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| The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20) |
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| djc:
--- Quote from: awemawson on May 02, 2021, 06:01:46 AM ---So I think the operations are probably.../ --- End quote --- Sorry to keep posting on this. I hope I am not teaching you to suck eggs, but when you invert it, depending on which axis you flip it about, either 12 and 6 will remain the same and 3 and 9 will be mirrored or the other way around. Clearly the code for the second side has to match what happens to the part. In the sequence of operations, I do not think you included the long 6mm holes. Maybe it is 'G' or later. If it is, is there anything you can do before 'G' to assist it (e.g. small witness mark for clocking/angle of drilled hole - but maybe extended pins in the larger holes that the 6mm intersects could be used on the edge of a square to set verticality)? |
| awemawson:
Absolutely no problem re more comments, the more input on this the better as far as I'm concerned ! Some time ago, and probably a page or two back up the thread, I cut a disk of thin plywood and glued prints of the A2-6 and A2-5 drawings on each side to ABSOLUTELY check that I had the correct orientations and handedness, as the original drawings that I was getting dimensions from were confusing to say the least, and I was deriving female cavities from drawings of male bosses. (It's illustrated in reply #1008 above) Unless I can come up with a foolproof method of being able to demount and remount the part in the correct radial orientation I fear that the long 6 mm holes will have to be done just before turning the A2-6 female taper on the manual lathe. I cast another machinable wax billet this afternoon, and will have a full 'dry run' using it before attacking the EN24T. I had thought that it would be easy to place a nice thick alloy spoil board under the part, drill two of the 6 holes that pass through the adaptor all the way into the spoil board and use them for locating pins, but sorting out clamping in that scenario is not straight forwards. Bolting the spoil board using the mills Tee slots is easy, but then re-clamping the inverted part that is impaled by the two locating pins becomes an issue. Clamps can only be on its sides as the entire top is being machined. Side bearing clamps will tend to dislodge it. I'm sure that there's a way but it's escaping me at the moment. |
| djc:
--- Quote from: awemawson on May 02, 2021, 04:06:17 PM ---...spoil board... --- End quote --- What I was afraid of with the flipping is that the operator would physically flip it in the X-axis and the CAM jockey would flip it in the Y-axis. The drawings on the part are good as long as both sides have high noon clearly marked on them. It came to me in my sleep that you can use the T-slot as your spoil board. Make two T-nut blanks, three times the normal length. Drill and tap the first and last third of the length for grub screws to jack them into place against the slot bottom. Loctite the sides if paranoid. Location pin goes in the middle third. Relieve the underside of the middle third a little for breathing space when through drilling and reaming and for swarf clearance. Ideally, blow out drillings before reaming. On the clamping, the old planer-era books show clamps that are like a standard milling machine strap clamp but with a pin sticking horizontally out of their nose. So the 6mm holes you need in the side of the stock could be spotted/counterbored maybe 1/4" and clamps with pins used in them. Spotting the holes slightly bigger allows wiggle room before final drilling and also gives a flat surface for the long hole to start on. Found one: http://www.cartertools.com/spill.html |
| awemawson:
Another one who solves issues in bed !!! Now that's certainly an idea to consider. I also was cogitating last night : Suppose I plasma cut a thick flange that will loosely encircle the billet, with hold down holes that are a loose fit to bolts into the spoil board and sidewise pressing bolts that allow the inverted billet to sit impaled by the locating pin and clamp up tight as the flange and not the billet will be moved. Then when those are tight the hold down bolts into the spoil board can be torqued down and theoretically all parties are happy. So this morning I did a quick cad drawing and cut a flange. The sidewise clamps are the current slight issue. I am limited to a total height of 25 mm or it will be clobbered by the milling operation, the easiest option is to weld pairs of M10 nuts on - flange is 6 mm nuts are 17 mm, 6 + 17 = 23 mm so low enough. (picture actually shows M12 nuts and bolt 6+19 = 25 so too high) |
| awemawson:
So I've just done an experimental weld of two M10 nuts onto a bit of 6 mm scrap plate to prove that it's possible and that the threads stay usable. I'm glad to say that they do - I'd expected to have to run a tap through the pair but although they are a bit stiff when both engaged, they are usable. No doubt the heating / cooling of the welding has drawn the two tighter together on the thread but at least it shows that the method IS possible. Saves making 8 steel blocks to weld on ! |
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