On Friday 23 September 2016 03:47:51 Erik Christiansen wrote: > On 23.09.16 01:02, Gene Heskett wrote: > > So what I am looking for is a bb holder that will work with the > > smallest QC holder. And will hold it solidly in the face of a 1 > > horse motor's solid torque. > > My long boring bars have flats top and bottom, so they just go into > the 4-way toolpost like the square TCT holders, with the 3 hex-socket > screws squeezing them firmly in place. Only the sides are rounded. > > When a small boring bar was needed, I axially drilled a length of > square Al, cut a slit in one side, pushed in a small end mill, > squished it all tight under the aforementioned toolpost screws ( with > slot and one end-mill tooth horizontal), and bored away. (The softer > Al probably grips better than steel would.) > > The cutting tooth is small, and the holding area is proportionally > enormous. The screws were reasonably tight. The end mill was sharp. > There was no slip while making several bushes. > > Gene, is that Al bar a machinable alloy (i.e. at least a bit of Cu in > it), or plain toffee? That stuff can be a drag. > 6061, so it's not quite as "gummy" as some I've cut. But I've now some bigger blocks of 7075-T651 to play with also. so the spacer stuffs to locate the Z screw will be cut from that. I have to get it about as high as I can so it clears the x motor under it. But the higher I put it is limited by the nut wanting to hit the swell in the underside of the bed. That alone assures that the screw is not shielded from swarf by the bed rail overhang. So I've bought some long bellows that should collapse enough that the saddle movement isn't restricted. These 6 bolt flanged nuts are a PITA, but they guarantee everything else will clear if the nutholder clears. The nut designed for a clearance hole in a piece of plate with a big nut would have been a much better choice. But they are hard to find of fleabay.
At the drive end of the Z screw, its bearing holder will be bolted to the back of a piece of 1/2" alu plate bolted to the 3 holes the removed QCGB was, but spaced outward enough that everything clears but just barely. The big nema 34 motor will be hung on the front face, with two 40 tooth xl pulleys and a belt, length yet to be determined, connecting the two. Swarf protection for the bare x screw is in the form of a 1/8" plate of rack panel alu let into the top of the long carriage and glued in, and a similar but much shorter piece of 24 gauge sealing up the bottom of the saddle between the ways, and the rear of the saddle that used to carry 60 lbs of taper attachment stuff, will be walled off to prevent swarf ingress from air hose cleanup activities. All that work on the rear of the saddle is in the future yet of course, as is fitting and shimming a full length brass front gib, wide enough to ride the unworn underside of the bed once I get as much of the paint washed off as I can using enough acetone I might get raided to find the meth lab. :( None here. That pair of steel postage stamp sized plates that served that function are badly worn and so is the under edge of the bed for the first quarter inch they rubbed on. If the brass wasn't such a pita to make, I'd consider makeing a tapered gib. I have a block of cast partially machined to replace the junk compound. I am debating with myself about putting 4 holddown bolts in the base, but would have to make the other 2 bolts. Belt and suspenders approach to getting a truly rigid mounting point for that big Phase-II QC tool post. Thats another thing I did to TLM, a solid block of cast to replace its flexible compound, and with the tapered gibs, precision is now limited by the 2 ball screws moving it. And thats nice!! But the screw is wearing out its nut from swarf sneaking past the felt seals, so z backlash was reset a couple weeks ago to 0.163 mm's.:( It's setup to do metric natively, to train me if for no other reason. :) The coffee and morning pills have kicked in about as much as they can, so I'd best be up the hill & into the shop building in front of TLM making that special hub I need for the x screw's pulley. Thanks Erik. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
