RE: [CAD_CAM_EDM_DRO] Re: CAD experiment entry

Tim,
Please don't take it personally, I know most machinists would have the same answers, but they all sound to me like rationalizations for not doing it rather than real problems.

If setting up a rectangular bar feed (a fixed cost) saves material (an ongoing cumulative cost), tooling (sharpening/cutter replacement is also an ongoing cost), and machine time, then it should be considered.

While it is true that rectangular stock may be less precise than round stock, it is just a matter of giving the gripping parts (the feed grippers and the collet) more range of adjustment, and of designing the process to take into account the lower tolerances in the input stock.

So yes, you have to make a special collet and special grippers on the feeder. Once.

Yes, the collet will not hold the work as reproduceably centered. So you have to mill a few thou off the perimiter of the part. That is still less that what must be milled off round stock to make the same size rectangle.

Note that I am assuming that the lathe involved has direct control of the spindle angle (not just speed control) so the rectangular stock can be indexed to the correct position.

As for a bar feed for the mill, it seems to me it could be done with a set of roller stands to support the stock and two power clamp sets controllable by the G-code. An extra cutoff saw controlled by a 4th axis means the extra stock doesn't have to get dragged along for the ride during the entire milling cycle.

-Kevin Martin



-----Original Message-----
From: CAD_CAM_EDM_DRO@yahoogroups.com [mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of timgoldstein

[...]
Round collets are standard, square are not.
Round stock has better tolerances. Square is not really square and tends to have raised corners and bellies on the faces so even in a square collet you get jambing issues.
Bar pullers have a hard time grabbing non-round shapes. Hex is better, but it still is a feed issue. A missed pull tends to lead to scrap and broken tools.
Round stock is easy to locate, other shapes are not as common.

I have pondered a bar feed on the mill as well. No reason it could not work, but it would take custom design and custom macros in the G code and for the machine. In a lathe it is already baked in. Just have to spend the $500 or so for a bar puller.