Hardinge TL (and HLV ?) Metric Threading
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  1. #1
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    Herein is presented a solution for generating all 23 standard and model
    maker's metric pitches on a Hardinge TL.

    All gears are from Boston Gear Works' 20 DP 14-1/2 PA change gear series,
    and are readily available from Boston Gear distributors.

    Recent quotations have been in the neighborhood of $15.20 for 20 teeth to
    $34.83 for 60 teeth, with other sizes being priced more-or-less
    proportionally to the respective teeth count. All gears are steel except
    for 55 and 60 teeth which are cast iron. The total cost of all gears, by
    recent quotation, is $289.55.

    All solutions require a (37/47) transposer, and this is the only compound
    gear in the train. This transposer generates 0.020 percent error for all
    pitches.

    The "final" gear will be 40 teeth for all fine and some medium pitches
    (0.25 to 1.5mm) and 20 teeth for some medium and all coarse pitches (1.75
    to 6mm).

    The "first" gear will be 20, 24, 28, 32, 36, 40, 48, 56 and 60 teeth for
    all fine and some medium pitches, and 20, 35, 40, 45, 50, 55 and 60 teeth
    for some medium and all coarse pitches.

    These are "by fours" solutions for all fine and some medium pitches, and
    "by fives" solutions for some medium and all coarse pitches.

    Second best solutions (*) are utilized where necessary to avoid
    purchasing duplicate "first" and "final" gears.

    Third best solutions (**) are utilized where necessary to avoid
    purchasing 30, 48 and 56 teeth gears.

    Operators are cautioned against attempting anything but light cuts when
    the "final" gear is 20 teeth (***).

    Therefore, 20, 24, 28, 32, 35, 36, 37, 40, 45, 47, 50, 55 and 60 teeth
    gears are required to be purchased and altered as necessary to fit the
    "first" shaft, the studs, and the "final" shaft. In most instances, the
    required alterations will be minimal.

    The Boston Gear catalog numbers are GAxx for all steel gears and GAxxB
    for the two cast iron gears, where xx is the teeth count.

    The pitches and the associated "3 change" position, "first" gear and
    "final" gear are as follows:


    0.25mm, 3, 20, 40

    0.30mm, 3, 24, 40

    0.35mm, 3, 28, 40

    0.40mm, 3, 32, 40

    0.45mm, 3, 36, 40

    0.50mm, 2, 20, 40, *

    0.60mm, 2, 24, 40, **

    0.70mm, 2, 28, 40, **

    0.75mm, 3, 60, 40

    0.80mm, 2, 32, 40

    1.00mm, 1, 20, 40, *

    1.25mm, 2, 50, 40

    1.50mm, 2, 60, 40

    1.75mm, 2, 35, 20, ***

    2.00mm, 2, 40, 20, ***

    2.50mm, 2, 50, 20, ***

    3.00mm, 2, 60, 20, ***

    3.50mm, 1, 35, 20, ***

    4.00mm, 1, 40, 20, ***

    4.50mm, 1, 45, 20, ***

    5.00mm, 1, 50, 20, ***

    5.50mm, 1, 55, 20, ***

    6.00mm, 1, 60, 20, ***


    A suitabe placard is shown below ...





    ... and is available as camera-ready art
    Here.


    Peter.

  2. #2
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    Doggone Gearhead [img]smile.gif[/img]

  3. #3
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    "Doggone Gearhead"

    A badge of honor, coming from you, Don!

    Funny thing about metric conversions of English lathes ... many folks turn it into an ordeal rather than a science. Disorganization rather than organization might be another way of looking at it.

    I looked at all those proposals for metric threading on a Hardinge, most of which required two steps of compounding, some adapted from Boxford or Myford concepts, and ultimately decided on a completely fresh start, much as I did with my work on metric threading for the Monarch 10EE.

    Each machine requires a different approach, some differing in very fundamental ways, others differing in very minor ways.

    What initially appeared to be the Hardinge's fundamental weakness ... only three usable "box" ratios whenever a "banjo" was installed ... was turned into a strength, as it was ultimately possible to provide all commercial and model maker's metric pitches, 23 in all, from 0.25mm to 6.0mm, using a little more than one-half of that number of change gears if one counts the two gears in the transposer, and a little less than one-half of that number if one doesn't count those two transposer gears which must always be present for any metric conversion.

    You've got to be prepared to think "outside the box", so to speak, whenever you're trying to make an English (quick change gear) box speak metric.


    On another forum, nigel9454 commented:

    "10 team points and a gold star for that effort sir.

    "I am very impressed with this set of solutions; very elegant, compact and accurate enough for nearly every purpose. Precisely what I was hoping for when I first started this thread."

    Thank you, Nigel!

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    Explanation of metric conversion on the Hardinge TL (and possibly other similar Hardinge screwcutting lathes) ...

    It turns out that there are only two possible "minimal" solutions for metric threading on a Hardinge TL: 20/40 "final" gears, and 40/80 "final" gears, with "first" gears as necessary.

    The reason is the "three change" portion of the box has fixed 1:2:4 ratios, while the spindle-to-three-change ratio is also fixed, but at at 5/4, thereby turning the 8/16/32 tpi lead screw into a 10/20/40 tpi, effective, lead screw.

    Thus, "first" and "final" gears (my terms, not Hardinge's) are limited to 20/20, thereby producing 2.0000/1.0000/0.5000mm, 40/20, thereby producing 4.0000/2.0000/1.0000mm, 80/20, thereby producing 8.0000/4.0000/2.0000mm, 20/40, thereby producing 1.0000/0.5000/0.2500mm, 40/40, thereby producing 2.0000/1.0000/0.5000mm, and 80/40, thereby producing 4.0000/2.0000/1.0000mm, 20/80, thereby producing 0.5000/0.2500/0.1250mm, 40/80, thereby producing 1.0000/0.5000/0.2500mm and also 80/80, thereby producing 2.0000/1.0000/0.5000mm, with increments of 0.0125, 0.025, and 0.050mm or 0.025, 0.050 or 0.100mm being possible within those limits.

    Only those "magic" numbers of teeth ... 20, 40 and 80 ... on the "final" shaft, and the these and their intermediates on the "first" shaft can produce the required increments, therefore these are the only "good" solutions.

    This will cause many repeats within the range of available pitches, but it will cover all of them.

    The "art", here, is selecting from so many repeats, only those which cover all pitches from 0.25mm to 6.0mm, and yet use the fewest number of gears, hopefully with no duplicates, and with the smallest total teeth counts, thereby reducing inventory and cost.

    One might ask why there are two distinct sets of "first" gears required: "by fours" for the finer pitches, and "by fives" for the coarser pitches.

    This because the requirement for the finer pitches is 0.05 increments, and the sequence produced is 0.2500, 0.2625, 0.2750, 0.2875 and 0.3000mm, for example, so "by fours" produces the required 0.05mm change from 0.25 to 0.30mm, for example; whereas the requirement for the coarser pitches is 0.25mm increments, and the sequence produced is 1.0000, 1.0500, 1.1000, 1.1500, 1.2000 and 1.2500mm, for example, so "by fives" produces the required 0.25mm change from 1.0 to 1.25mm, for example.

    By extension, this gives the otherwise very difficult to produce 0.7000, 0.7500 and 0.8000mm and 1.0000, 1.2500, 1.5000, 1.7500 and 2.0000mm sequences.

    The remaining pitches are produced in a straightforward manner.

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    BTW, the above placard is also valid for the 100/127 case, too. It's just that the pitches are absolute, and produce no error at all.

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    OK, I have 127/50 for my TL. Use 40 & 80 final to make your chart work?

    (smt, looking for an easy answer instead of getting out the parts, the drawing, and looking at them )

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    "OK, I have 127/50 for my TL. Use 40 & 80 final to make your chart work?"

    100/127 comes from the identity 2.54cm = 1.0000... in., exactly, by international agreement.

    So, 100 * 1.0000... and 100 * 2.54 is 100 and 254.

    But, a 16 DP 254 T gear is 16.0000 in. in dia., so the 254 was "factored" into 2 * 127.

    (For 20 DP, the corresponding dias. are 12.8 in. and 6.45 in.)

    Now, 127 is a "prime" number, one which cannot be factored any farther, so we're stuck with that.

    I will examine 50/127, specifically, and see what kind of "first" gears would be required for this specific situation, for your TL.

    Obviously, there are several solutions, depending upon how coarse you want to go.

    My 6.0mm solution actually goes to 8.0mm, which is not a standard pitch.

    Perhaps you'll be satisfied with 4.0mm. Perhaps not.

    Anyway, I have my spreadsheets all setup to try just about any combination of "first" and "final" gears, and any transposition ratio, and I will post my results, later.

    [ 10-20-2005, 10:31 PM: Message edited by: peterh5322 ]

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    Peter-

    Thanks for looking at it. But don't work too hard. A while back, I bought a mish-mash of gears on ebay because the lot included the 127 gear. There are 8 gears, but it is not a "set" and I always assumed it would be necessary to eventually set up the shaper and machine whatever was needed. So a 100T gear could be made as easily as any of the others, as that is a common division on a plain dividing head.

    The biggest problem is getting a full box of round to-its. I tend to save stuff and squirrel it away during times of work busy-ness, in anticipation of the project. In the wink of an eye, everything is a project everywhere one looks

    smt

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    With a 50/127 transposer, the coarsest thread you can cut with an 80 teeth "first" gear and a 20 teeth "final" gear is 4.0mm.

    So, 50/127 may not be a good approach for your requirements as it favors very, very fine pitches (0.125mm, minimum) at the expense of coarse pitches (4.0mm. maximum).

    Just the same, all standard and model maker's pitches from 0.25 to 4.0mm would be covered, without any exceptions, although some duplicate gears would be required to cut some common pitches.

    My 37/47 (and, 100/127) solution required no duplicate gears at all.

  10. #10
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    Hope nobody minds me reviving this year-old thread... bookmarked it way back when I first thought of getting an HLV, finally got around to it...

    Thanks again to Peter for such an elegant and economic solution. Just a couple of questions if I may:

    - Does this solution require the 'metric' banjo? Presumably that's the lower of the two seen here:


    (sorry, don't know whose image that is - saved it off some ebay listing ages ago.)

    I have the 'standard' banjo shown on top. Looking at the diagrams on page 34 and page 64 of the HLV manual it's clear why the metric banjo is needed with the 127 gear. But with the much smaller 37/47 pair, could I get away with the standard banjo? Have checked through previous topics and while it's sort of implied in some of them, I can't see it stated anywhere definitively.

    - I guess this also means the standard gear cover door will also be fine? Not that it really matters...

    FWIW I've also just priced the set of gears from HPC Gears in the UK: in 20DP, 20 deg PA, 'PG' series (no bosses), steel, it works out at:

    20 9.79
    24 10.34
    28 10.73
    32 11.05
    35 11.42
    36 11.58
    37 11.70
    40 12.16
    45 12.68
    47 12.89
    50 13.37
    55 13.97
    60 14.50

    Total GBP 156.18 plus VAT and delivery.

    Not bothered asking Hardinge UK what 'real' ones cost . My HLV only came with 30, 30, 40, 44 and 60 so it looks like starting from scratch with the new system will be WAY the cheapest way to go. Thanks again.

  11. #11
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    Another possibility is an exact solution, one which uses 40 DP 20 PA gears for the initial reduction step.

    In this case, you would have several 40 DP 20 PA gears for the reverse shaft, these driving a 127 teeth 40 DP 20 PA gear on the banjo, this being compounded with a 20 DP 20 PA gear, and with all remaining gears also being 20 DP 20 PA.

    Alas, the Hardinge gears are 5/8" bore and 3/8" face, whereas the 40 DP 20 PA gears from HPC are 1/4" bore 1/4" face, so there would be some boring and broaching to be done. And, this would have to be done quite accurately, too.

    However, a 127 teeth gear in 40 DP is 3.2250" dia., so this may fit within the confines of the existing banjo and change gear cover.

    There is a very good precedent for this approach.

    The Monarch 10EE uses a compound transposer with a 127 teeth gear which is twice the DP of the remaining gears, which are 16 DP 14.5 PA, so this 40 DP 20 PA approach is well-founded.

    In the 10EE case, the gears on the reverse shaft are 45, 50, 55, 60, 65, 70, 75 and 80 teeth, 32 DP 14.5 PA, in order to obtain all metric pitches from 0.25 to 4.00mm, while the transposer is 127 teeth 32 DP 14.5 PA.

    I haven't worked out the details of this new approach. Naturally, I would lean towards doing so using the fewest number of gears, of whatever DP.

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    I had a similar gear calculation problem in 1982. I wanted to make a screwcutting attachment for my watch lathe. Levin and Derbyshire attachments were either horribly expensive or no longer available. I had both metric (1 mm leadscrew) and inch (40 TPI leadscrew) slide rests and I wanted to be able to do both metric and inch pitches with either one.

    I had no way to make an accurate 127 tooth gear, so I did the math to look for alternatives that I could make myself. I settled on transposing gears of 40 and 63. I had to drill a blank index plate for my dividing head with 63 holes, which could not be done with the standard dividing head plates. My indexing rotary table had the right worm gear and index plate to do 63 holes. It all worked out perfectly. My gears are 48 DP 14 1/2 PA, by the way. My 18 metric pitches are from .20 to 1.5 mm and my 39 inch pitches are from 10 to 200 TPI. Recently, I calculated the gear tables over from scratch, using MS Excel, so that I could have them in the computer, on CD, and printed and laminated.

    I was curious to compare the 47/37 and the 40/63 conversion accuracy. I think I may have looked at 37/47 back in 1982, but I can't remember. I was worried that I may have missed a better solution. So here is the math:

    47/37=1.27027027 an error of 0.02128112 %

    2 x (40/63)=1.26984126 an error of 0.01249843 %

    I am happy with my solution. But there is no practical benefit to being better by 0.008782686 %, so I think Peter's work is excellent. I just wish I had an HLV-H to try it on.

    Larry

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    Thanks Peter.

    The 0.02% error does niggle I guess, though I'd be surprised if I ever ran into a case where it actually mattered. Over a threaded length of say 300mm the cumulative pitch error, if I figure it correctly, would be 0.06mm or about 2.3 thou.

    But the idea of an exact solution does appeal. I had a go at coming up with a set for the layout you suggest, only going up to 4mm as I doubt I'd ever need more. Any comments would be most welcome:



    I might give some thought to modelling the gear sizes on my banjo just to make sure all the combinations are physically possible...

    Incidentally, it turns out that HPC can do the bores larger for not that much money, and the keyways too for a bit more yet.

    All the best,

    Peter

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    Oops, just realised I can replace the 30/25 20dp combination in row 12 with 24/20, avoiding the need to buy a 30 gear.

    Looks like I also missed the 35T 20dp gear (GBP 11.42) off the gear list/prices at the end, so the amended total is GBP 142.30.

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    "Incidentally, it turns out that HPC can do the bores larger for not that much money, and the keyways too for a bit more yet."

    Looks like they can accommodate an increased face width, too.

    Maintaining 3/8" face, 5/8" bore, with keyway, from the factory, would certainly be preferred.

    I have begun some work, assuming that the primary reduction would be from the reverse shaft (previously called the "first gear") to the 127 teeth gear at 40 DP 20 PA, and the secondary reduction from the 127 teeth gear's shaft to the box shaft (previously called the "final gear") at 20 DP 20 PA, with the 20 DP 20 PA gears being exchangeable in order to obtain the maximum number of combinations.

    The solution for 4.00mm defines one extreme, as this has but one solution.

    The remaining pitches have many solutions.

    The issue, then, is to minimize the number of 20 DP 20 PA gears which are actually required to cover all the desired pitches.

    "By fours" and "by fives" are required, of course, as some pitches (the finer ones) differ by 0.05mm, while others (the coarser ones) differ by 0.25 or 0.50mm.

    [ 11-20-2006, 09:29 AM: Message edited by: peterh5322 ]

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    Thanks Peter.

    I think my solution as shown above is along exactly the lines you suggest if I've understood right. The top series, rows 5-9, is the 'fours' and below that the 'fives' for coarser pitches.

    I agree re face width. It crossed my mind that 1/4" 40DP gears might be getting a bit fragile.

    Have replaced the spreadsheet screengrab above with an amended version with the corrections included, in the hope that this will be less confusing.

    Look forward to seeing what you come up with!

    All the best,

    Peter

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    Change gear train design and minimization is part science and part art.

    I usually start with a PERL program which I adapted from an early effort by Dave Erickson.

    Dave's program utilizes an array of candidate gears, and then it produces a second array which is the reverse of the first.

    The intention, therefore, is to allow for gears to be used on either the box or the transposer, while eliminating duplicates.

    However, in many cases, duplicates are unavoidable, as Dave's program, at least in the form I am using it, does not eliminate duplicates.

    Therefore, I massage the output to eliminate duplicates, if and where possible.

    I prefer initial solution sets which result in only one possible solution for a given pitch.

    This, then, gets me pretty close to a minimized set, at the outset.

    In the instant case, I employed this strategy with the result that all conventional and model maker's pitches from 0.25 to 4.00mm, including two odd-balls (0.9 and 1.2mm), may be produced using only these gears ...

    1) 40 DP 20 PA - 70, 80 and 127 teeth, and

    2) 20 DP 14.5 PA - 20, 24, 28, 40, 45 and 50 teeth,

    ... with no duplicates.

    (I usually throw in 0.9 and 1.2mm as these are natural extensions of 0.45 and 0.6mm, yet inclusion of these pitches usually forces the solution sets in a direction which favors better utilization of the available gears. I guess this is the "art" part at play. 1.2mm is also the pitch employed by the collets which Dave's Deckel FP1 uses).

    Note that there is no 40 teeth 40 DP gear in the set I am proposing.

    I found I needed a 70 teeth 40 DP gear for one particular pitch (neither 0.9 nor 1.2mm), while inclusion of this gear made the 40 teeth 40 DP gear redundant.

    "By fours" gears are still here, in the sequence 20, 24 and 28, while "by fives" gears are also still here, in the sequence 40, 45 and 50; all of these being 20 DP 14.5 PA.

    The 20 DP 14.5 PA gears are all available domestically from Boston Gear Works. 20 DP 20 PA gears from HPC could be substituted.

    The 40 DP 20 PA gears would be specially ordered from HPC with a 3/8" face and a 5/8" bore, with standard keyway.

  18. #18
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    Here ...





    ... is a placard for the new TL (HLV-H) metric threading system which employs a 40 DP 20 PA 127 teeth transposer, and the minimum number of additional gears.

    A larger version can be found Here.

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    Science and art have certainly triumphed - hats off to you sir!

    Cheers!
    Peter

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    Further to the above, a happy thought just occurred.

    Myford change gears, widely/cheaply available in the UK at least, are, it seems from a quick google search:

    20DP 14.5 PA
    3/8" face
    5/8" bore
    1/8" keyway

    That all seems to fit, though I can't find confirmation of the Hardinge keyway dimensions just now - will measure when I get home later. If this matches they'd be some way cheaper than modified 20DP 20PA stock gears from HPC. See e.g.

    http://www.rdgtools.co.uk/acatalog/M...SERS_NEW1.html

    That would then just leave the three 40DP gears to be sourced from HPC.


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