Major flaw in the world of engineering

[Pete RimmerParticipant @peterimmer30576]

If 4 jaw self-centering chucks held any significant advantage over 3-jaws you'd see them everywhere, but as it happens they are not common at all.

3-jaws are superior is almost every way.

[JAParticipant @ja]

Posted by Pete Rimmer on 22/04/2023 20:44:29:

If 4 jaw self-centering chucks held any significant advantage over 3-jaws you'd see them everywhere, but as it happens they are not common at all.

3-jaws are superior is almost every way.

Are you from Mars?

I never saw a 3-jaw chuck during my apprenticeship. Almost the only reason they exist is because no one with a brain can use one.

The only time I use one is to hold a fly-cutter.

JA

[Pete RimmerParticipant @peterimmer30576]

Posted by JA on 22/04/2023 20:55:37:

Posted by Pete Rimmer on 22/04/2023 20:44:29:

If 4 jaw self-centering chucks held any significant advantage over 3-jaws you'd see them everywhere, but as it happens they are not common at all.

3-jaws are superior is almost every way.

Are you from Mars?

I never saw a 3-jaw chuck during my apprenticeship. Almost the only reason they exist is because no one with a brain can use one.

The only time I use one is to hold a fly-cutter.

JA

You used a 4-jaw SELF CENTERING chuck for everything but holding a fly cutter?

[ZanParticipant @zan]

A 4 jaw sc chuck is vastly superior to a 3 jaw. It grips much tighter so with it, the horror of the bar slipping when threading has gone. It grips lighter thin pieces more gently without crushing , it is highly accurate at all diameters. it holds hex bar easily and has no problem with cast bars

A chuck on a hobby lathe does not need an accurate register. My 5” is a loose fit on it which enables it to be clocked dead on centre, where it remains thus the accuracy The register is only needed if the metal removal is higher than the lathe is capable of giving I can easily take cuts of 6 mm on my S7 without any problems

Anybody who condemns a 4 jaw sc chuck obviously hasn’t used one I hardly ever used my 3 jaw fir so long, that I mounted it permanently on a milling vice rotation base ( also never used from new!) to form a spin fixture for the miller

so the OP should should skim his backplate then bolt the chuck to it and get turning Send me a pm if you want advice on how to do this

Edited By Zan on 22/04/2023 21:25:32

[Pete RimmerParticipant @peterimmer30576]

Course I've used one, they grip great for truly round stock but not better than a 3-jaw. Accuracy has nothing to do with number of jaws but quality of manufacture and state of wear. Same goes for gripping force for threading, 3-jaws are not reportedly poor for that because of some flaw in the design.

Where they fall over flt is on materials that is not truly round. Just like a 3-legged stool which sits stable on an imperfect floor where a 4-legged one will rock, the 4-jaw can allow stock to rock on 2 jaws where a 3-jaw will not.

As I said, if they did actually hold significant advantage they would be much more prevalent but they are not. You'll find perhaps one 4 jaw self centering for every couple of hundred 3-jaws.

[JAParticipant @ja]

Posted by Pete Rimmer on 22/04/2023 21:15:52:

Posted by JA on 22/04/2023 20:55:37:

Posted by Pete Rimmer on 22/04/2023 20:44:29:

If 4 jaw self-centering chucks held any significant advantage over 3-jaws you'd see them everywhere, but as it happens they are not common at all.

3-jaws are superior is almost every way.

Are you from Mars?

I never saw a 3-jaw chuck during my apprenticeship. Almost the only reason they exist is because no one with a brain can use one.

The only time I use one is to hold a fly-cutter.

JA

You used a 4-jaw SELF CENTERING chuck for everything but holding a fly cutter?

Pete

My apologies. I miss-read your posting. (I should not post at night).

I have never seen a self centering 4 jaw chuck in my life. I don't intend to see one.

JA

[Pete RimmerParticipant @peterimmer30576]

Posted by JA on 22/04/2023 21:36:48:

Posted by Pete Rimmer on 22/04/2023 21:15:52:

Posted by JA on 22/04/2023 20:55:37:

Posted by Pete Rimmer on 22/04/2023 20:44:29:

If 4 jaw self-centering chucks held any significant advantage over 3-jaws you'd see them everywhere, but as it happens they are not common at all.

3-jaws are superior is almost every way.

Are you from Mars?

I never saw a 3-jaw chuck during my apprenticeship. Almost the only reason they exist is because no one with a brain can use one.

The only time I use one is to hold a fly-cutter.

JA

You used a 4-jaw SELF CENTERING chuck for everything but holding a fly cutter?

Pete

My apologies. I miss-read your posting. (I should not post at night).

I have never seen a self centering 4 jaw chuck in my life. I don't intend to see one.

JA

No sweat I am often guity of the same. I get corrected more when posting whilst tired.

I actually keep two identical 4-jaw independant chucks on my rack one with the jaws set inside and the other with the jaws outside. It was the late John Stevenson who gave me the idea when he mentioned that he did this because swapping the camlock chuck was far quicker than reversing all of the jaws. He was of course, quite correct.

[Howard LewisParticipant @howardlewis46836]

Tyhe argument is about horses for courses.

A 3 jaw can hold round or hexagon.

A 4 jaw INDEPENDENT chuck can hold sqaure or round material, and hold it more concentric, (or less eccentric ) than a 3 jaw. The concentricity depends upon how accurately you want to work.

A goof 3 jaw will probably hold work concentric within 0.005" (0.127 mm), in a 4 jaw indemdent, you can setb it to better than 0.00005" (0.0127mm ) if you wish.

AND, if wated / needed, work can be deliberately set eccentric.

I once reamed a 1"diameter hole, 1" from the edge of a 6" diameter piece of cast iron!

You select the tool best suited to delivering the result that you want.

Howard

[Mick B1Participant @mickb1]

Posted by Howard Lewis on 22/04/2023 21:48:48:

Tyhe argument is about horses for courses.

A 3 jaw can hold round or hexagon.

A 4 jaw INDEPENDENT chuck can hold sqaure or round material, and hold it more concentric, (or less eccentric ) than a 3 jaw. The concentricity depends upon how accurately you want to work.

A goof 3 jaw will probably hold work concentric within 0.005" (0.127 mm), in a 4 jaw indemdent, you can setb it to better than 0.00005" (0.0127mm ) if you wish.

AND, if wated / needed, work can be deliberately set eccentric.

I once reamed a 1"diameter hole, 1" from the edge of a 6" diameter piece of cast iron!

You select the tool best suited to delivering the result that you want.

Howard

A good 3 jaw can hold work concentric within 0.0002 – 0.0005" :

Clocking the WM250V

Some horses can run better courses than they used to.

If a 4 jaw S/C can hold bare hex bar, I'd be interested to know how. If I wanted to do that with one, I'd expect to make a slit bush in brass, bored to the across corners size of the hex bar (generally measured rather than calculated, 'cos of the usual break edges), much as I do when I need to hold square material in the 3 jaw and prefer not to disturb it by swapping to 4 jaw independent. For most purposes, there's no significant concentricity issue.

Edited By Mick B1 on 22/04/2023 22:26:42

[FulmenParticipant @fulmen]

Zan might not be entirely wrong (but not right either).

They might work better on thin walled parts for the same reason that a 6SC (6-jaw Self Center) is even better. And they might even be more rigid than a 3SC assuming you get full contact on all jaws. But can you?

According to Wobbly Table Theorem you can always get a 4 legged table to be stable by rotating it. But that assumes point contact, while chuck jaws are anything but. So it might be worth a shot when working with one, but it's no argument for choosing it over a 3SC.

As mr Rimmer points out, if they were that superior we would have seen more of them by now. A 3SC is the obvious all-round choice. It will hold almost any shape reliably, and even cheap Chinese chucks can hold 0,03mm or better when new. Anything will wear in time, and cheap stuff tends to wears fast. But 9 times out of 10 they are the simplest solution by far. A 4IA will do anything the 4SC will do and a lot more.

Having a loose fit on the back plate is a simple fix for a loose chuck, but with a new chuck one should obviously try a slip fit first. You can always remove more metal later, adding it back is a bit more work.

[Paul LousickParticipant @paullousick59116]

The first paragraph of Paul's post was " I am becoming increasingly frustrated about the lack of help for wanna be engineer's to start out. Without any basic knowledge" and as already said, machining is an engineering trade qualification which takes years to learn at a technical college.

Youtube is a good place to start for a beginner with hundreds of introductory videos about using a lathe and mill, such as those by Harold Hall (**LINK**) , Joe Pie (Piecynski), Quin at Blondihacks (**LINK**), etc

Paul

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Mick B1 on 22/04/2023 22:23:08:

.

If a 4 jaw S/C can hold bare hex bar, I'd be interested to know how.

.

Rotagrip will show you: **LINK**

http://rotagriponline.com/Photos/4%20Jaw%20SC%20chuck%20Hex.jpg

MichaelG.

[jimmy bParticipant @jimmyb]

I've got a 4 jaw self centring chuck, only every used on square bar.

My regular 4 jaw only gets used for "odd" shaped parts.

99% of the time I use a 3 jaw chuck, with either hard or soft jaws.

I also have an ER40 collet chuck that gets used on production work.

As a skilled engineer with 40 years experience on both manual and CNC lathes, I have never really understood most of the arguments for 4 jaw chucks………..

Jim

[JasonBModerator @jasonb]

Well I don't have a SC4-jaw and have not really felt the need to buy one.

SC3-jaw gets used for a lot of round(ish) things and the soft jaws get regular use more as a backstop for shallow work than for concentricity. Mine is better than half a thou runout, I notice the cheap SC4 jaws on the ebay have accuracy of 0.003" so you may not even get all jaws in contact even if a "round" item were gripped.

Independent 4-jaw gets used for odd shapes as well as square, rectangular and offset. As it it larger than my 3-jaw I also hold larger round items or smaller ones I want a tighter grip of and 4 points of contact will distort large tube less than 3 points anyway.

The hobby engineer is more likely to use the lathe to turn odd shaped items (Ind 4-jaw & Faceplate) than in industry as they don't have the choice of tooling available that a machine shop would have, particularly so in the past before many had mills in the home workshop. Same goes for size as the 4-jaw is often larger than the 3-jaw eg typical Myford would have 6" Ind 4-jaw and 4" 3-jaw so the 4-jaw will get used at home whereas a machine shop will just stick a large round item into a large 3-jaw.

Small detail work I like to use the 5C collet chuck as it grips short lengths and is better if you need to get your hand close for using a graver or file. I do have some imperial hex and square collets but these days tend to start off with round and machine the metric profile I want as it gives a crisper profile.

[Michael GilliganParticipant @michaelgilligan61133]

The famous myfordboy seems well-pleased with his:

.

.

MichaelG.

[roy entwistleParticipant @royentwistle24699]

I always thought that a SC four jaw chuck was intended for woodturning

Roy

[Michael GilliganParticipant @michaelgilligan61133]

It’s amazing what we ‘always thought’ and how effectively the internet can disseminate alternative ideas.

There is of course a good reason why wood is perhaps more appropriate: it’s soft enough to let the jaws settle into it.

… the harder the material, the more severe the risk of only getting three point contact.

MichaelG.

[Mick B1Participant @mickb1]

Posted by Michael Gilligan on 23/04/2023 01:44:33:

Posted by Mick B1 on 22/04/2023 22:23:08:

.

If a 4 jaw S/C can hold bare hex bar, I'd be interested to know how.

.

Rotagrip will show you: **LINK**

http://rotagriponline.com/Photos/4%20Jaw%20SC%20chuck%20Hex.jpg

MichaelG.

Doh!

Thanks – yes, I should've thunk of that.

Nevertheless, as a turner who started in 1974, I don't believe I've ever actually seen a 4 jaw S/C, never mind used one, though I've known of them for I don't know how long.

I would expect one of those with a matching level of concentricity to be more expensive than a 3 law.

[paul mcquaidParticipant @paulmcquaid48093]

Since reading all the above comments some very informative (some judgemental for lack of my knowledge!) I have also bought the much talked about 100mm three jaw, Which seems to be very accessible, with a backplate available (pre-machined too!) Strange that. But of course it's my own fault for not knowing these things… Learning all the time though.

It's just a shame that not everybody knows the things that make engineers roll their eyes up at eh?

Thank you for all the helpful answers by people that understand where I'm coming from. It's good to know there are some that like to share their knowledge not just scorn…

[larry phelan 1Participant @larryphelan1]

When I started out with my lathe , bought new from Chester 20 odd years ago, I knew as much about the machine as it knew about me, So many things to learn about, but now I know twice as much nothing as when I started.

It,s called " The Learning Curve". My machine came with two chucks and a faceplate [Do they still supply faceplates now ?, never see them listed } However, later on I bought another 3 jaw chuck, from another supplier which came with no backplate. This was not really a problem because surprise, surprise, I found it easy enough to buy a piece of round bar from a steel supplier, just a slice off a length of stock bar to make my own backplate. A smaller piece of round was used to bore and thread this to suit the spindle. Both welded together [ dont cringe ! ] and the whole thing mounted and turned to suit the chuck. Still using it, so it can be done.

As others have pointed out, there are too many different chucks, lathe spindles ect not all interchangeable, so it is quite normal to sell chucks without mounting plates. Also, a 4 jaw sc chuck is not a great idea to start with, I used to think it was, now I know better.

Someone mentioned Sparey ? I think you could do worse than buy and read that book, carefully, since it will answer many of your questions in plain fashion. I seldom refer to it now, never more than every two days or so. It covers almost everything you need to know at hobby level and way above ! and it deals with the type and size of machine you are dealing with.

When all else fails, do not be afraid to ask stupid questions on this Forum, I do it all the time, to fill in the many gaps in my knowledge, most of them quite large,. Remember, no question is stupid if you dont know the answer, that,s why you have to ask them.

Do not be disheartened, it will come to you OK. Yes you will make mistakes, cock ups ect but that,s all part of the game, and the start of a scrapbox which will get bigger and BIGGER as yo go along. Dont ask how I know !

Guys take years to learn this stuff, so dont expect to know it all overnight.

[Mick B1Participant @mickb1]

Posted by paul mcquaid on 23/04/2023 10:10:14:

Since reading all the above comments some very informative (some judgemental for lack of my knowledge!) I have also bought the much talked about 100mm three jaw, Which seems to be very accessible, with a backplate available (pre-machined too!) Strange that. But of course it's my own fault for not knowing these things… Learning all the time though.

It's just a shame that not everybody knows the things that make engineers roll their eyes up at eh?

Thank you for all the helpful answers by people that understand where I'm coming from. It's good to know there are some that like to share their knowledge not just scorn…

I thought there was quite a bit of adverse judgement in your initial post. It's OK to rant, but don't be surprised if others rant back.

[DalboyParticipant @dalboy]

Posted by roy entwistle on 23/04/2023 09:24:03:

I always thought that a SC four jaw chuck was intended for woodturning

Roy

The SC 4 jaw chucks for woodturning have different jaws than those designed for metal turning as the jaws have a much wider jaw face which form a complete circle at a set distance out of the fully closed position this is the ideal size of a spigot to give maximum grip.

Many also have interchangable jaws so allowing for larger spigots to be made to fit this is so larger pieces can be turned.

Metal working sc chucks have a very small contact area making it unsafe to use on wood as fibres compress and can lead to wood departing the chuck.

Look at this chuck as an example. There are a few exceptions but they are more specialist jaw types

[Howard LewisParticipant @howardlewis46836]

MickB1

Thye one and only 3 jaw that I have ever seen held work, AT THAT DIAMETRER, without eccentricity. Tyhe worst was worn and the work (Solver steel) was 0.036" eccentric.

As you say a GOOD 3 jaw, in reality a rare beast!

But handled on the correct way, even a bad 'un can be used to produce concentric work.

Howard

[Mike PooleParticipant @mikepoole82104]

The only chuck that has no runout is the 4 jaw independent and this is only if you have the patience or desire to adjust it to that level. Any self centering chuck will have a tolerance and this can vary with the work diameter, the scroll mechanism can eat a swarf chip at any time and lose the accuracy you thought it had. If you need the surface you are holding in the jaws to be concentric with the surface you are machining then you will need to check with an indicator it is within the tolerance you require. I have no idea of the runout of my three jaw chucks because it does not matter to me. If the job needs to be concentric and cannot be completed without repositioning then it will have to be remounted in an independent jaw chuck or a collet. The accuracy or a three jaw should be of little concern for most work and some thought given to the order of operations can often make the runout irrelevant.
Mike

[Martin ConnellyParticipant @martinconnelly55370]

Mike, 3 jaw self centering with freshly bored soft jaws at the required diameter or a Griptru adjustable chuck.

Martin C

[Author]

Posts