Step ladder

A convertible step ladder having a back section (13) comprising a pair of rails (101, 102) cooperable with a detachable section (16) provides a step ladder that can be used on stairs as well as a flat surface. The detachable section has a horizontal cross member (168) spanning a pair of channels (162, 163) having orifices (162a, 163a) and bolts (166, 167). The rails (101, 102) seat in the channels on the cross member and have orifices (102b) registering with orifices (162a, 163a) whereby insertion of the rails (101, 102) onto the cross member (168) permits locking of the channels together by insertion of the bolts (166, 167) into the corresponding orifices.

BACKGROUND OF THE INVENTION 
This invention relates to a step ladder and, in particular, to a step 
ladder that can sit properly on a flight of stairs. 
Step ladders of various configurations have long been known. Examples of 
the prior art on step ladders include U.S. Pat. Nos. 131,442; 455,973; 
1,379,419; 1,672,020; and 3,037,580. Such patents include step ladders 
that are self leveling or have extensions or can be adjusted for uneven 
surfaces. However, none of the prior art step ladders address the problem 
of positioning a step ladder on a flight of stairs so as to enable a 
painter or carpenter or other worker to have a safe and secure means of 
climbing and doing work on an elevated position such as a wall or ceiling 
adjacent to a flight of stairs. 
One object of the present invention is to provide a step ladder that can be 
used in a conventional way but also on a flight of stairs. 
Other objects and advantages of this invention will be apparent from the 
description and claims which follow taken together with the appended 
drawings.

Referring now to the drawings, the step ladder illustrated therein 
comprises a front section 11 having a left side rail 11a and a right side 
rail 11b. A flat top section 12 is attached to front section 11 and 
pivotally connected to the ladder back section 13. Foldable links 14 and 
15 connect between the front and back sections 11 and 13 of the ladder. A 
foldable conventional paint pail support 17 is spaced below the top step 
12. 
The back section 13 comprises 2 channel rails 101 and 102 which are 
connected to the bottom rear detachable section 16. Section 16 comprises 
right bottom channel member 161, and left bottom channel member 160 which 
are inserted and joined to left upper channel member 162 and right upper 
channel member 163 by rivets 162b and 162c. The 2 pairs of vertical 
channels are spanned by cross member 168 with struts 169 and 170 extending 
between the cross member and the pairs of channels. Stiffening bars 164 
and 165 are spaced in the pairs of channels where the cross member 168 
joins. Rivets 163c, 163d, and 162c attach the cross member 168 firmly to 
the channel members and the stiffening bars. 
The detachable section 16 is attached to the legs 101 and 102 by means of 
bolts 166 and 167 extending through orifices 163a and 162a into 
registering orifices 102b in the rear legs. 
As shown particularly in FIG. 4, the ladder can stay level on a flight of 
stairs when the detachable section 16 is removed, thus enabling a firm and 
secure step ladder for use by a person wanting to do work on the walls or 
ceiling adjacent to a flight of stairs. 
When the need for work on the stairs is completed, the rear bottom section 
16 can be readily attached by inserting the channels in one another 
whereby legs 101 and 102 sit readily on cross member 168 and locking bolts 
166 and 167 can be inserted. The result is now a conventional step ladder 
which can be used on ordinary flat surfaces.