Quick Change Tool Post for a small lathe.

  1. optima21 Forum Supporter

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    its been one of those jobs that I've been meaning to do for years, but now I've finally got round to making a new tool post for my Hobbymat MD65 lathe. Here are a few pictures taken along the way. I was originally going to make one which has the tool holder clamp about a circular post, but after I started changed my mind and use an eccentric driven plunger, after having a closer look at how normal qick change tool posts work.

    the main post began life as a 60mm dia x 50mm long steel bar, and its amazing how much swarf you can create from one peice of metal

    DSC03087.JPG

    then I started making tool holders from black bar, faced up using a flycutter, in my milling machine using a vice which has jaws which bolt into the T slots, so the vice can be as long as the milling machine table

    DSC03097.JPG

    then the tool holder blank needs boring out to fit the post. the cente bore of my 4 jaw chuck was a couple of mm too small, so I needed to use a faceplate on my lathe, but as I needed to bore the centre out and not damage the faceplate, I use an outer race form an old bearing to work as circular parallel and the tool holder blank is then held in place by a metal plate. and is it is being centred on centre punched mark using a spare lathe centre and dial indicator.

    DSC03110.JPG

    then milling the slot for the lathe tools in the tool holder

    DSC03114.JPG

    then I had a change of plan and decided to fit a a locking plunger in the tool post.

    I ended up milling the end of some square brass on a rotary table to match the radius of the tool post, and lucky for me the post is 25mm diameter which is the same diameter as a 5mm penny washer, so one was used as a template. this hole was later bored out so the eccentric would work in it, and then turned in a 4 jaw chuck so that it would fit into a hole in the toolpost

    DSC03122.JPG

    and boring a hole in the toolpost for the plunger. I didnt have a boring bar small enough do ended up using an end mill in a boring head, which ended up working pretty well

    DSC03123.JPG


    and the completed items to assemble in the toolpost. to operate the eccentric, I decided to use a M8 cap head bolt and turned it down to 6mm, and the eccentric was later loctited it to it using a high strength retainer. the eccentric is between the plunger and cap head bolt in the picture below

    DSC03132.JPG

    and how the plunger and eccentric will work in the tool post body

    DSC03133.JPG

    and the assembled tool post

    DSC03139.JPG

    and with a tool holder, the height is adjusted using a flange head cap screw and the tool holder is locked/ released buy using the cap head bolt on the end of the tool post.the tool holder is just under 50mm x 50mmx 25mm

    DSC03137.JPG
     
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  2. optima21 Forum Supporter

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    ohh and my old tool post next to the new one

    DSC03134.JPG

    just need to make a couple additional tool holders now
     
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  3. DanielW

    DanielW Member

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    Am I missing something? hows that a quick change toolpost?
     
  4. doubleboost

    doubleboost Member

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    The tool holder simply lifts off the centre shaft
    It can rotate & is locked by the eccentric
    Looks like a nice job to me
     
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  5. optima21 Forum Supporter

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    it works in the same was as this, using a eccentric operated plunger but I used a round post instead of dovetails. the cap screw on the top take less than 1/4 turn to lock/ release the tool holder

    [​IMG]
     
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  6. rory1

    rory1 Member

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    That is a fine job, I'm always amazed by the ingenuity of folk on here that make thier own tooling. Well done.
     
  7. 711jrp Banned

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    540
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    london uk
    Looks good but I think it would rotate and back the tool out, I know you are going to say it's a small lathe and only takes light cut but all the same it's not too rigid.
     
  8. DanielW

    DanielW Member

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    You have a point,should the tool start juddering ie parting off then it cause loosness of the post and do some right damage? these small lathes are not comfy when it come to parting off hard steels.
     
  9. optima21 Forum Supporter

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    halifax, England
    I hadn't thought about an issue with vibration, but it turns out it wasn't a problem, I could get the saddle assembly to vibrate using heavy interrupted cuts, but the tool post didnt budge. it also didnt move when knurling some height adjusting knobs, using a single wheel knurling tool.

    the main reason why I needed a new tool post was because I needed a better quality boring bar so I could bore out some new rollers for my bead roller in this thread (which I hi-jacked a bit)

    http://www.mig-welding.co.uk/forum/threads/edwards-jenny-swager.51616/

    DSC03146.JPG

    so I've now got a couple of normal tool holders for 8mm shank tools, a boring bar holder and spare holder for future use.

    DSC03151.JPG

    and at least I remembered to stamp the diameter of the height adjusting screws that I knurled onto the knurling tool shank, so I don't need to remember it next time, as its been a few years since I've done knurling as its the work of the devil getting it right.

    as Im not in a production environment, its not worth the time making half a dozen extra tool holders for the time it saves in changing tools in a tool holder. one thing that is far easier that on my old tool holder, is the height adjustment, and I'll be glad to see the back of shiming up a tool to centre height
     
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  10. 711jrp Banned

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    I wasn't tasking about the eccentric as such, more the design is basically like a like a pulley on a shaft with the eccentric doing the job of the set screw, this is somewhat different to say a Dickson with the large nut in the middle, in that case the large nut clamps the square toolpost to the flat compound and it is the friction between these two flat surfaces that gives an advantage over this design. As you say... nothing wrong with cam-locks and I'm sure if you replaced the centre nut on a Dickson with one it will be fine.
     
  11. 711jrp Banned

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    Yep i saw that and thought it was a bit weird, as with anything a chain is only as strong as the weakest link, the toolpost is bolted on very well but the tool holder is not held onto the post too good. I was going to say something about the eccentric on the Dickson but didn't want to confooos matters. I have two Students here (don't ask why two,it's a sickness) and their toolposts can twist if you don't hoon them down when using a long boaring bar or if you run out of common sense which I can also suffer from.
     
  12. optima21 Forum Supporter

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    Location:
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    yeah there are 4 mounting cap head screws on mine, and so far its not moved while being used including boring with a 3" overhang, or parting off 60mm diameter steel bar. the eccentric (cam) is 0.7mm off centre, so its a very gentle "wedge" but doesnt need much force to lock it in place, just a standard 6mm allen key.
     
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  13. I'm getting on a bit Member

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    The diskson tool post uses a dowel rod to stop the toolpost turning.

    It is meant to be fixed with all the adjustment carried out with the tool holders
     
  14. 711jrp Banned

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    Both mine don't have any form of location other than the centre nut.
     
  15. I'm getting on a bit Member

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  16. Pete.

    Pete. Member

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    Neither of mine have locating dowels either but I have had 4-ways that did. If you have a number of tool holders you can grind left, right, facing and finishing tools and have each mounted in a separate holder but if you only have a couple of regular holders in your set you're going to have to either keep swapping tools or use one tool for more than one purpose, and that usually means rotating the post.
     
  17. I'm getting on a bit Member

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    That really defeats the purpose of a qc. I think I have 30

    But my lathe is cnc so they are essential
     
  18. Pete.

    Pete. Member

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    It defeats one purpose, but for most non-professional users of QC toolposts the main benefit is easy adjustment of centre height.
     
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  19. Maker

    Maker nEw mEmBeR

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  20. I'm getting on a bit Member

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    512
    Location:
    London UK
    You drill and ream a matching hole in the top slide (compound slide) you do this insitu

    Put a tool holder on the post and use a dti to clock parallel to the crossslide the compound must be clocked 90' to the crossslide beforehand

    It's gonna be 10mm or 3/8 most peeps use a length of bar with a short bend on the end (think Allen key shape) then you can use a piece of tube to wiggle it out when needs be
     
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