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Repair of Lathe Change Gears - I Need Advice.

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  • Repair of Lathe Change Gears - I Need Advice.

    Hi all. I have a Monarch lathe that was built in 1967. It came out of a school shop and so probably did not receive the best of care. The ways are in good shape and all of the feeds and speeds work. The lathe has been more than accurate enough for the machines that we build for our plant. (I’m looking for a face plate by the way – LO). I have recently come across a problem, however. Maybe some of you could give me some advice on the best way to correct it.

    I was fixing to cut some 7/16-14 threads. After setting up the machine for this thread and getting ready to cut this thread I turned the machine on and engaged the half nut to take a slight cut to make sure that I hadn’t made a mistake and had it set correctly for 14 threads before I took a heavier cut. When I engaged the half nut the leadscrew stopped. I cut the motor off and double checked the levers to make sure they were engaged properly. Sometimes you have to fiddle with the levers to get all the gears in mesh on this lathe. No luck. You turn the lathe on engage the half nut the screw stops – no torque. I figure there might be a clutch of some kind that needed adjusting or maybe a key or pin that was broken or partly so. I took the cover off to take a look inside the gearbox.

    What I found was the following: The change gear for 14 threads has one tooth missing. The teeth on this gear are partly stripped on one side maybe a forth of the width of the face. The biggest problem is that the main gear which is always engaged on every change gear and transmits the torque to each change gear, the one which is moved laterally to engage each change gear, is also stripped on about a third of the face width. Evidently there has been a wreck in the past between these two gears. If these two gears are not lined up exactly then when torque is applied the screw can be stopped. Eveidently I didn’t have these lined up exactly when I noticed the problem. The problem is that now I know how the main gear is weakened and could go under a heavy load which , of course, is sometimes applied. The gears, as near as I can tell without taking the gears out, are hardened.

    What to do? ( 1) I’m told that to get a hardened gear made might be as much as $350-$450. (2) I could sell the lathe but I’m honest and I would point this problem out to a perspective buyer. This would also cost me money, maybe more than replacing the gear. (3)Make a gear myself but it would have to be a soft gear and might not hold up with the hardened gears it would mesh with. (4) Find a used gear, but where? That might take forever. (5) Find a similar lathe that is worn out for parts. Might take forever. (6)Make a whole new set of soft gears in the shop, maybe several spares. Can anyone give me some advice on this? I would appreciate it.


    Charles Dunn

  • #2
    I purchased a feed gear from Boston Gear to repair my Monarch when I had it.
    At least some of the gearing is standard
    (Between spindle and change box).
    Ebay regularly has parted machines with all kinds of gears etc.
    If you make "soft" gears, they will last a long time.
    Good excuse to buy a new lathe in 20 years
    If in doubt make two.



    • #3
      I expect if you make a gear out of cast iron, it will last as long as you need to worry about it. If it doesn't...make another one!

      If you made the gear from cast iron, a local heat-treatment place could harden it for you, too. As long as you're willing to wait for them to be doing a batch of the same stuff, I bet they'd add your gear to the furnace for not a huge amount of money.

      I'd first check to see what Boston Gear or other supplier can do for you, though.

      [This message has been edited by SGW (edited 05-03-2002).]
      Try to make a living, not a killing. -- Utah Phillips
      Don't believe everything you know. -- Bumper sticker
      Everybody is ignorant, only on different subjects. -- Will Rogers
      There are lots of people who mistake their imagination for their memory. - Josh Billings
      Law of Logical Argument - Anything is possible if you don't know what you are talking about.
      Don't own anything you have to feed or paint. - Hood River Blackie


      • #4
        I'm not surprised at the quote you got for a new gear. I had a similar sticker shock a few years back, which forced me to concoct an alternative.
        Your 3rd Para implies that the bad gears can, with some finesse, be aligned so that it does work. If that's the case I'd just live with it and conduct a vigilent Ebay search (and all other sources) til some replacements turn up. That won't do much for the mental anguish of knowing of the problem, but it might do wonders for your pocketbook. From your description it sounds like a replacement for either of the two gears would fix the problem. That would double your probability of success.

        Here again, it's a shame ebay doesn't offer a "Want to buy" option.

        [This message has been edited by lynnl (edited 05-03-2002).]
        Lynn (Huntsville, AL)


        • #5
          hi, fellas.

          I appreciate your advice. You've made me feel a whole lot better about my problem. After thinking about it, I've decided to just not worry about it. I'm looking for another lathe anyway. If nothing happens before getting my next lathe then I can pull the machine out of service and deal with it then. As you say, in the meantime maybe some replacement gears will turn up and make it a small problem anyway.

          Charles Dunn


          • #6
            Hey, if you can make a soft gear, go for it!
            This IS a Monarch after all. The other gears won't mind if it's soft and it'll probably outlive you.


            • #7
              Yeah, what they said. Give the old girl a hug & a kiss for us - talk nice to them and they never break down.


              • #8
                Hey, snorman, Thrud. You'll have to exscuse my asking a stupid question every now and then. I'm not a professional machinist. I went through a machine shop trade course but didn't even get to the lathes. I dropped out because the instructor wouldn't let me make parts for a machine I wanted to build for my plant. I had a family and couldn't justify the cost (lost wages). The parts were similar to what he was grading us on and I was willing to furnish the material. He said no he couldn't do it. I quit and talked my father into buying a drill press, a horizontal bandsaw, a welder, cutting torch, and bridgeport mill. That's what I started with. That was 23 years ago. After a while I got a lathe. It wasn't much of one but it worked. I built the machine (a four spindle vertacle drilling machine) and it was a good machine. We used it several years. I've been building machines off and on ever since. My machine building isn't full time. We have a 156,000 sq ft moulding plant. I am responsible for all of the maintenance and repairs, mechanical and electrical. I also do the engineering for the plant. And since I'm part owner I have other responsibilties as well. I will always regret not being able to work under well trained and seasoned machinist. I have the utmost respect for the trade. What little I know has been self taught. I am more of a Jack of All Trades, master of none. Now, I'm starting to build a lot more complicated equipment. It is very challenging and interesting. At times it is difficult because of the constant interuptions that I have to put up with. The one thing that I can count on when I get up every morning is that I will run into things that I'm not sure how to handle. But somehow I manage. For sure, every day I find out about more things that I don't know - about how little I know. But, boy howdy, it sure is fun. If you go to you'll see the bridgeport we bought 23 years ago. The lathe in question is in the background. That's me with the mill. Yep, I wear overalls every day.

                see ya'

                Charles Dunn


                • #9

                  Beautiful shop.

                  Another way of repair is clean the broken area really well and built it up with braze.
                  Skim o.d. and faces off.

                  Lay another gear on top and layout tooth location.

                  Band saw and file, or re- machine new teeth in the braze.

                  Or press and loctite pins in at the tooth centerline, and file or machine.

                  Or cut a slot and insert (press and pin or silver solder) a "Dutchman" in the slot. finish as above.

                  All quick and dirty methods used many times before.

                  Should hold up if you don't crash lathe like the last guy.



                  • #10
                    hi, mite.

                    i sure do appreciate the tips. are you a professional? i'm sorry that i don't know. i'm a new comer hear. i wish i had more time to spend hear. everybodies friendly, and it sure looks like there's a lot of know how represented here. i'm sure i'll recieve more useful advice than i'll give. as i say, i'm pretty much self taught with trial and error.
                    so, i've probably picked up a lot of bad habits and do a lot of things bass-ackards. thanks

                    Charles Dunn


                    • #11

                      Nice plant! Hey, there are no stupid questions - there are however - stupid answers. Had a few myself, like glass being a quasi-crystal and not a viscous fluid as I was led astray by Scientific American. But let's not bring that up again.

                      Life is a continuous learning experience. No one person has all the answers - if anyone at all.

                      When in doubt, just remember to ask - it is free! The advice, not the beer.