For most woodworkers, the Reverse Glue Joint Router Bit is not one of the more common wood router bits ... in fact, few even know about it. For cabinet makers, this is one their more common router bits and in some shops, there are router tables dedicated to this bit because it is used so often. The setting up of this bit can challenge your patience, but once set will give quality joinery to your project.
Watch it on Youtube: https://youtu.be/QW02XiEBo08
In my case, I have not used this bit for many, many years so it was a good chance for me to give myself a bit of refresher in using this bit ...
The nice thing about this router bit is the that is does 2 important things
1 - It allows for a larger surface area for connection 2 materials together which also means it gives a greater area for the glue to be applied which means a stronger bond.
2 - It helps to provide "ribbing" that helps to keep the 2 materials aligned for gluing
It also has one drawback ... it's a bit of a "pain" to set up ... in other words, you don't just pop this bit in your router table and go ... no, you have to very carefully align both pieces of material.
The woodworker who would use this bit more often going to be someone who is using plywoods or MDF materials, and is probably wanting to join natural woods or other plywoods or MDF materials together and is looking for a greater gluing surface, and that's what this bit does.
For this exercise I am using the Freud version of this bit, there are similar versions from a number of other manufacturers so there could be differences in how the bits are set up. For commercial shops that use this bit and have a dedicated router table already set up, they are purchasing materials from the same source so they will likely have to do little in terms of re-setting the bit because their materials will be consistent in thickness.
For anyone else using any of these bits, you will want to make sure you know ahead of time the thicknesses of the material you are using because if you have some scrap pieces that you set the bit up with, then switch to some other production material to make the final joints ... those joints could be off if there is a slight difference in thickness between them.
Remember !!! ... this is a REVERSE bit, that means any variations in settings are done on BOTH edges to be joined so that means any small error is compound double when they are jointed, so a small amount like 1/32 error will be added to make a 1/16 total difference on the surface which is far too great for laminating or veneering.
All of these bits have one thing in common, they will have one or two "lugs" of carbide protruding, of which one or the other, or the middle will be the center point.
The best way to align ALL of these bits is to start of LOW and raise the router a small amount on each test cut until you reach the required height.
The reason you don't want to start off high and work down is because some routers can tend to "stick" when dropping them down. You can often overcome this by giving the router a few taps to make sure it is seated, and this is why it is always best to work up and not down. BTW - this applies to any router bit that needs to be aligned to the wood it is cutting.
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Copyright Colin Knecht