if space allows why not just overshoot a bit in the corners, then a
rectangular part can fit snugly, I've done this.
Dennis Saputelli

Andrew J Jenkins wrote:
> 
> On 09:52 AM 2/15/01 -0800, Hamid A. Wasti said:
> >Andrew J Jenkins wrote:
> >
> > > I'd still like to know some more specifics regarding optimizing this new
> > > rule. My 31's DO live a much shorter life than the 62's, on average,
> > and I'm
> > > sure everyone else would ultimately benefit from the information too. A
> > rule
> > > is only useful if its substance can be decoded...
> >
> >I am not sure what exactly you are asking me to elaborate on.
> 
> The nitty-gritty details...
> 
> I wasn't being clear, and it seems from you last reply  to Geoff, that what
> you're talking about is high-speed, mass manufacturing, not one-offs, or
> even small runs.
> 
> For instance, my tooling runs at  24Krpm, (no, not suitable for tef.,
> ceramic, or flex materials..) with a (62mil tool) contour-routing speed
> (PCB cutting tool) of about 30-35 inches per minute, for 62 mil thick FR-4
> material, faster for 31mil material, and significantl;y slower when using a
> 31mil  dia contour-router bit, but I have never seen any obvious evidence
> of the chatter problems you're talking about. The tool (or more precisely,
> its software,  and stepper motor controller module) uses ramp-up and
> ramp-down machine code instructions to control the various steppers
> start/stop behaviors involved in the translation process, so perhaps you're
> also talking about a more primitive translation system, I don't know...
> 
> What I meant by my question is that
> a) I accept what you're saying wrt to the problem, even though I don't
> necessarily see it, because it makes _sense_ to me, from my knowledge of
> Physics.
> b) I accept that it _could_ result in a change to mfg costs, especially in
> large runs (again, if a then b)
> c) Because I run a milling machine to produce a great number of my designs,
> I want to understand how to __apply__ the rule, not just in a qualitative
> manner, but in a quantitative manner, ie,
> 
> If tool radius R1, then min_path_radius1 = ???
> If tool radius R2, then min_path_radius2 = ???'
> If tool radius R3, then min_path_radius3 = ???''
> .....
> result: mathematically, a polynomial (perhaps too much to ask) or
> experientially another _rule-of-thumb_  for specification of min
> milling-path radii to one's design(s). I figured that if you knew enough to
> make the warning, you could also answer that question.)
> 
> Perhaps the answer is a simple as "If you use a 62mil dia  tool, use a
> minimum path radius of 63/2 mils)", and perhaps that's a naive assumption o
> my part, but it's a logical outcome of the simple statement "Make the path
> radius larger than the tool", though perhaps no better in the real world
> than making it equal. On the other hand, I could take your suggestion to
> the other extreme, saying instead that then all radii should be measured in
> multiples of the tool radius, like twice, three times, ten times, etc. But
> then I might just cost myself by adding unnecessary post-process hand work
> by doing so...(generally speaking, I don't give a hoot about a 31mil
> offset, and so don't generally worry about that small a radius)  Obviously,
> a radius of curvature of 31.0001 mils isn't going to change the dynamics of
> the situation very much, in fact virtually nil...it's pretty obvious that
> the stresses exerted upon tooling will be almost exactly the same as in the
> case that it was dead-ended.
> 
> So, where specifically do we find that there's a benefit to designing this
> way, which outweighs the reduction in the "rectangularity" of the hole?
> 
> Does this make a little more sense than my first question?
> 
> As you say, mfgs are responsible for determining the best routing speeds to
> maximize their profit margins. Routing speed, material thickness, material
> type, copper weight, tooling flute #s and type all play a role in
> maximizing mill speed and performance. Generally, if one wants a square
> corner, one should simply specify a square corner, and let the pros worry
> about it. Unless I'm not mistaken, the costs only begin to appear in large
> runs.
> 
> As a designer, I'm just not sure how much one should worry about it. As a
> mfg, one should already know that there are a great number of variables
> that come into play in making the equipment work properly to one's
> advantage, as well as to that of their customer.  I'd like to be corrected,
> or confirmed in that assumption.
> 
> I hope that I've made myself clearer.
> 
> Sorry for the long-winded-ness of my response...
> 
> regards,
> 
> Andrew J Jenkins. NCMR @ NASA-GRC
> [EMAIL PROTECTED]
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