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  • Thread cutting for Dummies

    When I bought my nice new craftex Lathe from Busy Bee, it came with a whole damn box of extra gears, and 2 sheets of poorly translated documentation.---None of which dealt with thread cutting. I have purchased an excellent book, "The Amateur's Lathe" by L.H. Sparey and read up on thread cutting, and there is a chart of sorts, (that I don't know how to read) on the face of the lathe. What book can I purchase that deals comprehensively with thread cutting, gear selection, how to read the gear/thread chart on the front of my lathe, and just where the heck these gears go on the inside of my gear cover on my lathe. I am slowly re-aquainting myself with turning, facing, boring---things which I did on a lathe during an engineering apprenticeship 40 years ago, but I don't think I ever did master setting up to cut threads even back then.---Brian
    Brian Rupnow

  • #2
    Unfortunantly, where the gears go and the appropriate gears to use are generally specific to the manufacturer.

    Basically, your chart should have something like

    . A B C D
    18 H
    27 L 27 64 72 13

    (I just completely made up those numbers mind!)

    Usually, you will have two TPI corresponding to either a high or a low on the gear box. Some gearboxes don't have the high/low feature so in those cases you'd just have one TPI listed. So, you find the TPI you want. For this imagninary lathe, lets pretend like we want 18 TPI.

    We find the 18 TPI on the chart (it could appear more than once if there is a high/low feature) and then moving across the chart there are a bunch of numbers that correspond to the number of teeth on the change gears. The way my BS chart reads, a 27 tooth gear goes in location A, a 64 tooth gear goes in location B, etc. The letter locations should be listed near the chart, next to the place where you'll be sticking the change gears (crap whats that called?) or in your two page, changlish "user manual"

    You can work through those gear ratios yourself, if you know the TPI of your leadscrew, any hidden gearing between the bull gear and the leadscrew and then the # of teeth on the change gears. That is generally a mess to do - you'll fill up a page of scribbled notes with a bunch of ratios fairly quickly.


    <edit> hmm my chart looked alot more like a chart before ... Lets do it this way:







    In both of these images, you can see the table and the location of the gears. Looking at the ratios and the picture, I expect that the blank spots correspond to no gears used - but I'm not sure. That is not how my threading chart works; like I said it depends upon manufacturer.
    Last edited by Fasttrack; 05-06-2008, 09:24 PM.

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    • #3
      Brian,

      "Screwcutting in the Lathe" by Martin Cleeve, Book 3 in the Workshop Practice Series tells you everything you could possibly want to know about the subject, including how to work out the gear trains required for any thread from first principles. He has managed to write 173 pages on what seems on the surface to be a fairly simple process. It is well worth buying a copy.

      franco.

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      • #4
        Change gearing set-up

        Originally posted by brian Rupnow
        When I bought my nice new craftex Lathe from Busy Bee, it came with a whole damn box of extra gears, and 2 sheets of poorly translated documentation.---None of which dealt with thread cutting. I have purchased an excellent book, "The Amateur's Lathe" by L.H. Sparey and read up on thread cutting, and there is a chart of sorts, (that I don't know how to read) on the face of the lathe. .---Brian
        Hi Brian.

        If my memory is correct. I have the same lathe as you do. Mine is the 3-in-1 (mill-drill-lathe).

        I have the hand-book scanned in digital form.

        I will post a pic of my head-stock panel for the set-up later in the day and will go through the set-up for metric and "inch" screw threading for you. That hand-book is pretty poor but if what I have is more than you do it will help. I will post the links and you can down-load it.

        Just one thing - my lead-screw has a pitch of 3mm. Is this the same as yours or is yours a pitch of 1/8" (ie 8 tpi)?

        I will get back to this later in the day or this evening.

        These are pics on my 3-in-1 and may help in confirming whether the lathe is the same as yours:
        http://i200.photobucket.com/albums/a...AirSmith11.jpg

        http://i200.photobucket.com/albums/a...Lathemill1.jpg

        http://i200.photobucket.com/albums/a...fie/Lathe2.jpg

        http://i200.photobucket.com/albums/a...fie/Lathe1.jpg

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        • #5
          Brian, I am pretty much in the same boat as you. I am just begining to read the book suggested by franco. It does look good.










          If you want the Martin Cleeve book and can't get hold of it, let me know and I will try and get it and send to you, It is not an expensive book here, maye $18.00 AUD so no big deal to help you out.
          I forgot the ISBN, 0-85242-838-3

          Rgds
          Last edited by miker; 05-06-2008, 10:58 PM.
          Michael

          Australia

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          • #6
            A good reference source

            Originally posted by miker
            Brian, I am pretty much in the same boat as you. I am just begining to read the book suggested by franco. It does look good.

            http://img.photobucket.com/albums/v4.../Scan10724.jpg

            http://img.photobucket.com/albums/v4.../Scan10725.jpg

            http://img.photobucket.com/albums/v4.../Scan10727.jpg

            http://img.photobucket.com/albums/v4.../Scan10728.jpg

            If you want the Martin Cleeve book and can't get hold of it, let me know and I will try and get it and send to you, It is not an expensive book here, maye $18.00 AUD so no big deal to help you out.
            I forgot the ISBN, 0-85242-838-3

            Rgds
            Thanks Michael.

            That looks to be a very handy book and very good value as well.

            I am in OZ as well (Victoria).

            Can you let me know (post to this thread, PM or email) where you sourced it in OZ and I will send for it.

            Is it a part of a series?

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            • #7
              Books

              I usually get mine from a local cut price bookseller. Can't always rely on what they will have in stock.
              Plough books down in your neck of the woods should have it.

              http://www.ploughbooksales.com.au/002766.htm

              This is the series:



              I have most of them.

              Rgds
              Michael

              Australia

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              • #8
                Hi Brian,

                I believe the Craftex from Busy Bee is a 7x10 or 7x12 so you can get considerable documentation for this machine from a number of sources.

                Basic setup for threading is covered in some detail on pg 24 of this guide from LMS:
                http://www.littlemachineshop.com/Inf...UsersGuide.pdf
                (LMS also supplies parts and accessories for this machine.)

                The guide has a nice picture of the gear end of the lathe that identifies the shafts where the change gears should be installed (helps make sense of the chart on the machine) plus lots of other threading information specific to the 7x machines.

                "Screwcutting in the Lathe" is perhaps the best general reference available for threading and very well written - the jig for sharpening threading bits is worth the price of the book.

                John
                Last edited by GadgetBuilder; 05-06-2008, 11:54 PM.

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                • #9
                  Brian:- I Know that Busy Bee sells at least SOME of the Workshop Practice series of books. Suggest that you call head office, since you are close.
                  Duffy, Gatineau, Quebec

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                  • #10
                    Ref the Cleeve book

                    Don't know about BB in Barrie but the Ottawa store stocks several of the books in the series. The Cleeve book is out of stock and "soon" for my copy has translated into many weeks. Not BB's fault.

                    Edit: Toronto Public Library, North York Central branch has this book. Call # 621.942 C . Should be an inter-library program to borrow it or just visit. To see the entry search the catalog using "screwcutting"

                    Edit 2: Go to www.littlemachineshop.com/default.php & click on "Learning Center" then "Mini Lathe Users Guide". Open/download (Adobe Acrobat Reader required) it and go to page 24 or 25. Pretty good explanation of what's involved.
                    Last edited by Dunc; 05-07-2008, 12:56 AM.

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                    • #11
                      I have a copy of "Screw Cutting in the Lathe" by Martin Cleeve
                      FOR SALE, Send a private message if interested.
                      R W

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                      • #12
                        The craftex lathe which I have is a 10" x 18", and is not classed as a "mini-lathe". This is a picture of it from the Busy Bee brochure.---Brian

                        Last edited by brian Rupnow; 05-07-2008, 04:23 PM.
                        Brian Rupnow

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                        • #13
                          And one last picture---
                          Brian Rupnow

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                          • #14
                            I think the point was that more general information on the process of screwcutting could be had at littlemachineshop.com. I would add mini-lathe.com

                            Its probably not any more reasonable to expect your lathe manual to teach you to cut screws than it is to expect your car owner's manual to teach you to drive. The general assumption is that if you buy a machine tool you either will have or will get enough basic information on processes and practices (which are general and applicable to lots of machines). I think that its also generally assumed that owners of machine tools will have some basic mechanical aptitude too. You will find yourself applying that aptitude even after mastering the basics as its what helps you figure out the not-so-basic ways around more complicated problems. Change gear lathes have been around for over a century, making a basic text like "How to run a lathe" from South Bend (now out of print and available as a free .pdf) very useful. Once you get the basic understanding of end gear trains driving your lead screw which moves your carriage a fixed distance per turn down, the specifics of which combination of gears is needed for which thread pitch (as pictured in the gear chart on the front of the machine) will all make sense to you. I can see both a picture of the gear layout as well as the number of teeth on the gears for each thread represented in the chart in your picture edit (which is really all you need that is specific to your lathe).

                            mini-lathe.com is another good source...not because you have the same 7x lathe as depicted there since you don't, but rather because it shows some of the basics.

                            Paul
                            Last edited by pcarpenter; 05-07-2008, 05:11 PM.
                            Paul Carpenter
                            Mapleton, IL

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                            • #15
                              Wow---I actually did it---cut my first thread. I figured out the change gears, and it seemed to be right. I didn't have a peice of 3/4" round bar stock, and I don't have a proper thread cutting tool. So---just to verify that I had figured out the change gears, I used a peice of 3/4" hardwood broom handle and a V shaped carbide tool. I didn't cut a deep thread, and it tore up the hardwood, but when I took it out of the lathe and measured it, it is cutting 10 threads per inch, like I had calculated. I am thrilled beyond measure!!! This weekend I will buy a proper shaped thread cutting tool and a setting gauge, and try this for real. Next challenge will be to figure out the thread cutting dial that lets you start a second cut in the same track.
                              Brian Rupnow

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