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  1. #1
    Join Date
    Jan 2004
    Location
    Mackay North Qld
    Posts
    6,446

    Default A question for experienced lathe drivers

    Hi Men,
    I just noticed the cross feed dial markings on my lathe.
    As per picture .

    Notice that the value given for the smallest millimeter increment is stated as .04 of a millimeter. The dial is divided into 50 segments .

    Conversely the imperial dial is divided into 125 segments.

    I know I am a bit thick but, shouldn't the millimeter dial read .02mm and the Inch section read .004". OK! maybe the dial marker fluffed up for the day.

    The following to quote Lewis Carrol however is getting curiouser and curiouser..
    Place dial indicator to read on the cross slide .One full millimetre rotation of the dial equals a reading of 0.41mm on the cross slide wheel dial. The second full millimeter rotation shows 0.92mm .

    I would have expected that the reading doubled exactly and given 0.82 perhaps. I have taken backlash into account and slippage on the dial rings.

    If the calibration is out as I think it is can some kind soul suggest how I could return it to a true reading.

    Or explain the intricacies of reading a chinese dial.

    Grahame

  2. #2
    Join Date
    Aug 2003
    Location
    Christies Beach
    Age
    59
    Posts
    121

    Default

    Quote Originally Posted by Grahame Collins
    Place dial indicator to read on the cross slide .One full millimetre rotation of the dial equals a reading of 0.41mm on the cross slide wheel dial
    I understand that your scale is marked as "Diametrical"

    That is, you advance the slide one division 0.04mm and it physically moves 0.02mm removing 0.04mm from the diameter of your job.

    But as for your measuring the travel as 0.41mm and not 0.5mm may be down to a shonkily? turned, inaccurate leadscrew?
    The secret to creativity is knowing how to hide your sources.
    Albert Einstein

  3. #3
    Join Date
    Sep 2004
    Location
    Glenhaven, NSW
    Age
    81
    Posts
    205

    Default

    Grahame,
    I would set up your dial indicator on the cross slide and measure its travel for at least 5 full rotations, compare the result with the table in your instruction book. The scale ring may be slipping on the shaft, is it easy to turn while holding the wheel still? Using a larger number of wheel turns will allow you to work out what the actual pitch of the lead screw is, ie. is it metric or imperial, then work backwards (mathematically that is) to see if the scales are on back to front or are correct. It will also tend to reduce any error due to backlash. I ended up making a table giving the required number of divisions to advance the screw for different tool penetrations (?) in both millimetres and decimal inches for tool movement AND diameter reduction.
    I hope you can make sense of the above. It sort of says what I mean but not very well!
    I'll take a pic of mine next time I have the camera.
    Cheers
    Graeme

  4. #4
    Join Date
    Mar 2005
    Location
    Hobart
    Posts
    17

    Default

    Grahame

    Just looking at your picture, it appear that your dial is divided into 100 segments as I can clearly see the 90 on the RH side of the dial.

    As the icon indicates that 1 division = 0.04 off the diameter, this equates to 0.02mm per division. 100 x 0.02 = 2mm. This should be the pitch of the cross slide screw and from my experience, it sounds about right.

    I am struggling to make sense of the imperial scale. From the photo there is 127 divisions equating to 0.002" per division. 127 x 0.002 = 0.254" (6.45mm)

    I used a Taiwanese lathe back in the 80's and I remember that the boss had made a paper scale for one of the scales as that machine was not right either.

    I would check the pitch of the cross slide screw with a vernier and if it looked like 2mm, then make sure the dial is securely locked to the shaft, rotate one full turn and see if it translates to 2mm movement with your dial indicator.

    An inaccurate dial is less than useful. If the metric one is not right, I would measure the exact pitch, then measure the diameter of the dial and calculate its circumference (pi x dia.) Cut a strip of paper to that length and divide and mark divisions by a suitable multilple of the cross slide screw pitch. Then carefully wrap it around the dial and secure with a good quality clear tape.

    Regards

    John

  5. #5
    Join Date
    Nov 2006
    Location
    Hobart, TAS
    Posts
    51

    Default

    Hi Graeme,

    I reckon you've actually got an imperial leadscrew. I reckon it's 10tpi. The puzzle is that it seems the dial is on back to front. Turn it around, and give it a good clean when it's off.

    John is correct with his observation about the 100 divisions and 127 divisions. You'll note that 127 divides into 25.4 to make metric units.

    I reckon Tankstand is also right about it being diametrical.

    For a 10tip leadscrew, each turn = 2.54mm or 0.1"

    Divide that by 100 you get 0.001" which taken diametrically equals 0.002" (sound familiar).

    Take 2.54mm and divide that by 127 and you get 0.02mm or diametrically 0.04mm (also sounding familiar).

    Thus the red dial is the metric one and the black one is the imperial one.

    If they turn independently, then you might be able to swap them around, otherwise, get the texta out and make some corrections, or get fancy and engrave yourself a little vernier scale.

    Your dial measurements seem odd. I concur that you should do a few turns and see what is going on. Friction dials can be a pain sometimes, so pulling it apart will show you how it works, and may give you an idea as to how to make it a bit better. Lathes sometimes just take off more than expected, so beware of relying on the dial too much. It always pays to creep up on your final dimension.

    Chinese lathes are usually metric. I don't know why this one would be imperial. Perhaps it is an export only lathe, and the designers have become confused with the imperial system?

    Chris

  6. #6
    Join Date
    Jun 2007
    Location
    sydney ( st marys )
    Age
    64
    Posts
    4,887

    Default

    if it becomes that much of a worry with your depths of cut why dont you just take all your finish cut dims with the dial indicator

  7. #7
    Join Date
    Feb 2006
    Location
    Melbourne
    Age
    65
    Posts
    316

    Default

    Hi Grahame,

    I am sorry to say but I have never in my life seen a dial on a lathe that has had an odd number other than a 5 match up with the 0 (ZERO). The more I see see of this machine the more sorry I feel for you. Didn't you pursue in trying to change the lathe or get your money back - or are there warranties not worth the paper they are written on?

    As pipeclay said, I would use a dial indicator(s) but remember whatever measurement is on the dial you will be taking twice the amount off. You could also buy the cheapest readout around, that will save a lot of grief in the long run - but don't buy a CHINESSE one.

    Regards
    David

  8. #8
    Join Date
    Jan 2004
    Location
    Mackay North Qld
    Posts
    6,446

    Default Lathe is roughly finished

    G'day Metal Head,
    I spent several months looking at many,many lathes, some in person ,some on the internet.Believe me it wasn't a quick choice made just on finances alone.There were lots of emails,phone calls and visits in person.There were many conversations with other teachers,tradesmen and any body else who could talk some sense about lathe matters.

    In the end I think the mistake I made was , I believed some of the s..t shovelled by the dealer.
    Because the eventual purchase was made from a major dealer selling selling really big industrial machinery I thought I was getting good value for money. It was not like buying from the internet with little information and no apart from the ad.

    To answer your question yes I probably could send it back but the freight cost alone would kill me.The dealer has been reasonable, so I have decided to be that too and will send it back only if a major fubar is discovered.

    My wife who sees builders machinery sold in her job, tells me it is normal practice to cover warranty but not the cost of return freight-that is on the purchaser and is part of the terms of purchase.I checked on my situation and it is the same.
    Essentially the situation is,that I have a lathe that does what is is reasonable in terms of operation ,but the fit out and finish was completed by poorly trained people.
    Having had most of it apart the basic casting and machining is quite ok.

    Knowing what I know now ,yes I would go straight to a Taiwanese machine. Having seen the difference in the overall quality, I would be happy to bear the extra costs associated with Taiwanese machinery.

    At the moment I still feel it is well worth persevering with to tune and tidy it up. If it becomes a real problem I"ll get rid of it.

    Thanks to all that have offered explanations and advice.
    If I were to offer advice to anybody considering a lathe now,it would be research first,then see the bloody thing in person.
    Grahame

  9. #9
    Join Date
    Feb 2006
    Location
    Melbourne
    Age
    65
    Posts
    316

    Default

    Hi Grahame,

    I apologize if I was coming across as a cynical and arrogant d------d - if so it wasn't my intention. As we all have to do in life is having to make the best of a bad thing sometimes. Putting a positive speil on it, you may yet be teaching us old dogs a new trick or two given the different methods you may have to adopt to do carry out the work on this machine. But remember always use a 4 jaw when possible.

    Regards
    David

  10. #10
    Join Date
    Jan 2004
    Location
    Mackay North Qld
    Posts
    6,446

    Default

    I have just checked the cross feed screw with a pitch gauge and found it is pitched at 2.00 mm.

    I played around using a dial indicator and mag base last night and was able to turn out a socket for a threaded button holder spot on. Its child's play if theres a reference point to work from.(make mental note to put plastic bag around mag base next time)

    The term lead screw was mentioned in an earlier post. I understood the lead screw was the screw that the threading function is carried out on. My model also has a second screw at the bottom that can drive the saddle and cross slide screw.Is that the feed screw ?

    Disassembly of the friction dials is next on the agenda which may give me some clues on making a dial I can follow.

    Thanks again
    Grahame

  11. #11
    Join Date
    Jan 2004
    Location
    Mackay North Qld
    Posts
    6,446

    Default

    Metal Head
    No problems David,we are all here to help each other in the long run. I supposed I am a bit dogged in pursuing repairs and corrections .I do give in too easily orsend things back unless I really have to.

    I really enjoy improving, repairing or correcting stuff.I am slowly preparing myself for a working retirement.The smaller repairs welding and machining don't get done here as the shops have too much big mine money coming.

    I am setting myself up as niche welding repair industry to do those repairs that other shops are not interested in. If I can sort stuff like this out it only contributes to experience I can use in my future business.

    Grahame

  12. #12
    Join Date
    Jun 2004
    Location
    Grafton, N.S.W.
    Age
    63
    Posts
    185

    Default

    G'day Grahame.

    Fit DRO's to the lathe and you don't need the dials.
    That's what I did.
    Hooroo.
    Regards, Trevor
    Grafton

  13. #13
    Join Date
    Nov 2006
    Location
    Hobart, TAS
    Posts
    51

    Default

    Sorry Graeme, meant the cross-slide screw amd not the feed screw per se. If it is a metric pitch than the imperial dial just seems plain wrong. Should be either 40 or 80 divisions (and then it is just a close approximation). Probably seems a little odd to the Chinese that we are still clinging on to the imperial system that was phased out 40 years ago!

    A DRO would certainly solve all your problems, and makes inaccuracies in the screws irrelevant. If there is a problem with your cross-slide screw, then it may pay to check your feed screw. If that's inaccurate, then you'll have trouble with thread-cutting, and there's not a lot you can do to fix it.

  14. #14
    Join Date
    Feb 2006
    Location
    Melbourne
    Age
    65
    Posts
    316

    Default

    Hi Grahame,

    As 3 of us have mentioned the DRO's would be definately the way to go, especially if you are thinking of starting your own business someday. What with that phone keep ringing when you are trying to count those little segments on the dial(s) and with your not so good eyesight. In the long run it will safe you heaps of time and we know that time can cost a lot of money especially when you haven't got it.

    Regards
    MH

  15. #15
    Join Date
    Jan 2004
    Location
    Mackay North Qld
    Posts
    6,446

    Default Dro's it is then

    Thanks guys,
    Thats a valid point about time and money.
    What sort of check should I do on the feed screw?
    I did a bit of turning yesterday and used the dial indicator.
    It worked well to to a point and that was where it ran out of stroke.

    Being me, I know I could still go out and search for a DRO and still buy the wrong bloody one.

    To start me offI would ask some basic questions to ask of DRO owners
    What does one look for in a DRO and more importantly which ones ,should you not buy?
    Are they bought specific to the cross slide and lineal travel dimensions of one's lathe?
    How are they powered batteries or mains power,and whats best?
    What sort of dollars should one pay for their DRO?

    Thanks again
    Grahame

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