Sandpaper

I keep my sandpaper in a filing folder. Folder then slips in the book rack/reference books on the shelf above my bench.

I have a Bank of Small Pigeon Holes made from Square Rain Water Down Pipe, one Hole for each grade.

Details on my web site at

one of numerous Tips in the Hints n Tips Section. RVS

Since I use it (mostly) at the lathe I've set up my "system"

At the lathe, I use 1/4 sheet pieces, folded into quarters, with one seam ripped, so that grit doesn't touch grit. I keep all of them (and the discs for my 2" disc sander) in an old sour cream container. (Well usually. What I mean is that when I pick up the work area, they go back into there, so they are available when I want to sand. Just grab the container.)

I also keep the rest of the full sheets of each grit clipped with a thesis clip in that same container. The rest of the full sheets are kept in their cardboard backing from the store, flat in a drawer.

That means that when I wear out one of the quarter sheets, I just pull the replacement out of the pack (and THROW AWAY THE OLD WORN OUT ONE SO I DON'T PICK IT UP AGAIN! EVER!) and keep on sanding. When I have used all 4 quarters, I have to trek to the drawer, pull out the next sheet and rip it into quarters, but I probably needed the break anyhow.

I still find folded sandpaper lying around (I wonder who does that?) but on straighten up, it goes back to the sour cream container, and gets used up and then thrown away.

To me, having the stock of quarter sheets easily available, and throwing away the worn out pieces seems to reduce the hassle.

Other tips on sandpaper and using it....

To keep your fingers from burning while sanding place a small piece of folded cloth behind the paper. It's an old trick that our instructor said won't be found in a book. Works great!

And...(many already know this I'm sure)....I was tearing off strips of sandpaper only to discover after sanding that I forgot to write the number on them. Yesterday a light came on :O) If the strips are torn top to bottom instead of sideways the number is always there. (Hey - everyone has to see something for the first time!)

Keith

Hi Salmo

Salmo, I'll give you another tip for not burning your fingers on the sandpaper. TURN DOWN THE SPEED !!!! That way the wood will not get to hot as well, it's the better of the two IMO.

Have fun and take care Leo Van Der Loo

Salmo wrote:

Thanks..I sand at the last speed I used while turning and have yet to change the speed to slow. The wood doesn't get hot because I don't keep the paper there long enough to burn as I'm changing from 100-120-180-220-320-400-800 until a sheen shows. ...

The cloth piece behind the sandpaper really does do the trick. I'll try the slower speed anyway just to compare the finish difference (or non difference).

Keith

On some woods, you can cause heat checks in the end grain from overheating. My rule is that if it's too hot to continue sanding, then slow it down.

Years ago, a regular to this group, Lyn Mangiameli, discussed slow speed sanding. After I tried it I was a convert - I now rarely sand above 500 rpm - and oftentimes it's much slower depending on the work diameter. I'll see if I can look up the thread and post the link.

Hmmmm, my book says sand with less pressure at whatever speed you care and you'll get less heat. Coefficient of friction being basically the same, (might actually be less at low pressure) it all depends on pressure, not speed.

Yeah, Lyn discussed a lot of things. Some of which made good sense. This is not one of them. Lathe speed when paper is unpowered is worth keeping at a reasonable rate, but that's for the operator's safety. When paper is powered and circular, you can have an additive, subtractive, or composite speed _at any given point on the circumference_, which really complicates things. Makes pontification on speed just that, though once again, speed doesn't produce heat.

Sort of like your comparison of the weight of the Robust vs Oneway, it's meaningless. Rigidity is what counts. The rest can be bolted securely in place, and already is on the heavier lathe.

George, what you say is true, but only for limited ranges of pressure and speeds. Few things in nature are linear. My book, The Machinist's Handbook, says this about friction:

For low pressures the friction is directly proportional to the normal pressure between the two surfaces (Just as you say), but goes on to say:

At very low velocities the friction is independent of the velocity (similar to what you say)

For high velocities the friction (and coeficient of friction) decreases (the opposite of what you say)

The friction is independent of the areas in contact.

What this means for heat buildup is that pressing with the same force with three fingers instead of one yields the same friction (and stock removal) but it generates less heat per surface area since it is spread out over a larger contact area. Going faster reduces the friction (and therefore heat buildup), leading to longer abrasive life, and at the same time the increased speed will have a cooling effect upon the surfaces, too.

However, increased speed will result in increased injury in the event of an accident.

Dan

Well, no. Five pounds per square inch pressure is still five pounds per square inch whether you have six square inches in contact or three. If you had a constant weight (pressure) what you said about reducing the force per unit of area would be true. That's why the corrugated sole on the jack I'm using to level some panels just now generates essentially the same friction as a solid one, less a bit of suction on its own, but different depending on how hard I press. I am assuming, of course, that 200 pounds of Polack is not capable of exerting the consistent pressure of his entire bulk - a limiting factor - in this case or with the sandpaper.

Factor in the next obvious step, Dan. As you press, you dig in deeper, burying the grit more to the backing, increasing the coefficient of friction and resistance. If you don't press, your depth of "cut" is less, coefficient of friction less, and so forth to the obvious conclusion.

I've been following this thread and think this is a comparison of apples and oranges.

I feel that a good point to start is an empirical test and then come up with an explanation to fit the results.

Test 1. Rest your hand on a rotating smooth spindle of wood at a low speed and at a high speed and decide on which your hand get hotter.

Test 2. Run the spindle at 500 rpm and grip lightly then tighten your grip on the wood.

For those cautious ones who are concerned about health and safety, loosing their hands, stripping the skin from their palms or suing me. The answer is the faster it goes and the harder you grip it the hotter it gets (but you knew that already).

If we are talking about sanding then the concern is kinetic friction which increases with the force applied (as has been stated) and presumably varies with the grade of sandpaper but is not dependant on the area of contact. It is also a dimensionless quantity (it is just a number). So friction does not generate heat, something else has to be happening also.

Checkout 'Energy of friction' at the bottom of the page on:-

The energy (heat) = the normal reaction force x coefficient of kinetic friction x distance travelled. 'The normal reaction force' = how much you press on the sandpaper 'Coefficient of kinetic friction' = depends on the wood and sandpaper 'Distance travelled' = in any unit of time, say 1 min = rpm x Pi x diameter of the piece being sanded.

So the more you press on and the faster the lathe goes the more heat is generated.

This would seem to tie the theory to empirical test.

OK finished now for those still reading this and I'm going to find my flak jacket.

BillR

Aren't we sidetracked here? The question is not heat or friction, but what delivers the best looking piece of work.

My experience is that when I slow down the work, it looks better after I sand it. Not exactly sure why, but it does. I have fewer deep scratches, and better control so I don't sand off the sharp details. And high speed sanding on softwood face turning, is a guarantee to ripples because the softer summer wood is removed, leaving the harder spring wood (?).

Also it doesn't throw the dust as far, and the feel of the project is less frantic--like I'm in control, not the machine.

My $.02

Old Guy

I think if you sand without support for the sander other than the work itself, you'll find that to be true. Less energy on the slow piece to throw the tool back at you if you get a bum angle, and less likely that the bum angle that tosses you (dare we say high-friction contact?) will cause a dig when it does. Stopping the work entirely is risky business, however. Now the scratch arcs form quickly from an improper tilt, and worse than arcs, digs are possible. I like to sand with the support of my toolrest, more or less an extension of the cutting process, where the work comes to the edge for removal. Makes it easier to compensate for surface hardness differences as well.

You must be sanding in some completely different format that I if travel on the dust is a concern. I like it to travel, and encourage it to do so - straight into my strategically place collector. Keeps it low and away from my nose.

or push

It's much more difficult to judge excessive heat buildup when machine or rotary sanding. The heat will shorten the life of Velcro pads and if one is not using the finger-backing method. The hooks melt away and then the paper won't stay stuck.