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  • Another power drawbar question???

    Hey guy!
    I was staring at my mill/drill today trying to figure how to mount the riggin for this project. It would be very easy to mount it right on the top of the lid.
    But...I have several R-8 tool holders and an idexable endmill that are really cranky about coming out. Usually I undo the drawbar a few turns...whack the end with a rawhide mallet, loosen it off a bit more...whack it again and so on till it comes out.
    Will a power drawbar shake and force these loose? Or do I have to reduce the size so they fit a little looser?
    I'm a bit hesitant to do that as they all have pretty decent runout. The only way I have to reduce them is to use abrasive strips and I'm a bit concerned about affecting the runout.
    Also the lid wouldn't be tough enough if the wrench really got pushing on the toolholders that stick a bit. I could re-enforce it but it'd cause a lot mopre problems.
    Thanks!
    Russ
    I have tools I don't even know I own...

  • #2
    Russ,

    It's been so darn cold here I haven't spent much time in the shop. I have some tooling that required a bit of a whack to knock loose, so I was concerned about how well the drawbar would deal with them. In the little bit I've experimented with a couple of the 'sticky' tools, it hasn't been an issue, knocks 'em right out. I think the impact induces enough pressure and vibration to knock them loose. It did get me thinking about the long term consequences to spindle bearings though. That said, there are at least 2 differences between mine and yours.

    First, I've got a BP clone. I tapped a couple of holes in the top of the mill and bolted the power draw bar (pdb) directly to the head. The riser blocks are 1.5"x2.5" and 1.25" tall, made out of aluminum. The plate that runs between them that the pdb mounts to is 3"x8" and 1/4" thick. It is a pretty ridgid mounting. I understand your difficulty in mounting due to the sheetmetal belt cover. If you're going to try to mount directly to the lid, I'd use as large a plate as I could. The more mass you can get the better it's going to damp out some of the vibration and provide a bit more rigidity. I think you'll be fine.

    The second concern is the difficulty you're having with removing some of your tooling. From what I understand, the R8 taper is supposed to be self releasing. Although we all have some tools that stick, they shouldn't stick so badly that you have to whack it off that much. My worst tool takes a single whack to break the taper loose then it falls out. Even the self locking tapers like B&S, Morse, etc. should only need enough of a whack to break them loose then they should fall out. Before going to drastic measures like reducing the OD on tooling, you should determine what the problem is. It really sounds like the ID of the upper part of your spindle is tight. If it was the lower tapered part, I'd expect the tooling to possibly be tighter to knock loose initially, but not take additional hits after breaking loose the first time. Also, if the taper were causing it, I think it would be because the tooling was too small so reducing it further would make it worse. In contrast, if it's the upper, straight ID that's small, it's going to bind some distance on the straight OD of the shank therefore taking multiple smacks to knock it out. I would mic out the stubborn tooling and compare it to some that comes out easily. Then look up the standard dimensions/tolerances for R8 tooling to give you an idea if it's the tooling that's a bit big, or the spindle that's tight. Once you get an idea of where the problem lies, you can then decide on what the best solution is going to be.

    Keep in mind, I'm just a home shop hack so I might be completely off target here, in which case hopefully someone else will come up with something better!

    Marc -
    The early bird may get the worm but the second mouse gets the cheese.

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    • #3
      I've had one tool stick once. A little light tapping around the sides with a mallet and it finally popped loose. Not much hope at the top--you have to remove the powered drawbar to get more medieval with it.

      Said tool was a big Albrecht on an R8 shank. After getting it out, I looked it over real careful and did find a burr that needed stoning off. It's never stuck since.

      Best,

      BW
      ---------------------------------------------------

      http://www.cnccookbook.com/index.htm
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      http://www.cnccookbook.com/CCGWizard.html

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      • #4
        Russ they shouldn't be sticking like that,everyone I ever cut loose only needed one tap to pop out.It could be as Marc mentioned the od of the small end is too big(most likely on the male side) or that weasley setscrew is set too deep and dragging in the keyway on the shanks.

        Round up like said above your R-8 shanks,some loose some tight and mic all of them,if the tight ones are bigger then you know what the trouble is.

        If that fails,look careful at the keyways in the ones that stick and see if they are marred up.If thats the case remove any burrs that are sticking proud and then remove that setscrew,you don't need it.
        I just need one more tool,just one!

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        • #5
          Thanks guys! I read this then went back down to the shop and measured these. It is the small male end that's the problem. Just a wee hair bigger than the rest...maybe a 1/4" of a thou....whatever it is really called
          So what would you guys do to polish these down? Wet and dry 600 grit paper...spin in the lathe? I have 1000 and 2000 grit paper also but it takes forever to remove anything with it.
          Thanks!
          Russ
          I have tools I don't even know I own...

          Comment


          • #6
            Russ, I would probably go with an oil stone, coarse to rough it, then fine to clean it up. If you don't have a stone, paper backed with something hard & flat would be the next option. I'd probably start with 220 or so and clean up with the 600. Since you have less than half a thou it shouldn't be too bad. If you can get it in the lathe then I would use that approach. Be sure to cover up the ways to keep the grit out. Keep in mind the tooling does register on this surface so go slow and do your best to keep it even.

            Happy Sanding!

            Marc -
            The early bird may get the worm but the second mouse gets the cheese.

            Comment


            • #7
              Marc...good idea! I have a nice big oilstone with course and fine on the same stone. Have some India hard stones also. Never thought stones. It'd be easier to keep a stone flat than paper.
              I'll have to take care of that before I install the drawbar wrench that I haven't built yet (but I did order a butterfly wrench today!)
              I have tools I don't even know I own...

              Comment


              • #8
                I have some collets and tooling that stick worse than others, too. the problem appeared to be light rust on the collet taper. My fix was to chuck the collet up in the lathe, cover the ways, and lightly sand any corrosion present on the outer taper of the collet. I then completely clean off the grit and grime and apply a film of oil. I've done this to 3 or 4 of them, and now they either pop out on their own or by using the heel of my hand on the top of the drawbar.

                I also don't torque collets down nearly as much as I used to. There was a thread here a while back that suggested that a lot of people tighten the drawbar way more than necessary. Maybe it's just me, but I can't think of a time I'd work the mill hard enough to have something slip in the collet. Seems to me that the clamping force generated is pretty huge, even with light tightening.

                -Mark

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