Joining back panel plates

[jonfranzis]

Hi there, first builder here.
Having trouble truing up the edges to join the back of a mandolin. I have tried routing to get true, square, faces but get slight "waves" that show light when matched.
Have also tried a shooting board and sharpened the plane so it shaves my arm, but still getting light show, when matching back boards before gluing.
I am making an F5 style, carved mando.
Someone suggested using carbon paper to find the highs then using a squared jig to sand them off with 300 grit? Reluctant to sand the surfaces at this stage.
Can anyone suggest another way to get these edges perfect before gluing?
Thanks

[Parker135]

I just had exactly the same problem. First time for building a mandolin also. I made a nice shooting board, tried two a couple of different sized planes (both very sharp) and still couldn't quite get the waves out of the figured maple pieces without trying to focus on the high spots, then take another full length run at it, etc., still to no avail. I ended up going to Lowes for a 1-1/2 X 1-1/2 inch extruded aluminum angle and a packet of 1 inch wide 120 grit sanding belts. I cut the angle a few inches longer than the edges I'm joining, glued a piece of the sanding belt along it, and used that instead of the plane. It always makes contact along the full length of the edges. It worked perfectly the first try. I then used a square cabinet scraper, pulled along the shooting board, to lightly remove the sanding fuzz. The pros may laugh at this, but it worked great for me.

[Bill McCall]

Are you shooting the pieces one at a time and reversing the second piece? Since it’s unlikely everything is perfectly square, reversing the secon piece makes it complementary to the first, rather than having additive error.

You’re seeing the reason this is a skill.

Once you solve this, it’ll always be solved.

[pops1]

Set your plane to take finer shavings.

[fscotte]

I clamp the two pieces together just as they would have looked before sawing them in two pieces.

Then put the clamped sides into a table clamp, sides facing upwards, then I use a #5 plane just to make the surfaces relatively square and take out any bumps and ridges.

And now the secret sauce... I glue a couple pieces of 80 grit sandpaper to a flat surface, and sand the clamped pieces across the sandpaper, careful to not tilt this way or that way, and keep even pressure on the whole surface. Then jump up to 120 grit, repeat, then 220.

I get two surfaces that match perfectly.

[David Houchens]

Also have the two halves as close to final thickness as you are comfortable with. Makes less drag on your plane iron and like pops said set it for very thin shavings.
Also I have my plane clamped on it's side and push the piece of wood. A little trick John Hamlett showed me that made it easier for me.

[Parker135]

Here's my sanding setup described above. It's interesting to read about the various techniques. I want to continue practicing with the plane, but this solved the problem for now.

[Walt]

I had a similar problem and posted a thread seeking advice. Here's the thread from (yikes!) ten years ago if you're interested.

https://www.mandolincafe.com/forum/t...shooting+board

I got great advice from several Cafe members, but Sunburst's (John Hamlett's) advice has stuck with me all these years and is probably the single most important piece of woodworking advice I have received:

"Good job!...and you've learned a good lesson. Tools are not automatic; you can't, as you say you thought, just run the plane down the wood and it magically becomes straight. It's up to you, the user, to get tools to do what you want them to do. That applies to every tool that I can think of. Planing a straight edge is not "difficult", it's just something you have to learn to do."

[jonfranzis]

Hey, thanks for the great suggestions.
I will play with the different ideas and see what works for me.
Unfortunately I have planed my wood too narrow so will have to get some more and use this for tests.
I am using a no.6 Stanley plane and wonder if the blade needs re hardening, as is seems to need constant sharpening.
Just sharpening tools is a world of its own!
Do you think I should buy a thicker, newer blade? Mines at least 30 years old?
I remember my tutor in woodshop 50 years ago. I tried getting planing right for ages. He picked up the plane and did it perfectly first time. Definitely a skill I need to acquire!
I also have a Stanley No.3 (I think the No.6 is better for the back because its longer and hopefully produces a flatter result) and a 102 small block plane. I was thinking of using the latter for rough shaping the top as its a very useful tool...no good for hollowing of course.

[sunburst]

...Once you solve this, it’ll always be solved.

[CarlM]

I am using a no.6 Stanley plane and wonder if the blade needs re hardening, as is seems to need constant sharpening.

Blades do not lose hardness over time unless they are gotten very hot (over 400F). If they have been burned rehardening usually will not help because they have lost carbon needed to harden. Sometimes commercial plane blades and less expensive chisels are not as hard as they should be. It is difficult to tell if you do not have access to a Rockwell hardness tester. But rehardening is hit and miss. If the alloy is not good enough it will never get full hardness.

How you sharpen can be part of the problem if you are putting a belly into it. I do not use a sander or grinder unless the blade has been dropped and badly nicked. When I do I do not get it any hotter than can be hand held(under 150 F) I sharpen progressively on stones using circular motions through softer Norton carborundum and harder India stones as needed to get any nicks or rolled edge out. You should not see any shiny spots on the edge when held up to the light. The coarse carborundum stones will remove fairly large nicks without too much work. I watch continually to maintain the angle and make certain it is not getting bellied. Then my last passes are with 600 grit paper on a flat surface then a hard Arkansas stone to remove any tiny burr. I can usually just touch up every so often with the 600 paper and Arkansas stone and do not have to use the other stones very often. I can shave with them when done. A wood carver I knew when I worked in the tool and die shops taught me how to sharpen. He was a lot better than I am at it and could get things razor sharp in under 5 minutes no matter how dull they were. Everybody has their own system for sharpening but that is what works for me.