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Datum Dilemma – Fixed Glass Parts


Datum’s, locator’s, locator pin’s, those little critters used by engineers in the robotic manufacturing of vehicles to repetitively and precisely locate a part on a vehicle as it rolls down the assembly line. By themselves they are harmless, gang them up with an adhesive bead of very high strength polyurethane and you have a different situation. Add to that OEM recommendations on removing that very part.


Datum’s are adhered to a glass part with a liquid adhesive, adhesive foam pad or other means. Datum’s are located at the top corners of the part in most circumstances. The body of the datum can be the thickness of the desired setting height (Z) of the glass part or can just be large enough to offer a surface to bond to, no regard to height.


The bottom side of the datum has the pin that aligns to a hole in the body panel. This provides the repeatable X and Y accuracy required when using robots to install the part. Datum’s have as many different pin configurations as they do body designs.

Over 95% of all vehicle manufacturer’s recommend or specify that wire (or synthetic filament) be used to remove fixed glass parts. But nobody is instructing on how to get past these little plastic beast that impede the progress of the wire as it is being drawn through the adhesive.


The problem is this, using a thin bladed tool to push between the datum and the glass to sever the adhesive AND provide a path for the cutting element to follow can cause glass breakage, something we don’t want even if we are replacing the part.


In the process of cutting with wire on the outside of the part, pulling from the interior, the method brings the wire close to the body panel as the wire severs the adhesive, in order to ride the wire UP over the datum lifting force (or a guide) is required against the path the wire wants to travel. This can cause the wire to break, the glass to break, body panels to dent and deform as well as slow the process down.

Going under the datum is preferred.


As it is now we are fishing around where we think the pin is and using a variety of home improvement tools cutting through the pin with the hopes of the cutting element finding that same path. It is totally hit and miss as some pins are beyond the reach of some tools. Specialized tools need to be developed and instructions on how to disable the datum to allow the cutting elements to sever the adhesive bead unimpeded. Or.


Make the datum with a small flat flange on the pin near the bottom. This flange will position the glass part to the Z position.


Now, here is the great IDEA, just above that flange have an area that will break easily across the X, perforations, indents, whatever, just make it easy for wire or the new method, synthetic filament, to pull through the pin. Problem solved, still use the datum’s, still get alignment and if you need to remove the part, no problem.

Great idea right?

Good, somebody go make them and make our jobs easier.


Rick Nelson is the Senior Product Manager at Nelson Glass Tools, manufacturer of the Glass Bot® Bonded Glass Removal Systems in Garden Valley, CA.