I have a couple of Reverse glue Joint bits for my router and one cutter for my shaper.
I don’t use them very much, and as I had some left over timber from my Slope Tray work, I decided to give them a run.
Or at least the shaper cutter.
The timber had been jointed previously so there was not a lot of preparation required.
Shop bought finished timber would be the same, rough sawn would require jointing prior to use.
The Reviews I read on using a Glue Joint Bit has a mixed opinion as to their usefulness and the process required to set them up.
So why would you use them in the first place? as there are T&G joints, Biscuit Joints and their various commercial counterparts, and lastly there is also a simple butt joint which work fine any way.
Reported advantages are:-
50% increase in glue surface area.
That’s got to be good both for the reliability of the joint and the glue supplier!
Self alignment when assembled.
Definitely a bonus when clamping multiple pieces together.
One cutter/bit does both joints.
This is correct and makes cutting a one cutter process, no different to a slotting cutter though.
Some Disadvantages I found were.
1. The cutter required using test blocks to setup to get precise fit-up.
2. You need a shaper or a table mounted router with fences, and so set up of the fences is then required.
Now depending if you need an excuse to buy the equipment this could be a plus or a minus!
3. There is a loss of width from 5mm to 10mm min depending if you do two cuts or just the one on the outer sides or ends. No different to T & G cutters.
The General set up View
A bit hard to see anything but there it is.
Setting the height
This is where the center of the cutter is aligned vertically so its dead center of the timber to be cut.
Thus can be done by eye as after the first test cut there may be an adjustment required anyway.
Ignore the lack of precision as I was holding the phone camera and the rule as well.
Cutting some test blocks
There are a couple of methods you can use to cut set blocks.
Cut the test “A” piece face up and the “B” piece face down. Turn the “B” piece right side up and fit them together to see how even the pieces are at the joint.
If the “B” piece is low, raise the bit one-half of the difference between the boards. If the “B” piece is highest, lower the bit one-half of the difference. Repeat the test cuts and adjust as necessary until the faces of the two boards are flush when fit together.
Cut a section of test material long enough to cut off 1 end. Mark the off cut B and the remainder A
Invert B and mate it to A check the alignment and adjust to suit. If a re cut is required cut off A and start again.
Don’t forget, the material for the test blocks does not have to be your expensive project material.
The only requirement is that is that the Test Block material must be the exact thickness of the project material.
Checking the alignment.
As everything was good to go the timber was profiled. If not minor adjustments are now required and new test blocks as well, as you cannot re use them over the previous profile.
Preparing the timber for clamping.
Here we go all in a row.
In the clamps
I used 2 x simple sash clamps and a couple of F clamps
At Glue up.
You may not need any vertical clamps but I was not taking any chances with bowing.
Take a note of the raggedy ends, this is where I cut the piece from showing the cut off edge
inspection of the joint from a cut off edge
A very tight fit I thought. Most satisfactory
Prepare to lose some width
The loss in width comes from the 5mm profile cut in the timber, and dependent upon setup can be deeper, add this to both sides/edges to be glued and a overall loss of 10mm min is revealed
Other types of cutters.
These are two other bits I have the left one is capable of cutting material from about 12mm up to 40mm.
I am not sure what the bearing is for as it would be outside the edge of the timber when in use.
Its possibly for doing joints at 90 degrees.
The one on the right is a router shank bit and works exactly the same as the shaper mounted bit
Depending on how much emphasis on the joint strength is placed its not necessarily a “Must have” cutter, but certainly ensures correct alignment at glue up, and is capable of producing an excellent joint.
-- Regards Robert