Six Foot Tandem Disc Harrow 13A-BE-21
Disc harrows were an important implement for cultivation right back into the 19th century. Tractor power encouraged their use until, by the time of the second world war, discs were probably the most preferred cultivator to follow after the plough, especially on turf. Harry Ferguson envisaged a disc harrow for use with his new system as far back as the mid 1920s but it was not until 1939 or 1940 that a commercial set was marketed for use behind the 9N to be followed by a the great variety of types which will be the subject of this series. When tractor production started in England in 1946, the design sold in North America was modified to improve the control and hitching system. It is this implement, the Six Foot Tandem Disc Harrow, type 13A-BE-21, that is the subject of this first article by John Baber.
The type 13A-BE-21 Six Foot Tandem Disc Harrow is a trailed set of 24 discs, 18″ diameter, 6″ spacing and arranged in the usual 4 gangs, each of 6 discs. The axles run on hard wood bearings boiled in oil, an old and successful method, and made in such a way that they resist the ingress of dust and grit. Approximate weight is 7851bs. This specification is typical of discs of that period. Where the Ferguson model differs is in the hitching and control arrangements. The hitch is directly on to a special drawbar between the lower links that may be raised or lowered hydraulically. This same action is so arranged that the angle of the disc gangs is altered so that when the drawbar is fully up the gangs are straight, while the lower it is the more the gangs are angled. The working height of the hitch, and thus gang angle, is set by a link from the special drawbar to the top link rack and may be adjusted from the tractor seat. Thus it follows that the disc gangs can be angled or straightened on the move and straightening of gangs whilst turning means a narrow headland with minimum overworking and compaction. Another important and unique feature of this implement was the fact that the gangs were straightened AUTOMATICALLY if the tractor rear wheels entered a depression in the ground or if soft ground was encountered. This relieved the tractor of some tractive effort though retaining weight transference and draft control whilst traversing the difficult area. The design also satisfied the usual requirement of implements for this type, whether trailed, mounted or otherwise, in that a low hitch point was necessary for good penetration provided that the discs were kept sharp. This was certainly the case with the type 13A-BE-21 due to the design of the towing mechanism and its operation by the hydraulic three point hitch.
Operation of the tractor and discs was as follows. (The operators hand book is quoted in parts here)
Installation and attachment of the implement was the normal three point linkage procedure with the addition of the yoke and top link rack as seen in the illustration. The top link was threaded through the yoke before fitting, the rack being at the tractor end. The top link yoke and rack is the same as that employed with a mower, hammermill or other implement where downward movement of lower links require restriction. Stabilizers (stay links) were not necessary provided normal working speeds were used, though severe swaying from side to side could occur with higher horsepower tractors if excessive speeds of operation were employed.
Movement of the tractor hydraulic control lever to LIFT will’ cause the disc gangs to immeadiately straighten. The operators hand book recommends this to be done at headlands or when making short turns to prevent strain on the implement or tractor and linkages as well as to avoid ridges and hollows at headlands and overworking of that area of the field.
Moving the control lever to LOWER will cause the linkage to fall and the disc gangs to angle when the tractor is driven forward. The degree of angle of the gangs is controlled by the distance the tractor lower links fall. This is preset by use of the of the top link rack at the tractor (forward end) of the top link and by placing the yoke in the desired notch of the rack. For maximum angling of the discs the yoke is placed in the notch furthest from the operator’s seat thus allowing the linkage to drop to its lowest operating position. Conversely, the minimum angle is achieved by placing the yoke in the rack notch nearest the operator’s seat (the one with the elongated notch if rack is correctly fitted).
AUTOMATIC ACTION. This was another novel feature of the design which so well embraced the Ferguson System and all it set out to achieve. The accompanying illustration will help clarify its operation. To quote from the instruction book:-
‘A skid rest ‘B’ is incorporated below the implement drawbar. It is designed to travel close to the ground in order to contact the soil if the tractor wheels sink into a depression or soft ground or if the discs are, in turn, in a depression. When this occurs, the contact of the skid rest imparts a forward thrust to the tractor top link which immediately caused the hydraulic pump to opere rate, raising the lower links and straightening the gangs. The load on the tractor is thus relieved and forward motion is not arrested.
This automatic action can only take place if, when operating, the tractor hydraulic control lever has been moved forward ONLY SUFFICIENTLY FAR TO ALLOW THE LOWER LINKS TO FALL FREELY. When past the obstruction, the gangs are again automatically angled without any necessity to move the control lever’.
It can be seen from the above extract from the instruction book that the advantages of the Ferguson System were utilised to the full even on a trailed /’semi-mounted’ implement.
If desired, the rear gangs could be angled independently from the front or removed altogether. An adjustment was also provided to maintain even penetration across each gang. A further facility was that weight could be added in the field over each gang in order to aid penetration. To keep the discs clean in sticky conditions, scrapers were fitted in such a way that each assembly of six could be adjusted as a unit or each individual scraper adjusted on its own. Road wheels, ‘H’ in the above illustration, could also be fitted easily and quickly for transport on hard surfaces. This ingenious device utilised the geometry of the layout in such a way that only two road wheels were required, these being placed under each of the rear gangs with tie rods ‘G’ to the front gangs. The cross brace ‘J’ secured the two wheels as well as keeping rear gangs level during transport. This assembly was fitted in such a way that, on lifting the tractor’s linkage, the front gangs were raised clear of the ground with only the rear gangs resting on the road wheels. The weight was therefore spread between the tractor and the implement’s road wheels.
The above therefore, is a brief description of the Ferguson 6′ Tandom Disc Harrowt ype 13A-BE-21 as supplied to the UK market. What is not always realised, however, is that the origins of these harrows lie some years further back than the launch of the TE tractors in 1946, in fact back to 1939/40 and indeed beyond to the mid 1920s. That will be the subject of the next article in this series.
Published in Journal Volume.4 No.3 Winter 1991