Converting model "C" SB lathe to "A"
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  1. #1
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    Default Converting model "C" SB lathe to "A"

    After years of owning various "other" lathes, I somewhat impulsively picked up a SBL 9" "C" workshop lathe. The overall condition of the lathe I would consider to be "good" albeit very greasy and in need of a thorough cleaning. A quick search of the forum for converting to a quick change box and power cross feed didn't net me any info (which, I'm sure, is due to my limited search skills).

    Thus, my question: what, specifically, is needed to retrofit a QC box and power cross apron? Obviously, the basic pieces are needed but I'm concerned about the not-so-obvious bits and pieces that will be needed to properly retrofit the lathe. Looking through Ebay will net you lots of parts but I'd like to be informed before spending any money. Also, are there more appropriate places to look for parts?

    TIA, Sam

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    Hi Sam,

    Check out this link:

    Lathe - Converting C to A


    Hope it helps.

    Paula

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    Sam,

    There are also a few SBL discussion groups on Yahoo where you could get some great info. The Southbendlathe group has a summary of what to do for the A to B or C conversion, authored by paul_hvidston:

    **************************

    South Bend 9” Lathe Conversion to Model “A”

    Introduction:


    This document is provided as a guide to those who have an interest in upgrading their Model “C” or Model “B” lathes, to Model “A” configuration. It is by no means a definitive work, but it is a compilation of practical information provided by the South Bend Lathe, Yahoo Group, which provides a good understanding of the hardware and modifications necessary to complete the transition.

    The Models:

    Model A: This model is equipped with a quick change gear box, which allows quick changes in lead screw rotation rates relative to headstock rotation. The Model “A” apron (attached to the saddle) has a clutch fed power take off (from a slotted lead screw). The apron has a detent lever with three positions, which may be selected to either power the saddle lengthwise along the lathe, drive the cross feed assembly, or have no action at all (neutral). When in neutral, the operator can manually manipulate the cross feed and move the saddle by either engagement of the half nuts onto the lead screw or through the use of the hand wheel.

    Model B: This model is equipped with the apron features of the Model “A”, but has no quick change gear box. Gear changes are accomplished by manually replacing selected gears from a supplied set and realigning the gear meshes.

    Model C: There is no quick change gear box, gears are changed manually as in the Model “B”. The apron only supports half nut engagement or hand wheel drive of the saddle. There is no power cross feed drive.


    What do I need (parts wise)?

    To convert to Model "A" from Model "B":

    20 tooth stud gear
    40 tooth stud gear
    Quick change gear box w/ 56 tooth gear
    Lead screw w/ drive gear


    To convert to Model "A" from Model "C":

    20 tooth stud gear
    40 tooth stud gear
    Quick change gear box w/ 56 tooth gear
    Lead screw w/ drive gear
    Model "A" or "B" apron assembly
    Cross feed screw (gear driven)


    Can I use my existing gears and/or lead screw?

    The only gears that are used from the Model “B” and “C” units are the 80 tooth, which is utilized as an idler, and the reverse gears on the reverse bracket assembly. The existing 24 tooth stud gear on the reverse assembly is not utilized and is replaced by either the 20 or 40 tooth stud gears (see below). An existing 72 tooth gear may also be used be employed as an idler in place of the 80 tooth.

    The required 20 and 40 tooth stud gears and 56 tooth gear box input gear do not come with the Model “B” and “C”, nor does the lead screw gear which engages the gear box output gear. The two stud gears are manually interchanged depending on the required operating range of the gear box. The stud gear not in use is stored on the input shaft of the gearbox, as a spacer, next to the 56 tooth gear.

    Since a newly installed gear box will take up a portion of the span formerly occupied by the lead screw, the lead screw becomes too long to work in conjunction with the gear box. Again, the Model “C” lead screws do not have the longitudinal slot, which allows the apron to take power off the lead screw. Some people have supposedly cut down the Model “B” lead screws to work. Remember, the proper lead screw will be determined by overall bed length of the lathe (3”, 3 ½’, 4’ etc), gearbox/ no gearbox, and slot for apron power take off.

    What other modifications do I have to make to my lathe?

    The gear box mounts to the lathe bed through three counter sunk holes through the lathe bed. On Model “B” and “C” lathes, two of the three holes (located next to the headstock) are already present. A third hole must be drilled to properly mount and support the gear box/lead screw assembly. Most of the hole is drilled through relatively soft cast iron, however, part of the area of countersinking is through a piece of hardened angular way material adjacent to the hole. Drilling through two different consistencies, vertically, at the same time, may cause the drilled hole to be misaligned. Some people have used their milling machines to achieve acceptable results. The rest of the project should be a straight “bolt-up”.

    Where do I find the parts?

    Newspapers, user groups, wanted postings, E-bay, and second hand parts dealers (check the back of Home Machinist).

    How much?

    It depends on how much you need and where you get your parts. Several hundred dollars is probably average for a “C” to “A” upgrade. Some people have good access to parts and others don’t.

    Can I add the gearbox now and add the apron later?

    Absolutely.

    Where can I get more information?

    Read the past postings on this group.
    Last edited by Paula; 03-02-2008 at 03:21 AM.

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    Paula,

    Thanks for the help; this is exactly what I was looking for. Couldn't seem to make the link work but I'll monkey with it a bit more...

    Thanks!

    Sam

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    Just curious ... Why convert a "C" to an "A"?
    There are plenty 9" and 10" South Bend lathes available with QC gearboxes ... And it's neither difficult nor time consuming to change gears on a "C".

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    I suppose it's an individual decision. If you already own a "C" lathe that you are otherwise very happy with, converting to an "A" would likely be a more cost-effective way to upgrade than purchasing a different lathe.

    As to whether it's even "necessary" to convert, that's apt to be based on the lathe owner's approach to their hobby: the variety and volume of work performed, how they value their leisure time, etc. For me, it's partly kind of a pride/ego thing. I just think it's so neat to have a small lathe in my home shop that has a QC gearbox, and separate carriage/crossfeed capability, just like the big lathes.

    Paula

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    I rarely use power crossfeeds but they've
    invaluable when needed.

    The issue of running longitudinal feed via
    the leadscrew is real. It's not such a good
    thing to do and will wear the screw out.

    As far as the QC box goes, that's a real bonus
    if only for feeds. I'm always fiddling
    with the tumblers on my 10L gearbox, to get
    the feed where I 'like' it. Doing that with
    change gears would have be yanking my hair
    out in short order. I think if I had a
    changegear lathe I'd probably fit a Bodine motor
    to the leadscrew before too long.

    Jim

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    Paula and Jim,

    I agree that having a QC gearbox, and power crossfeed can be useful ... but it seems to me as an owner of a 9" model C that the time and money spent on upgrading a "C" would be better put to other uses ... making stuff ... intead of enhancing the means for making stuff.

    Now i'd likely be singing a different tune if i was in production instead of making one item at a time at home. When i do get to the point of needing rather than wanting a QC gearbox ... it seems to be enough motivation to make it an upgrade to a Heavy 10 or better ... and leave the 9" Model C for its current uses ... unless i'm really missing the economics?

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    It's a valid point. The upgrade would be to
    simply purchase a model A instead of doing the
    work to retrofit the C into an A.

    It's not entirely clear that one cannot purchase
    a model A for what the upgrade parts will cost,
    aside from the labor issue. A related point is,
    those parts came from a model A somewhere - unless
    one is sure that it was a junker or wrecked
    machine, there's an A that's being destroyed
    every time a C gets turned into an A.

    Jim

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    Just a brief estimat for comparison.

    to make the conversion you will need parts:
    (estimates for a plain-jane length unit )

    leadscrew (estimated $50)
    A model Apron, (100?)
    gearbox,(125)
    stud gears( probably) (20 each)
    crossfeed screw (30)
    miscellaneous bushings, pins, etc. - not priced

    thats about $300 something not including some miscellaneous bolts and guards which you may or may not get with the parts you buy. keep in mind that heavily worn parts are cheaper but give lesser service, these $ are estimates for serviceable midrange parts, not new, not ragged out. shipping costs are added to the prices above as these vary by the place that you have to go to get the part.

    now for the work

    teardown the C apron
    teardown the C crossfeed
    remove the C leadscrew
    install the A leadscrew ( including refit the end bearing to the proper fit)
    install the A gearbox ( drill and counterbore the ways casting in proper alignment)
    fit the crossfeed screw
    install the A apron

    guessing this is probably not less than a 4-hour job, throw in something for cleaning up the A parts before install because you bought used, not new parts. if you work cheap this is still about $100 of time because you could have easily spent a whole day in teardown,cleaning, and re-assembly of the old parts.

    Ignoring the cleaning cost, now we have about $400 for the conversion to A model. Ebay prices for A versus C models do not often vary by this much for comparable condition machines so this comparison says that you should buy the A model you want and skip the work. most C-models do not have the full set of change-gears with them and when they do include these - the machine brings nearly the same price as an A model, or more depending on whether the buyer intends to part it out for more than they paid for it. recoup of $ from selling the C-parts not included.

    had a shortbed A model in fair shape, bought cheap for parts and threading work, and a 54 inch C floor model with almost no change gears. after pricing the gears, thought I could/would make an A or a quickchange-C from the C until I saw what all this entailed.( very hard to find an A model 54 inch leadscrew). I could buy almost another machine for the cost of converting this, more than the machine cost. Better to part out the A and use to buy more tools or sell all and buy a newer machine with the features. my tools are here to work. nice to see them well kept but this is no museum effort.

    YMMV but look around - there is a very brisk market in parts because people are buying parts to restore machines that are heavily worn. parts prices can easily be far above what the entire machine would bring if sold complete. if you are in interested in the conversion for the functions, look at the cost of a better machine versus the whole upgrade procedure before you start buying the parts. if you just like to work on the machines, then you should do the conversion. it takes time and good skills to do it and you will probably learn some things about your abilities and machines in the process, just dont expect to ever get your money back for the effort and cost invested.

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    Only a guess, but I suspect that lucywalker's
    cost estimates for the parts is probably low
    overall by a factor of nearly two. This is
    not to say that one cannot find one or two of
    the items at the prices mentioned, if one is
    in ebay haunt mode.

    But still consider what condition a 30 dollar
    crossfeed screw is going to be in - and how
    much a brand *new* one would run from southbend,
    er, leblond!

    I guess what I'm getting at is, if one had a
    cherry model C and wanted to just 'do it' all
    at once and convert, chances are some premium
    money would be paid to get the needed parts right
    away.

    Jim

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    Lucy,

    Thanks for that well-described analysis. Your response saved me a lot of time figuring out the economics on my own. The only thing that could be added is the time no machine is available during the conversion process ... Oh, and the crossfeed screw might be a bit more ... a friend replaced a worn-out crossfeed screw on a heavy 10 for about 10x that which you estimated (new, not used) ... making the overall conversion cost even potentially more.

    Jim,

    Maybe that "A" that's being sacrificed to convert a "C" into another "A" is being parted -out becuse it's worn out ... leading to yet another question regarding the overall benefit of upgrading ... leaving well-enough alone that which is adequate.

    My 9" Model C ... based upon the above ... and thanks to all who contributed ... will remain a "C".

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    I converted my "B" to an "A" when I purchased the gearbox, lead screw and gears on Ebay about 2 years ago. I then sold the stuff I removed off the "B" versions for more than the gear box I purchased. Everything bolted up without any additional work.

    I still have the leadscrew that is like new. I believe this lathe only had about 50 hours on it since the original flaking still everywhere on the ways.

    Jeff

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    I noticed an A apron on ebay now for $10! Obviously I dont need one or I wouldnt have posted this, but regularly search "south bend" on ebay.

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    Quite a bit of traffic on this since I last visited and some good points.

    I guess one of the factors would be the initial cost of the Model C. Obviously, paying nearly an "A" price for a "C" and then converting isn't really cost effective unless money isn't an issue and you're a bit of a masochist.

    But... If you purchased the "C" for low price and you don't mind a bit of labor, it seems the conversion would be worthwhile. In my case, it's worth it; I like the ease of a QC box and definitely like the option of a power cross. How much time do I actually save? I dunno' but my frustration level is lower- and that's a good thing.

    As Jim points out, the issue of using the lead screw & half nuts for turning rather than threading is something that can't entirely be ignored. An old Craftsman/Atlas lathe I had utilized this and I cringed every time the half nuts were engaged to turn rather than thread. Was it really an issue? Probably not- but I sold the lather before things ever got out of hand.

    At any rate, lots of good input from everyone- thanks.

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    Default Picture of gear placement

    Does anyone have a picture of the gear placement -20-80-56-40 ?
    Thanks in advance.

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    Default

    Wow- way to revive a 6 year old thread

    20 or 40 on the reverser stud, 80 idler on the banjo, 56 on the leadscrew/gearbox input.

    allan

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    Default gear placement

    Thanks Allen: I wanted a picture to see how it actually looks. I know how they go on and what order. I need to make a bushing for the 80 idler and I was wondering how it was put on the banjo and if the 24 was left on the inside of the stud gear mounting. Or do I have to remove both of the 24's from under the spindle gear to put the 20 on. Pictures make it so much clearer. Thanks Boot

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    Default QC convert on a "C"

    Oh by the way I just converted my "C" to an "A" yesterday that's why it's realvant to my questions. My gears don't have bushings in them just plain bores .562 with a keyway.

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    do NOT attempt to remove the 3 gears from the reverser. your 20 or 40 tooth gear goes on the outside of the stud, on top of the 24 t gear. All the banjo gears will fall into that plane.

    Search on ebay for 'south bend idler' will show you what the bushing looks like. Just a top-hat shape, though the thickness of the 'brim' and the over-all length need to be pretty close to get the gear to line up. If you have an 80t with a keyway- that is NOT the normal idler gear.

    allan


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