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Parting or cutoff tool modification for a small lathe

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  • Parting or cutoff tool modification for a small lathe

    We get a lot of threads here related to issues when parting off, especially in regards to the smaller lighter weight lathes.
    One of the key recommendations regards increasing the rigidity of the parting tool setup. There are various factors here that can lead to chatter if one is not diligent when addressing any number of sources of slop or flex in how the parting tool and it's attending hardware are setup in order to increase the overall rigidity.
    I realize this is not as much of an issue in larger more rigid lathes but anything one can do on the smaller lighter lathes has got to be an advantage and a step in the right direction.

    I stumbled upon a Youtube video this afternoon that looks like it might be an easy fix for a lot of folks that are looking for another tool to use in the fight against chatter. Who knows some here may have already tried this technique.
    The link to the video below describes the use of a support used underneath a carbide insert parting tool used in conjunction with a simple support plate that straddles the lathe bed.

    https://www.youtube.com/watch?v=lGPM_XuufLk
    Home, down in the valley behind the Red Angus
    Bad Decisions Make Good Stories​

    Location: British Columbia

  • #2
    That's an interesting technique. I don't think I would use it.

    Both of his parting tools had a lot of overhang, much more than was needed for a 1 inch bar. Something was not very tight in the carriage/cross slide / compound areas. The tool was not bending, but you could see the tool post dip to the side. When mine did that I tightened the crossslide gibs and it stopped that behavior right quick.
    At the end of the project, there is a profound difference between spare parts and extra parts.

    Location: SF East Bay.

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    • #3
      Originally posted by danlb View Post
      That's an interesting technique. I don't think I would use it.

      Both of his parting tools had a lot of overhang, much more than was needed for a 1 inch bar.
      Common problem with small lathes and insert parting tools. The Shars tool shown seems to be particularly bad.

      Comment


      • #4
        He also appeared to be hand feeding. Use power crossfeed for a consistent feed and learn to "ride the chip". You should have a nice ribbon continually curling from the tip of the cutter. It can be done by handfeeding, but use both hands and keep the tool moving with a smooth, aggressive feed.
        Jim H.

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        • #5
          And his tool was NOT on center. The bump left on the stock was quite obvious . I get the kids in high school to do better after a few tries.
          ...lew...

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          • #6
            Another mousetrap...

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            • #7
              I greatly improved parting on my last 9" South Bend. I installed the T-slot table and rear toolpost holder from MLA. Then I fitted an Armstrong parting tool upside down, held in the rear toolpost setup. It really worked a lot better.

              metalmagpie

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              • #8
                I too noticed that there was definitely an issue with both his technique and his tool. For example he uses a shorter chuck in order to get closer to the headstock then uses a poorly designed parting tool that sticks way out into space. Ive seen that type of tool on these pages before so I'm sure he's not the only one to have bought one.
                The point to posting his link though was to show that his answer to the chatter issue did make a huge difference in the quality of the cut, in spite of the other issues.
                It should taken as an example of another possible tool that can be used to quell the chatter when the possibility of doing so exists. It should not be taken as a verbatim guide as to how to part off.
                Home, down in the valley behind the Red Angus
                Bad Decisions Make Good Stories​

                Location: British Columbia

                Comment


                • #9
                  Originally posted by metalmagpie View Post
                  I greatly improved parting on my last 9" South Bend. I installed the T-slot table and rear toolpost holder from MLA. Then I fitted an Armstrong parting tool upside down, held in the rear toolpost setup. It really worked a lot better.

                  metalmagpie
                  Success on my 10" Logan began with the purchase of an aloris tool post and hss cutoff blade holder. Just what the video said doesn't work. Final move was to grind a small trough in the top of the blade. Trough folds and rolls the chip which keeps it from binding. Soft materials like brass and aluminum I cut at full speed. Steels at half speed including drill rod. All manually fed. No issues of any kind. Cut off is now a goto method rather than a cringing last resort method.

                  Comment


                  • #10
                    Start by fixing the obvious stuff. Much of it was mentioned above already.

                    Things that will help in no particular order are;
                    • Adjust the gibs on the cross slide and compound slide if you use one so they are snug but you can still move them. The compound in particular should be noticeably stiff to turn the wheel.
                    • Move the compound back so that your tool post is well supported down through the dovetails and directly into the bed
                    • Consider removing the compound and making up a large solid spacer to mount in its place. The compound on smaller machines like shown in the video can be surprisingly flexible even when the gib is correctly adjusted. Another member here is the one that champions the idea of switching to a solid spacer replacement for general turning where you don't NEED the angle travel of the compound.
                    • Be sure the lathe is bolted down to a good solid bench or stand. This not only aids with the rigidity issue it also gives you a good basis for truing up the bed so it cuts parallel
                    • Run as slow as you can.
                    • Use a fairly narrow parting tool. Convert less metal to chips and the machine will see less torque and other forces from the cut. I'm actually a fan of HSS for this reason. But it has to be a good blade in a good holder to be a good option.


                    I saw that video a while back and my first thought was that the idea was fairly clever. I'd have done the support slightly differently but the idea is actually quite decent. It's a kludge solution of course. But it's a kludge that could greatly aid those with small lathes with the same problem of flexing due to their light weight. Especially when equipped with QCTP's that tend to accentuate the overhang issue like the one in the video does But be sure that other stuff, the proper gib screw settings in particular, are done first.

                    JCHannum, not a lot of smaller lathes have a power cross feed so it may not be an option.
                    Chilliwack BC, Canada

                    Comment


                    • #11
                      Originally posted by BCRider View Post
                      JCHannum, not a lot of smaller lathes have a power cross feed so it may not be an option.
                      Which is why I made the comment regarding hand feeding. The object is to keep the tool moving in the cut.
                      Jim H.

                      Comment


                      • #12
                        Originally posted by JCHannum View Post
                        Which is why I made the comment regarding hand feeding. The object is to keep the tool moving in the cut.
                        Good point.... which I missed....
                        Chilliwack BC, Canada

                        Comment


                        • #13
                          Originally posted by BCRider View Post
                          Start by fixing the obvious stuff. Much of it was mentioned above already.

                          Things that will help in no particular order are;
                          • Adjust the gibs on the cross slide and compound slide if you use one so they are snug but you can still move them. The compound in particular should be noticeably stiff to turn the wheel.
                          • Move the compound back so that your tool post is well supported down through the dovetails and directly into the bed
                          • Consider removing the compound and making up a large solid spacer to mount in its place. The compound on smaller machines like shown in the video can be surprisingly flexible even when the gib is correctly adjusted. Another member here is the one that champions the idea of switching to a solid spacer replacement for general turning where you don't NEED the angle travel of the compound.
                          • Be sure the lathe is bolted down to a good solid bench or stand. This not only aids with the rigidity issue it also gives you a good basis for truing up the bed so it cuts parallel
                          • Run as slow as you can.
                          • Use a fairly narrow parting tool. Convert less metal to chips and the machine will see less torque and other forces from the cut. I'm actually a fan of HSS for this reason. But it has to be a good blade in a good holder to be a good option.


                          I saw that video a while back and my first thought was that the idea was fairly clever. I'd have done the support slightly differently but the idea is actually quite decent. It's a kludge solution of course. But it's a kludge that could greatly aid those with small lathes with the same problem of flexing due to their light weight. Especially when equipped with QCTP's that tend to accentuate the overhang issue like the one in the video does But be sure that other stuff, the proper gib screw settings in particular, are done first.

                          JCHannum, not a lot of smaller lathes have a power cross feed so it may not be an option.
                          You've mentioned 6 points.
                          Points 2 & 6 in particular are important on the less rigid lathes out there (Southbend 9 et al) and help out a lot...

                          Comment


                          • #14
                            When I bought my 9" South Bend it came with a lantern style tool post and a parting tool holder like this



                            I was never satisfied with the way it performed so one day I bought a Sandvic blade and holder.




                            I made a substantial plinth to replace the compound and it mounts to the cross slide in the exact same manner. I attached the blade holder solidly to it and it is a great deal more rigid then what I had. Parting is now easy-peasy.

                            I can exchange it with the compound in a very short time, less time than the fellow in the video took to attach his support to his cutoff tool.
                            Location: Saskatoon, Saskatchewan, Canada

                            Comment


                            • #15
                              So that would be the big solid spacer suggested by some.

                              It's worth nothing that a plinth or spacer to replace the compound would likely benefit by having the tool post mount off center a bit to the front and tail of the lathe. So when the tool holder is mounted and the tool extends out that it sticks out past the spacer by only a little instead of a lot. And "a lot" would be the case if the tool post sat on the spacer in a way that was centered.
                              Chilliwack BC, Canada

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