the present description will be directed in particular to elements forming part of , or cooperating more directly with , the apparatus in accordance with the invention . it will be understood that elements not specifically shown or described may take various forms well known to those skilled in the art . referring to fig1 there is shown a sheet metal frame 12 that forms a skeleton for the chassis of a print engine . in the preferred embodiment , sheet steel of 0 . 090 in . thickness ( nominal ) is used to provide sufficient strength . sheet steel members may be stamped or cut from stock using laser cutting techniques , well known in the sheet metal art . sheet metal frame 12 comprises side walls 22 a and 22 b , inner walls 24 a and 24 b , a rear wall 26 , and a front member 28 mounted on a base 64 . sheet metal frame 12 further comprises supporting and bracing structures provided by full - length cross - struts 30 a and 30 b and cross braces 20 a and 20 b . a left cross - strut 34 spans between side wall 22 b and inner wall 24 b . a right cross - strut 32 spans between side wall 22 a and inner wall 24 a these parts , which form the sheet metal frame 12 , are collectively referred to as rigid members . referring again to fig1 rigid members that form sheet metal frame 12 are joined using slot - to - tab or slot - to - slot construction . at each junction of rigid members , a slot 38 is provided . in this arrangement , slot 38 mates with a corresponding slot 38 on a joining member or slot 38 is fitted to a tab 36 . a bracing box 56 having a slot at each vertical corner fits about the junction of cross braces 20 a and 20 b . side wall 22 a and inner wall 24 a form a right side cavity 58 . side wall 22 b and inner wall 24 b form a left side cavity 60 . using an arrangement of sheet metal members configured as is shown in fig1 it can be seen that a design can be implemented that allows the same members to be used for different print engine configurations . for example , inner wall 24 a could be disposed further to the left within sheet metal frame 12 . this might be preferable , for example , where the weight of supported motor structures requires additional support . by cutting additional slots into front member 28 , cross braces 20 a and 20 b , and rear wall 26 , inner wall 24 a could be suitably repositioned in a number of different locations , at different distances from side wall 22 a . alternately , the overall dimensions of sheet metal frame 12 could be altered while using many of the same rigid members . for example , the length of a chassis frame could be changed simply by altering the lengths of full - length cross strut 30 a , front member 28 , and rear wall 26 . fig2 shows sheet metal frame 12 reinforced using the method of the present invention . a filler material 54 is poured into left side and right side cavities 60 and 58 , into bracing box 56 , and into troughs formed by left cross - strut 34 , full - length cross - struts 30 a and 30 b , and right cross strut 32 within sheet metal frame 12 . filler material 54 is also poured or pumped into front member 28 . filler material 54 hardens and locks sheet metal members of sheet metal frame 12 rigidly into place . filler material 54 is preferably a castable polymer concrete , such as “ super alloy ” polymer concrete manufactured by philadelphia resins , located in montgomeryville , pa . castable polymer substances such as the “ super alloy ” mixture provide a stable structure for the print engine chassis . for print engine applications , castable polymer concrete is particularly well suited , since this substance provides excellent vibration damping . moreover , since aggregate size can be changed , castable polymer concrete can be modified to optimize vibration response characteristics for specific equipment applications . the process of pouring the castable polymer requires a minimum of preparation . holes 62 in sheet metal members are sealed with tape in order to trap the castable polymer within a cavity while the polymer is hardening . slotted junctions can also be sealed with tape as preparation for pouring . in the preferred embodiment , tabs 36 include holes to allow flow - through of the castable polymer when poured . upon hardening , the castable polymer fills the hole , further locking tab 36 into place . referring again to fig1 and 2 , it is noted that various mounting components can be embedded within the castable polymer concrete . when the castable polymer concrete hardens , embedded components are locked into position . this technique could be used for parts that require precision alignment , effectively using the castable polymer concrete to lock components precisely into place . tubing could also be inserted within a cavity to allow routing of wires or air flow circulation through the polymer concrete material . referring to fig3 there is shown a print engine 10 having a vacuum imaging drum 14 , driven by a drum motor 16 . drum 14 is mounted to rotate within a left hub end 50 and a right hub end 52 that support drum bearings ( not shown ). both left hub end 50 and right hub end 52 are held in place by the castable polymer concrete that acts as filler material 54 within right side cavity 58 and left side cavity 60 . a translation motor 18 drives a printhead transport 40 containing a printhead 42 by means of a lead screw 44 . a front guide rail 46 and a rear guide rail 48 support printhead transport 40 over its course of travel from left to right as viewed in fig3 . referring again to fig3 it can be seen that the design of sheet metal frame 12 , reinforced by filler material 54 as disclosed herein , allows a flexible arrangement of components for print engine 10 . for example , relative widths of left side cavity 60 and right side cavity 58 could be reversed to reverse the arrangement of drum motor 16 and hub ends 50 and 52 . print engine 10 could thereby be modified to optimize a writing direction , such as by reversing the path traveled by printhead transport 40 . while the invention has been described with particular reference to its preferred embodiments , it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements of the preferred embodiments without departing from the invention . for example , sheet metal could be replaced at selective locations in the chassis , such as by rigid plastic members . a variety of filler materials could be used , with formulations optimized for the specific application . the invention has been described in detail with particular reference to certain preferred embodiments thereof , but it will be understood that variations and modifications can be effected within the scope of the invention .