> On Sun, 14 Jul 2019 at 03:25, John Dammeyer <[email protected]> > wrote: > > > > > Work holding is the issue. What's an ideal process? > > > If you are making one, what I would do is: > Machine to width and length. > Clamp in the vice supported by parallels [1]. Possibly with a bit of > polystyrene packing or a loop of cable tie or similar to keep the parallels > from wandering. > Skim the top surface, Machine the slots all the way through (or not quite > all the way through if a parallel is in the way. Drill the holes deep > enough to meet the rebate. > Turn over in the vice and use parallels that allow the rebate to be > machined, skim to finished thickness (opening up the slots if not milled > through) and mill the rebate. > > If there were features on the other side that needed to be positioned then > I would have the G-code origin for that side be one of the through-hole > centres and would probe that for the second ops. > > [1] It's well worth getting a set or parallels, I have these: > https://www.amadeal.co.uk/acatalog/Precision-Parallel-Set-8pair-set- > 8x120mm-AMA_AC_637_7972TD.html > though I imagine you would look for a set closer to home, and would be > able > to pay rather less.
Thanks Andy, I have two sets of parallels. One with a few scars and a brand new set still in the wrapper. I was starting with material that was already 0.375" thick so the idea of protecting the parallels by not drilling/milling all the way through had not occurred to me. Flipping over and then surfacing to final thickness to expose the holes/slots is an interesting approach. Thanks. The other suggestion where the raw material is hanging it out the end is what I did for the switch mounts. I placed a support under the end to keep it from flexing downwards. Photo attached. These are now attached to the cover over the Y axis DRO Scale and I have consistent homing on Y and X now. One of these switch holders will also be screwed to the base plate I asked about. The rabbet on the underside of that base plate is there to clear the casting as it curves towards the dovetail ways and would not make the base sit flat. There doesn't seem to be much point to making a Z axis limit switch since that limit will change depending on what tool is loaded and if there's a vice or rotary table on the mill. Unless there's some way that a tool change operation can change the soft limit for -Z. And even then, work held in a rotary table 3 jaw chuck might have chuck jaws higher than the workpiece so a -Z limit would be counterproductive. However, an absolute one tied to the tool length to forever protect scarring the mill table would be nice. John
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