This study on the design and construction of a modified cassava milling machine was done, owing to the inability of existing mills to meet the demand of cassava flour in bakery
industries. Rational design by drawing and calculations and fabrication in the Centre for Industrial Studies (CIS) FUTO were used to bring this mill to reality. The modified cassava milling machine has a milling efficiency of 82.3%, it is dust free and self-cleaning and due to proper air circulation does not destroy the cassava flour produced by overheating. The cassava flour produced was found to have a fineness modulus (fm) of 0.31, Uniformity index (U) of 0: 1: 9
(coarse: medium: fine) and effective size (D10) of 0.075 mm which is better than that produced by an existing mill (hammer mill) of fineness modulus (fm) 2.32, uniformity index (U) of 4:1:5 and effective size (D10) of 0.085 mm.

Cassava  (Manihot  specie)  is  a  tuber  crop  grown  in many parts of the tropics. In Nigeria, it is known by many names such as â��akpuâ�� by Igbos, â��eyeâ�� by Yorubas, â��Igariâ�� by  Ikas  and  â��boboziâ��  by  Ishans.  Nutritionally,  cassava contains  potassium,  iron,  calcium,  vitamin,  folic  acid, sodium, vitamin C, vitamin B-6 and protein (IITA, 2005).
Cassava  can  be  processed  into  many  products  in Nigeria (Odigboh, 1985). Some of the products are garri, â��abachaâ��, flour, nodules, starch and animal feed. The unit operations  involved  in  processing  cassava  is  shown  in Fig. 1. The Federal Government of Nigeria gave a directive that all baking industries across the country should add 10%  of  cassava  flour  to  bread.  This  directive  by  the Federal  Government  on  baking  industries  made  the
demand for cassava flour to rise.
The  traditional  or  indigenous  way  of  producing cassava flour in our rural areas, that is, by pounding the
dried chips in a mortar with a pestle and sieving it with a screen,  can  no  longer  meet  the  demand  for  the  cassava flour. Also, the existing mills such as the attrition mill, the
hammer   mill   used   by   some   industries   show   some inefficiency. Such inefficiencies are:

•  Inability  to  produce  uniform  grind  of  the  cassava flour.
• Time taken to crush material to the size of the screen as in the hammer mill.
• Contamination of cassava flour due to multi-purpose nature  of  the  mill,  particularly  in  non-specialized production processes.
  

This  research  is  aimed  at  developing  a  modified cassava  milling  machine  that  can  address  nearly  all  the concerns of the existing milling machines. Hammer mills for fine pulverizing and disintegration are  operated  at  high  speeds.  The  rotor  shaft  may  be vertical  or  horizontal,  generally  horizontal  (Perry  and Don, 1998). The shaft carries hammers, sometimes called beaters. The hammers may be T-shaped element, bars, or rings fixed or pivoted to the shaft or to disks fixed to the shaft.  The  grinding  action  results  from  impact  and attrition between lumps or particles of the material being ground,  the  housing  and  the  grinding  elements.  It  also consists  of  a  heavy  perforated  screen  (Henderson  and Perry,  1982)  which  can  be  changed.  Though  it  is  a versatile machine and its hammer wear does not reduce its efficiency, yet the power requirement is high and it does
not  produce  uniform  grind.  Common  types  available  in the  industry  include  the  Imp  Pulveriser,  the  Mikro Pulveriser, the Fitz Mill, etc.
Another class of size reduction machines is the Ring-roller mills. They are equipped with rollers that operate against grinding rings (Perry and Don, 1998). Pressure is applied with heavy springs or by centrifugal force of the rollers against the ring. Either the ring or the rollers may be stationary. The grinding ring may be in a vertical or a horizontal position. Ring-roller mills also are referred to as ring roll mills or roller mills or medium-speed mills.
Ring-Roller mills are more energy efficient than hammer mills. The energy to grind coal to 80% passing 200 mesh was  determined  as:  hammer  mill-22hp/ton;  roller  mill-9hp/ton  (Luckie  and  Austin,  1989).  Common  types available include the B/W Pulveriser and the Roller Mill.
The third class available is the Attrition Mills. The disc  attrition  which  is  sometimes  called  the  Burr  mill consists  of  a  set  of  two  hard  surfaced  circular  plates pressed   together   and   rotating   with   relative   motion (Onwualu et al., 2006). Stones are replaced by steel disks mounting  interchange  metal  or  abrasive  grinding  plates rotating at higher speeds, thus permitting a much broader range  of  application.  They  are  used  in  the  grinding  of
tough organic materials, such as wood pulp and corn grits (Perry and Don, 1998). Grinding takes place between the plates,  which  may  operate  in  the  vertical  or  horizontal
plane.  The  material  is  fed  between  the  plates  and  is reduced  by  crushing  and  shear.  Though  the  power requirement is low, operating empty may cause excessive burr wear and a lot of heat is generated during shearing action.
The objective of this study is the development of a modified milling machine which combines both an impact and shearing milling action with a pneumatic conveying and clarifying action. The combined action is intended to lead  to  lead  to  efficient  milling  of  cassava  into  fine powder. Unlike the normal hammer mill, it does not use a screen classifier; rather it employs air classifier in which the  fine  product  is  carried  in  the  air-stream  through  the blowerâ��s   chamber.   Also,   less   time   is   required   for pulverization and due to the air-tight nature, dust spillage is minimized. The air circulating in the machine helps to cool  the  processed  flour  which  makes  the  flour  a  High Quality Cassava Flour (HQCF)