# Re: [Emc-users] Nother math problem

```What you are looking for is a function that can smoothly transform from a
line to an arc while always passing through to given points?   An eclipse
could do that as its eccentricity changes.  The problem is the amount of
computation required.```
```
Cheaper to draw both the final and starting lines and take a weighted
average.  Keep moving how much weight to give to each line.  Still a lot of
computation but it's easier and after all we do all have computers.

But what most do is cut at the final line in increasing waterline depth,
then make a final finishing cut to remove the last .0005  That is what most
CAM software would do.

On Sun, Sep 18, 2016 at 1:32 PM, Gene Heskett <ghesk...@shentel.net> wrote:

> Greetings all;
>
> I am trying to carve the curve/arc in the toolpost base that replaces the
> bad compound in this Sheldon.  Currently mounted about 3/4" off center
> so I am basically cutting away anything on the front of the base that a
> workpiece could hit. I did this in 1/4 size, for TLM, and that, plus the
> tapered gibs almost make TLM a decent but smallish lathe. Any remaining
> tendency to chatter seems to be in the flexing of the spindle itself.
>
> My code at the instant starts out with a huge radii in order to start
> with a light enough cut TLM can power thru it. The start and end points
> are fixed, and this of course is hard on the tool insert as it dulls and
> starts skidding before it starts cutting at both ends.  Next pass
> reduces the radii, but I cannot get a straight line increase in the
> belly of the curve, which is about a 60 degree arc section.
>
> Is there a math function that would give me a uniform increase in the
> belly of the center of the arc?, which I am now convinced was a error in
> my concept of how to do it.
>
> So, should I just give up and use a fixed radii curve, but move its xz
> anchor radii point? That would get me a constant depth of cut, and would
> likely be easier on the tool insert too. I haven't a clue whats in this
> cast, intended for large car wheel hubs, but its tough, and abrasive
> stuff. You could call it found iron I guess.
>
> H&K casting where I got it, probably considers that proprietary info
> since its a contract that specifies the alloy's ingredients.
>
> I think the reason I didn't originally was that I was running out of out
> x motion to use a fixed offset for cutting the starter angle.
>
> What say you folks, how would you do it? Keeping in mind TLM cannot pull
> more that about a .4mm cut at this nearly 4" working diameter, at about
> 150 rpms.
>
> I need to take about 1/4" off the top of this yet, so while the "hive
> mind" is cogitating, I'll go do that, with a nominal 2 thou dish in the
> center so that big Phase-II toolpost is sitting on its outside corners
> and much more capable of resisting turning forces in the middle of a
> boring bar job.  I did a 1 thou dish on the smaller post I made for TLM
> and that little QC holder hasn't moved on the post since.
>
> Thanks for any advice everybody.
>
> Cheers, Gene Heskett
> --
> "There are four boxes to be used in defense of liberty:
>  soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> Genes Web page <http://geneslinuxbox.net:6309/gene>
>
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--

Chris Albertson
Redondo Beach, California
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