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Part Off Blade Selection

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  • #16
    I used to have some pretty serious problems with parting using a parting blade holder and a HSS blade. I now use a water soluble oil dripped on the cutter using a wash bottle. No more worries.


    • #17
      My take on the subject

      I use a carbide inserted tool for steel with cutting oil fed into the slot, i have just parted off some 1 3/4 steel stock at 200 rpm ( this is the max depth for my parting tool) , but for cast iron ,brass and cast bronze i use HSS


      • #18
        This is where I used to get my cut off blades:


        • #19
          Another tool source! Can't have too many. Thanks


          • #20
            The secret to easy parting off is to use a thin blade. That is much more important than the blade material. For small sections I grind up a parting tool from a HSS blank with a blade profile that is zero rake on top, raked back at about 30 degrees on the cutting edge and about .063" thick. It will chop off nearly anything except for hardened material. A thin blade has a lot less work to do and the loads on the blade are much less than a thicker one so it doesn't have any greater tendency to break.

            For deeper cuts I take a store bought blade and thin it down by grinding the side. I have no trouble parting off 2" stainless steel shaft or 1040 half hard steel shaft.
            Free software for calculating bolt circles and similar: Click Here


            • #21
              either one has pros n cons

              I use both and agree with most of these guys, keep it as thin as possible, and use a good cutting fluid/oil for best results. Also spend the time to get it set square to the workpiece. With the HSS blades the benefit is that it can be customized to the situation. You may want lotsa rake or even a neg rake depending on material etc. In my experience with HSS most people that have problems don't keep the tool sharp, you may have to resharpen part way thru parting the part. did that part make sense? lol
              I spent most of my money on women and booze, the rest I just wasted.


              • #22
                Originally posted by The Fixer
                In my experience with HSS most people that have problems don't keep the tool sharp, you may have to resharpen part way thru parting the part. did that part make sense?
                For the most part, yes.

                "Accuracy is the sum total of your compensating mistakes."

                "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton


                • #23
                  Part off Blades

                  We've been through all this before and before.

                  The classic answer is to use a rear tool post and run the lathe forwards but using a tool inverted at a 7 degree slope. Set at exact tool height, of course.

                  The top of tool remains straight but has a convex grind along it. The recommended grind is a vee of 140 dgrees but I found a simple curved female grind( calm down, fellas) was enough. The front of the tool had a male 140 degree vee'd edge.

                  With the tool dead on to the task and the lathe running fairly briskly, the swarf comes off in a narrowed ribbon thus avoiding a jam!

                  So far, the rest of this diatribe about parting off, is old granny stuff talk.

                  All my stuff mentioned dates back to perhaps 30-40 years ago and all these stepped narrowed blades and vees ground in carbide are merely a stage on from this.
                  The nice thing about HSS is that it is relatively cheap and can be reground and reground on a home workshop grinder- for nothing.Moreover, it all works on a lathe which is long past its first or second flush of youth.



                  • #24
                    I screwed around withh all types of blades on my similar sized Boxford VSL.

                    By far the best cut off tool I have used is an Iscar insert tool. It's amazing. Also turns/faces like a dream. They can be had of Ebay for pretty cheap, and inserts last a long time. My smaller lathe has zero toubles with it. I'll never mess with hss for parting again.


                    • #25
                      Part off Blades

                      Perhaps the experience of thousands of other Boxford and Myford owners is wrong or mis-guided.
                      Despite it all, castings for the George Thomas rear parting tool seems undiminished. Moreover, the design has now moved onto a larger one suitable for applications on larger lathes than the Boxfords, Myfords and cheap sh1te Chinese 9x20's etc.

                      Again and again, people with far vaster experience than I have have been using castings etc from HemingwayKits. I, on a succession of lathes including a 9x20 over decades have had no problems.

                      It does suggest that that I have been using a failed or very inferior system all these years.

                      Where have I and the rest of us, gone wrong? Well????




                      • #26
                        Perhaps the rear inverted tool works well if the gibs are well adjusted and/or the carriage is quite heavy, but it does tend to want to lift the carriage and cross slide if there is any slack to be had there.

                        The bigger issue that scares me with an Aloris style QC toolpost back there is that the only thing to prevent lifting the whole tool holder off and heaving it (perhaps at the operator) is the friction of the holder's clamping mechanism. In normal use, the cutting forces are working against the stop/adjusting nut on top. Even if you sheared the adjuster screw on the QC tool holder or ripped the big nut off the top, the tool holder would just drop to the top of the compound and away from the operator.

                        I now have one of the Newcomer kits and another (Seco) blade and inserts that is thicker so I can reach further. Having had an "un-pretty" result once when I tried adjusting the tool point on center only using the "ruler method", I can say that on-center setup is critical no matter what tool you are using. So much so, in fact, that I would have to say that a guy can get good results with either a HSS blade or carbide insert holder...but that proper adjustment and tool shape mean more than the choice of tool. I think that often the carbide insert blades are so highly touted primarily because they have some of the correct architecture defined for you. They do also do a better job of curling the chip up and out of the way because of their molded in chipbreaker design.

                        On thing that the insert type blades offer is built in blade clearance. The insert is inherently centered and enough wider than the blade to guarantee side clearance and this is critical (as is having the blade square to the work and on center). If you want to use HSS blades (and I do) then I highly recommend the t-shaped blades even if you have to modify your holder to get them in proper orientation. The t-shape is strong and the necessary side clearance is already there by design.

                        What to me is an issue with either is keeping cutting fluid down in the cut. The continuous curly chip amost immediately pulls what was applied up and away from the cut. I intend to make a needle "dripper" as someone showed here, just for this purpose. It doesn't take lots of cutting fluid, but rather just needs to be constantly supplied.

                        Last edited by pcarpenter; 01-30-2009, 11:03 AM.
                        Paul Carpenter
                        Mapleton, IL


                        • #27
                          I had some large woodworking planer blades I ground them to shape then adapted a holder for them by making a new holder fitting dovetailed it etc woks greatr.Alistair
                          Please excuse my typing as I have a form of parkinsons disease


                          • #28
                            I've been parting off on a succession of elderly lathes for 40 years now, and the only one I used a rear toolpost on was a pre-war Myford, which really wouldn't part off from the front, mainly due to the split headstock bearing design. I use an Eclipse holder and HSS blade, and can part off from the front on my s---y 7x12 chinese, and on my Raglan Littlejohn. I had big trouble with the chinese lathe when I was using QC holders, but once I reverted to an old fashioned 4 way toolpost, so that the parting tool was rigidly clamped down on the top of the topslide, not overhung at the front, then those problems went away. I don't think that QC (the cheap ones anyway) or rocker toolposts are rigid enough for reliable parting off, you need to have the parting tool as rigid as possible, no overhang on the topslide, really sharp and set exactly at centreheight. Very few lathes now have those old split headstock bearings, so I can't understand why parting off still gives so many people so many problems.



                            • #29
                              Good information all around but I must admit that I could use some photos or diagrams to assist my understanding of the various shapes and setups. I have little to no experience with parting off as what little I do have is not happy

                              I use a 9x20 and an Atlas QC54. I would like to learn to grind the HSS as that is what I am using (learning to use) in my regular turning and threading operations.




                              • #30
                                Part off Blades

                                The 'why's and wherefores' of successful parting off were explained in the greatest detail by Thomas in his Model Engineers Workshop Manual.

                                Again, I recall Ken Metcalfe writing in Model Engineer years back and there being a design which held a rear mounted parting tool in a vice like grip.
                                Again, I recall someone explaining in Model Engineers Workshop how he had done the grinding of the kerf to which I refered earlier. Again, Myford produced a rear tool and something similar is being sold with a 'boat like' tool holder in the UK. Yer pays yer money an' yer gets a heap of ***********?

                                I addressed the question of a 5/8" HSS blade and so far, I am the only one to have said 'Look, Sunshine' this is what you do with a 5/8" HSS blade!'

                                Ok, I CAN grind up a carbide parting tool or cut a planer blade down to size and I have a Quick Change 'How's yer father' and a lot of cast iron door stops. However, my 5/8th blade by Eclipse is upside down on the back of me Myford and Paul- I use a jam jar full of a congealed mixture of deceased wasps and once purified lard oil and a child's paint brush as an applicator.

                                I dab it on- face Mecca and utter a meaningful prayer and--It works every time.

                                And if you want to take your copy of Hamlet into the workshop- well?

                                'Parting is such sweet sorrow'