I want the arrowhead to look more natural as opposed to goofy (which is the present state)

\documentclass{article}
\usepackage{tikz}
decorations.pathreplacing, patterns, decorations.pathmorphing, positioning}
\newcommand{\AxisRotator}[1][rotate=0] {%
\tikz \draw[x = .5em, y = 1.25em, line width = .2ex, -latex, #1] (0,0)  arc (-150:150:.5 and .5);%
}

\begin{document}
\begin{center}
\begin{tikzpicture}[scale = .75]
\draw (-2,0) -- (-3,1.5);
\draw (2,0) -- (3,1.5);
\draw (-2,0) -- (2,0);
\draw[-latex] (0,.75) -- (0,2);
\draw (0,1.5) node {\AxisRotator[rotate = -90]};
\begin{scope}[yshift = .25cm]
\clip (-2.5,1) -- (2.5,1) -- (2.5,.25) -- (-2.5,.25) -- cycle;
\draw (0,1) ellipse (2.75cm and .5cm);
\end{scope}
\end{tikzpicture}
\end{center}
\end{document}

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Perhaps using a decoration:

\documentclass{article}
\usepackage{tikz}
decorations.pathreplacing, patterns, decorations.pathmorphing, positioning}
\newcommand{\AxisRotator}[1][rotate=0]{%
\tikz[decoration={
markings,
mark=at position 1 with {\arrow{latex}}}]\draw[x = .5em, y = 2.75em, line width = .2ex,#1,postaction=decorate] (0,0)  arc (-150:150:.45 and .5) -- ++(-95:2pt);%
}

\begin{document}
\begin{center}
\begin{tikzpicture}[scale = .75]
\draw (-2,0) -- (-3,1.5);
\draw (2,0) -- (3,1.5);
\draw (-2,0) -- (2,0);
\draw[-latex] (0,.75) -- (0,2);
\draw (0,1.5) node {\AxisRotator[rotate = -90]};
\begin{scope}[yshift = .25cm]
\clip (-2.5,1) -- (2.5,1) -- (2.5,.25) -- (-2.5,.25) -- cycle;
\draw (0,1) ellipse (2.75cm and .5cm);
\end{scope}
\end{tikzpicture}
\end{center}

\end{document}


For comparison purposes, here's the result with the original code in the question:

And here's the result for various angles:

\documentclass{article}
\usepackage{tikz}
decorations.pathreplacing, patterns, decorations.pathmorphing, positioning}

\newcommand{\AxisRotator}[1][rotate=0] {%
\tikz[decoration={
markings,
mark=at position 1 with {\arrow{latex}}}]\draw[x = .5em, y = 2.75em, line width = .2ex,#1,postaction=decorate] (0,0)  arc (-150:150:.45 and .5) -- ++(-95:2pt);%
}

\begin{document}

\begin{tikzpicture}[scale = .75]
\foreach \angle[count=\xi] in {0,45,...,315}
\draw (0,1.5) node at (0,1.5*\xi) {\AxisRotator[rotate = \angle]};
\end{tikzpicture}

\end{document}


I used -- ++(-95:2pt) at the end of the arc path just to extend it a little allowing the arrow to be well positioned.

-
I don't think that is much better. –  dustin Apr 19 '13 at 23:41
@dustin please see my updated answer. Perhaps it is a little better now? –  Gonzalo Medina Apr 19 '13 at 23:45
can you explain ++(-100:1pt)? –  dustin Apr 19 '13 at 23:55
@dustin sure! It's just a trick: I added a little line segment at the end of the arc path to move the arrow tip a little. –  Gonzalo Medina Apr 19 '13 at 23:58
FWIW metapost arrows follow the curve a little better (mp actually curves the arrowheads). For arrowheads where the curve is too tight they look goofy in a completely different way! So if you're interested in a metapost (or asymptote, or pstricks) solution, then indicate that, and several advocates of their favourite graphics language will leap to your aid. –  Andrew Kepert Apr 21 '13 at 5:57

arrows.meta library (TikZ 3.0, section 16) introduces more flexibility for drawing arrows. This version also presents pics which help to avoid drawing tikzpictures inside tikzpictures. Next code combines both tools.

The AxisRotator pic is placed according ellipse's center (which has been defined by trial and error).

\documentclass[tikz,border=2mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows.meta, positioning}

\tikzset{
pics/AxisRotator/.style={
code={
\draw [x=1em, y=1em, line width=.2ex, -{Latex[length=.5em, quick]},rotate=#1] (-.25,-.7) arc (-150:165:.3375 and 1.375);
}},
pics/AxisRotator/.default=0
}

\begin{document}
\begin{tikzpicture}[scale = .75]
\draw (-2,0) -- (-3,1.5);
\draw (2,0) -- (3,1.5);
\draw (-2,0) -- (2,0);
\draw[-latex] (0,.75) -- (0,2);
\draw (0,1.5) pic {AxisRotator=-90};
\begin{scope}[yshift = .25cm]
\clip (-2.5,1) -- (2.5,1) -- (2.5,.25) -- (-2.5,.25) -- cycle;
\draw (0,1) ellipse (2.75cm and .5cm);
\end{scope}
\end{tikzpicture}
\end{document}


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