalked, so easy to tell!

[SillyOldDufferModerator @sillyoldduffer]

Well I just spent an hour playing with my 4-jaw chuck and a 60mm length of 38mm diameter brass rod. I used a DTI to measure how close I got with 3 centring methods:

• Using the jaw markings only as a guide : 0.4mm (best )
• Using the tool-tip as a visual guide: 0.09 – 0.15 (best and worst)
• Chalk – 0.14mm

Didn't have time to test adjusting by tool-tip and the cross-slide micrometer dial.

Not sure I've given chalk a fair crack of the whip yet. The Playgroup chalk I have is too hard to mark shiny metal well. I think the method might work better with a softer chalk. Too cold to carry on tonight, but I shall try a felt-tip next. I'm sure all the methods would be better in skilled hands.

I can only admire the old guys who managed without fancy tools – so far I find the DTI to be the most straightforward way to get stock centred in a 4-jaw and, for me, it's more accurate as well.

Dave

[Bernard ReillyParticipant @bernardreilly64467]

I have used all the methods suggested but prefer my DTI mounted in a QCT. I know of a chap who used the lathe chuck key in a similar manner to the chalk method .For the life of me I do not know how he knew what chuck jaw to adjust.. Needless to say he was a time served turner.

B. Reilly Glasgow.

[John McNamaraParticipant @johnmcnamara74883]

A DTI mounted on the right height mag base wins by a mile for me. after eyeballing the rings for a rough setting.
The whole process should only take a minute or two to get it within a thou. less than that can be a fiddle maybe a bit more.

I keep one on the lathe at the ready.

[SillyOldDufferModerator @sillyoldduffer]

The other disadvantage of chalk is that the work needs to be fairly big. I experimented with a 38mm diameter rod. I doubt the chalk method would work well on a 10mm diameter rod, or at least would require more skill of the operator.

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