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[IMG] Turning threads in steel: badly torn finish with ground and honed HSS

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  • #16
    I'd agree with the top rake and super sharp hss. No top rake many times material seems to just be "smeared" off the parent part leaving a rough finish. I also find sometimes if you have enough clearance setting the toop slightly above center will produce a better finish.


    The absolute best finish I have ever seen strait off the tool was in titanium. Like a mirror!

    Andy

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    • #17
      Originally posted by Mcgyver View Post
      well it is why they call 12L14 screw stock - I can be difficult getting good finishes with the broad cut threading requires, in gummy materials. The only way I've been able to get through tear out like that in threading is super sharp hss tools - not quite a mirror as a wood worker would but almost - head in the that direction. Use heavy cutting oil, light cut and as slow as the lathe will go. Slow is the key, with oil and a super sharp tool.....think of scraping, where a super sharp tool going very slowly will make a shiny cut in otherwise difficult to machine steels. My suggestion is toward trying to replicate those cut dynamics
      Hear hear.
      Dealing with BUE (build up edge) and tearing it helps to go either really slow or really fast. The "really fast" for soft gummy materials is probably not realistic for manual lathe threading as it might be something like 200...400m/min.
      Location: Helsinki, Finland, Europe

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      • #18
        I've been there myself, the material isn't easy to get a nice finish, but it shouldn't be difficult to do better than what you're showing. Assuming the geometry of the tool is sorted out, and that it has a truly sharp edge, then start to look at your depth of cut for the final passes. You'll want them to be really shallow, and follow the final one with several spring passes. My final pass before making some spring passes is usually 0.02mm or less. Also, for threads this size in this sort of steel, you'll want to make sure you're feeding in via the compound slide set at about 29 degrees, rather than plunging straight in. The chatter in your photos really looks like the threading tool was feed straight into the work, but it could have had other causes (such as depth of cut or tool geometry).
        Max
        http://joyofprecision.com/

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        • #19
          Rake on the tool will change the geometry, and can require different angles.

          The simple case is if you use rake across the tool, so the left edge is not changed, and the right edge is not asked to cut at all, in which case you do not need to consider the angles aside from the normal angle of left edge.
          2730

          Keep eye on ball.
          Hashim Khan


          It's just a box of rain, I don't know who put it there.

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          • #20
            I feed straight in on all my threading
            Not my experience.

            As J Tiers says, "right edge is not asked to cut at all" --feed in at an angle with your compound so that only the left edge of the tool is cutting and needs to be considered as having correct geometry. If both left and right were cutting their chips would collide, and you can't possibly have the same rake on both without pretty fancy grinding equipment.
            "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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            • #21
              Rigidity also helps. I used to get the same type of results on my old Sheldon 10x36 with the stock lantern post setup. I sold the Sheldon and bought a much newer Jet 12x36 with an Aloris QCTP setup and the problem went away. This was using the same cutting tools and steel source.

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              • #22
                Originally posted by HWooldridge View Post
                Rigidity also helps. I used to get the same type of results on my old Sheldon 10x36 with the stock lantern post setup. I sold the Sheldon and bought a much newer Jet 12x36 with an Aloris QCTP setup and the problem went away. This was using the same cutting tools and steel source.
                As the OP is using a "Multifix" toolpost, that is unlikely to be a problem. Look closely at the pic of his shop.
                2730

                Keep eye on ball.
                Hashim Khan


                It's just a box of rain, I don't know who put it there.

                Comment


                • #23
                  Originally posted by J Tiers View Post
                  I suspect I know what you mean, but just in case; a sharp edge actually disappears. It is only dull edges that show any shiny or bright line etc at the actual edge itself.
                  Right you are, I of course ment that the area just below/adjacent to the cutting edge was honed/brightened up. The cutting edge itself is in my eye sharp enough to not reflect light.

                  Originally posted by MattiJ View Post
                  Supercut II is what I was also using until I get allergic to it. Speed sounds reasonable but you could try and see what happens if you drop the speed really slow.

                  Material is part of the problem but in my experience the VP15TF coated Mitsubishi inserts work very nicely also on S355 cold drawn bar stock that is common here in Europe.

                  If you hone hand-held with diamond lap its also possible that you get slight radius on the cutting edge so that its not really sharp. Depends how good your technique is. I have seen it happen to "my friend" but I'm of course not such a clumsy bastard.
                  Or your HSS is some crap quality chinese import, "my friend" had also that.
                  I'm sorry to hear about your allergy to the cutting fluid. I haven't tried them all by a long shot, but the CRC stuff seem to work well for me. I've tried cutting speeds on workpieces 16-20 mm. OD (5/8" ~ 3/4") from 45-355 RPM, seemingly without much difference in the cutting action. Good call on the Mitsubishi inserts, I have a lot of inserts from them already and the quality is quite good. I'm very careful when lapping and at all cost avoid dulling the cutting edge in somewhat of a chamfering maneuver. I do have a lot of HSS tool steel from the far east, specifically that one unmentionable country, but most of it holds an edge well for general turning and profiling. I'm careful with the cutting speed, though.

                  Originally posted by Toolguy View Post
                  You might try to find the local equivalent of 1215 alloy. It's the easiest, cleanest cutting low carbon steel I've found so far.
                  I'd love to try some one day.

                  Originally posted by 10KPete View Post
                  My take is that the tool needs about 10* of top rake for this gummy stuff. That's been my experience anyway. I have a tool for this stuff with the top rake going away from the left cutting edge. I don't care much about the right 'cutting' edge because it never cuts! With the compound at 29.5* I feed in with the compound only thus I'm always cutting with a high rake tool. The old lard/sulfur oil is my go to for this. Good threads every time...

                  Cheers,
                  Pete
                  Thanks for the tip. I already use a tool with side rake, but have not tried using any back rake, or a combination thereof. It very well could be something for me to look into. I eyeballed the rake angle I'm currently using, and it actually appears a lot closer to 15° than 10.

                  Originally posted by MrWhoopee View Post
                  Definitely related to the material, it looks just like threading cold rolled steel at low speeds. Several things occur to me:
                  1. Increase RPM (I know, it gets scary).
                  2. Sulphurized cutting oil.
                  3. Stress relieving or annealing with a torch.
                  4. Using hot-rolled 1020, 1215, 12L14 (if it's still available), 1144 (Stressproof), or even 303 stainless.
                  5. Lapping the tool seems like over-kill and may be counter-productive. The fine grooves in a ground cutting edge can act as tiny chip breakers.
                  Thanks for the tips. I've tried having the tool upside-down and threading away from the headstock when making right-hand threads, but maybe I haven't used a high enough speed? Sulphurized cutting oil is on my shopping list already, but haven't tried it yet. (Reverse) heat treatment; would not that make the material even more gummy? I believe I'll continue to lap my cutting edges, if not for anything else, it reduces the tendency to form a built-up-edge.

                  Originally posted by 754 View Post
                  I was thinking top rake too .. it looks like its not cutting freely..
                  What method do you use for centre height ?
                  I feed straight in on all my threading and finish is rarely an issue.
                  No top rake yet, only side rake. Maybe I'll try adding some top rake at a later time. The center height gets set by pinching my 150 mm. long, thin ruler between the cutting edge and the workpiece. I believe flank infeed at an angle is the way to go, and especially for more coarse threads.

                  Originally posted by danlb View Post
                  It seems to me that you might be cutting too shallow. Look at the page https://www.sandvik.coromant.com/en-...s/default.aspx to see what Sandvik recommends.

                  In the case of the 1.5 mm pitch, Sandvik was calling for 6 passes of decreasing depth, starting with .23mm and finishing with .010mm.

                  Dan
                  Yes, I've tried fine infeeds for finishing, and will often dial in 0.20 - 0.25 mm. for the "roughing" passes to start with, and reduce the infeed as I progress. I'm actually already making 1.5 mm. pitch threads in 5-8 passes, depending on how I hit/miss the mark for sizing near the end of the threading cycle.

                  Originally posted by MattiJ View Post
                  12L14 or 1215 equivalents are hard in here to find. Hardly anyone stocks it or is willing to deal with small customers.

                  Calcinated Imatra M-steels are reasonably nice to work with:
                  http://www.ovako.com/Products/M-Steel/
                  Imatra 4M ( close to 1045), or MOC 410M (4140 prehard)
                  Ovako is quite high quality I've heard, but never seen it for sale here in Norway. I guess I can order some and have it delivered to the border town of Kilpisjنrvi perhaps.

                  Originally posted by boslab View Post
                  Nothing wrong with it lovely bit of rebar.
                  Looking at the marks it looks almost like a chatter type of thing as well, tool rigid?
                  Mark
                  Rebar, huh? The workpiece I've been having a hard time with recently is a 20 mm. OD hard-chromed shock absorber rod, most likely even from a Volvo passenger car. I'll have you know, my good Sir, that both me and my lathe is very much above turning just any kind of junk and road-side trash, I only use the highest quality of free, surplus, gifted, begged-for, inherited, found, stolen, and/or recycled "Mysterium Stahl" ™.

                  Originally posted by Mcgyver View Post
                  well it is why they call 12L14 screw stock - I can be difficult getting good finishes with the broad cut threading requires, in gummy materials. The only way I've been able to get through tear out like that in threading is super sharp hss tools - not quite a mirror as a wood worker would but almost - head in the that direction. Use heavy cutting oil, light cut and as slow as the lathe will go. Slow is the key, with oil and a super sharp tool.....think of scraping, where a super sharp tool going very slowly will make a shiny cut in otherwise difficult to machine steels. My suggestion is toward trying to replicate those cut dynamics
                  I believe I've tried this approach already without much success, but perhaps I'm not sharpening the tool enough? Not fine enough infeed? I'll do try to get some other cutting oil, but the CRC I'm already using works well for other turning operations using the same HSS toolbits.

                  [END OF PART 1, PART 2 WILL FOLLOW WITH MORE COMMENTS AND PICTURES]

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                  • #24
                    [part 2]

                    Originally posted by vpt View Post
                    I'd agree with the top rake and super sharp hss. No top rake many times material seems to just be "smeared" off the parent part leaving a rough finish. I also find sometimes if you have enough clearance setting the toop slightly above center will produce a better finish.


                    The absolute best finish I have ever seen strait off the tool was in titanium. Like a mirror!
                    Nice threads right there. I have not tried cutting above center because I'm afraid to run out of clearance and start smearing and rubbing. I do have tried to set the tool below center without any appreciable difference to the cut.

                    Originally posted by MattiJ View Post
                    Hear hear.
                    Dealing with BUE (build up edge) and tearing it helps to go either really slow or really fast. The "really fast" for soft gummy materials is probably not realistic for manual lathe threading as it might be something like 200...400m/min.
                    That's quite fast, yes. Probably not a good idea to even try when near any form of shoulder or tailstock support.

                    Originally posted by mars-red View Post
                    I've been there myself, the material isn't easy to get a nice finish, but it shouldn't be difficult to do better than what you're showing. Assuming the geometry of the tool is sorted out, and that it has a truly sharp edge, then start to look at your depth of cut for the final passes. You'll want them to be really shallow, and follow the final one with several spring passes. My final pass before making some spring passes is usually 0.02mm or less. Also, for threads this size in this sort of steel, you'll want to make sure you're feeding in via the compound slide set at about 29 degrees, rather than plunging straight in. The chatter in your photos really looks like the threading tool was feed straight into the work, but it could have had other causes (such as depth of cut or tool geometry).
                    I do not believe this is chatter. It makes no such distinctive noise. I have not tried spring passes because I've heard that that is just a crutch / Band-Aid indicative of another problem with the cut.

                    Originally posted by J Tiers View Post
                    Rake on the tool will change the geometry, and can require different angles.

                    The simple case is if you use rake across the tool, so the left edge is not changed, and the right edge is not asked to cut at all, in which case you do not need to consider the angles aside from the normal angle of left edge.
                    I don't hone the right cutting edge as I'm feeding in at an angle and the right side of the tool does not touch the work at all. I do use a 60° included angle reference guide when grinding the tool to make my flanks straight and in alignment.

                    Originally posted by mickeyf View Post
                    Not my experience.

                    As J Tiers says, "right edge is not asked to cut at all" --feed in at an angle with your compound so that only the left edge of the tool is cutting and needs to be considered as having correct geometry. If both left and right were cutting their chips would collide, and you can't possibly have the same rake on both without pretty fancy grinding equipment.
                    I agree and will continue to use flank infeed at an angle. I have tried plunging straight in in fine-pitch threads in brass and aluminium without ill effects though.

                    Originally posted by HWooldridge View Post
                    Rigidity also helps. I used to get the same type of results on my old Sheldon 10x36 with the stock lantern post setup. I sold the Sheldon and bought a much newer Jet 12x36 with an Aloris QCTP setup and the problem went away. This was using the same cutting tools and steel source.
                    Oh, I'm quite rigid already. A two ton Czech lathe and a Multifix "B"-size QCTP from Wuhan Create Tool in China. I sometimes do hogging in 3-4" diameter mild steel with parameters along these lines: 700-1000 RPM, feeding 0.30 - 0.40 mm./rev, taking up to 4-5 mm. depth of cut (removing 8-10 mm. of the diameter). The lathe does not make a squak, except for the loaded sound of the motor. It consumes around 17A @ 230V 3-phase at idle, and peak loads near 35A when roughing would by my math have the active power approach ~15 horsepowers at most.


                    Cutting edge as presented to the workpiece. It's ground at an all-around 9-degree offset to have the cutting edge approach close to the chuck without shearing the drive pin on the threading leadscrew for the fourth time.


                    Front view of the toolbit:
                    EDIT: the toolbit is 10 mm. square, or midways between 3/8" and 7/16":


                    The lapped cutting edge, viewed from below:


                    More of the imperfect finish, this is with a fresh grind and hone on my toolbit:
                    Last edited by Oyvind Ryeng; 11-10-2017, 05:09 PM.

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                    • #25
                      Lowered the cutting tool:


                      Lowered it some more and reduced the speed to 45 RPM and a very fine infeed:


                      100% crop of the picture above from my Olympus E-3 with Zuiko 50 mm. f/2.0 macro lens. The surface is brutal enough to be a death-metal album cover:
                      EDIT: It looks like a scaly dragon is wrapping itself around a round rod. A small dragon, to be sure, with a diameter of 1.5 mm.


                      This is with an 11IR carbide insert boring bar, upside-down and threading away from the chuck at the same slow 125 RPM:
                      Last edited by Oyvind Ryeng; 11-10-2017, 05:07 PM. Reason: sepling arror

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                      • #26
                        Speeding it up:


                        Speeding it up again:


                        Speeding it up some more (700 RPM):


                        Same setup, but something went wrong. Too high DOC, perhaps:
                        Last edited by Oyvind Ryeng; 11-10-2017, 04:53 PM.

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                        • #27
                          Now trying Mystery Stainless, 96 mm. OD x 1.5 mm. pitch. Excellent result @ 63 RPM. Feeding in 0.20 mm., down to 0.02 mm. when finishing. I got a continuous stringy chip as expected.





                          Last edited by Oyvind Ryeng; 11-10-2017, 04:57 PM.

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                          • #28
                            The steel you are using is prone to galled or torn threads when cut at low surface speed. It may not be feasible to run fast enough to get a decent finish. In the shop where my son worked the shop foreman ordered the cheapest steel he could get to make some short shafts. In order to get sufficient speed to cut smoothly the RPM was so high the Z axis servo couldn't keep up, resulting in drunken threads. Try to get a steel better suited for machining. Others have posted their preferences. All are better suited for threading than what you use. Hot rolled and 0.2% carbon are a lousy combination.

                            Take a tip from pipe fitters. They die cut threads in really gummy steel all the time. They always use dark cutting oil that contains lots of sulfur. They seem to get decent threads at low speeds most of the time. Try the dark oil.

                            One of my favorite materials to machine is cold finished 1144 (Stressproof). Because of its sulfur content it is not recommended for welding.

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                            • #29
                              I did some test runs on crappiest S355 cold drawn stock they sell around here.
                              HSS tool with couple of passes with 0.2mm plunging straight in:



                              Nasty nasty... decrease the cutting depth to 0.04mm per rev and 0.02mm for last 5 passes:



                              The one on the left is turned with HSS tool and the one on the right is turned with ER16 VP15TF carbide insert.
                              Took probably 3 times longer with the pretty sharp sharp HSS tooling because it was tearing a lot more compared to insert. Insert tool did tear some but it was nowhere near as bad.
                              On some parts of the thread the finish looks great on the piece turned with HSS tool but there is still tearing marks visible. .The one turned with insert has more constant finish from thread to thread but doesn't look as nice as the piece turned with HSS in the best parts.

                              Both run @100rpm and last few finishing passes @ 40rpm.
                              Location: Helsinki, Finland, Europe

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                              • #30
                                P.S. The part turned with HSS tool is probably already teared too much in the first pic. The tears look rather big and extend deep in to the stock material.
                                Should have gone with smaller cut of depth right from the start.
                                Location: Helsinki, Finland, Europe

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