How to flush splines in plywood?


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I've been working on a plywood box reinforced with splines. My question for the group is how to flush the splines with the surrounding plywood while managing not to damage the plywood veneer?

What I did was flush cut the splines, then used a block plane to trim as close to the plywood as I was comfortable (probably 1/16-1/32"), and then hand sanded, trying to focus on sanding the spline and not the plywood. The challenge is the spline, being end-grainish, is much harder than the plywood and what I ended up with is splines that look fine, but if one runs their fingers over them, you can feel they are proud and pillowed. In other words, my sanding took down the edges more than the center and I'm worried if I sand the center of the spline down flat, I'll start taking off too much veneer from the surrounding plywood (I did this in one spot when I wasn't careful keeping my sanding block flat). So the result is more than good enough for a shop project, but can I do better?

Thanks for your thoughts.

Von

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My grandfather would say carefully.

You could try some blue tape around the spline and sand it that way. That would leave the spline only the thickness of the blue tape.

Thinking out loud here, but perhaps a router plane?

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On 6/5/2024 at 1:59 PM, curlyoak said:

Did your paper have something flat? Or was it sanded with fingers?

 

Preppin' Weapon sanding blocks. Fairly firm but hard for me not to tilt them the degree or two it takes for them to come in contact with the plywood surround the spline. Just not enough surface area on the spline.

On 6/5/2024 at 1:41 PM, legenddc said:

My grandfather would say carefully.

You could try some blue tape around the spline and sand it that way. That would leave the spline only the thickness of the blue tape.

Thinking out loud here, but perhaps a router plane?

Very good ideas - thank you! Blue tape would also have helped with glue clean up putting the splines in place.

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Assuming that the answer isn't limited to hand tools, a flush trim router bit with the bearing on the work end would do the trick .... if it is long enough to reach the splines from the edge (small box).

Or, you can make a "jig" from a scrap of plywood, with notches cut to fit around the splines when clamped to the box side. Align the notched edge with the adjoining box side, and your router can clear the splines on the current side so the bit can remove them from the adjoining side.

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An L-fence is my preferred method for flushing splines on anything. You don’t have to worry about chipping the corner of the spline, and it’s pretty easy to get it set so that you really don’t need to do any additional cleanup of the spline. 

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On 6/5/2024 at 10:00 PM, wtnhighlander said:

Assuming that the answer isn't limited to hand tools, a flush trim router bit with the bearing on the work end would do the trick .... if it is long enough to reach the splines from the edge (small box).

Or, you can make a "jig" from a scrap of plywood, with notches cut to fit around the splines when clamped to the box side. Align the notched edge with the adjoining box side, and your router can clear the splines on the current side so the bit can remove them from the adjoining side.

Power tools fine. You've identified the challenge, which is the spline interferes with the router since it protrudes from both sides of the corner. I think I understand your suggestion of a jig fitting around one side of the spline to give a flat surface to flush the other side of the spline.

On 6/6/2024 at 6:55 AM, JohnG said:

An L-fence is my preferred method for flushing splines on anything. You don’t have to worry about chipping the corner of the spline, and it’s pretty easy to get it set so that you really don’t need to do any additional cleanup of the spline. 

Similar to the router and flush trim bit, I see a challenge getting a flat surface to run on the table saw top because of the spline protruding in two directions. Once I get one side of the spline flush, the other seems straight forward, but I don't see how to get the first one flush with an L-fence.

Thank you both.

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If you are hand sanding, I think the Prepin Weapon is too large.  I'd try wrapping a small bit of sandpaper around a small scrap of 3/4" wood, then slowly & carefully work the spline using the 3/4" side.  I'd also try to have my line of sight even with the sanding surface.  Blue tape or packaging tape, too.

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1 hour ago, Don Z. said:

I find it interesting that only one person has identified the utility of a paring chisel in accomplishing this task.

 

I agree with the paring chisel idea, but it had already been put forward.

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On 6/6/2024 at 8:44 AM, Von said:

Power tools fine. You've identified the challenge, which is the spline interferes with the router since it protrudes from both sides of the corner. I think I understand your suggestion of a jig fitting around one side of the spline to give a flat surface to flush the other side of the spline.

Similar to the router and flush trim bit, I see a challenge getting a flat surface to run on the table saw top because of the spline protruding in two directions. Once I get one side of the spline flush, the other seems straight forward, but I don't see how to get the first one flush with an L-fence.

Thank you both.

 

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On 6/6/2024 at 10:40 AM, Mark J said:

I agree with the paring chisel idea, but it had already been put forward.

Yep.  And I am in violent agreement with the person who mentioned it.  I'm just surprised more people didn't mention it, in favor of jigs or routers or...

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