End Grain Cutting Board Sanding Question

I have made a few End Grain Cutting Boards lately following the stanard procedures. I glue up panels of contrasting woods (mesquite, maple, cherry, purple heart, walnut and etc.) using Tite-Bond III, plane the panels so that they are flat, rip them into 1-1/4" sections and then glue and clamp them together with Tite-Bond III for a minimum of 24 hours.
Then using a combination of a Random Orbital sander and a wide belt sander and I finish them to 220 grit. I go through 60 grit, 100 grit, 120 grit, 150 grit and end with the 220. I know that I have skipped a grit or two but I am using what I have. By the time that I am finished with the sanding the board is very smooth and I am satisfied with the results.
To finish it I use mineral oil and parafin wax mixed approximately 6 to 1 and I apply 5 or more warmed coats. No here is where the problem comes in. About the time that I am finished with the mineral oil finish I can actually feel the glue lines. How can I avoid or eliminate this? Do I need to wet sand the mineral oil finish as I am applying it? What is causing this?

You can feel the glue lines to be proud or recessed?

The Glue lines are proud of the board. Almost as if the glue has expanded or has been raised. I have had people compliment me on the joinery. Many of the joints really can't be seen but they sure can be felt!!

I don't have that much experience with Titebond 3. I do know that sandpaper is cheap. :eek:

Most likely the glue lines are proud because the the wood had not completely equalized after the water in the glue swelled the wood. You sanded it flat then the wood shrunk. Wait longer before sanding the glue lines flat.

Scott so are you saying that I should "wait longer" until I begin to apply the mineral oil finish and during that time I should sand "the glue line flat" as they appear?

+1 on shrinkage. Yes, wait longer (will vary with your environment) before sanding.

A month or so after my workbench was finished (5" thick fir glue-up of 1-1/4" boards) I left several handplanes resting on it for a day or so and was surprised to find rust in thin lines on the planes that looked like I left them on a hot grill. It turned out the moisture from the glue was still gassing out, even after a month or so. I was really surprised how long it took to stabilize the glue.

Here is an explanation of the problem. Unfortunately, there is no real solution as long as a PVA type adhesive is used.

Creep has been known about for many years, perhaps even centuries. It's nothing new and has already been defined precisely, so no need to reinvent the wheel here. PVA is the classic and renowned creeper.

The tendency of the glue to ooze out of joints is one form of creep. A classic example is in a slab edge to edge glueup, such as a table top. When ambient humidity rises the timber and the the glue swell. When the ambient humidity goes down the timber shrinks again, and so does the glue, but the glue doesn't all shrink back into its original place resulting in a raised line disfiguring the finish. Actually, under sustained high humidity my anecdotal observations are that the glue keeps on absorbing moisture and creeps out of the joint without the need for the timber to shrink. The symptoms can also be seen sometimes at the shoulder line of other joints such as mortise and tenons.

The problem can be minimized by being sure to adequately acclimate the wood to your shop before doing a glue up. Re sanding periodically will gradually cause the glue lines to stabilize.

Along the finish line you may want to read up Bob Flexner's take on "food safe" finishes too (good advice I think).