HF 7x10/12 Lead Screw Mod?

Discussion in 'Machine Modifications' started by rfresh737, Dec 26, 2017.

  1. Dec 26, 2017 #1

    rfresh737

    rfresh737

    rfresh737

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    I was wondering if there is a mod to replace the lead screw on the Harbor Freight 7x10/12 mini-lathes...to sync the dials, in Imperial units, to the lead screw, which is in mm?

    This would provide the correct amount of travel with the dials.

    Thanks...
     
  2. Dec 26, 2017 #2

    rfresh737

    rfresh737

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    I'd like to match the lead screw with the factory mm dials. In order to do that, do I just need to install a mm lead screw?

    UPDATE: I mis-spoke above. I actually have a need to cut imperial threads, so what I'd like to do is make sure my HF 7x12 has an imperial lead screw and the matching slide screws and dials.
     
  3. Dec 26, 2017 #3

    RM-MN

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    Some of the Harbor Freight mini lathes come with metric lead screws, some with imperial. Verify which you have. You probably can purchase either lead screw if you want to go that route.
     
  4. Dec 26, 2017 #4

    tornitore45

    tornitore45

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    Do not forget to order the matching split nut,
     
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  5. Dec 26, 2017 #5

    ShopShoe

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    Check this out:

    https://littlemachineshop.com/products/product_view.php?ProductID=2383&category=1687114045

    I have ordered one of these, but not installed it yet as I am doing a comprehensive rebuild and group of mods to my 7x.

    Lack of shop time and cold weather means it will be a while before I am done with my lathe, but I will try to post when I am done.

    If you also look around LMS carefully, you can find the metric leadscrews and many other parts to customize your lathe.

    I have also had to talk to them on the telephone and they seem to be helpful folks. (Usual disclaimer, no affiliation with them, but a happy customer.)

    Let us know what you do,

    --ShopShoe
     
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  6. Dec 26, 2017 #6

    rfresh737

    rfresh737

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    @ShopShoe
    I'm still trying to wrap my head around this stuff. So your link to LMS makes the cross and compound slides and dials into imperial units of measurement (I believe).

    So, if my main lead screw is also imperial, then my lathe is completely 'synchronized' to imperial units, right?

    @tornitore45
    Thank you, I will remember to ask about that when I order the parts I need from LMS.

    I googled how to determine if one has a metric or imperial lead screw but either came up empty or I didn't just understand what I was reading!

    If my cross and slide dials range from 0-40 then they are imperial units? What does the 0-50 range do for me?
     
  7. Dec 26, 2017 #7

    Wizard69

    Wizard69

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    Well probably not. Your dials will need replacement as will you half nuts. In any event your machine should be able to cut both metric and imperial threads as is.

    Frankly i see an investment in linear scales as a better use of ones money here.
    Thread pitch gages are a good investment. Another approach is to simply rotate the leadscrew one revolution and see how far the slides move. This isn't rocket science just sit down for a minute and think about it.

    The dials end up calibrated for the leadscrew used on the machine. Change the lead screws and you will have to change the dials. You will probably have to change legend plates that shows you the lead for various gear box / change gear settings too.

    In any event, considering the questions posted i fear you are jumping the gun here. It might help to tell us why you think you need to change the leadscrews because im hearing more confusion than anything here. I just smell a rush to try to fix something that you don't understand yet.

    That being said there maybe good reasons for you to do a completely imperial machine but i haven't heard them yet from your posts.
     
  8. Dec 26, 2017 #8

    rfresh737

    rfresh737

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    My first project will be to do some outside thread cutting: 5/16-18. Perhaps I don't need to do any lead screw mods then. I probably got confused by all the reading I have done on the subject. I was just concerned about what I read regarding turning the cross dial one full turn (0.040) and not having the slide move the same amount. I saw a Youtube video showing the errors adding up after making 10 turns. I was just trying to avoid having those errors.
     
  9. Dec 27, 2017 #9

    ShopShoe

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    rfresh737,

    I think "jumping the gun" is probably relevant to what I said and what you asked.

    IF your Harbor Freight lathe has the most common leadscrew/dial combination on the cross slide and compound it is true that after SEVERAL turns of the dial the actual distance you have advanced your cutting tool will be different than what the dial says. Add to that the fact that you must remember that you are advancing the tool a fixed amount, but cutting the overall diameter of the part you are making: some math is involved.

    If you prefer to operate by marks and math, then you probably want the dial calibration to match the actual advance.

    BUT, if you are learning, your process will be to cut a bit, measure the part, cut, measure, etc. You should probably use a micrometer to check the final
    diameter of the part. The dials are not as important in this situation.

    Now, the leadscrew that advances the carriage for screw-cutting is controlled by the change gears you set in the headstock, so using a leadscrew with a different thread pitch will need a different set of change gear setup tables to determine what pitch you want to want to set, whether this is metric or imperial is not entirely relevant (see note below). What the gearing will do is rotate the leadscrew a given amount relative to the number of times the spindle turns, which will control the advance of the carriage and thus the cutter.

    If you are trying to make a part to fixed dimensions by calculations, then knowing exactly where the cutter is is important, but as a learner, it is usually cut, measure, cut, measure, etc.

    IF you really want to know where your cutter is at all times, what you need is a way to convert the POSITION of the tool to numbers as accurately as possible, which would be by a digital readout system (DRO), modified calipers mounted to the slides, rulers screwed to the bed, dial indicators, or any combination of the above as found on hundreds of posts here and elsewhere. Note that an accessory available for the 7x lathes is a digital readout which mounts on the cross slide and compound leadscrews but which works by counting turns of the leadscrew, which puts you back to a digital version of the loosely-calibrated dial problem. This is not a true positioning DRO. LMS and others sell this, and some find it helpful, but I would not get one myself.

    What you are getting to is that you may want to get some more experience making parts to precise dimensions with what you have before you try making your minilathe perfect. Your personal situation will help you determine what you will do.

    (NOTE ABOUT METRIC THREAD PITCHES ON THE MINILATHE) There is some information from several sources that more accurate metric threads can be cut on the minilathe if a 21-tooth gear is in the changegear setup. This gear is not normally included in the set of gears supplied with the lathe. It is not strictly necessary, as short lengths of metric threading can be done with the regular gears set up by the standard charts.
     
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  10. Dec 27, 2017 #10

    ShopShoe

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    Checking your cross-slide and compound advance calibration.

    (In order to keep the post above shorter and more to-the-point, I am writing this separate post.)

    If you want to check the advance of either of these slides, mount a dial indicator so that it can measure the advance of the toolpost directly. Advance the relevant slide according to the calibrations on the dial and note the advance as shown by the indicator. Try it more than one time and at several different extensions (threads can be cut inconsistently). There are videos on YouTube of this process, but I don't have any links handy.

    While you have this setup, try to move parts of the cross slide, compound, and toolpost assemblies around by hand to see if you can detect any play and note the amount of backlash in the leadscrews.

    --ShopShoe
     
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  11. Dec 27, 2017 #11

    RM-MN

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    On the cover of the headstock of my mini lathe is a table showing what combination of gears it will take to make a certain thread pitch. Look for it on your lathe. If the thread pitches are listed there and are imperial (threads per inch) just use the gear combination that it shows. 5/16-18 is a common thread and easy to do on my mini lathe.

    I own 2 lathes, one a 7x14 and the other a 10x24. On the 7x14 the dials on the cross slide are calibrated to show the amount the diameter is reduced. The bigger lathe is calibrated to the amount the cross slide moves, reducing the diameter by twice what the dial shows. I'm only partly confused.
     
  12. Dec 27, 2017 #12

    rfresh737

    rfresh737

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    @ShopShoe

    Thanks very much for the detailed help. It's nice to see several folks jump in with their advice to help a newbie like myself.

    Regardless of my skill level with a lathe, it just bothers me that their is a built-in 'error' with the lathe. I understand the low price point and that you get what you pay for. The MicroLux 7x16 lathe makes a big deal out of the fact their lathe does not have this error and tuning their cross or compound screws are *always* accurate and correct. But that lathe cost $800.00 USD. My Harbor Freight 7x12 cost half that amount.

    Anyway, I'm going to buy the kit from LMS for $60.00 that will 'fix' this problem on the mini-lathes: https://littlemachineshop.com/products/product_view.php?ProductID=2383

    I will also take everyone's advice and cut, measure, cut measure, etc.

    I am the founder and admin of a mini laser forum (located here www.BenboxLaser.us). We have a great community of folks who, like I'm finding out here, are eager and willing to help new folks with their specific hobby, no matter how dumb their questions might be or how confused they might be!

    Thanks again to everyone for the help!
     
  13. Dec 27, 2017 #13

    Wizard69

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    Shopshoe has some good points with respect to how a lathe is used. I would go so far as to say the use of manual lathes is similar even with professional machinist. If one is doing manual work it is very much a matter of measuring and adjusting based on results. Even if you have a DRO you likely need to measure and calibrate.

    In any event this common usage pattern is why i would suggest a DRO upgrade over a leadscrew, dial and nut replacement program.

    Now this point is limited to lathes, for a mill id be far more concerned that the table moves precisely with respect to dial indications. There are a couple of reasons but the longer distances traveled means errors are more significant. Also it is often harder, sometimes impossible , to measure a feature or reference from that feature to locate the tool accurately in a mill. That is sometimes you cant use the measuring tools you have on a work piece setup in a mill. Probably not a good explanation. Even with a mill you gain a lot from a decent DRO.
     
  14. Dec 27, 2017 #14

    Wizard69

    Wizard69

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    We try to help! Just remember opinions are just that.
    Now this bothers me because all machines have built in errors. The lead on a Leadscrew isn't perfect even on fancy ground leadscrews. Now that isn't the same thing as putting inch calibrated dials on metric screws but if you are expecting perfect don't count on a leadscrew.
    One might call that exploiting the novice user.

    By the way the Microlux is a very nice lathe and a considerable upgrade over the shorter bottom end machines. That however has more to do with other features than the dials and leadscrews.
    As an owner of a HF 9x20 i fully understand what it is to buy the bargain basement machinery. At this point in my skills department there is little i can blame on the lathe itself accept for it being a bit small. It is the lathe operator that makes the machine work.
    You are free to do so but i don't see it solving any problems for you. In fact it might add to your frustration level.
    Id strongly suggest spending some time on youtube with a focus on professional machinist like Adam Booth, Kieth Fenner and others doing one off machining jobs. Both of the guys mentioned are highly adept at lathe operation and are constantly measuring and adjusting based on those measurements.

    To look at this another way, if you stick a new tool in the tool post where is that cutting tip in relation to the dials. The reality is you don't know so what good are those leadscrew dials at that point?

    Another point to make is that Adam and Kieth are working on rather large and professional equipment, but equipment with wear. Neither one of them relies upon the dials for precise work. They resort to DROs, travel dials, or the use of dial indicators often held with magnetic bases.

    So i have to repeat, I'm left with the feeling you are jumping the gun here. That $60 would be better spent on a decent magnetic backed dial indicator, a carriage stop ir a number of other things. Just my opinion.
    Remember there are no dumb questions. For the most part everyone here tries to be helpful but what is right or wrong is a matter of perspective. From my perspective you are reacting to a perceived problem that might have zero impact in reality.
    No problem; it is great having new people here. Many of us are just starting to outfit our shops so we share common frustrations. One of those frustrations is the cost of tools which has us buying HF tools instead of new 10EE's. In the end we need to learn to get the most out of these challenged machines.
     
  15. Dec 30, 2017 #15

    crystalspec

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    Try little machine shop. they sell mod kits for both metric and imperial mini lathes. I recently extended my 7x10 to 16 in. it turned out nicely. It helps if you have a mini mill to drill the mounting holes with.
     
  16. Dec 31, 2017 #16

    lathe nut

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    I have the Imperial lead screw, I cut Imperial and metric threads, just changes the gear and on metric don't disengage the half nut.
     
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  17. Jan 13, 2018 #17

    rfresh737

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    My tear down for cleaning is now complete.

    I'm lucky I live fairly close to the Little Machine Shop here in the Los Angeles area ('close' means within an hour with the kind of traffic we have). In a week or two I'm going to take my spindle case into Chris's shop and install his roller bearings kit. Chris has a hydraulic press to press the bearings which he said he would help me do. I'm not able to do that kind of a job at home.

    While I did buy a magnetic dial/base unit for checking my lathe when I start to put it all back together, I am going to stay with my plan and buy his Imperial lead screw/dial kit for the slides while I am there. I can save a little on shipping costs.

    I understand I cannot do machining by just using/trusting those dials, so I will get into the habit of cut/measure/cut/measure etc.

    Mini-lathe Complete Tear Down.png
     
  18. Jan 13, 2018 #18

    DJP

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    You actually can trust the dials but not until all of the wear, backlash and slack are taken up in the machine. I had a 1940s Southbend lathe that at over 75 years old would still do good work as long as I used the cut/measure/cut/measure/stop technique.

    You have discovered this wisdom in the responses so you are on your way. Rebuilding your lathe is a different project that has merit on its own so enjoy that journey too.
     
  19. Jan 13, 2018 #19

    XD351

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    There are so many mods that can be done to those little lathes it is almost a hobby in itself !
    My one has tapered spindle bearings , taper gibs on the saddle , runs a 1hp three phase motor and inverter control ,custom control box with tacho and the list goes on.
    I haven't fitted a DRO yet and wouldn't bother with the type that replaces the dial on the cross slide as they are just a rotary encoder driving a display so any errors in the cross slide feed screw and backlash are not accounted for .
    I need to tweak the way the motor drives the spindle as i kept the two speed system as fitted originally with steel gears fitted which are very noisy !
    If you are fairly new to machining you could take a look at Thatlazymachinist on youtube i think you will learn something there .

    While you are at LMS pick up a test bar that fits into the spindle taper so you can check the head for alignment with the bed - sometimes they have to be shimmed , mine was ok for the most part but the vee groove in the head was cut too deep so the head could rotate a little on the bed . I set the head up so the spindle bore was parralell to the bed and measured the gap at each end and both sides of the vee groove with feeler gauges and made up some shims to fit .
    When i get around to fixing the noisy gears i might set the head up on my mill and give the base and vee groove a skim so i don't need shims .
     
  20. Jan 13, 2018 #20

    rfresh737

    rfresh737

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    >While you are at LMS pick up a test bar that fits into the spindle taper so you can check the head for alignment with the bed.

    Do you have a link showing what that test bar looks like? I can't find it on the LMS site.
     

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