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  • Stepperhead 2

    Click image for larger version  Name:	 Views:	0 Size:	562.6 KB ID:	1929875 Stepperhead 2
    What to do in the Covid lockdown? I wish you the best of health and hope you are coping with this trauma. In my case I have tried to deal with these long lockdowns by trying to design a smaller version of the Stepperhead lathe that I built and displayed in 2008. I managed to get access to Solidworks and intended to teach myself in the process. You may have seen that the Model Engineers Workshop magazine has recently published an article on this design. So this is a follow on from that and I am sticking my neck out here venturing for opinions from the forum members. I have added a few screenshots and a basic description, if there is any interest I can describe it in more detail and screenshots.
    I set myself a design brief as listed below:
    1. Size - A table top lathe suitable for the home workshop; or even indoors - with senior management approval of course! The machine is to be mounted on a baseboard of 750mm wide x 500mm deep. Of course the size can be easily increased, but a design for a limited footprint is more demanding in the use of the space.

    2. Concept – Similar and smaller than Stepperhead design but with changes and improvements to simplify construction and operation. A cast iron one-piece bed. The spindle drive motor and all the electrical components are housed in a box at the rear of the lathe which will also form the splashback or chip guard. The raising and lowering of the head, overarm and tailstock will be done by a vertical screw. similar to a milling machine table. This keeps everything above the base board.

    3. A Camlock spindle nose fitting. This is such a boon enabling easy chuck changes and the safe ability to rotate the spindle, under power, in either direction.

    4. The spindle motor is a 0.37 kW three phase motor, frame size 63, driven by an inverter also mounted in the splashback box. The motor is pivoted at its lower front so it can move as the head and tailstock is raised. This uses the motor weight to tension the belt. The motor & spindle pulleys have three steps for a wide speed range. The largest spindle pulley enables a low back gear speed range at the spindle. The belt is accessible and can be easily, and quickly, changed to the various pulleys. A polyvee belt drives either the spindle or a shorter length belt is used for an overhead drive shaft mounted in the upper section of the splashback box. The motor pivot point enables both drives to be adjustable. The pivot may benefit from some friction damping adjustment.

    5. The spindle runs on taper roller bearings and has a 26mm bore. The bore is as big as can be made without substantially increasing the head block size of 80mm square. It uses the same Camlock chuck mounting arrangements as Stepperhead. I tried to design a slightly smaller Camlock fitting but there was little to be gained with keeping the mandrel bore size and ER32 collet fitting.
    The drive from the spindle stepper motor is via a worm wheel mounted on the spindle inside the head block. The stepper motor worm engagement is spring loaded when moved to into this wormwheel to drive the spindle. This gives a backlash free drive to the spindle. The worm drive is positively locked out when not required. This is to ensure that cannot be accidentally engaged. The motor belt can also be disconnected at the motor for additional safety. The stepper motor mounting box also incorporates an optical sensor and its circuit board for screwcutting etc.

    6. New ideas – I have incorporated some new features I have been experimenting with over the last few years. There are always reader comments about gibs and their settings for smooth shake free sliding. It is a fundamental requirement that dictates the performance of the whole machine. This requires accurate slideways and careful adjustment and is very difficult to achieve on less than perfect fits.

    So here I would like to propose my oval gib idea to replace the conventional gib arrangements throughout. It seems to me such an improvement and simplification and has become subject to a patent application. It eliminates the adjustment and locking screws at intervals along the gib length. It contacts, solidly, both the sliding and fixed guideways the full length of the moving slideway. It is simply rotated to set the close sliding requirements by setting and locking an eccentric stop. If the gib is further rotated away from this stopped position it will lock the full length of the moving slideway solidly to the fixed slideway. Rotating it back to the stop will return it to the set close sliding position. It is also easy to make.

    The oval gib itself can be solid or it can have a surface that is segmented into slightly springy zones. This will spread the loading and be of great assistance for smooth operation. It will also enable it to adapt to, and make the best of, less than perfect surfaces due to local wear or less than perfect machining. Of course it cannot compensate for non-parallel sliding surfaces and poor fitting, but it will tend to slightly deflect over the bumps and troughs, so to speak, and promote smooth shake free movement. It is also easy to remove and replace for inspection and can be made from a variety of materials. The oval gib system has also been used to guide and lock the vertical column in the radial and vertical planes, avoiding the triangular gib which works well but was difficult to make.

    7. Tightening and undoing ER style collets seems to be a subject of contention, especially for the smaller diameters. So I have suggested a method of tightening the collet nut without having to lock the spindle, or use a second spanner to hold the chuck body. The castellated mandrel mounting body has fifteen notches and the nut has sixteen holes so there is always an appropriate zone for the locking/unlocking spanner. The collet nut has two hardened discs positioned to enable the collet to be withdrawn rather than an eccentric diameter.

    8. Vertical parting tool - I have shown a design which mounts on the front of the lathe and rests solidly on the cross slide, preventing any downward deflection and allowing free chip flow. Inserted tips could also be used in a suitable mounting. With the topslide locked by its oval gib it becomes a virtual Gibraltar mounting point because the upper and lower slides are locked together. The cutting tool height can easily be set even when the machine is in operation.

    9. The upper part of the splashback box provides a mounting for a horizontal secondary driveshaft in a similar manner to watchmaker and earlier instrument lathes. A cover panel at the centre of the splashback front panel can be either, slid to the left or just removed to reveal a rectangular cut out exposing this driveshaft with a pulley drive for round belts. The pulley is positioned along the shaft to provide the overhead drive. To fit the round belt, the shaft is moved to the left enabling the belt to be fitted over the end of the shaft. A locked collar retains the shaft in the righthand end bearing. The spindle drive belt is removed and a shorter length polyvee belt used to drive the shaft.

    This makes use of the main motor with its inverter control, enabling a wide speed range for a milling spindle mounted on the topslide for example. The arrangement I used on Stepperhead with a milling head driven by a DC motor with electronic control worked but had a limited speed range around 2000 rpm. It had limited power and got quite hot, its bulk was also restrictive. The problem with the high speed was that a carefully shaped carbon steel cutting tool would overheat and lose its hardness halfway through the operation, say when cutting a gear, especially in steel. High speed steel cutters solve the problem but are difficult to make and shape compared to carbon steel. So to be able to slow down the cutting speed without power loss would be of great benefit. Round belt pulleys and belts of various diameters can be used. This would enable a wide use of operations say, using the stepper driven spindle via manual or CNC control for a myriad of operations, including decorative ornamental designs etc.

    10. The milling spindle has a bore for No 2 Morse taper collets and a locking/eject drawbar. It has bronze self-lubricating bearings and uses a double taper similar to a watchmaker’s lathe headstock design. Ball bearings have been avoided to keep the overall diameter down to 40mm.
    Comments welcome
    Alan
    Click image for larger version  Name:	3-Front panel removed-Left.jpg Views:	2 Size:	527.2 KB ID:	1929876 Click image for larger version  Name:	5- Overhead drive.jpg Views:	2 Size:	805.6 KB ID:	1929877 Click image for larger version  Name:	10-ER collet spanner- ghosted.jpg Views:	2 Size:	684.5 KB ID:	1929878 Click image for larger version  Name:	11-Vertical parting tool 1.jpg Views:	2 Size:	674.0 KB ID:	1929879
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    Last edited by jackary; 02-22-2021, 07:19 AM.

  • #2
    Outstanding! I want one!

    Comment


    • #3
      I think it's a great design. I really like the 1st one, too!. For this one, I have an additional suggestion. If there were a hinged bar on top of the headstock with a pin that would fit both the slots and holes for collet tightening, it could be used for spindle indexing. The bar could be slideable lengthwise to engage either the holes or slots. Then the slots (16) could be used for multiples of 2 and the holes (15) could be used for multiples of 3 and 5. The bar could be swung up to vertical when not needed.
      Kansas City area

      Comment


      • #4
        Man I like that crank-spanner for the collet chuck.
        Good thinking right there.

        -D
        DZER

        Comment


        • #5
          Yes, the collet tightening system is brilliant!
          Kansas City area

          Comment


          • #6
            Is the spindle height adjustable?

            Comment


            • #7
              Cool system for tightening the collet, but why go with ER type instead of a 5C or similar? With a 5C you can grip a smaller portion while still getting a secure grip, ER collets would require a spacer/filler to do the same.
              Cayuga, Ontario, Canada

              Comment


              • #8
                Hi toolguy & Elf,
                Toolguy your idea to use the collet chuck for indexing would work ok, but as the spindle already has a stepper motor drive for indexing etc it is not really necessary. The spindle can be indexed and rotary driven for all permutations.
                Elf, the spindle , overarm and tailstock can be raised about 50mm and lowered about 20mm from the position shown even when the spindle is turning.
                I will add a description of this and the lathes other features to this thread.
                Alan

                Comment


                • #9
                  The lathe has a cast iron flat topped bed and incorporates the mounting block bored for the vertical column. The overall length is 580mm.The front guide is 40mm wide with a semi-circular groove on the front face. This groove houses an oval gib mounted in the saddle. The rear guide is 20mm wide and has a similar groove on its outside face for a similar oval gib.

                  The bed width is 110mm which exceeds the nominal 80mm centre height giving the saddle a wide platform to slide on. The saddle is narrow guided on the front guide while the rear slideway supports and prevents the saddle from lifting. There are four intermediate stiffeners connecting the guide sections, so this should provide a rigid platform for the saddle and tailstock bed slide. The bed mounting point at the headstock end incorporates a 10mm thick damping pad at its connection point with the mounting block. This is to promote quiet operation and minimise any vibrations due to the machining operations from propagating into the mounting board.


                  With a cast iron bed, a cast iron head block and saddle, plus the overarm bracing the whole structure (a big plus I am going to say). The combined structure is really very solid, and much more rigid than the equivalent small lathe.

                  The ability to raise or lower the head and tailstock relative to the bed has many advantages, enabling varied operations. The overarm connects the headstock to the bed and when the clamps are locked it provides additional rigidity to the headstock, tailstock and bed. The tailstock is incorporated into the overarm and supported at the headstock and bed. The tailstock vertical column has an eccentric connection to its bed block, this enables a fine setting for the tailstock to set its concentricity with the spindle.

                  The space underneath the tailstock becomes available as an additional bed length (which is usually occupied by the tailstock foot) to be used by the saddle. The overarm also provides a convenient attachment point for accessories.

                  The saddle is guided by the front bed bar providing a long narrow full length guide using an oval gib in a curved groove; the inner guide face is 13mm deep and extends the full length of the saddle. It does not have to be reduced in length to clear the tailstock foot, as is normal in conventional flat bed lathes. The handwheel at the far right of the bed controls the saddle movement and can be engaged or disengaged from the stepper motor drive by rotating the lever shown to the right of the saddle drive stepper motor.

                  The biggest change is at the cross slide which usually straddles the raised vee slide on the saddle with the gib arrangements on the right hand side and a central feed screw. On this design a full size feed screw and oval gib are combined by cutting an oval gib contour on the screw thread periphery. This simplifies the construction and operation substantially. The saddle has a sunken vee slide and the cross slide has a raised vee slide on the LH side and an oval gib groove on the RH side. This has advantages in that the cross slide is much thicker and stronger even with tee slots. Somewhat similar to a milling machine table. This gives space for central groove to be cut into the underside of the cross slide to accommodate a DRO.

                  The threaded oval gib has a reduced area of contact in that the sliding surface is the top of an acme screw thread. But it gains by both the gib and screw thread being inherently parallel to each other and one robust item. This gib can also be rotated away from its set close sliding position to lock the cross slide to the saddle along the full length of the sliding contact.

                  The cross slide handwheel drive is set at an angle to the cross slide and has thrust bearings and the provision to eliminate backlash. The stepper motor can be engaged or disengaged by the lever next to the feedscrew handwheel.

                  A topslide could be avoided completely as a cost cutting exercise. Topslides seem to be a source of problems, with rigidity reduced by large cut-outs in the cross slide to mount the topslide in a fixed location and inadequate clamping methods. Some have little or no support directly under the cutting tool and this is further compounded by fitting an overhung toolpost mounting. This seems to be a weak point in many lathes.

                  I have shown a lever locking topslide that can be mounted and moved anywhere at any angle on the cross slide. A screw cutting withdrawal lever for internal or external screwcutting is incorporated. Plus, of course, a full length oval gib, that can be rotated away from its set close sliding position to lock the upper and lower slides solidly together, by a lever beneath the feed dial. The lever wedges the slides together and the friction grip of the oval gib keeps the lever in the locked position until it is pushed down, virtually creating a Gibraltar toolpost.

                  The topslide handwheel drives a 10mm wide toothed belt via an adjustable idler to set the belt tension. This positions the handwheel high and clear of the tailstock barrel. The feed screw runs in a long plastic nut which has slits to enable adjustment for zero backlash. The toolpost is a simple design with no overhang from its support point and includes a mounting hole for a boring bar. The toolpost can be inverted and the lathe run in reverse if desired. There is no need for shimming or setting the cutting tool height at the toolpost. This can be done by the vertical height adjustment even when the tool is cutting.

                  The vertical column is radially guided by an oval gib. The lever can rotate the gib to lock the column in position or allow it to slide. The gib extends the full depth of the guide block. There are also two additional locking points in the bed block. These will not generally be required but are available to clamp the column for additional rigidity. The oval gib guide can also be removed, allowing the headstock and overarm to be rotated relative to the bed; enabling various machining operations using say the milling spindle. In general taper turning can be carried out using CNC or the topslide. The overarm and tailstock assembly can also be removed enabling a maximum diameter of 290mm to be swung over the bed.

                  I have also shown a 150mm o/d four jaw chuck of my own design using (guess what?) oval gibs for the jaw slides. The screw that adjusts the jaw is located beside the jaw instead of to the rear where it is normally placed. This enables a slimmer chuck body. The body of the one shown is 32mm deep. The chuck may seem large for the lathe but it can also be used as a faceplate. Removing the reversible jaws reveals the threaded sliders which can be used as adjustable screw fixing points for the faceplate.

                  The tailstock barrel has a Morse No 2 taper and a screw ejection at the far end. The capstan handwheel has a micrometer feed dial for the 75mm travel and gives a sensitive feel when drilling and enables quick retraction of the drill.

                  Conclusion
                  This proposal is for a lathe that can do all the things a basic machine can do and also have the additional capabilities to perform very many operations that the home workshop could encompass and more. It could also be a machine with the built in ability to be upgraded in various stages. First a basic lathe with an inverter controlled drive motor and manual operation of the saddle cross slide and elevating the mandrel and tailstock. Secondly with the addition of stepper motor drives to the saddle and cross feed for optional power operation. Thirdly with a stepper motor drive added to the headstock, a laptop computer, and a CNC program.

                  All these features can be used independently or together. For example, it is possible to power feed either the saddle or cross slide, or just use the spindle stepper drive for indexing. Or of course use full CNC control, or dare I say, CNC control with manual override. This would provide a very versatile lathe with machining capabilities beyond its small footprint. Capable of any screw thread system, tapers and profiles as well as easy indexing for gear cutting etc. and many other operations including milling and keyway cutting.


                  The versatility can be further enhanced by additional attachments. The tee slotted cross slide and the overarm provide convenient mounting points for them.
                  As to cost there are gains and trade offs. There are savings in eliminating the following items; a clutch assembly, a separate back gear drive shaft and gear assembly, the change gears and banjo arrangement, a tumbler reverse and a feed/screwcutting gearbox; and these could well equate to the cost of stepper motors and their drivers. The added bonus in avoiding these items, which are often a source of noise and vibration, is the potential for a quiet machine.


                  Here is a brief specification:
                  Nominal centre height 80mm (can be varied from 70 to 150mm)
                  Max. distance between centres 350mm
                  Spindle bore 26mm
                  Max diameter at normal headstock height. 170mm
                  Max diameter over saddle at normal headstock height. 100mm
                  Max diameter clearing overarm. 170mm
                  Max diameter over saddle with headstock raised. 210mm
                  Max diameter with overarm removed. 290mm
                  Spindle speed range. 15 to 3500 rpm
                  Cross slide travel 200mm
                  Tailstock barrel travel 75mm (No 2 Morse taper)
                  Attached Files
                  Last edited by jackary; 02-23-2021, 01:45 PM. Reason: Spaced out text

                  Comment


                  • #10
                    Please explain the rounded shape guideway. Is this a proven design? I'm not trying to be critical, rather curious. Do you rotate the gib to adjust?

                    Seems difficult to manufacture, small contact area, and in conflict (redundant vertical constraint) with the flat way above. I must be missing something.

                    Comment


                    • #11
                      I reread your earlier description. Please post back any further comment. I'm interested.

                      "The oval gib itself can be solid or it can have a surface that is segmented into slightly springy zones. This will spread the loading and be of great assistance for smooth operation. It will also enable it to adapt to, and make the best of, less than perfect surfaces due to local wear or less than perfect machining. Of course it cannot compensate for non-parallel sliding surfaces and poor fitting, but it will tend to slightly deflect over the bumps and troughs, so to speak, and promote smooth shake free movement. It is also easy to remove and replace for inspection and can be made from a variety of materials. The oval gib system has also been used to guide and lock the vertical column in the radial and vertical planes, avoiding the triangular gib which works well but was difficult to make."

                      Comment


                      • #12
                        you've put a lot of thought into it....and yes, a brave move posting it here lol. A few questions and comments occur....not intended as criticism, just what occurred and you asked for feedback

                        whats the column coming through the lathe headstock for, and how does that work; a column and a spindle intersecting?

                        Oval gib.....how do you make that? how do you fit it?

                        spindle motor 1/2 hp, seems really light. Its going to be D1 3 cam lock? Visually, that makes me think its a fairly large desktop lathe....I'd want more umph for a lathe that size

                        Why traditional plain bearing linear motion vs say linear rails? I like plain bearings, just curious as it pretty much says scraping will be needed

                        I'd use a split collet in the headstock. As a general thing, ER's are great for tools and splits are better for work. There's lot of overlap of course and ER's can hold work....but there a bunch of good reasons for preferring one over the other...so if you're making it as good as it can be from scratch....

                        whats the spindle bearing arrangement?

                        tailstock support via overarm - why? seems weak with a big moment vs supporting off the bed

                        Is this something to do as a study or are you making this lathe?

                        your long follow up post would be a lot easier to read with blank lines between paragraphs
                        Last edited by Mcgyver; 02-23-2021, 01:25 PM.
                        in Toronto Ontario - where are you?

                        Comment


                        • #13
                          Hi Mcgyver,
                          Thank you for your comments. I have spaced out the text as you suggested. The Camloc is not D1 3 but my own smaller version (outside dia 75mm). This lathe is mini lathe size, the base board is 750mm wide x 500 deep. This is a smaller tabletop version of my Stepperhead lathe I made in 2008 and many features are similar to this design see http://www.lathes.co.uk/stepperhead/

                          This should explain the spindle through the column and the tailstock support via the overarm which is also supported at the bed. It will also explain the spindle bearings. I have already made the Stepperhead lathe and am not sure if I want to make Stepperhead 2 but I have had these ideas for some time and this "study" is showing these ideas. As to the oval gib I will write something to describe this as strokersix has also asked the same question.
                          Alan
                          Last edited by jackary; 02-23-2021, 02:09 PM.

                          Comment


                          • #14
                            Hi strokersix,
                            I wil endeavour to answer your questions about the oval gib.

                            The bed semi-circular groove is lower than the facing saddle semi-circular groove by a small amount creating an offset aperture between the fixed and sliding surfaces. The oval gib has a profile that closely matches but is slightly smaller than the aperture profile to permit insertion. The gib is rotated to set the sliding clearance and is then set in this position. Further rotation will lock the slides together.

                            The gib is anchored axially to the saddle but is free to contact both the fixed and sliding grooves. The gib urges the saddle to contact the bed flat top surface and the inner guideway surface in a manner very similar to a dovetail gib. The gib contact area will closely match the groove surfaces. I also have a design (not revealed here) that matches both grooves exactly, regardless of the offset distance.


                            The vertical column grooves would form a full circle when aligned but are purposely mis-aligned to form an offset aperture by the oversize first gib. A secondary gib is added below the first upper gib which can be rotated to urge the offset grooves into alignment, therefore locking the column in its slideway. The gib can have a simple oval profile or be more profiled to match the groove surfaces giving closely matching contact surfaces.

                            I do not think the grooves would be any more difficult to manufacture than a dovetail groove. The grooves have to be parallel, but to my mind there are no stringent machining requirements. Avoiding the adjusting and locking screws for a dovetail gib is a worthwhile simplification and avoids the point contact with the gib and the screw ends. To be able to lock the slideways over the full slideway length and return the gib for sliding contact is a bonus.

                            The gib makes full contact with both the sliding and fixed guideways. This makes it better at absorbing the machining forces and provides the benifit of a tapered gib without the precision requirements a tapered gib demands. I made a topslide featuring an oval gib for my Colchester Chipmaster lathe about 10 years ago and it works superbly.


                            Alan

                            Comment


                            • #15
                              OK. I now understand your concept. Thank you.

                              Comment

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