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  • Rebuilding an old JET?

    Just finished installing and levelling the new Grizzly mill, so now it's time to start collecting data on rebuilding the old JET.

    It's worn, but there's lots of life left. It's Vari-drive type mill-drill, and the whole belt assembly needs a good going-over.

    I've heard of switching to some sort of polymer or elastomer belt can make the thing run smoother. Any opinions on this? Who makes such a belt? Should I bother, say, having the pulleys balanced?

    On the quill- if I replace the bearings, do I need to buy real live Class 5? Do I source them from JET or from another supplier? Should I bother trying to regrind the spindle collet taper?

    Is it worth replacing the hollow cast-iron column with what would probably be a very expensive rod of solid steel? Mild steel, cold rolled or chrome-moly? I've heard it suggested that the hollow stock column be filled with mortar or concrete to add stiffness without the cost- any thoughts?

    Considering that I'm in Alaska, and tool rebuilders are few and far between, if I have a worn saddle or want to recondition the top of the table, where do I start?

    Any advice welcomed.

    Doc.
    Doc's Machine. (Probably not what you expect.)

  • #2
    i know of several machines filled with concrete. The added mass at least changed the resonate frequencies. Concrete was chosen because of its mass (better than sand or gravel), its ability to cling to meatal (like a rebar) and the coefficient of expansion with concrete is pretty close to iron. Only bad thing is that if itfils to acomplish its purpose, it is hard to revert to the original configuraton. I would wait til I had a problem before I poured. Cast iron has good dampening properties- which is one reason it is still used.

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    • #3
      One thing that comes to mind about filling columns with concrete... I think I would line it first. All the tubes I've seen filled with concrete seem to have rust pitting on the outer surface. Don't know if it's related or just poor maintenance. Could be just temperature changes, I guess.

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      • #4
        It's Vari-drive type mill-drill, and the whole belt assembly needs a good going-over.

        I am not familar enough with Jett Vari-drive mill/drill to know how similar it is to a RF-31 type mill.

        I've heard of switching to some sort of polymer or elastomer belt can make the thing run smoother. Any opinions on this?

        I have tried the Powerflex linked belts purchased from Grizzly and they work ok but are expensive and a little took big (5/8" size)to go around the idler and motor pulleys. However, just this past week I purchased a pair of Gates BX series notched belts for my mill/drill and I like them. These belts were mentioned in the article by Tom Clarke in the newest issue of Machinist Workshop magazine. I find these belts work very well, for one thing they are definitely more flexible than the standard belts and they are much less expensive (I paid about $14 for both belts from Motion Industries).

        On the quill- if I replace the bearings, do I need to buy real live Class 5?

        Yes, the ones that came on my Harbor Freight 33686 model were P5s (equivalent to ABEC 5s). Many of the mill/drills these days use the 30206 and 30207 ISO bearings (these is an older designation for these bearings 7012 ??). In any case you can buy these bearing for ~$50-70 in P5 for the pair. I got FAG bearings from Consolidated Bearings for about $70. P6 or ABEC 3 are much cheaper, ~ $10-15 per pair.

        Do I source them from JET or from another supplier?

        Sure, I am sure Jett would sell them to you, but, you will probably pay more.

        Should I bother trying to regrind the spindle collet taper?

        I don't know. If it is really worn that much I would be inclined to just replace it, if it is still available.

        Is it worth replacing the hollow cast-iron column with what would probably be a very expensive rod of solid steel? Mild steel, cold rolled or chrome-moly?

        I doubt this would be cost effective and probably wouldn't make it work a whole lot better unless this machine is really worn out.

        I've heard it suggested that the hollow stock column be filled with mortar or concrete to add stiffness without the cost- any thoughts?

        Gee, I never thought of doing that. I have put several bags of sand in the metal stand that the mill/drill is bolted to. I also braced the top of the column to the wall and ceiling of my shop. It allows me to take more aggessive with the mill without as much complaint.

        Considering that I'm in Alaska, and tool rebuilders are few and far between, if I have a worn saddle or want to recondition the top of the table, where do I start?

        I guess that would depend on how worn they are. I don't have much experience in that area.

        Any advice welcomed.

        Doc.[/B][/QUOTE]

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        • #5
          Doc
          There is a Polyurethane liked belt that is exceptional on all powered machinery. They run quieter as well and should last much, much longer than standard belts.

          You can fill the column with concrete - I would use sand and (fine or) no aggregate in the mix. As a precaution you can spray the inside of the column with a rust inhibiter before pouring. It will stiffen the column and dampen somewhat. There are structural machinery concretes for this (Hardinge uses them on the new hydrostatic bed lathes) but I have no idea where or who you could purchase it from - sorry.

          Don't expect big improvements.

          As for the spindle - unless it has excessive play leave it alone. If you buy higher quality bearings it my be to your best interest to have the bearing house install them for you.

          I would just sell it and look for a better bidgeport, lagun, or similar machine.

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          • #6
            Doesn't anyone click links?

            I just installed a full-size Grizzly mill, and I'm quite happy with the improved performance. But rather than junk the JET or sell it for scrap- even up here I'd be hard-pressed to get $600 out of it in the noisy condition it's in- I like the idea of having the redundancy. Or at least a second mill I can leave a jig setup in for short-run production.

            The JET came with a sturdy but undersized stand. The last time I moved everything a few years back, I used some heavywall drill pipe and some 3/8" plate to make a much stronger stand. The stand also has two pillars- the back legs extend up- at the back that clamp to the top of the column. That alone helped dampen vibration considerably, but I've wondered about the concrete idea for a while.

            The column is cast steel or cast iron. The inner bore looks, as my dad used to say, like it was cast around a corn cob. I hold little illusion it's as stiff or rigid as it could be.

            The column also needs to be aligned better- the base needs to be shimmed, as the head is out of tram by a small but significant margin.

            Doc.
            Doc's Machine. (Probably not what you expect.)

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