Andy, Roland, and Joe, Thank you for your help. I responded inline below to your 3 posts. Also, one thing I'm forgetting is that this is currently done by hand, so it can't be that accurate. I worry that I over-engineer it...
Might be a bit before I get back and a little hurried as I'm off to two birthday parties today. Not too mention honey-doos that have accumulated... Mark > Message: 3 > Date: Fri, 5 Jun 2015 21:47:01 +0100 > From: andy pugh <[email protected]> > Subject: Re: [Emc-users] OT: Grind a hemisphere or ball end on rod > To: "Enhanced Machine Controller (EMC)" > <[email protected]> > Message-ID: > < can1+yzxt6_iuibjztvjo5h34fugwuho_kpfmufj61psa9t-...@mail.gmail.com> > Content-Type: text/plain; charset=UTF-8 > > On 5 June 2015 at 21:19, Mark Johnsen <[email protected]> wrote: > > To turn 1.25mm x 2m you would need to spend more effort on the support > than on the machining. > > So, perhaps the best idea is to hold the work stationary and rotate > the cutter / grinder. > > You would need a machine spindle with a CNC-controlled rotating radial axis. > Here is one I prepared earlier: > https://picasaweb.google.com/lh/photo/1gX6p3sVta2YivGyk8rrX9MTjNZETYmyPJy0liipFm0?feat=directlink > I think I said it, but will say it again, your boring bar is amazing. I looked at the pictures (again) and saw your motor and winding plates and it's awesome. I'm not sure how the lamb fits into the boring bar project, but that was cool, too. :-) I really like John K's video, I would envision a grinding wheel w/ the axis of rotation perpendicular to the long rod and the grinding wheel would have a hemishpere on it so that when grinding different dia's it would be tangent to the cut, otherwise the smaller diameters would grind on the corners of the wheel. At least that's how it seems to me w/ the theta rotation and linear axis (if I explained that decently?). > From: Joe H <[email protected]> > Subject: Re: [Emc-users] OT: Grind a hemisphere or ball end on rod > To: "Enhanced Machine Controller (EMC)" > <[email protected]> > Message-ID: > <CAJxtsQgm1F6rY5ceS5xRrPBSBjUqSW7u_v_L-c76K= [email protected]> > Content-Type: text/plain; charset=UTF-8 > > That set up sounds sensible. It made me envision a simple arrangement > using a mounted angle grinder on a fixture with different pivot points. > Maybe CNC not needed at all. Joe - At one point I had more than 50 tabs open in a few browsers looking at various ideas (driving me crazy!). One of the links was to an MIT class PDF on degrees of freedom and 3, 4, and 5 bar linkages. It was really cool with all kinds of mechanisms and I found one that sorta looked like it might work. But I thought that getting the diameters of 1.25mm to 8mm would mean a linkage would have to change position, which why not just use a XY type setup? I'm sure the guy who figured out the radial boring bars could do this, but not me... I even started modeling something in Solidworks, but didn't finish it... > > On Sat, Jun 6, 2015 at 12:46 AM, Roland Jollivet < [email protected]> > wrote: > > > In point form > > > > - lay the rod in a long V (angle iron will be fine) > > - rotate the rod at about 10RPM from the far end with a small reduction DC > > motor and a 3-jaw chuck The only issue is that the rods can be less than 1 meter to 2 meters long, so I'm thinking a through hole chuck that can be driven closer to the working end, if such a thing exists? And, to complicate it, it needs to be able to go from 8mm to 1.25mm dia... I'll look around and see what I can find. I've found pneumatic collet closers, but then you need a collet the correct diameter... At least that's my understanding. > > - at the working end, support the rod with two large (80mm) overlapping > > rollers (like used for balancing) This is exactly the kind of thing I'm looking for... I could envision wheels holding the end, but how big and how do you do it, this helps. I was thinking I'd have to grind/cut near the chuck. Plus, the forces probably aren't that strong and we don't high precision anyway. > > - have a third roller lightly pressing down > > - make a small X-Y table and mount a grinding wheel on it (axis of grinding > > wheel is parallel to rod) I'm thinking of a hemisphere'd grinding wheel parallel to the rod. Then, it would be similar to point of contact of John's machine for the grinding wheel. But, I guess when I cut on one of the sides, sparks would fly up and I was actually thinking of mounting the mechanics up-side-down to have the sparks fly-down into a tray or bin for easy cleaning and removal. This thing will run all day and grinding is dirty after a few parts... > > > > - system is easy to load and unload > > - you can program the X-Y to any arc you like, and is easy to edit the code > > - have a sharp point nearby so you can dress the wheel automatically > > - since the X-Y is very light duty, you could use as small as 4mm threaded > > bar for the feedscrew. Light spring pre-load and brass nuts. > > - best to use rollers instead of slides for the axes. > > > > > > Regards > > Roland ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
