\clearpage
\section{Assembly Procedure}
The assembly station allows in principle to produce chamber with a precision below 20~\um (of the wire positions). To build about 100 (similar) chambers in
a few years with a few persons, a fast production procedure with 
quality monitoring during the essential steps is necessary.

The speed of the production is limited by the glue curing of the spacer, which takes a nigth, followed by the gluing of the tube-layers in six subsequent days. The monitoring of the spacer position and that of the end-plugs are of the
highest importance. Additionaly, the gravitational deformation of the spacer (with tuber-layers on it) has to be compensated and monitored.

\subsection{Assembly of the bare spacer}
The spacer parts, the two longbeams en the three crossplates, are put together
on the granite table. 
The precision of the bare spacer can be as low as 500~\um, far below than the
precision of the granite table. However,
the sag-compensation, RASNIK and other facilities available at
 the granite table are used during the spacer assembly.

During the first day the RASNIK components (see Fig.~\ref{rascompon}), temperature sensors and cable 
guides are mounted and fixed. The longbeams are positioned at by temporary
 mechanics and supported by the sagcompensation system to remove the 
gravitational sag. We use a pressure corresponding to
 50\% for the centre and 25\% for the outer compensation towers of the weight
of the longbeams. 

\begin{figure}[tpbh]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,14)
\put(-1,0){\mbox{\epsfysize=14cm\epsffile{rascompon.eps}}}
\end{picture}
\end{center}
\label{rascompon}
\caption{\sl a) Picture of the RASNIK-Mask components. b) The mask-image as
seen by the image sensor (CCD). c) Pictire of the lense and its holder. d) Pictucer of the housing of the CCD }
\end{figure}

  
After the overnight glue curing the RASNIK systems (in-plane, cross-plate and also RASAS) on the spacer are calibrated. For the in-plane alignment system we use the central stacking position and take the average of
the up and down orientation. 
For the RASAS system we take reading in all stacking positions and up/down
orientation and set all offsets individually to zero. 
 Dedicated calibration
software checks the internal consistency of all the readings. Additionally
 a comparison is made with the calibration values of previously build chambers. The rotations, $Y$ values and the ref-side $Z$ values give strong indications
when something is wrong.  
The RASNIK reading 
(which were set to zero to faciliatate their interpretation by the assembly crew members) 
should now be reproduced within 10~\um during the assembly.

After the spacer has been assembled the In-Plane calibration tower (see~\ref{tools}) is placed in front of the four in-plane masks. From these readings we
obtain the absolute orientation of the in-plane masks. At the end of the chamber assembly, final measurements with the 'airborne' spacer in 'up' and 'down' position provide a consistency check as described below. 



\subsection{The gluing of tube layers}
The wire tension of the tubes are checked just before
the tubes are used for a new tube-layer. Then the tubes have to be properly positioned in the jigs. Although this appears straitghforward, only experienced crew members have developped enough
 feeling  to perform this task flawless.

 In the longitudinal direction the gas-jumpers are temporarily mounted to aling the tubes such that length differences
 (which amount 200~\um on average) are absorbed. The orentation of the
tubes is controlled by a smal orientation pin, contrained by the North-side tube-comb. Finally, the tubes are sucked to the combs by small vacuum suckers.
the procedure is checked by the Guido-laser system, discussed below.

Glue is dispensed (see~\ref{glumach}) between and on the raakvlakken of the tubes for the first two (and following) tube layers. The spacer is lowered to the tubes (see Fig.~\ref{lowering}) and the sagcompensation system is turned on. We use pressures that corresponding
 to about 90\% of the weigth of the spacer (and the layers glued on it). 
To avoid an assymtric (tube-layer) weigth distribution,
 we flip the spacer between the glueing of tube layer 1-2, 3-4 and 5-6  by 
 rotating over its $Z$ axis
 (its 'short' symmetry axis in the horizontal plane). 

\begin{figure}[tpbh]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,14)
\put(-1,0){\mbox{\epsfysize=12cm\epsffile{glumach.eps}}}
\end{picture}
\end{center}
\label{glumach}
\caption{\sl Glue is dispensed on a tube layer by the gluing machine.}
\end{figure}



\begin{figure}[tpbh]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,14)
\put(-1,0){\mbox{\epsfysize=12cm\epsffile{lowering.eps}}}
\end{picture}
\end{center}
\label{lowering}
\caption{\sl Lowering of the spacer with some tube layers already on it, on a tube layer on the granite table.}
\end{figure}


\begin{figure}[tpbh]
\begin{center}
\setlength{\unitlength}{1cm}
\begin{picture}(14,14)
\put(-1,0){\mbox{\epsfysize=12cm\epsffile{finished.eps}}}
\end{picture}
\end{center}
\label{finished}
\caption{\sl Picture of the finished BOL0 chamber.}
\end{figure}










  













