Sanding ??

[dabeeler]

When sanding our blanks, if each higher grit replaces the previous grits scratches with smaller ones till we reach the point the sanding scratches are no longer visible, what do we gain by stopping the lathe to sand length wise to remove the circular sanding marks? Aren't we going to get to the point they are not visible without this extra step? What is the benefit of having the last grit's scratches run length wise if they can't be seen anyway?

 

[Sylvanite]

To my mind, longitudinal sanding in intermediate grits serves as a guide for scratch removal. Without that, it is more difficult to determine when you have removed all the scratches from the previous grit.

For example, let's say I started sanding with 220g:

1. Sanding the blank smooth with the lathe running leaves circumferential scratch marks.
2. I turn the lathe off and sand lengthwise until the previous marks are removed. Now the blank has longitudinal scratches.
3. Move to 320g sandpaper and sand with the lathe running. I sand until the lengthwise scratches are gone. Had I omitted step 2, I'd be replacing one set of circumferential scratches with a different set. I wouldn't have any visual reference as to when to stop. Because I'm sanding in a different direction, however, I can tell when the previous grit marks have been removed.
4. Turn off the lathe and sand lengthwise until only longitudinal scratches are visible.
5. Switch to 400g and sand with the lathe running to remove the 320g scratches.
6. Turn off the lathe and sand lengthwise again
7. If I want to go to higher grits, repeat until I've reached the desired scratch pattern. Regardless of grit, scratches with the grain are less visible than scratches across it so sand with the grain last.

I hope that helps,
Eric

 

[Shock me]

Eric's explanation is exactly right. I agree that sanding lengthwise is kind of a pain, to prove it's necessity to yourself, I'd suggest trying it once without. It's a step that I spend a lot of time on, inspecting carefully under good light and sometimes a magnifying lens. If I skimp on this step, chances are good that someday I'll be using or showing off the pen and suddenly in a new light see all sorts of scratches that just shouldn't be there.

The guys who sell their pens for big money will tell you that it's not unusual for their customers to pull out their own 40x loupe and check for scratches.

 

[jskeen]

and also, remember that a piece of sandpaper or MM held with your finger is not a truely flat surface that is just taking the top of the ridges off as you sand. If you only sand with the lathe on, each grit is not only removing material from the high spots, it is also deepening the existing grooves by removing material from the inside of the scratch. This is what a quick lengthwise sanding eliminates (assuming that you do get rid of all the circumferential scratches).

I actually differ from Eric (sometime, consistency is not my strong suit) in that I usually move up a grit to do the lengthwise sanding. IE sand with 320 with the lathe on, then get a fresh piece of 400, sand lengthwise till all scratches are gone, then power on lathe and sand with the 400 till I get a nice consistent surface, turn off and get a new piece of 600 sand lengthwise, ect. Not sure why, really. Just seems logical that if you removed the 320 scratches with the 400 when the lathe was on, then the 600 will remove the lengthwise 400 scratches easily enough, no need to use the 400 again. Also, the next grit will be newer and sharper, and cut more easily for the hand sanding part, and for the sanding with the lathe on, that's not as critical.

I never really invested a lot of scull sweat into that part though, so I may be missing something obvious here. I may try it both ways next time just to see if there is any appreciable difference between the methods, but I tend to doubt it.

 

[Sylvanite]

There's no reason, other than convenience, not to switch grits each time you change sanding direction. That said, I prefer to swith grits as I described above.

It's easier to sand with the lathe running (the motor helps you) than with it off. It's harder (marginally I know, but harder) to remove scratches with finer grit sandpaper than the grade that created them. I let the lathe help me with the harder part (changing grits), and do the easier sanding (changing direction) by hand.

That's just my preference. Others may (and do) have a different process that works better for them. Find what works for you and stick with that.

Regards,
Eric

 

[jttheclockman]

Placing a hard backer in back of your sandpaper will help elliminate some of the thoughts about hills and valleys.

Actually one of the main reasons to sand lengthwise is visual effects. Our eyes are trained to follow the grain of the wood and when you changed the scratch pattern to circular then the eye picks this right up. Now sand lengthwise with the grain pattern our eye tells us those scratches are just grain pattern.

Don't forget to wipe the blank down after each grit size.

 

[1080Wayne]

To expand the discussion a bit , the function of the coarsest grit used is to remove tool marks caused by the skew or other tool . Subsequent operations should remove all traces of the previous sanding . Tool marks are frequently seen in posted photos where there is an obvious break in the shine line , even though the pen has been through the whole Micromesh range . Dull tools are the cause as more pressure has to be applied to the blank .

For me , it is standard practice to inspect the blank under a 3 diopter lens after the first lengthwise sanding ,with light coming in at a low angle . Remaining tool marks are sanded out lengthwise , before going up in grit . I don`t usually sand lengthwise again until 600 grit , then another magnified inspection . At that point I get radically different and only sand lengthwise , by hand , off the lathe , through the other grits , to ensure no radial scratches on the finished barrel .

That practise was arrived at by not being fastidiously clean when switching grits . When I remember , I now vaccuum the lathe before sanding , wash my hands , wipe the blank with DNA after each grit , keep each grit in its own bag , etc . The same principles apply if you choose to buff rather than sand . These practises are more critical in a shop such as mine where metal work is more frequent than woodwork .

In short , do what you need to do to meet the quality standard you set for your work .