Making a fixed tool post for my Harrison M300

  1. Paul in Wiltshire Member

    Messages:
    56
    Location:
    UK Wiltshire
    (also posted on Harrison Lathes group)
    I have ordered a Multifix QCTP and holders for my M300. I have ordered size E from CreateTool in China, it should arrive in early July.

    I have decided that I’d like to install the new tool post on to a fixed post to replace the top-slide. It’s not my idea, or a new idea, but I thought some of you might be interested. Robin Renzetti has a very detailed explanation on his YouTube channel, although I won't be going to his extremes.

    As I see it there are three main benefits to removing the top slide:
    1. Rigidity: parting and heavy cuts with the top slide gib clamped show much less chatter. Having a fixed tool post should be even better;
    2. Repeatability: I have a DRO fitted to X and Z, the top slide can mean that tool offsets aren’t repeatable;
    3. Optimum tool post height: The fixed tool post can be designed to be at the optimum position to allow all your tools to be adjusted to centre height without resorting to spacers/machining tool holders.

    The downsides seem to be:
    1. Harder to cut long tapers: I don’t have a taper attachment, I do have a hydraulic copier, but it isn’t fitted yet. I can cut small tapers with a form tool;
    2. Inability to offset top slide for thread cutting: I have cut threads without offsetting the top slide and with it set at 29.5 degrees (for metric / UN). To be honest I can’t see much benefit from spinning it around and make cuts just using the cross slide. I think this use of the "compound" is popular in the US, but in Europe it only seems to be practised by those that learnt from YouTube;
    3. Modifications to the lathe: No one wants to turn their lathe into Swiss cheese with lots of new machining to fit parts. I intend to fit the fixed post with the minimum amount of non-reversible changes. I will keep my top slide and its Dickson QCTP for those occasions when I really need it, and my design should allow me to swap between fixed post and top slide in minutes;
    4. Clearance for large/odd parts: Sometimes extending out the top slide can be useful to give clearance/access when turning parts that won’t swing over the cross slide.
    The M300 top slide is fixed to the cross slide using two t-nuts that run in a circular slot. The axis of rotation is fixed by a 20mm pin. Here is a picture of the cross-slide with the top slide removed.
    cross slide.jpg
    I intend to fix my post using four t-nuts and the central pin. I have decided to make my own t-nuts with curved sides to fit the slot. As I want my post to have a fixed angular position, I am also adding a location dowel to register the post. Drilling/reaming this hole for the registration pin is the only modification I will be making to the original lathe parts. I have sketched up all the parts that I am going to make in Fusion 360. Here is a view of the fixing hardware for the fixed post.
    post fixing.JPG
    The post itself will be cast iron (meehanite). It will have the features needed to fix it to the cross slide, the bottom surface will have some relief cut so that it isn’t bearing over the whole surface. On its top surface will be a hole for the stud to fix the QCTP, and a hole to register the QCTP. The QCTP isn’t mounted centrally, so that the tool is presented in front of the cross slide to give more clearance when facing large diameters. Don’t want to extend it forward too far or it will compromise rigidity.

    The front of the post will have a flat machined to allow it to be indicated in square and to aid machining. I plan to turn a taper on it so that chips don’t build up.

    I will machine a stud to fix the QCTP, this has a 20mm feature to locate the QCTP, and two threads to fix it in the post and for the nut. Here is the sketch of the post and fixing stud+nut.
    Fixed post.JPG
    Here is the sketch showing it all together.
    assembly.JPG
    Cross section.JPG
    I’ll make some additional posts showing the manufacture of the bits.
     
  2. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

    Messages:
    15,248
    Location:
    East Yorkshire
    OT but I believe relevant...

    The only problem I foresee with this idea, is you are going to lose the macro feed of a topslide.

    I have thought about this problem, not because I want to remove the t.slide assembly, [I don’t have problems with chatter etc] I just don't use it, and more importantly it’s not connected to my DRO so any adjustments renders the DRO reading void.
    To get around this I’m thinking of fitting a pair of reduction gears to the apron, that would act upon the handwheel, effectively giving fine adjustment. I know its still acting upon a large coarse rack, but it would be better than ‘bumping’ the saddle handwheel.

    Thoughts?
     
    Maker likes this.
  3. Paul in Wiltshire Member

    Messages:
    56
    Location:
    UK Wiltshire
    With the DRO I’ve never had a problem feeding to a Z location using the carriage hand wheel. I sometimes snug up the carriage lock then tap/bump the wheel, easy(ish) to set to .01mm on the DRO. I usually find that my Z dimensions rarely require the same degree of accuracy as the Y.

    Using the top slide to set Z dimensions also requires the top-slide to be trammed in other wise you may end up making small adjustments to Y. On my previous lathe I would sometimes set the top slide to 6 degrees, this would give you a more precise infeed, as 10 thou on the top slide was 1 thou infeed.

    I should be able to swap between my fixed post and the top slide in a couple of minutes. It’s just a case of removing four 8mm socket head cap screws, pulling the post off and dropping the top slide on and fixing with two cap screws.
     
  4. Paul in Wiltshire Member

    Messages:
    56
    Location:
    UK Wiltshire
    Here is the machining of the reference pin hole in the cross slide. The hole is to take a 1/4” (6.35mm) dowel to accurately locate the fixed post. I decided to place the dowel at a radius of 35mm from the 20mm axis pin. I think that you want this as far out from the axis as possible, but not too close to the t-slot. So the 35mm is an arbitrary round number. I decided to place it at 45 degrees to resist cutting loads, again the angle is arbitrary.

    Having stripped and rebuilt the lathe, removing the cross slide is easy. The only annoying bit is that I have to re-clock the DRO scale back in when I re fit it.

    Here is the cross slide clamped in my mill vice. Only clamped fairly lightly as it just has to hold location for drilling. B8AEC76A-92A3-43D7-BA37-F32B4EBFF1DE.jpeg

    Here I’m using an edge finder to locate the centre of the 20mm pin. I checked this centre using an coaxial indicator as well. The fixed jaw of the vice is trammed in and this provides an angular reference for the hole.

    My milling machine is a Kearney and Trecker 2D, it has a rotary head that makes it easy to off set the head and cut radii or drill features on a pitch circle. Here I am set up to spot drill with a 6mm carbide spot drill.
    A94E3BB0-DCC1-4854-B603-59733730DA4C.jpeg
    The dial on the left (set to ‘1’) shows how far the head is offset. It reads 2mm per revolution, turning the handle below that dial moves the head towards or away from the column. Here it has been set 35mm toward the column. The big handle top right rotates the whole head, behind it is a scale showing minutes. There is also a scale below the grease nipple that you may be able to see is set to 45 degrees. You can machine curved features by turning the rotary handle while cutting, or you can power feed the rotary head (engaged with the lever top right of the picture). The small handle on the side of the head feeds the quill. Or you can power feed it with the controls on the front of the head.

    So I spot drilled with a 6mm 120deg spot drill, followed that with a 6.1mm drill to depth, then a 1/4” reamer. The result is a nice air tight fit with a 1/4” dowel.

    I love my rotary head mill, but that could have also been done with a bit of maths and a DRO (or even the dials).
     
    Last edited: Jun 12, 2020
    Guzrik and daleyd like this.
  5. Agroshield Member

    Messages:
    796
    Micrometer bed stop could help overcome this. Hold the carriage up against it and twiddle the micrometer barrel. Large barrel could get you half a thou' or less resolution.
     
  6. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

    Messages:
    15,248
    Location:
    East Yorkshire
    In my case its more to do with problems with my hands, I cant use them as hammers anymore. And that includes tapping a hand wheel. Also speed its easier to close up on a Number with a fine feed than coarse.

    Paul, have you taken into consideration the reduced overlap on the cross slide to saddle?
     
  7. Agroshield Member

    Messages:
    796
    Have you seen the Multifix page at lathes.co.uk? It shows a "special adjustable tool-change holder with a miniature D.T.I. as used on a Cri-Dan screw-threading machine". If the dovetail slide of this was at a different angle, it could do what you want specifically for threading, without compromising rigidity elsewhere.

    Sized, I guess, so they fit through the access hole in the underside of the cross-slide.

    Here's a nit-picky one. Should it be square or should it be parallel? AIUI, lathes are set to face very slightly out of square (concave) from the factory.

    It may also be prudent to make 3D printed covers for the counterbored holes in the post so they do not fill with swarf.
     
  8. Paul in Wiltshire Member

    Messages:
    56
    Location:
    UK Wiltshire
    Not certain what you mean. Do you mean the fact that with the top slide the centre of the tool post is offset towards the chuck, giving clearance over the cross slide/saddle? If that is what you mean, then yes, it's why the centre for the tool post stud is offset. In my design that offset is currently 18mm, that was arrived at to ensure the tip of the tool should clear the front of the cross-slide to allow facing of diameters larger than the cross-slide clearance. This offset will be finalised once I have the Multifix in my hands and can take some real world measurements.

    I suppose you may also mean the X position of the cross slide will be different, it should be the same for me as my top slide normally "lives" in the 0 deg position. I know some people leave it in another positions, so it would be different for them.
     
  9. Paul in Wiltshire Member

    Messages:
    56
    Location:
    UK Wiltshire
    I have seen those, CreateTool will sell you the FI (internal threading holder) or FE (external threading holder) to order. I think they are about $500 each. They provide a quick and repeatable retract. I'm doing this as a hobby, so the speed of work isn't that important to me. I get on fine just retracting with the cross slide and referencing the DRO.
    Yup, I found I had about 30mm of "width" in the underside, which gave me an arc of 15 degrees for the t-nuts. (spoiler, I've already made the t-nuts and they fit)
    In my case it will be set up so the QCTP runs parallel to the Z axis. With this dialled in, I will be able to mount a drill chuck in a tool holder and power feed drills using the carriage feed.
    As you say that could mean a few minutes of error in the QCTP being parallel to the cross-slide travel, that would have a very minor effect on grooving/profile tools. I'll measure that error next week.

    The flat surface isn't so much for dialling in the fixed post when re-fitting it, more to give me a reference whilst machining the top and bottom features of the fixed post. The flat is actually parallel to the front of the cross-slide because of the way that I machined the flat and the dowel hole between the fixed post and cross-slide.
    The rendering is a bit inaccurate as the counterbores are set up as a circular pattern feature, so they all go to the same depth. The front ones won't actually be so deep, so the socket will be just recessed enough, as it is on the back two. They will still be a bit of a swarf trap. I may give 3d printed covers a go, but not sure how long they'd last being showered in hot chips. My other thought is that removing the covers would be a pain. The problem they solve is that chips wouldn't block the sockets so removal of the post would be easier, but I've come to the conclusion that a blast of air to remove the chips would be quicker than removing covers.
     
  10. Guzrik Member

    Messages:
    114
    Location:
    Holland Noord Brabant
    This thread is a bit disturbing to me:laughing:, because (having worked with lathes for 37 years) I was never aware of the existance of all this:o
    First was that someone would want to give up their cross slide, I am used to work with a positionable support block and for small series use the top slide to set the different steps in the product. Also making somewhat bigger 45 or 60 degree chamfers with it.
    Second is the existance of a mill with a rotary head, what an amazing machine that is!
    And last but not least that lathes are set to face very slightly out of square (concave) from the factory; how much is this and is this for all brands and why?
    So if I skim from center to the back I would get a convex shape?
    I am on this forum for a few weeks now and liked it a lot, but this is really fantastic, thank you.
     
    Ton-up and Shox Dr like this.
  11. Agroshield Member

    Messages:
    796
    The one I was talking about is this one:

    http://www.lathes.co.uk/multifix/img8.jpg

    As I see the picture, it is not quick retract (the FE and FI are shown in a different picture). It has an micrometer-adjustable dovetail slide between the serrated bit and the tool holding bit. I guess in the application shown, it is for fine adjustment of the tool, more than could be done with the hydraulic copier on which it is mounted. As shown in the image, the tool moves straight in. But if you made the same thing with a dovetail angled at 29 or 30 degrees (still keeping the tool itself at 90 degrees to the lathe axis), it would have the same effect or function as a topslide at the same angle and be usable on the fixed toolpost. It would be like having a fixed-angle topslide just for screwcutting purposes.
     
  12. Brad93

    Brad93 M J B Engineering

    Messages:
    8,476
    Location:
    Essex
    I think the best multifix toolpost Mount I’ve seen, is eccentric engineerings idea. Few videos on Facebook.
     
  13. Agroshield Member

    Messages:
    796
    I meant to say that the eccentricity of the bolt relative to the cross slide stud is a very good idea as if you have some huge diameter part, you could rotate it 90 degrees for a bit of extra reach. If you have some very long part, way up near the tailstock, you could rotate it 180 degrees.
     
  14. Agroshield Member

    Messages:
    796
    We have an expression that says 'horses for courses'. You do not use a thoroughbred arab stallion to pull your hay cart. You have to look at the work you are doing and configure the machine best to do that work. The lack of a topslide gives a large increase in rigidity for heavy, straight turning. Also, if you are using a DRO and tool offsets, it helps with repeatability, and thus speeds things up as it can eliminate the cut-measure-cut again for every tool.

    The pre-CNC people were very clever. Have a look at a Volstro head for a Bridgeport. A lot of the clever attachments originated in the die-making industry where you need complex 3D shapes from a manual machine.

    I believe all lathes should be set up in this way. It is so that two mating faces will always touch at the rim and not rock at the centre. I have it in my mind that it is something like 1 thou' per foot of crosslide travel (sorry for the imperial units). The classic text on this is Schlesinger and online pdfs of this are available. I believe it is often reported in the calibration sheet that accompanied a new machine. Again, for some machines, pdf copies of these sheets are online. I have never thought about facing from rear to front and I believe you are correct.
     
    RobCox and Guzrik like this.
  15. Brad93

    Brad93 M J B Engineering

    Messages:
    8,476
    Location:
    Essex
    On a big Monarch spinning a 12” dia piece it’s about 3 tenths
     
  16. Paul in Wiltshire Member

    Messages:
    56
    Location:
    UK Wiltshire
    Hadn’t thought of that, always good when a design has unintended benefits.
     
  17. Paul in Wiltshire Member

    Messages:
    56
    Location:
    UK Wiltshire
    Interesting idea. Having the dovetail at 29 degrees could make it a large tool holder, although the travel wouldn’t have to be more than a few mm.
     
  18. Brad93

    Brad93 M J B Engineering

    Messages:
    8,476
    Location:
    Essex
    Another take by Stefan Gotteswinter
     
    • C0C0711B-A30D-4EC8-9CA0-49E6BE88B66D.png
    • 9D25E05A-99A1-42B8-A68D-8CD1C588EA7B.png
    Milkybars likes this.
  19. Paul in Wiltshire Member

    Messages:
    56
    Location:
    UK Wiltshire
    My tool post arrived from Wuhan today. I had stopped work on the fixed tool post as I wanted to have the QCTP in my hand to measure and check the location for the post that I had come up with.
    It seemed that the height of the fixed post would be critical to be able to adjust all of my holder and tool combinations on centre height. The Create spec shows only 6 mm of height adjustment on the ED25100 holder. I’m pleased to report that the adjustment is much greater, so the height is less critical than I thought. I have put together a spreadsheet that allows you to work out the ideal riser height for your holder and tool combinations. I’ll share that later.

    I’ve roughed out the meehanite for the post, and drilled/reamed the features on the bottom.
    334ED39F-13B2-4136-96A9-7DAA0BCEDE88.jpeg
    C7E2F5B2-5229-435F-AB0C-E7BAC0659C1D.jpeg
    10F2EE4B-89B8-4A74-88F0-ADE5B016E32D.jpeg

    I also machined a stud, but I am now going a different way with that. The one here is male both ends, then I made a nut. The new one is male at the bottom, then female within the post. Then on top is a screw with a thrust washer. This has a hex cap that the QCTP spanner fits on, so the one spanner can lock the post or tighten/loosen the whole post. I’ve also made my curved t-nuts using the circular head on my mill.
    04C36784-D93A-460D-B2E5-C447794002FD.jpeg

    Here’s my box from Nina:
    EB70DFD9-0C60-4D21-8955-0E821FD2A75B.jpeg

    A selection of size E tool holders
    E0E50DF6-A83D-48D6-9E08-94539964CF5B.jpeg

    Here is a selection unboxed
    62837AC9-CD54-4F6F-91D9-45069E9A7FCC.jpeg
     
  20. Brad93

    Brad93 M J B Engineering

    Messages:
    8,476
    Location:
    Essex
    Out of interest, what size is the hex for the E type handle?
     
Advertisements