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"Resting" HSS tool bits after grinding

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  • "Resting" HSS tool bits after grinding

    This morning I was in the process of grinding a 55* Whitworth form threading tool and got to thinking about my dad's habit of setting a newly ground tool bit aside for a few days after grinding and the final polishing with a stone. He claimed a HSS tool bit treated like this would last longer between re-grinds and cut better. I've been told the same thing by two long retired tool makers for whom I have a great amount of respect. My dad passed away four years ago and I inherited many of his machinist tools (which I treasure) and as well quite a number of 1/4 and 5/16 HSS tool bits which he had ground and polished for particular jobs. Each one of the tool bits are still razor sharp and on the occasions when I've used them they've cut steel like a hot knife in butter. Each time I've used one I've touched it up with a stone after I'm done and I've never seen any pitting or eroding at the tip. Those bits I grind and polish and then put right to work invariably need regrinding after several hours' work. When I get done polishing the 55* threading bit today I'm going to set it aside for a few days before using it and see if it benefitted from its "rest". Has anyone else heard of this?

  • #2
    With all due respect to your Dad and others, this may be one of those old wive's tales that gets passed around for no other reason than because it came from an old retired machinist.

    Your own experiences may be just coincidence. It'll take some better evidence to convince me.


    • #3
      I'll believe it when somebody does a controlled double-blind test.
      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've never heard that one. Metallurgy is not my stongest point, but I wouldn't think that much significant change happens in steel (once it cools down) within a day or two.
        It might just be organized machinists not wanting to explain how they can be so patient.
        I've been wrong before. What time is it?


        • #5
          I was watching a program about plane construction and they did just that with the alloy panels the plane was made out of.
          something to do with the ductile-ness if i remember right.
          but that is not hss I dont know.
          all the best..mark


          • #6
            Well, my dad also did such things as weeding the garden and cutting down trees (for firewood) during the waning moon and planting and grafting during the waxing moon. He was an A&P mechanic with a doctorate in structural engineering, could play any musical instrument by ear, wrote poems, and rode motorcycles all his life (when he was 78 he and another old-timer drove from North Carolina to Guatemala and back on motorcycles and had a bodacious good time). Oh, and he spoke Spanish and high German as well as English. I've learned through the years that despite my doubts the various things he's told me inevitably turn out to be true. Since I'm the youngest of his five children I ended up with the least of his abilities.

            On the HSS steel he explained that the grinding "excites" the molecules and letting it rest a few days before putting it to work gives them time to settle down.
            Ben Rich


            • #7

              Could depend on the grade of HSS he used.

              Perhaps it would be better to sharpen two pieces for ordinary turning,use one and let the other "rest" and see which lasts longer in use.

              Hard to tell screwcutting as its a long time between sharpens.



              • #8
                Good way to have 8 hours more spare time 5 days a week if you boss catches you.


                • #9
                  Could it be for stress relief? Like in seasoned cast iron. Don't know just throwing it out there.
                  Jon Bohlander
                  My PM Blog


                  • #10
                    I can't say, cause I haven't tried it, but anythings possible. I remember a former boss of mine, who's judgement I respect, telling me that the only way to machine a rough cast iron angle block so that it didn't move around after finishing, was to rough mill it, toss it outside for a year, through one of our very cold winters, and then finish grind it.


                    • #11
                      Mark's comment about the aluminum alloys used in aircraft construction is dead on. If a panel or other heat treatable aluminum alloy has been re-heat treated to enable forming of some type then it will regain it's full strength after a couple of days "resting". This is a well documented fact of heat treatable aluminum alloys.

                      Reference: Kaiser Aluminum Sheet and Plate Handbook.

                      I don't see any reason why this should not apply to the formation of the particular granular structure in steel alloys as well. The effect is probably not very pronounced but it may well exist.

                      However Guero, I think that the main reason is that your dad knew what he was doing. Study the grind on those bits and replicate them. I suspect you can still learn something from him.

                      [This message has been edited by Evan (edited 09-05-2004).]
                      Free software for calculating bolt circles and similar: Click Here


                      • #12
                        Let's put this to rest. Ordinary grinding temperatures and superficial abrasion might have some measurable effect in the surface microstructure of newly hand sharpened Vs old HSS tools but not enough to make a noticable difference in how they cut.

                        How do I know? I have hand ground tools from up to 40 years ago. Boxes of stuff I inhereted from retirees, left over from jobs, etc. I just tried out a selection of form and threading tools both old and newly ground on mild and alloy steel remnents. I made a lot of chips but try as I could I could see no superiority in their performance.

                        In fact while there was any number of different HSS brands in the mix there wasn't much difference in their cutting qualities other than longevity so long as the service was oil drenched forming cuts at lower than production speeds.

                        If there is a difference it's lost in the statistical scatter.

                        I'd say the original assertion was BS like when my grandpa told me to hum when baiting a hook with a worm because it makes them straighten out.


                        • #13
                          I agree Forrest. I have some bits that were ground by the original owner of my 35 year old Unimat. They are somewhat odd in the grind, with curves where I would grind them straight. But, they cut better than my tools. I have to study this.
                          Free software for calculating bolt circles and similar: Click Here


                          • #14
                            I also feel that this is an old wife's tale and if you re read your original post you can probably find some clues.

                            You state with your fathers tools "and on the occasions when I've used them"

                            But later you say " Those bits I grind and polish and then put right to work invariably need regrinding after several hours' work. "

                            Could it be that you don't use your fathers tools as much.

                            Lets be honest HSS isn't carbide and several hours work for a HSS tool is probably it's life on that edge depending on the work being done.

                            I can appreciate safety matters in things like aeroplane panels but cost isn't high on the list of aerospace components.
                            Now if someone could point me to an article where they do this to say saucepans that are produced by the millions then it may have a bearing on the matter.

                            It certainly wouldn't have been a nessesity in industry when HSS ruled because as Forrest has said you would have been down the road.

                            John S.

                            Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


                            • #15
                              I appreciate the responses and it won't hurt my feelings if my dad was wrong on this. He was not a machinist by profession but he did use machine tools all his adult life. For all I known, this about "resting" tools might have been something taught in the various trade schools right after WWII - the two long retired tool makers I mentioned were of my dad's generation and had attended some of the same institutions my father had gone through.

                              Ben Rich