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  1. #1
    Join Date
    Jul 2006
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    Adelaide
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    Default are precision chucks worth having

    I am fed up with the std chuck on the AL960 of removing stuff from it only to find i need to go a little longer/deeper/forgot to do something etc etc having to stick it back in the chuck and then find it cuts different to what it was ..hahaha, so was wondering if you guys believe that getting a 3 jaw precision chuck is worth it..or should I just stick the 4 jaw on and centre the work every time

    $600.00 buys a lot of beer...or do you reckon i should give up for week or two and get a precision 3 jaw

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  3. #2
    Join Date
    Apr 2011
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    Sydney
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    Default

    You're talking about the adjustable 3 jaws right? the ones you can 'dial' in?

    I was under the impression they are more suitable for repetitive work of similiar or same dimensions, that once you changed diameter you had to re-dial them in? I'm probably horribly wrong on this.

    That hasn't stopped me wanting to get one to replace my standard 3 jaw chuck - but at $1k I simply can't justify it when for now I can use the 4 jaw chuck if the work requires any accuracy.

    If you do decide to get one, can you post your feedback on it?

    Cheers
    Jon

  4. #3
    Join Date
    Aug 2009
    Location
    Lara, Vic, Oz
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    58

    Default

    Hi Eskimo

    I'd suggest either soft jaws for your chuck, so that you can ensure that they are absolutely concentric for the diameter you are turning (for critical work) by taking a lick off the ID of the jaws, or using a collet system. Soft jaws would prob be much cheaper option than starting from scratch with collets.
    Cheers
    Si

  5. #4
    Join Date
    May 2010
    Location
    Lower Lakes SA
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    58
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    Default

    Soft jaws won't help much if your chuck won't repeat. Check the runout specs on any scroll chuck you're considering. I don't think any of them will get you as close as a 4 jaw. I think the answer is planning. I'm not being smart. It's a real skill that needs practice.

  6. #5
    Join Date
    Aug 2008
    Location
    near Rockhampton
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    Default

    I believe a precision chuck is called a 4 jaw

    But seriously for most work a precision chuck is not worth the money... The stock 3 jaws seem to do about 0.1mm TIR which I find adequate...

    Also is you have a precision chuck and crash it, chances are it will not be so precise anymore at least at the diameter it was set at when you crashed it... They are a bit fragile...
    Light red, the colour of choice for the discerning man.

  7. #6
    Dave J Guest

    Default

    Why not go all out and get a Bison precision 6 jaw set true chuck/back plate, it will only cost you half of what the lathe cost you.

    Seriously though, just use you 3 jaw you have now and if you need to remount it, either mark the position it comes out and try to re align it, or replace the 3 jaw with the 4 jaw. Another way of doing things to remount them is to do it between centers and it will remount spot on every time.

    Dave

  8. #7
    Join Date
    Aug 2011
    Location
    Melbourne
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    2,951

    Default

    Hi all,

    I is interesting to note that yesterday I discovered that the accuracy of a chuck (3 or 4 jaw) is not only limited to the TIR but also how parallel it holds the workpiece to the bed (or axis of the lathe). I found the limitations of this yesterday after spending much time dialling in an electric motor rotor, only to find that the other end was way way out! How could this be I thought? If you dial something in at one point but it's not held parallel then it's only dialled in at that point and that point becomes the intersection or apex of a cone when you rotate the workpiece. Nothing will fix that, no amount of adjusting, unless I remove the jaws and carefully machine them flat. I have learnt that planning is just as important as the actual machining process. Making a piece and planning the process so that you don't have to remove the piece until all the precise work is finished, if possible. I'm still learning this planning caper!

    Also as Dave says, the best truly repeatable system is to turn between centres.

    Good luck if you get a precision chuck, I'll never be able to justify one but would love to hear from someone who has taken the plunge!

    Simon

  9. #8
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    May 2010
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    Default

    It is possible to dial in both ends of a shaft. You get it pretty close at the chuck, but leave the jaws just firm. Move your indicator to the end and bump it true. Go back to the chuck, repeat, tightening a bit more each time. 3 cycles ought to do it.

    But something like a motor shaft would normally be done between centres.

  10. #9
    Join Date
    Aug 2008
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    near Rockhampton
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    Default

    And even quality 4 jaws are just as crap at holding something parallel to the bed axis...
    Light red, the colour of choice for the discerning man.

  11. #10
    Dave J Guest

    Default

    I would say to do it between centers Simon. Another way is to have a 4 jaw revolving chuck in the tail stock for something that doesn't have a centre drilled spot. This type of chuck is on my to do / want list as it would come in real handy when you get a shaft that someone has hammered away on and messed up the centre drill mark.

    Dave

  12. #11
    Join Date
    Apr 2010
    Location
    ringwood vic
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    251

    Default

    G'Day Fellas,
    There is always the bushwhackers precision chuck, a Post It note, about .003" thick which compress down to about .0015" under the low jaw(s), or the cellophane from a cigarette packet .001" for really fussy types.
    Regards,
    Martin

  13. #12
    Join Date
    Nov 2008
    Location
    Perth WA
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    71
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    5,650

    Default

    Richard,

    Stay on the beer diet and stick with a 4 jaw. I have a little 80mm Pratt Burnerd 3 jaw Griptru. I reckon it's easier to adjust a 4 jaw chuck than root around with the total of six screws on the Griptru. Three screws adjust the jaws and the other three tighten the backing plate after it has been loosened for adjustment. Might be worthwhile if you were making a bunch of parts but for a few.....

    I'd pencilled some prices next to the chucks in an old Blackwoods catalogue when I was dreaming ten years ago.

    For a 5 inch super precision Pratt Burnerd Series 9210 3 jaw they wanted $1053 plus gst.

    A 5 inch Griptru Series 9250, a mere $1816 plus. You could purchase a 6 jaw Griptru but I didn't bother chasing a price.

    A 6 inch 4 jaw, Series 9500 was $928 +.

    I bought a 5 inch 3 jaw TOS to replace the same size Burnerd that came attached to my lathe. Does the job. I have abused the TOS but with a bit of rotating and retightening I can trim the runout to around a thou. Good enough.

    I think the TOS cost me a touch under three hundred bucks.

    BT

  14. #13
    Join Date
    Aug 2009
    Location
    Lara, Vic, Oz
    Posts
    58

    Default

    Again, I'll say, I reckon soft jaws are the way to go for precision (look through any catalogues such as Kitigawa or Rohm and look at the prevalence of soft jaws vs hard for their quality kit).

    Choose a set of soft jaws close to the diameter you want to turn, preload the jaws with a washer towards the rear of the jaws, skim the ID of the jaws with a boring bar to close to the diameter that you intend to chuck and you'll have a diameter concentric as you can possibly can get to the spindle. Better than 4 jaw with hard jaws for reasons stated above. A scroll chuck will be repeatable close to a given diameter (give or take a mm) unless full of crud. I managed to pick up heaps of (Kitigawa) bolt-on soft jaws at various auctions (Kitigawa have serrations which are harder to machine at home, but others such as Pratt have simple registers for which I have made heaps of my own). They last ages as you seldom have to take more than a few thou off to get a clean register (of course going to wildly different dia will transfer them into the next diameter 'bin' more rapidly).

    Advantage is that you can get any old chuck with bolt on top jaws and have your own precision chuck with only minimal effort, and which gives you confidence in your precision.

    Bit like soft collets, a secret generally used / known by old school toolmakers (thanks to one such for introducing me to this...thanks Bob King)

    Cheers

    Si

  15. #14
    Join Date
    Aug 2007
    Location
    Melbourne
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    1,417

    Default

    Eskimo, only you can tell if it is worth it to YOU. All I can tell you that a precision chuck is worth it to me - and I mean both a 3 jaw and an independant 4 jaw chuck. Cause even an adjustable 4-jaw chuck may not clamp a workpiece accurately parallel to the centerline if of poor quality - meaning if you face all sides of a rectangle, you may NOT end up with right angles.

    I highly recommend that you download this .pdf brochure, and carefully study and absorb its page 4:
    www.peko-trade.com/tos/toskatalog.pdf

    You will see that a simple 3-jaw chuck has a number of different runouts. Six kinds of runout are listed. You see how these runouts are measured correctly, so that you can compare the readings between different chucks. And you instantly understand why each of these runouts affect your work in a different way, depending on how you clamp it.

    The table on the same page tells you what the allowable runouts are for a chuck of a given diameter, according to both DIN6386-I and DIN6386-II. Note that the DIN standards are quite old and represent the quality of industrial class chucks about 50 yers ago. If you buy today a quality brand name chuck, it should be substantially better than DIN6386 class I. Whilst cheap noname (or fantasy name) chucks from China or India as often supplied with low cost machinery are usually substantially worse than DIN6386 class II. I have heard of 3-jaw chucks supplied as standard with low cost lathes, that had 0.5mm runout from new.

    The reason that I link to the TOS chuck brochure is not that I have anything to do with this maker. It is just the only maker I know of, that publishes such valuable information for free. Normally, if you want this sort of information, you got to pay money to purchase the standard, be it DIN or the equivalent ISO. And I like chuck makers that are honest and open about their product.

    Chris

    PS: Runout alone is not everything. A good quality chuck will also remain accurate for longer. And spare parts or accessories like soft jaws will be available for many years to come, sometimes 20+ years. In contrast, try to buy spare parts for a new fantasy name chuck.

  16. #15
    Join Date
    Jul 2006
    Location
    Adelaide
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    Default

    thanks guys
    guess I'll be able to afford a few beers afterall.
    i might stick the 4 jaw on and play around with that for awhile to see if I can put up with having to centreing the work every time...else go back to the std 3 jaw

    those prices quoted by you lot have definitely scared me off...I was thinking these C2821 | PA-160/D1-4 3 Jaw Adjustable Scroll Chuck Camlock Mount | machineryhouse.com.au might have been the go....but I guess i as worng

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