Announcement

Collapse
No announcement yet.

rear mount cutoff tool

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • rear mount cutoff tool

    I wonder what you all have made to serve this purpose? What I'd like to do is make a lever operated cutoff tool which can be mounted on the rear way and swing in an arc intersecting the spindle axis. It might have an adjustable stop so it can be set for depth for grooving, and it might have a dashpot to limit the rate at which it can be moved. Levering it out should be quick, and perhaps the dashpot could have controls to set the rate of tool movement and the rate of return.

    Thinking about this today as I machined brass pins and cut them off. It would have been so much easier if I could just reach for a lever and swing the tool into the work piece till cutoff, then swing it out of the way- independent of the carriage. Anybody done something like this that works well?
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    Have one of these on my Wade lathe: https://www.ebay.com/itm/HARDINGE-LA...d=331941820419

    Comment


    • #3
      I looked through a lot of images, but didn't find the type of tool I was looking for. Most were carriage-mounted rear tool posts, whereas I'm looking for an independent type. Besides that, most used an upside down cutoff tool, which allows the spindle to turn the normal direction, but which puts an upwards force on the cross slide and carriage. On my lathe I have a spring-loaded rear way hold-down mechanism to keep the carriage in contact with the rear way at all times. Using this type of cutoff tool would make the carriage lift off with anything but light cuts. I could alleviate this by mounting the tool right side up, but I don't want to risk the chuck unscrewing. All the more reason to have the cutoff tool independent of the carriage.

      I have yet to figure out whether I can pivot the tool holder and have it keep the proper angles all the way from the outside of the work piece to the very center- it seems likely that if I get the tool angles adjusted for small diameter cutoff work, it won't be right for larger diameters. I may have to stay with a linear slide for the cutter holder.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

      Comment


      • #4
        On my lathe I have a spring-loaded rear way hold-down mechanism to keep the carriage in contact with the rear way at all times. Using this type of cutoff tool would make the carriage lift off with anything but light cuts. I could alleviate this by mounting the tool right side up, but I don't want to risk the chuck unscrewing. All the more reason to have the cutoff tool independent of the carriage.
        So you sort of want something that sits in place much like a steady rest which can be lifted up and plunked down when needed? One that rests on the tail stock ways so it can park up near the headstock out of the way without interfering with the carriage?

        Hinging in on an arc will be nothing but trouble. The issue being that a parting tool has to move inwards on a line radial to the center axis. Otherwise if you travel in on an arc of travel it'll be either pushed away strongly or want to dig in strongly. And depending on the pivot points it may do both during one cut. So I suspect you're going to be stuck with doing a dovetail or boxed in rectangular ram with a good adjustable close fit and some manner of lead screw.

        That spring loaded deal really messes things up. After all you want the upside down tool from behind to be easily and accurately positionable. And that really does tend to suggest using it with the carriage. But not if the carriage will be lifted up off the ways on a sprung keeper. That's a recipe for some nasty digging in or at the very least monumental chatter.

        Comment


        • #5
          What machine has spring loaded gibs?
          1601

          Keep eye on ball.
          Hashim Khan

          Comment


          • #6
            It's my mod. The usual thing is to have is a tab of sorts underneath the rear way to keep the carriage from lifting off. I added a spring-loaded roller- I think it's a ball bearing- to bring the rear of the carriage into full contact with the rear way, but without causing any binding as it moves across the whole distance of the bed. The roller runs underneath the rear way. The function of the tab is still there by an adjustable bolt, but it will inevitably have play in places and I wanted better control of the carriage.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

            Comment


            • #7
              Interesting idea.

              If you used a belleville washer as a spring, ypu could have consistent pressure over a range, and the range would be limited to a somewhat settable amount, which might do OK for the cutoff tool.
              1601

              Keep eye on ball.
              Hashim Khan

              Comment


              • #8
                I bought a recessing tool from KBC, long ago.
                Lever operated, could be mounted on rear as a cut off perhaps.
                Has stops.. I used it for I eternal recessing and chamfers .

                I still have it actually.. it has a 1 inch shank.
                I think they made 3/4 shank too.

                Duo you have dovetail or t slots onnthe back of your cross slide ?
                Last edited by 754; 04-09-2019, 02:55 AM.

                Comment


                • #9
                  Years ago I saw a picture of a kind of steady rest-style bed mounted cutoff attachment on lathes.co.uk, I think the slide came in from the top, but can’t remember what maker or even what country it was - maybe Russian?

                  A few lathes have cutoff tools on a shaft that pivots from behind the headstock. One for Schaublin 102 is shown on this page, 105-35.600, about halfway down: http://www.lathes.co.uk/schaublin/page11.html

                  Another, in operation on Frank Ford’s Rambold: https://youtu.be/gr4aN23XGz0?t=1m33s

                  Same principle but a little different arrangement on I guess what you could call a sliding headstock lathe: http://www.homemadetools.net/forum/l...538#post122981

                  Comment


                  • #10
                    I would caution against something tall and thin like a steady rest, it will be too flexible along the axis of the work, causing inconsistent cutoff lengths. The headstock mounted unit like Hardinge uses would be good, but it's positioning is limited.

                    allan

                    Comment


                    • #11
                      I made a rear mount for 26 and 32mm cutoff blades upside down, for the museum's Smart & Brown model A. It was on the rear of the cross slide, and as the forces were upward, I also added a rear saddle lock. It is vitally important that maximum rigidity for cutting off is maintained, so everything that can be locked is locked. Even three jaw chucks don't hold work as well as four jaw when it comes to cutting off. However, if nothing other than brass pins are cut off, a hinged upside down tool with the lathe in reverse could work. It would have to securely mount directly to the bed and have an extremely solid hinge without any play. I don't know how big the pins are, but anything over 1/8" diameter would require a cam operated slide to advance the tool.
                      Myford lathes had cutting off slides as accessories: https://www.ebay.co.uk/itm/Myford-Su...YAAOSw9Gdcqf1m

                      Comment


                      • #12
                        I'd have to say that old mart's mentioning of a saddle lock is the key for me. The issue with a spring style follower is that under the heavy lifting loads you'll get from a rear mounted parting tool on a small'ish lathe it WILL lift the carriage against the spring and lose contact when we least want that to be the case. Using the saddle lock to lock the carriage removes this movement and would be pretty well a "must do" step for any sort of carriage mounted rear parting tool post operation I would think.

                        And I'd also add a hearty "ditto" to the idea that a steady rest style of parting tool setup would need to be quite burly to avoid side to side flexing. And as much as the flexing issue also to reduce twisting in the vertical arm that supports the cutter and movement for that cutter.

                        Comment


                        • #13
                          Originally posted by BCRider View Post
                          I'd have to say that old mart's mentioning of a saddle lock is the key for me.
                          If you were to adapt a pull type DeStaco clamp to the spring loaded follower on the cross-slide, you could have a cut-off mechanism that pivoted off the rear.

                          Comment


                          • #14
                            Without the added spring and mechanism, my lathe is like anyone elses. The saddle will lift off the rear way, but by only the amount of play you get with the existing control tab. That could be 1/2 thou, it could be 3 thou- depends on the lathe. If the cutter grabs and lifts the saddle, it would only be by that amount. Not a killer, really- and the lock is a great idea. Pretty sure I could add a lock to my setup- with the saddle already being held to the rear way by some spring pressure, there would be no added movement when the lock is set, which would be a bonus. It certainly would be easier to create it all, as the cross slide movement is already there and the cutter would remain rigidly mounted in its holder.

                            Most of the jobs I'd do that require a repeated cutoff operation would already have stops set for the carriage, and for the length of material sticking out from the chuck. Because of this, the carriage is going to be up against a stop when the last cut is finished, so the lock can be applied at that point. The cutoff assembly would have to be laterally adjustable so it can also be given the correct position on the cross slide. By the way, I have the two slot cross slide with them going front to back, so it's easy to set the position of the cutoff tool in the front/back axis- I would just need to have slots in the tool mount so it can be adjusted side to side for positioning.

                            The cross slide has two dimples in it where the original compound mount would center on. I seldom use the compound anymore, and my tool mounting base now can be secured anywhere along the slots without needing the dimples. That makes it easy to set up two cutters and still have the slide moving mostly in the center of its range. Perhaps this will be the more optimum way to go about this project.

                            I would add the rear way lock- and then hope that the cross slide dovetails can be maintained in a close-fitting configuration. Otherwise, the slide could also lift off the saddle under the cutting forces. That will give the same kind of error- but it may not be as bad.
                            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                            Comment


                            • #15
                              I’m pretty sure this bed mounted cut-off slide isn’t the one I saw before but it works the same.



                              http://www.lathes.co.uk/saupe/

                              I imagine if you know where to position it you probably know what size stock you’ll use so some kind of bushing could be fitted to support the work.

                              Comment

                              Working...
                              X