Author Topic: Cenerting the Four Jaw (Read 31481 times)

Darren · « **on:** October 13, 2009, 03:57:10 PM »

I realise people shy away from four jaw chucks, mostly because of the time it takes to centre the workpiece properly. But it needn't take much effort at all and you can do better than most three jaws quite easily.

I'm not trying to teach anyone to suck eggs, just showing how I do it. Tips, suggestions or corrections welcome as ever

First I fit the workpeice by eye and then spin it noting movement against a fixed point. Usually a tool in the QCTP. Nothing too exact, just close by eye.

Then I fit a dial gauge to the toolpost. Select an opposing pair of jaws, lets say jaws one and three, and zero the dial gauge.

Rotate the chuck to line up jaw No3 and note the reading. In this case 34 thou

Divide the 34 by 2 = 17. Turn dial so that the halfway point (17) is on the needle

Now adjust jaws 1&3 until the needle points to zero on the dial.

That's it, if you spin the chuck to indicate jaw No3 it will also read zero. Now repeat for jaws 2&4.

It takes a lot longer to write this than to do the job, but once you have got your head around it you'll find centring the four jaw quite easy and much more accurate than the 3 jaw.

Gerhard Olivier · « **Reply #1 on:** October 13, 2009, 04:03:23 PM »

Nice write up Darren

I dont use the 4 jaw as much as I should because its big and scary

That would certainly save me a lot of time.

Gerhard

tinkerer · « **Reply #2 on:** October 13, 2009, 04:19:50 PM »

That sure does simplify it for me.

One day I will get some time in the shop and practice that. I bet you can use the same theory for off setting point on the work also.

mklotz · « **Reply #3 on:** October 13, 2009, 04:27:07 PM »

Your technique exactly matches what I wrote up for our metalworking club...

http://www.homemodelenginemachinist.com/index.php?topic=284.msg6405#msg6405

One detail that I included is the advice to make a clone of your chuck wrench. Since you'll be moving the two horizontal jaws in concert to zero the DI reading, it's far easier to have a wrench in each jaw to be adjusted than to constantly swap a single wrench between the two jaws.

Darren · « **Reply #4 on:** October 13, 2009, 04:32:48 PM »

Ha, I promise you I hadn't seen that, I don't read that site.... no pictures to see .....

like the idea of two chuck keys though, I'll copy that one ....

raynerd · « **Reply #5 on:** October 13, 2009, 04:38:59 PM »

What is the advantage of using the 4 jaw on round bar if centering - just better grip on the work piece? I have a 4 jour, think it is 6 inch for my boxford but have never touched it. I know I will need to some day soon....thanks for the write up darren.

Chris

Darren · « **Reply #6 on:** October 13, 2009, 04:44:09 PM »

Well in my case I only have a four jaw for this lathe (and 5c collets)

But apart from being able to centre work precisely you can also off centre precisely too as Tinkerer suggested.

You can also hold square or rectangular work which you can't in a 3 jaw chuck.

Andy · « **Reply #7 on:** October 13, 2009, 04:52:15 PM »

And the more often you use your four jaw, the easier it gets to set up work. I work on a lot of square and rectangular stock - three jaw no good for that.

mklotz · « **Reply #8 on:** October 13, 2009, 04:54:24 PM »

Darren,

I wasn't implying that you got the technique from me. I was merely surprised that you had arrived at the same procedure since I've never seen anyone else suggest it.

When you make up your clone wrench, check the clearances at the backside of your chuck. If things are tight (as they are on my lathe), you may want to make the clone somewhat smaller than the main wrench.

No pictures?! Perhaps you want to revisit HMEM. I'd rate it as photo-rich as this site.

Chris,

One reason to mount cylindrical work in the 4J is to guarantee concentricity of the machining with some previously machined feature. With a 3J, you'll be lucky to be able to hold concentricity to within a few thou. With the 4J, you're limited only by your DI accuracy and your patience. And, yes, the 4J has a better grip.

Darren · « **Reply #9 on:** October 13, 2009, 04:55:31 PM »

Quote from: Andy on October 13, 2009, 04:52:15 PM

And the more often you use your four jaw, the easier it gets to set up work.

Only having a four jaw for a couple of years I have to agree with you. I don't have any issues using such.

raynerd · « **Reply #10 on:** October 13, 2009, 04:59:19 PM »

Quote from: Darren on October 13, 2009, 04:44:09 PM

..... off centre precisely too as Tinkerer suggested.

You can also hold square or rectangular work which you can't in a 3 jaw chuck.

Yes, I knew it would come in at some point for when I want to turn square or off centre. No, I was just curious if there was any advantages for round. I know quite a few USA based sites, people seem to use 4 jaw self centering quite often so I guess the 4 jaws do hold the work more securely.

Anyway, thanks again for the write up. I`ll be sure to read it again when I come to put in on my lathe.

Darren · « **Reply #11 on:** October 13, 2009, 05:04:18 PM »

Hi Marv,

Just didn't want you to think I stole the idea, I often post info here that I find elsewhere but always give a link or referral.

I have no proper threading capabilities to make a 2" 8tpi backplate for this my main lathe and have only found one backplate to date. So I had to make a choice on what chuck to fit. I chose a four jaw because of it's versatility. But it sure was tedious to set up and I really got sick of it.

I was dti'ing something one day, setting the top slide to cut a morse 2 taper I think, and it struck me. Not looked back since ..... works perfectly every time

Re the second key, I have bags of room and would prefer two longer ones. Did you make yours, what from? ordinary steel?

mklotz · « **Reply #12 on:** October 13, 2009, 05:08:27 PM »

Yes, I made mine from CRS (Cold Rolled Steel here in the colonies). After two decades or so of use, it still works well.

NickG · « **Reply #13 on:** October 14, 2009, 06:29:06 AM »

I also thought this would be the easy way to do it but it didn't seem to go to plan and took me ages! Maybe it just needs practice! I found it hard chucking my crank off centre to machine the pin too so last time I made a split bush. Not as accurate way of doing it though, I was relying on milling machine head being trammed perfectly and don't think it was!

Nick

John Rudd · « **Reply #14 on:** November 09, 2009, 05:36:55 PM »

Ha...Another thread I've come across that saves a lot of grief.........

I need to spend more time reading than pratting about in the garage and getting it wrong...

Just goes to show how much or little as an individual we know...Knowledge shared and all that...

Thanks Darren

Baldrocker · « **Reply #15 on:** November 09, 2009, 06:51:30 PM »

On the subject of 4j self centreing chucks am I right in assuming that you
lose the idependence feature, or am I missing something ?

BR

Baldrocker · « **Reply #16 on:** November 09, 2009, 07:47:09 PM »

Quote

I need to spend more time reading than pratting about in the garage and getting it wrong..

Is there a name for that disease, is there a cure, did I catch it off of you?

BR

bogstandard · « **Reply #17 on:** November 10, 2009, 01:41:01 AM »

BR,

You are correct, a 4 jaw self centring is just like your standard 3 jaw, but, they just so happen to have 4.

Actually, I have found that my 4 jaw SC's are in fact a little more accurate than my normal 3 jaw SC's, and I tend to favour them for normal run of the mill use.

Like everything else, they do have specialist uses, like holding square bar.

Bogs

djh82uk · « **Reply #18 on:** November 23, 2009, 09:21:16 PM »

I have an 80mm 3 jaw SC and a 100mm 4 Jaw Independant.

Takes too long to keep changing so I have stuck with the 4 jaw, I just centre it by eye, then get the dial indicator on, I just turn it and memorise the highest and lowest number, figure out a rough middle point, turn the chuck so that the indicator reads the highest.

Now you should have a chuck key hole that is parallel to the indicator arm (once the key is in there), slacken the opposite one and tighten the parallel one until you reach the rough middle point on the dial, takes a few goes but takes me less than 2 minutes to get it down to half an increment (0.005mm)

Sounds like along way to do it, but very quick after a few goes, I only do it this way as it's self taught (had no idea how to do it any other way)

DJH

NickG · « **Reply #19 on:** November 25, 2009, 05:05:46 AM »

I hardly ever use my 4 jaw. Infact, I haven't used it yet on my new lathe. it is massive, I'll be able to do loco cylinders in it no problem!

Since I bought and fitted my £45 chinese 3 jaw from axminster, the run out was only about 0.001" which would take me a while to centre that well in the 4 jaw. More than good enough for anything I've come across so far. if not, I would probably try the ER collets.

Nick

bogstandard · « **Reply #20 on:** November 25, 2009, 06:22:33 AM »

I think I am a little like youself Nick.

A absolutely hate four jaw work with a vengance, and will use any other method available to me if the opportunity arises. I tend to favour a Keats angle plate or clamping to the faceplate.

I know some people love to use them, but for me, it is like trying to wear a barbed wire thong, a real PITA.

Unfortunately, sometimes a four jaw independent has to be used. Then it is a matter of me gritting my teeth, and getting the pain over and done with as quickly as possible.

I honestly don't know why, as I have never had any real bad experiences with them, just one of those things. I think everyone has at least one pet hate that they don't like doing when working in the shop.

John

Darren · « **Reply #21 on:** November 25, 2009, 06:40:52 AM »

Quote from: bogstandard on November 25, 2009, 06:22:33 AM

I think everyone has at least one pet hate that they don't like doing when working in the shop.

John

For me it used to be parting, till I went carbide ....

Four jaw, I actually prefer it over 3 jaw. But if I could get a runout of 0.001 like Nick that could quickly change ...

NickG · « **Reply #22 on:** November 25, 2009, 06:58:33 AM »

On my hot air engine before I got the new lathe I used a 4 jaw twice. I turned a square aluminium column and made the crank from 1 piece by offsetting. They both worked, but it was a PITA to get the offset, it just didn't work the way I thought it would!

But now, I would probably make a round split bush for the square aluminium - would probably grip ok with light cuts and I made a split bush to offset my crank on the rocking engine.

Like you John, I don't know why I am that anti-4jaw, I should use things like that as an opportunity to practice really.

Darren, parting is another one of mine - Cast iron, aluminium and brass I like doing - but steels my lathe doesn't seem to like much and I end up sawing!
I think I must have got lucky with my chuck, either that or I measured the run out incorrectly!

Nick

Darren · « **Reply #23 on:** November 25, 2009, 07:19:53 AM »

Nick, much the same here with parting .... try a carbide parting tool and you won't look back. I can now part steel at high rpm like it's butter.

NickG · « **Reply #24 on:** November 25, 2009, 07:50:12 AM »

Darren, I might just have to try that!

I have also asked for a set of carbide tipped tools for Christmas too so I can try them. Are the little sets you get (brazed top not indexable) all the same centre height? You can see my thinking - then I'd be able to have all the same packing pieces - or make 1 packing piece the right thickness to give me centre heigh, until i make or buy a QCTP!

Nick

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Author Topic: Cenerting the Four Jaw (Read 31481 times)

Baldrocker

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bogstandard

bogstandard