Chatter/finish problem

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Chatter/finish problem

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  • #564513
    Russell Eberhardt
    Participant
      @russelleberhardt48058

      You might find this link useful:

      **LINK**

      http://www.steves-workshop.co.uk/tips/toolgrinding/toolgrinding.htm

      Russell

      Edited By Russell Eberhardt on 27/09/2021 19:12:36

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      #564515
      Nigel McBurney 1
      Participant
        @nigelmcburney1

        Have a look at the workholding ,is the bar held firmly in the chuck jaws? From the photo the new chuck appears to be a self centering 4 jaw chuck, not the best way to hold work, I would never dream of using this type of chuck they are ok for woodturners. Never seen one used in a trade shop. And do not assume that a new chuck has perfect jaws to grip the work along the length of the jaws, I have seen a new european made 6 inch 3 jaw chuck where the jaws were bellmouthed ,due to poor manufacture. The tool looks suitable for brass ,though is there sufficient front and side clearance plus tools for brass turning must be sharp and honed with an India oil stone,some grades of brass can be difficult to turn and get a good finish, try going fast in top speed and take cuts of around 5 thou.The very rough cuts look as though they have been taken at very slow speed with tool set to take a far too great a depth of cut, like screw cutting to full depth at one cut only worse,that will not do the lathe much good.

        #564538
        John Reese
        Participant
          @johnreese12848

          David Wilkes in his You Tube videos preferred turning toward the tailstock. He turned some really long slender shafts without chatter.

          #564597
          Howard Lewis
          Participant
            @howardlewis46836

            Unless I'm not seeing clearly, the tool appears to have a short area of negative rake. If this is the case, whilst it reduces or eliminates the risk of dig ins, it may not be the ideal geometry for turning brass.

            FWIW, my method would be, for brass, a knife tool with zero top rake, and to wind the tool out before winding the saddle back. Front and side clearances are necessary, but only about 5 degrees

            (That coarse helix does look like the Saddle being wound back while the work was rotating. )

            Are you hand or power feeding?

            If the lathe has a Leadscrew, the changewheels / gearbox can be set to give a fine feed of 0.004" / 0.05 mm per rev. If the tool geometry is correct, and mounted on centre height, that should result in a good finish on brass.

            You will need to calculate the gear train to give 250 tpi, or 0.05 mm pitch for the fine feed. As aleady said, you are producing a screwthread of fine pitch.

            The finishing cut needs to be shallow, especially when using HSS tools, probably of the same order as the feed rate, or maybe less..

            Being brass, it is taken that no coolant / lubricant is being used.

            HTH

            Howard

            #564606
            Jeff Dayman
            Participant
              @jeffdayman43397

              Side note to John Reese – I haven't seen any new videos from David Wilks in a very long time. Do you know David, and if so, is he OK? I think he is from Sheffield.

              #564608
              duncan webster 1
              Participant
                @duncanwebster1
                Posted by Nigel McBurney 1 on 27/09/2021 19:24:02:

                Have a look at the workholding ,is the bar held firmly in the chuck jaws? From the photo the new chuck appears to be a self centering 4 jaw chuck, not the best way to hold work, I would never dream of using this type of chuck they are ok for woodturners………

                Never understood 4 jaw self centering chucks. As they work on a scroll all 4 points of the jaws are unlikely to be truly on a circle, and not all round bar is perfectly round, so chuck is likely to just grip on 2 opposite jaws. That's why self centering chucks traditionally have 3 jaws, 3 points always define a circle, and will cope with slightly out of round bar

                #564616
                Steve355
                Participant
                  @steve355
                  Posted by duncan webster on 28/09/2021 13:04:58:

                  Posted by Nigel McBurney 1 on 27/09/2021 19:24:02:

                  Have a look at the workholding ,is the bar held firmly in the chuck jaws? From the photo the new chuck appears to be a self centering 4 jaw chuck, not the best way to hold work, I would never dream of using this type of chuck they are ok for woodturners………

                  Never understood 4 jaw self centering chucks. As they work on a scroll all 4 points of the jaws are unlikely to be truly on a circle, and not all round bar is perfectly round, so chuck is likely to just grip on 2 opposite jaws. That's why self centering chucks traditionally have 3 jaws, 3 points always define a circle, and will cope with slightly out of round bar

                  It is a 4 jaw independent chuck

                  #564620
                  Steve355
                  Participant
                    @steve355
                    Posted by Howard Lewis on 28/09/2021 11:53:27:

                    Unless I'm not seeing clearly, the tool appears to have a short area of negative rake. If this is the case, whilst it reduces or eliminates the risk of dig ins, it may not be the ideal geometry for turning brass.

                    FWIW, my method would be, for brass, a knife tool with zero top rake, and to wind the tool out before winding the saddle back. Front and side clearances are necessary, but only about 5 degrees

                    (That coarse helix does look like the Saddle being wound back while the work was rotating. )

                    Are you hand or power feeding?

                    If the lathe has a Leadscrew, the changewheels / gearbox can be set to give a fine feed of 0.004" / 0.05 mm per rev. If the tool geometry is correct, and mounted on centre height, that should result in a good finish on brass.

                    You will need to calculate the gear train to give 250 tpi, or 0.05 mm pitch for the fine feed. As aleady said, you are producing a screwthread of fine pitch.

                    The finishing cut needs to be shallow, especially when using HSS tools, probably of the same order as the feed rate, or maybe less..

                    Being brass, it is taken that no coolant / lubricant is being used.

                    HTH

                    Howard

                     

                    Well, I ground my first HSS cutting tool. Is that right? Luckily I have suitable kit to do that due to my woodworking habit. I’ll give it a proper test after work.

                    fc2c5e08-121d-489c-be02-849c38485625.jpeg
                     

                    4b3667c5-5745-4ae9-bf4f-57d90d3906dc.jpeg

                    Steve

                    Edited By Steve355 on 28/09/2021 14:15:00

                    #564629
                    Dave Halford
                    Participant
                      @davehalford22513

                      From your photo it looks wrong, but if the point of that little triangle is not as far out as it's base (top of tool) then it will work. A rounded edge would be better.

                      PS I've never seen an HSS blank that didn't have polished sides.

                      Edited By Dave Halford on 28/09/2021 14:40:41

                      #564634
                      Steve355
                      Participant
                        @steve355

                        For some reason when I post pics here they are rotated through 90deg anti-clockwise, if you rotate it through 90 deg clockwise then that’s how the pic should look.

                        it’s not an HSS blank, it’s the rear end of another tool that I have re-purposed. I have ordered some HSS blanks but they don’t arrive until Friday.

                        #564637
                        Grindstone Cowboy
                        Participant
                          @grindstonecowboy

                          It's not the rear end of a brazed carbide tool is it?

                          Regarding rotation of photos, it's a continuing problem on here – done it myself – and it seems that one way to fix it is to open your photo in a photo-editing program and re-save it before posting.

                          #564638
                          Steve355
                          Participant
                            @steve355
                            Posted by Grindstone Cowboy on 28/09/2021 15:44:04:

                            It's not the rear end of a brazed carbide tool is it?

                            Regarding rotation of photos, it's a continuing problem on here – done it myself – and it seems that one way to fix it is to open your photo in a photo-editing program and re-save it before posting.

                            No, it’s the other end of the HSS tool shown in an earlier picture 😎

                            #564641
                            Grindstone Cowboy
                            Participant
                              @grindstonecowboy
                              Posted by Steve355 on 28/09/2021 15:48:20:

                              No, it’s the other end of the HSS tool shown in an earlier picture 😎

                              That's OK then wink

                              #564642
                              Dave Halford
                              Participant
                                @davehalford22513
                                Posted by Steve355 on 28/09/2021 15:14:49:

                                For some reason when I post pics here they are rotated through 90deg anti-clockwise, if you rotate it through 90 deg clockwise then that’s how the pic should look.

                                it’s not an HSS blank, it’s the rear end of another tool that I have re-purposed. I have ordered some HSS blanks but they don’t arrive until Friday.

                                I get the rotation, it's the little flat that you ground on the point to widen it looks to have no clearance

                                #564670
                                Russell Eberhardt
                                Participant
                                  @russelleberhardt48058
                                  Posted by Dave Halford on 28/09/2021 16:33:42:

                                  I get the rotation, it's the little flat that you ground on the point to widen it looks to have no clearance

                                  Agreed. It will in fact give a severe negative rake to the cutting point.

                                  If you want to have a small flat, or a rounding, on the point it should be ground all the way down the leading edge.  The top of the tool must remain flat.

                                  Russell

                                  Edited By Russell Eberhardt on 28/09/2021 19:03:17

                                  #564721
                                  Steve355
                                  Participant
                                    @steve355

                                    Right, thanks for all the help from this excellent forum, I think I’m starting to understand some of this. I think there are actually three problems:

                                    1) a problem With the collar at the tail end of the spindle, looseness was causing longitudinal movement of the spindle. I think I have fixed that.

                                    2) A problem with tooling, resulting in the finish being a “long thread” when tail support is applied. The tail support would also stop any longitudinal movement of the spindle. I will re-grind the tool tonight and give this another go.

                                    3) I have also noticed that in order for the spindle to turn, the bolts that secure the spindle in the headstock need to be only slightly more than finger tight. Whilst it seems that there is no lateral movement on the spindle, if I pull the spindle with a little force, I can feel the headstock slots flexing. So therefore there must be very little rigidity, and it may explain The test cut I did last night, where on an unsupported pace the finish is horrible further out, improving markedly closer to the Chuck.

                                    But if I tighten the headstock bolts, the spindle will not turn. A couple of questions:

                                    Does this make sense? Might this be a problem?

                                    What tension should the V-belt be? Is there any way I can measure it?

                                    It’s a basic cheapo eBay V-belt. Is this the wrong kind of belt? I have seen a myriad of different belt types on lathes.co.uk.

                                    I will get to the bottom of this!

                                    cheers

                                    Steve

                                    c0a1ec81-4a36-40b8-907a-51e4953eca8f.jpeg

                                    #564743
                                    Brian Morehen
                                    Participant
                                      @brianmorehen85290

                                      Hi Steve 255, Am i corrected in thinking your lathe is a Zxto , If so have a look on Ebay there is one that is a rebuilt may give you some clues. I think the original bearing was tapered like my Faircut

                                      I have found very gentle and light cuts produces a fine finish

                                      Regards Bee.M

                                      #564757
                                      Dave Halford
                                      Participant
                                        @davehalford22513
                                        Posted by Steve355 on 29/09/2021 11:27:25:

                                         

                                        3) I have also noticed that in order for the spindle to turn, the bolts that secure the spindle in the headstock need to be only slightly more than finger tight. Whilst it seems that there is no lateral movement on the spindle, if I pull the spindle with a little force, I can feel the headstock slots flexing. So therefore there must be very little rigidity, and it may explain The test cut I did last night, where on an unsupported pace the finish is horrible further out, improving markedly closer to the Chuck.

                                        But if I tighten the headstock bolts, the spindle will not turn. A couple of questions:

                                        Does this make sense? Might this be a problem?

                                        What tension should the V-belt be? Is there any way I can measure it?

                                        It’s a basic cheapo eBay V-belt. Is this the wrong kind of belt? I have seen a myriad of different belt types on lathes.co.uk.

                                        I will get to the bottom of this!

                                        cheers

                                        Steve

                                        Steve,

                                        Don't for one minute believe that when you acquire an old machine that it was assembled properly by the 10 previous owners.

                                        Looking at the 'lathes' Zyto photos there are no grubscrews, come to that I can't see a collar either. The bearing slits are approx. half the size of the head stock slits

                                        If both bearings are the same size I would try swapping front with rear so that the grub screws and oil holes still line up, but the bearing slot is now at the back, and see if that makes a difference. I still think there should be a dense felt strip trapped in the bearing slit which would also help. If this lathe was built like it is now the bearing bolts would be knurled knobs, hex heads imply more than finger tight was required. You can very easily crack the head stock with slits as large as you have using a spanner.

                                        You can also see the proper fit of the belt in more modern pullies, tension is about right when you can twist the belt 90 deg. or deflect the belt inwards 1/2"

                                         

                                        BTW your last photo shows a classic case of too much stick out from the chuck causing chatter.

                                        Edited By Dave Halford on 29/09/2021 15:29:33

                                        #564768
                                        Russell Eberhardt
                                        Participant
                                          @russelleberhardt48058

                                          The bronze (not brass) bush in the headstock is split for adjustment. The grub screw is to stop it rotating and shouldn't compress the bush. The casting the into which the bush is fitted is also split so tightening the hex headed bolt will compress the bush to take up slight wear. I would imagine that there should be a stack of shims in the slot in that casting to control how far the compression goes. Thet would allow the bolt to be done up tight without locking the spindle.

                                          Have you seen the section on Zyto lathes on lathes.co.uk ?

                                          Russell

                                          #564773
                                          Clive Brown 1
                                          Participant
                                            @clivebrown1
                                            Posted by Russell Eberhardt on 29/09/2021 16:38:28:

                                            The bronze (not brass) bush in the headstock is split for adjustment. The grub screw is to stop it rotating and shouldn't compress the bush. The casting the into which the bush is fitted is also split so tightening the hex headed bolt will compress the bush to take up slight wear. I would imagine that there should be a stack of shims in the slot in that casting to control how far the compression goes. Thet would allow the bolt to be done up tight without locking the spindle.

                                            Have you seen the section on Zyto lathes on lathes.co.uk ?

                                            Russell

                                            My first lathe, a Grayson had similar bearings to the Zyto, a split bush in a split housing tightened by a bolt. I think that arrangement was quite common with older, low-cost machines. There were no shims in my lathe. I understand that cracked bearing housings were not unknown if care wasn't taken.

                                            I suspect that the OP's poor finish is largely due either to the grinding of the tool, with the small flat on the tip, or possibly, and less likely, to bearings worn badly out-of-round.

                                            Edited By Clive Brown 1 on 29/09/2021 16:53:40

                                            #564792
                                            Steve355
                                            Participant
                                              @steve355

                                              Right, I am getting there at last…..

                                              I lashed up a belt tensioning system so could tighten the bearings to stop the chatter without the belt slipping….

                                              Belt tensioner

                                              I ground a radius on the tool bit….

                                              Radius

                                              and the result was a much, much better finish, and no chatter marks further out along the piece.

                                              now to watch some more videos on grinding tool bits properly.

                                              Thanks very much to everyone who has provided such great advice, all of it has made me think. I’m beginning to think I will be able to use these tools in the end.

                                              Better finish

                                              Edited By Steve355 on 29/09/2021 21:22:37

                                              #564846
                                              Howard Lewis
                                              Participant
                                                @howardlewis46836

                                                Some cheap V belts have a swollen area near the join.

                                                Good quality belts don't. A lumpy belt will cause a slight variation in speed of the Mandrel, which will not help your problem.

                                                Looking at the tool that you ground, it has a flat on the corner where it should be cutting.

                                                A Knife tool will have a sharp corner. By very slightly stoning a radius, as said, all the way down the edge, the finish will improve.

                                                But start with a SHARP corner, before trying to stone a radius.

                                                The radius must extend down the edge, or the tool will rub rather than cut. For the tool to cut, the pressure at the point of contact must be great enough for the metal to shear. Hence the need for an almost point contact, to give minimal area to support the applied load, and produce high pressure..

                                                I use a Tangential turning tool, and don't bother with a radius, since a fine feed, circa 0.002" (0.05 mm ) per rev produces a good finish on steel or brass.

                                                But that's just my preference!

                                                Whatever tool you use MUST be on the centre height. A quick check is to face across the end of the bar. If there is a pip in the middle the tool is not on centre height, and needs to be shimmed up or down, until it is.

                                                Once you get the tool on centre height, it would be worth making some form of Centre Height Gauge, so that in future, all tools can be set to it, Making it will be useful learning exercise in itself.

                                                It might be worth when the bearing bolts have been set to provide acceptable rotation of the Mandrel, to measure the clearance between the caps and the Headstock, and then to make up shims so that the bolts can be tightened down onto the shims to limit the "grip" of the bearing. There needs to be a minute clearance for lubrication, say 0.001" (0.025 mm ) but excess clearance will impair accuracy and surface finish. On a lathe of this vintage, lubrication will be drip feed no doubt, and should be operated at relatively low speeds (Hundreds of rpm not thousands!)

                                                HTH

                                                Howard

                                                #564865
                                                not done it yet
                                                Participant
                                                  @notdoneityet

                                                  Howard,

                                                  … Whatever tool you use MUST be on the centre height. A quick check is to face across the end of the bar. If there is a pip in the middle the tool is not on centre height, and needs to be shimmed up or down, until it is.

                                                  Once you get the tool on centre height, it would be worth making some form of Centre Height Gauge, so that in future, all tools can be set to it, Making it will be useful learning exercise in itself….

                                                  While that is an ideal, it just does not apply, precisely, to anything but a perfectly rigid lathe.

                                                  With an old (or even new light-weight) machine, the tip can cut perfectly to the centre while facing (the workpiece tending towards zero rotational surface speed and hence zero force, but when a force is applied tangentially, at a distance from the centre, the tip will only be deflected (to some degree) in only one direction – downwards.

                                                  The deflection will depend on the condition of the lathe, basically, but can be exaggerated by the operator extending the cutter, taking heavy cuts or moving the cutter away from the ideal position (like using tools/cutters overhanging the the top, or cross slides, particularly while using a QCTP).

                                                  #564896
                                                  Russell Eberhardt
                                                  Participant
                                                    @russelleberhardt48058

                                                    Well done Steve. You are definately getting there.

                                                    Russell

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