Using Chalk to Centre a 4-Jaw?

[not done it yetParticipant @notdoneityet]

would require more skill of the operator.

Disagree. They might need better chalk or better eyesight, but ten though is ten thou however you measure it.

[SillyOldDufferModerator @sillyoldduffer]

Posted by not done it yet on 30/11/2017 13:01:06:

would require more skill of the operator.

Disagree. They might need better chalk or better eyesight, but ten though is ten thou however you measure it.

Ah but the chalk method doesn't measure anything – it's an uncalibrated comparitor depending on a steady hand and – I think – experience. Chalking a small diameter rod is harder to do, harder to see, and harder to interpret. At least it is when I try it!

Same skill issue with me and a DTI. Compared with chaps who are practised in their use I faff around, often overshooting and undershooting due to over tightening the jaws as I get close to zero. I get there in the end but many others do the same job same faster. I think I'm unskilled compared with them.

Dave

[larry PhelanParticipant @larryphelan54019]

Chalk is good enough for most jobs we do [me,anyway ],so what if it,s a thou out,what,s a thou between friends?

[depends how many friends,I suppose ] Just give the job a wallop here and there,with a block of wood,and before you know it,it will be dead on,and then you,re away on a hack !

Life is too short to worry about such things. Mind you,I have used the chalk method on 24mm round but never on 10mm. I have DTI,s but only use them when I need to,and as for DRO,s and CNC,s!!!!! I stay well away from those things,they sound dangerous !!

[Clive FosterParticipant @clivefoster55965]

Posted by SillyOldDuffer on 30/11/2017 13:28:32:

Compared with chaps who are practised in their use I faff around, …… I think I'm unskilled compared with them.

Dave

Skill and practice issue is probably one of the advantages of the "put a block in the tool post and read the cross slide dial" method. Already halfway there as you use the dials all the time and are used to touching off the work before adding a sensible cut. A square ended block always hits the job on diameter there are no interaction issues where moving with one set of jaws to bring the job over a bit upsetting the reading on the other axis. Which can drive you nuts with a small job if the preliminary set-up using the rings to estimate central position is a bit too far out.

Shooting for tenths can be frustrating. Even with appropriate, or inappropriate, verbal encouragement.

Before getting a QC system, which made the block method fast I used to measure the jaw position relative to the chuck body using the depth probe of a calliper to verify that first set-up of a small job was reasonable.

As always its all about finding methods that suit your equipment, skills and the job in question.

Clive.

[MWParticipant @mw27036]

Posted by larry Phelan on 30/11/2017 13:53:33:

Life is too short to worry about such things.

Well, it depends on what you're making it for, if the shaft or holes you're making don't ask for anything other than "well, over there is good" then i'd agree.

But, there are some things that do need to be very nearly bang on. If you're making a chuck backplate for e.g, I would want the centring accuracy to be as good as possible when boring the female register.

Michael W

[not done it yetParticipant @notdoneityet]

Ah but the chalk method doesn't measure anything –

Maybe absolute measurement is not needed in most cases, but just look at your post at the top of this page – where you still measured it!

[thaiguzziParticipant @thaiguzzi]

Posted by SillyOldDuffer on 29/11/2017 08:45:34:

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

QCTP = not only turning tools etc, as we are discussing DTI's being held on centre in a tool holder.

One of my most used holders is a pair of "push" ball bearings on shafts for truing up wobbly (read thin or long) stuff held in a 3 jaw. Unbelievably quick (instant) and precise.
Got the idea from one of the early Doubleboost videos. So simple and works a treat.

[HopperParticipant @hopper]

Methinks the chalk method worked best for fellows who stood at a lathe eight hours a day, five days a week for decades earning their daily crust. Many used a four jaw chuck for every job to save time changing large heavy chucks between jobs. So they became very proficient at quickly "chalking" work. Model engineers truing work in a four jaw only occasionally, maybe not so much so. Certainly not me.

[Fowlers FuryParticipant @fowlersfury]

LBSC (Curly) wrote that during WW1 when in charge of girls operating lathes for munitions, he was amazed how quickly they could set up work in a 4-jaw to be "right first time" just by eye.
Perhaps I should request SWMBO comes into the workshop next time I'm going to spend 30 mins faffing around chasing the last thou on the 4-jaw ?

[Adrian GilesParticipant @adriangiles39248]

My old manager used to regale us with a tale about a factory visit to JCB when he was a ag student. Coming to a large lathe being used to turn a ram, all the students stood round watching as the old feller running the lathe stood watching it screech it’s way along the ram, spitting red hot chips everywhere. Roland asked him why he wasn’t using any cutting oil or coolant, the old feller turns round, puffs on his ciggie in the corner of his mouth, lifts his flat cap and scratches his head, and said, “You look like a intelligent and educated young man, I would have thought it was obvious why I’m not using any” When Roland looked back at him blankly, he continued, “it would wash off me chalk mark!”

Adrian

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