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  • Cutting left hand threaded nut

    I am making an arbor for a slitting saw that I want to use in my mill/drill By stararting on the wrong end of my stock I have elected to go the hard way.(It may come to turning the blade over and cutting right hand threads and running the machine in reverse)

    I am concerned that the stock will slip through my Logan 3 jaw chuck as I cut the left hand internal threads. At present I am thinking of leaving a small rib on the stock that it can be hooked behind the chuck jaws.

    It is obvious that this "newbie" needs a lot of help. Any suggestions will be appreciated.

  • #2
    Unless the nut is very thin wall you should have no problem holding it to be threaded. Threading is often done with very small depth of cut, especially by those of us who are learning how!

    Dont be discouraged if your first attempt does not come out right. If it does you have a lot of bragging rights. Just take it slow and easy. I would not attempt to thread it from the headstock out unless my lathe would not reverse. It seems a lot easier to me to see the starting point. Be sure you have plenty of clearance behind the nut to give yourself room to stop easily.

    Have fun and be careful.
    Last edited by Don Young; 12-06-2009, 11:24 PM.
    Don Young

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    • #3
      no need to worry, as Don says threading is done with many successive passes, there isn't/shouldn't be anything about it that will overpower the 3 jaw. Commercial arbors are keyed to the cutter but I'm with you, for very thin saws go no key - if it grabs with a key, shatter, no key hopefully it will just slip.

      if it hadn't already occurred to you, make the arbor first - measuring internal threads to spec is difficult, much easier to make the male first and use it as a gauge.

      if it is easier, cut right and flip the saw...no shame in that
      .

      Comment


      • #4
        It isn't clear what you are trying to do. Are you trying to cut left or right handed threads? Are you confused about which ones you need because of which end of the part you are working on?

        Since no one with more experience threading seems to have chimed in, I will take a stab at it.

        I thought most Logans with quick change had tumbler reverse for cutting left threads. If it is a change gear model, then you may be able to shoehorn any random gear between two existing gears to reverse lead screw rotation.
        If you need left handed threads at all.

        Most Logan models did have threaded spindles which means you run the risk of the chuck spinning off if you try to cut/run the spindle in reverse (or brake suddenly).

        If you turn the blade over and cut in reverse, you will be lifting the carriage which may not be securely held down. This can cause chatter (and chipped carbide bits) and dimensional error. Check the gibs on the bottom. The bottom ways may not be parallel to the top ones (or the top may be worn) making it hard to clamp down without play over the length of travel. Mounting the bit right side up on the back side of the cross slide may be more stable but you may not have holes/t-slots back there. But for an internal thread tool, flipping the blade over doesn't have the same effect as for an external one - it doesn't cut on the opposite rotation it just cuts on the back side (which can help with chip clearance). So all this may be moot. I think you need the opposite hand inside threading tool if you are going to run the spindle backwards.

        Is there some particular reason you are worried about the work slipping in the chuck? Yeah, it will throw your thread alignment off but slipping is something to be avoided even when not cutting threads. If the tool is on center, the chuck is properly tightened, and the depth of cut on each pass is reasonable, you clear the chips from the hole, and the ID of the hole being threaded isn't huge, the chuck ought to be able to hold - that is its job. You may have a wider width of cut (the full thread profile) than you might usually have which you compensate for with a smaller depth of cut. Higher cutting forces of a negative rake tool might increase chances of slipping. If you had turned down the work OD on the portion you will be holding in the chuck smaller than the thread diameter then the chuck is working at a mechanical disadvantage. Work that is very hard would too. You could use a lathe dog to prevent slipping. But if the dog is needed that may be a sign you are pushing things too hard. Forces when single pointing a thread should be a lot lower than when tapping, though they are higher than many light cuts.

        Are you sure you need to cut threads backwards? Your reason for that, starting from the wrong end of the stock, doesn't make much sense to me. If you flip a right handed bolt or nut end for end, the threads are still right handed. The direction you turn a screwdriver seems to change when viewed from a constant viewpoint since the screwdriver rotates when the bolt does but the threads still advance in the same direction, which means you cut them the same way, whichever end of the part is held in the spindle.

        However, trying to cut the threads for a typical arbor from the wrong (shank) end means your threading tool would need to be long and over extended. Flip the part over and thread from the saw end of the arbor.
        You might lose a little bit of concencentricity. No big deal, it is apparently just a mounting screw hole, it doesn't affect the concentricity of the saw. If you are way off, though, you will be trying to thread a hole off center. If the concentricity is an issue, check with an indicator and use a 4-jaw or shims to get the part back on center. Or have you already cut a taper that fits your mill but not your lathe spindle or chuck?

        Or are you worried about overtravel when threading towards the spindle (a common issue) and hitting bottom due to reaction time/consistency? That is a common problem but I don't see what it has to do with starting from the wrong end of the stock has to do with it. Some people do reverse the spindle so they can work left to right to avoid crashing.

        Threading towards the spindle, you need to avoid: crashing into a shoulder, crashing into the bottom of the hole, trying to cut threads on a deeper pass that weren't previously cut on a shallower pass (i.e. seriously digging in), and crashing any part of the tool, tool holder, compound or cross slide into the spinning jaws of the chuck, or powering the cross slide into the end of travel. Run the spindle slow, turning by hand if your slow speed selection is lacking. Setup an indicator to tell you when you have reached the end of the feed. Always feed to exactly the same point, or less, than on the previous pass - less gives you an incomplete thread but avoids digging in. You may want to cut a relief with a boring bar or even the threading tool past the intended end of the threaded section but just shy of the bottom of the hole. This allows you some over travel before you crash into the bottom of the hole or into a section that hasn't been rough cut by the previous passes.

        It is common practice in production environments to feed the tool using the compound rather than the cross slide. This produces a more manageable chip. On an internal thread, this may help. An off the shelf threading tool may have been preferentially ground for using this technique (i.e. with asymetric angles). For standard 60 degree threads you set the compound close to, but not to exceed, 30 degrees. I.E. 29, 29.5, or 30 degrees (make sure it isn't over 30 degrees). If you are even slightly past 30 degrees, you will erode one of the flank walls, deviating from the correct thread profile, as well as taking more of a chip on the side you are trying to avoid cutting on. The protractor on the compound, or your use of it, may not be accuate enough to set to 30 degrees without exceeding; hence 29.5 degrees (standard) or even 29 or less if you really don't trust it. The threading tool, however, is set symetrical to the part (30 degrees each side of perpendicular) with the threading gage. This way, most of the cutting is done on one side of the thread profile and the chip will roll to the side. You have to increase the distance fed to compensate for the angle. The cross slide, with a threading stop, is sometimes used to retract the tool at the end of each cut; at the start of the next cut, you run it back into the threading stop. Thus the compound is used to set the depth of each cut and the cross slide for traversing making it easier to keep track of where you are in the cutting process once you get used to using both. There is an illustration here:
        http://books.google.com/books?id=_sV...age&q=&f=false
        Bringing the tool in perpendicular to the axis of the part is called straight infeed or radial infeed. Coming in parallel to the wall is called flank infeed and coming in at slightly less than the wall angle is modified flank infeed. The term angular infeed is also used for flank infeed. 29.5 degrees in which direction? That direction which cuts a chip off the flank of the thread closest to the spindle. If you are cutting on the inside front side, you may want to rotate 150 degrees counterclockwise from the position where the compound crank is over the cross slide crank as rotating 30 degrees clockwise might put the compound too close to the chuck.

        If you don't have problems with chip clearance, you can use the simpler radial infeed method.

        Test your part with the screw before removing from the lathe. Due to tool deflection, you may end up with an undersized thread such that the screw won't fit. Needing to realign a part to resume threading is best avoided.

        You may want to practice on a piece of scrap first. Chances are you won't get it right the first time.

        You can also use a tap manually with the chuck locked using the lathe tailstock to guide rather than trying to single point.

        Comment


        • #5
          You're making a left handed thread so the nut won't loosen when the arbor turns the blade. Another way to do this is with a washer and a pin. The washer (make it a blade stabilizer if you have room) is placed on a bolt and the bolt threads into the arbor. The blade goes on, then the washer and bolt, and the washer is rotated til the pin goes in a hole, then the bolt is tightened. If the washer can't rotate, it can't loosen the nut. On the same hand, the bolt can't be forced to over-tighten as well. You can use a right hand thread. The blade fits onto the arbor, and if you like, the washer can be recessed so it also goes over a short section of the arbor.

          Another option with this method is to drill the hole for the pin through the blade and into the arbor. Then the blade is pinned as well. I don't like this way because it means the blade has to be drilled, plus there's no slippage in case of a jam. If you can handle the blade being pinned to the arbor (to the shoulder, actually), the arbor can have a threaded section which you use a nut on, instead of drilling and tapping the arbor for a bolt.
          Last edited by darryl; 12-07-2009, 03:47 AM.
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

          Comment


          • #6
            Thanks guys for the help. Don the nut is 1-5/16" diameter and the tread is 1 inch, and now that I look at these numbers I may use 1-3/8 diameter shafting for the nut. My Clausing MK 3 motor does reverse but I am concerened that the chuck will unscreww off the 1-1/2 X 8 headstock threads even with the light cuts.

            Mcgyver, youir heads up on not putting a pin in the sawblade notch makes sense to me . The arbor has been made including a finished 3/4' section for the R-8 collet. Not to brag, but the left hand threads do look pretty good.

            Whitis, thanks for the information, it is a lot better than what I received at VO-Tech. The truth of the matter is that I started out with a 1-1/4' thread cutting training spool that has multi-diameter threads on it and I had left hand threads on the brain. If I have to do this over I may well go to a right hand thread.

            Thank you Darryl, now I have a totally different design concept for the next one. You mentioned a blade stabilizer which brings up a concern, what should the blade stabilizers be for a 2-3/4" 72 tooth blade be?

            Thanks again.

            Ray
            .

            Comment


            • #7
              Ray, I didn't consider that the blade already has a slot. That would mean that you wouldn't have to drill for a pin. In any event, my philosophy on a stabilizer, which is basically just a washer, is that it would be slightly larger than the shoulder on the arbor that the blade seats against. Reason for this is to possibly prevent a resonance from building up in the blade. You obviously have to consider how much blade you'd be able to use, and how much the stabilizer would reduce that capacity.
              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

              Comment


              • #8
                So, why do you need a left hand thread? Won't your mill turn clockwise? What's up with that?

                Comment


                • #9
                  RD,
                  I'm with TDM: my slitting saw arbor has a RH screw that secures the saw collar. The mill rotates in the "normal" direction to use the saw.


                  That said, I once made a 1 1/4-8 LH square threaded nut for my big planer. Don't remember the details, but it worked out OK.

                  Comment


                  • #10
                    Direction of spindle rotation is a critical factor in selecting left or right hand threads. In some cases, if there is a key that prevents rotation of both the saw and the clamping ring on the other side of the blade relative to the arbor shank, then you might be able to get by with either. Get this wrong, and you may be confronted with a flying saw blade. And from your description, it sounds like you have left threads where right are needed.

                    With left handed threads on a normal mill spindle rotation, as soon as the saw encounters the work and cutting forces are present it will unscrew the retaining screw. This is true whether or not there is a retaining disk between the blade and the screw head. It would also be true if a nut is used to hold the blade on a threaded arbor; a jam nut would help some.
                    Lock washers can not be relied on to hold such an assembly together.

                    Rapid acceleration or deceleration of the spindle when starting or stopping can also cause the screw to unscrew, for either direction of rotation and either direction of threads. The blade, in particular, acts as a flywheel (though less so than a grinding wheel). This tends to favor coming loose over getting tighter as it takes more force to tighten an already tight screw than to loosen. Likely to be lower than cutting forces but still a consideration. This is an argument for having a keying mechanism between the shank and the retention ring, whether or not the blade itself is keyed to the arbor. Without a key, one must be careful to monitor the tightness of the screws/nuts in order to reduce the risk.

                    For a bench grinder with wheels on both sides, one arbor would want left threads and the other right.

                    Comment


                    • #11
                      Originally posted by rock_breaker
                      I am making an arbor for a slitting saw that I want to use in my mill/drill By stararting on the wrong end of my stock I have elected to go the hard way.(It may come to turning the blade over and cutting right hand threads and running the machine in reverse)

                      I am concerned that the stock will slip through my Logan 3 jaw chuck as I cut the left hand internal threads. At present I am thinking of leaving a small rib on the stock that it can be hooked behind the chuck jaws.

                      It is obvious that this "newbie" needs a lot of help. Any suggestions will be appreciated.

                      You are taking a simple job and making it way more complicated then needed.
                      good luck , im not going to tell you what to do, just go for it.

                      Comment


                      • #12
                        Thanks for helping guys there are a lot of good points to consider. the project has been put on hold until I get all the snow that blew in from the neighbors quarter section out of our driveway. I don't think he would come and get it if asked.

                        Comment


                        • #13
                          I think you are making it too difficult. Here is a sketch of a simple saw arbor. I have made several of these and they work well. And tapping a single hole is a lot simpler that lathe cutting matching internal and external threads.



                          I first mount the stock in a three jaw chuck with 1 to 2 inches of stock sticking out and I roughly face the end and drill with a center drill.

                          Then, I mount it with the full length exposed, using the three jaw and tailstock live center. The smaller diameter of the shaft is turned down and finished with abrasive cloth using oil or cutting fluid to keep the dust down and to get a better finish.

                          Now I reverse it and mount it in a collet to turn the head. Since the head is turned while mounted in a collet, the saw will run dead true. A small boss is turned at the center to precisely locate the saw. A hole is drilled on the axis, in the lathe and it is tapped for an appropriate diameter cap screw.

                          A thick washer is turned from the same stock. The face that goes against the saw is turned first with a slight depression in the center. This ensures that the saw is clamped by the outer diameter and not just in the center of the washer. The outer side of the washer does not need to be overly precise as the cap screw just bears on the center of it. So a normal cutoff tool could be used to separate it from the stock and then file or lap it to finish. Or it could be sawed off and finished in the three jaw.

                          If you need to eliminate the projection of a regular cap screw, a countersunk cap screw could be used.
                          Last edited by Paul Alciatore; 12-11-2009, 12:08 AM.
                          Paul A.

                          Make it fit.
                          You can't win and there is a penalty for trying!

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                          • #14
                            Thanks Paul , as I said earlier I started the wrong way on my stock and am now going to try finishing it; as tatoomike68 said "just do it". I have received a tremendous amount of good information and ideas. Rest assured that if I screw up the LH nut I will go right hand.
                            Ray

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