Bending in Mid Air
by Steve Hill
I must have led a sheltered life as a young technician. I always thought there was basically only one way to bend uprights to shape. Boy was I wrong. And it would appear that my method is actually in the minority.
As it turns out there are actually only two ways to bend metal uprights; use an alignment jig or ďbend it in mid-airĒ, as my teacher called it. This was method which I was taught as being the fastest and most effective way though thatís just a matter of opinion. In truth, whatever way you practice with the most is going to be the most effective way for you. It has little to do with one method being right and the other wrong but if you donít know both ways you may not know the best way for you.
For most of you the alignment jig is a common bench tool, though itís not something you see around OTS very often. Alignment jigs come in two basic varieties; internal and external. Obviously, internal jigs are placed inside of the cast, either during the pour or drilled to fit after the pour. External jigs are placed outside of the cast and connect the two joints externally, thus allowing it to be easily removed from the mold.
Internal jigs are most commonly used at the ankle joint where the alignment can be easily seen before filling the cast (Integrated Ankle and Gaffney).
External fixtures see most use at the knee, where alignment may not be so clear or varus/valgus corrections may need to be fine-tuned. These can be either the hand held fixtures (Becker and Cascade) or come attached to a much bigger system (V-Tech, Becker and O&P Equipment Corp). These systems, while efficient and cost effective, do require the initial investment in a multi-functional set-up and is not a job specific tool.
The ďmidairĒ method is, in my humble opinion, the least expensive and most versatile method. It allows for the invariable fluctuations in plastic spreading and shrinking.
What I mean by this is that, after the joints have been mounted in this inflexible metal jig to keep the joints square, the uprights are eventually screwed or riveted to the plastic cuffs, which, when taken off the cast, will either spread open a little or shrink inward a little. It doesnít take much shrinkage or spreading to adversely affect the parallel alignment of the joints. Then you have to go back over the uprights and re-bend them square again, doubling your work.
This is the way OTS does it. User results may vary, not valid in all states, registered FDIC, open away from face (heck, it canít hurt, right?). First, we draw knee center, just like everyone else. Then we disassemble proximal and lower sections from each other and contour each proximal side making sure that the knee center drawn on the cast is centered in the pivot hole in the proximal joint head.
Once each proximal upright is contoured theyíre nailed onto the cast, right through the plastic cuff. This will assure they donít slip while contouring the distal uprights. Also, the holes will align through the upright and plastic cuff where they will be attached by either a screw or rivet. I prefer a screw, but thatís a different storyÖ
Now contour the distal uprights to the cast. To hold the proximal and distal joint heads together, we use a little homemade tool. Using a left over joint bushing and a longer screw to quickly attach and detach the joint heads while bending. You can make one by simply screwing the bolt into the bushing. Make two and keep them handy, right next to the bending irons.
Once the uprights are contoured and all of the holes have been drilled, remove them from the cast and finish them out as usual. Drill out the holes in the plastic cuffs and attach the uprights. At OTS we use SS screws to attach our uprights to make adjustments and repairs easier, but thatís just us.
Now you can assemble the proximal and distal joint heads together and check alignment. Of course, itís not perfectly square, it never is. No matter if you used a jig or bent it up by eye, youíll have to re-square the joints. The reason for this very simple, actually.
As soon as you attach the uprights to the plastic cuffs the relationship of the uprights Ė and, by extension, the joints - is changed. Tightening down on the rivets and screws against the softer plastic makes it go all catawampus.
So, invariably, you must re-square the carefully prepared alignment. All of that extra work in the commode. So we just get them in the ballpark and then worry about how square they are after assembly. Thatís another good reason to attach with screws. If need be, and it only happens occasionally, we can sand any bend marks in the uprights should they need it.
And thatís it. I know that most of you use an alignment
fixture and will never even try bending it in midair, so to speak. But should
the need arise you now know the method used by professionals the world overÖ.
Or at least in