Removing shallow tool marks on leveling beam, necessary?

[llmk]

Hey guys,

I'm in the process of truing a couple of spirit levels in order to use them as leveling beams. One of the levels had tool marks all along, most of them are gone now after sanding with a 240 grit dry and then wet. I'd like to know if I need to go all the way and remove those last few marks. The level is straight at this point.
I'm thinking that they are very shallow, you can barely feel a few of them under the fingernail so they shouldn't have an impact on the leveling process once I put the masking tape, double-sided tape, and sandpaper on, right?
So, good enough, or should I eliminate those last few pesky marks?

 

[Gary_M]

Since they are perpendicular, yes I would eliminate them. They may be shallow, but that orientation will allow the tops of frets to catch slightly. Heavy sandpaper could mitigate most of that effect, but I'd get rid of those.

If the marks ran lengthwise, it wouldn't be as much of a concern, in my opinion.

 

[Jeff Siddall]

Hey guys,

I'm in the process of truing a couple of spirit levels in order to use them as leveling beams. One of the levels had tool marks all along, most of them are gone now after sanding with a 240 grit dry and then wet. I'd like to know if I need to go all the way and remove those last few marks. The level is straight at this point.
I'm thinking that they are very shallow, you can barely feel a few of them under the fingernail so they shouldn't have an impact on the leveling process once I put the masking tape, double-sided tape, and sandpaper on, right?
So, good enough, or should I eliminate those last few pesky marks?

View attachment 5297597

I agree with @Gary_M probably best to eliminate them if they are deep enough that the paper would conform to them, but it's difficult to tell from the photo how deep they are.

 

[Bruce Johnson]

In this case, you could fill the grooves with CA glue or auto body spot putty, or even epoxy. Then re-file the surface to flat.

 

[Gary_M]

In this case, you could fill the grooves with CA glue or auto body spot putty, or even epoxy. Then re-file the surface to flat.

^^ Really good point, Bruce. This would be a quick and easy fix without the need to remove more material.

 

[llmk]

This picture just made me realize that my beam is probably not completely straight. When I started sanding the scratches were all over the surface and now they are just in the center of the beam so I think the edges are straight but the center is ever so slightly concave.
I like the idea of filling the grooves but at this point, I think I should keep sanding to have a 100% trued surface, right? Since I am going in this direction, would there be any significant advantage to going as far as polishing the surface once I am done sanding?

 

[Major Seven]

View attachment 5298128
This picture just made me realize that my beam is probably not completely straight. When I started sanding the scratches were all over the surface and now they are just in the center of the beam so I think the edges are straight but the center is ever so slightly concave.
I like the idea of filling the grooves but at this point, I think I should keep sanding to have a 100% trued surface, right? Since I am going in this direction, would there be any significant advantage to going as far as polishing the surface once I am done sanding?

If you can feel it, it is significant.
This reminds me of something I do with car sheet metal sometimes: Spray with modern filler primer
which is designed to fill scratches. Then spray it again with a different color primer. Then sand. Assuming
your sanding block is true, high/low spots will be revealed when you see a color change peeking through.

I should add that I continue sanding all the way down to 1200 grit.
That gets it REALLY flat. Flat enough that after paint, the surface is
glass like reflective. You can see in paint jobs that are not quite flat
the reflected light produces irregular reflections. This may be overkill
since at that point we are probably looking at 0.001 in.

 

[llmk]

Done!

 

[Matt Liebenau]

Excellent fortitude and stick-to-itivness! You should a good lifetime tool now.