Universal Connector Aluminium Profile Adjustable Angle Joint Fastener M8 30 40 mm

Why a fixed-angle connector cannot do a diagonal

Every fixed connector carries its angle in its geometry. A standard connector is machined so that when it seats in the end face and expands in the groove, the two members end up at exactly 90 degrees. A mitre connector does the same for a joint where both members are cut at 45 degrees. Change the required angle and the connector no longer fits, because the faces it pulls together are no longer parallel to the direction it pulls in.

A universal connector avoids this by not carrying the angle at all. Its sleeve expands in the groove and its bolt pulls along the axis of the incoming member, and the angle between the members is whatever it is when the bolt is tightened. The connector holds the members in position rather than defining the position, which is the difference between an angle-specific part and an adjustable one.

How the angle is set and locked

The connector is fitted into the end face of one member in the usual way, then the second member is offered up at the required angle. With the bolt only finger tight, the joint can still be moved, so the angle is set by holding the members in the correct relationship and then tightening. The sleeve expands against the groove and locks the joint at whatever angle it was holding.

That means the angle has to be set by something other than the connector. On a one-off frame it can be set from a drawing with a protractor or an angle finder. On a production frame the members should be set in a jig, because a hand-held setting will vary by a degree or more between assemblies and the frame will not be square to itself.

One universal connector instead of a brace cut to angle

A diagonal brace in a rectangular frame is normally a member cut to a fixed length with both ends cut to a compound angle, because it has to land squarely on the two members it braces. Get the length wrong by a millimetre and the brace does not fit, and the angle at each end is set by the aspect ratio of the frame, so a brace cut for one frame will not fit another.

With a universal connector at one end, the brace can be a plain square-cut strut. The connector takes up the angle, and the brace is cut to length rather than to length and angle. That removes the compound cut, which is the operation most likely to be scrapped, and it means one stock length of strut covers every brace on the frame regardless of the angle it has to make.

Setting a universal joint correctly

1. Prepare the end face before assembly The connector goes into a hole in the end face of one member, so that hole is drilled and tapped before the frame goes together. It has to be on the groove centre line, because the sleeve expands against both flanks of the groove.
2. Fit the connector and leave it finger tight Slide the sleeve into the groove of the receiving member and turn the bolt only until it takes up the slack. The joint has to stay movable while the angle is set, so it must not be tightened at this stage.
3. Set the angle from a jig or a reference, not by eye Hold the members in the required relationship against a jig, a square or a protractor, and check the diagonal measurement across the frame rather than the angle itself. Diagonal measurement catches errors in both members at once.
4. Tighten to the specified torque and re-check the diagonal Tighten to the figure for the section and then measure the diagonals again. If they have moved, the joint was not held during tightening and the angle has to be reset.
5. Add a second connector or a pin on a loaded joint A universal joint is locked by friction in one plane, so it resists rotation less well than a fixed connector. On a joint that carries load or is subject to vibration, use two connectors or add a pin through the members to stop the angle moving.

Frequently asked questions