Abrasive effectiveness vs. rotational speed

[pfduffy]

OK, I am going to stick out my neck here and make a few incendiary statements and then ask the question; who has done a scientific study of the effectiveness of abrasives of various grit sizes as a function of speed? I am not taking about "workshop science" or Kitchen Science, but a real study based on measurable facts. My contention (and observation) is that higher speeds contribute to abrasives effectiveness. That statement contradicts everything I have ever heard about "going slow and don't get the heat going", etc. At 80 grit, I say "let her rip" at high speed and use the grit to grind down to a common level. After that, it is my observation that a moderate speed works very well, but that slow speeds do not help. It is also my contention that very fine grits, used midway in the process, will show you where the flaws are that need to be fixed quicker than working through the grits and then discovering a flaw. ( i think i spent too many hours at the lathe this week!)
Anyone got a scientific study to back up, or refute, what I am contending?
Happy Easter everyone!
Philip

 

[dkulze]

Well, Phil, first you gotta define what "fast", "moderate", and "slow" mean.

The "slower is better" mantra doesn't apply below certain speeds. It just highlights the tendancy to sand at the speed you were turning at without slowing the lathe down. If your "moderate" is about 4-500 rpm, then I'm mostly with you. I do tend to slow down as I get to finer grits due to tendancy to heat up and glaze.

It's possible to temper the wood fibers if you let it heat up too much. This is the same effect you get when you heat a wooden spear point to harden it. It's also possible to give yourself lots of tiny, hairline cracks from the heat expansion and contraction combined with flash drying the surface. Fine if you want that "crazed glass" look but a problem otherwise.

Since I power sand, I keep my lathe running at 2-400rpm on most bowls and vases. Higher and I risk melting my velcro.

As to the sanding at a higher grit to show up damage, I'm with you on that one.

Dietrich

 

[Dario]

This is no way scientific but I will share my experience as you just did.

Speed and sandpaper loading seems to be the wild card for me. The faster the rotation the faster sandpaper gets loaded. Loaded sandpaper + high speed = heat and poor sanding.

If you can have your sandpaper stay clean at high speed then yes, it will work. I do that a lot actually but watch the initial sanding. Some do power sanding (I do) and that solves some of the problem with the benefit of speedy sanding.

 

[MichaelMouse]

Careful about challenging convention. I won't say conventional wisdom, because most isn't. Simply put, if you take more grit to the surface in the same time, you can haul more dust. If you want proof of this, take paper in hand and sand at seven strokes per minute, then seventy. See how long it takes you to get through a veneer with 150 paper.

Linear it's not, and there are other factors, certainly, but the game of sanding is about removing material, so your contention is essentially correct. What you have observed has no effect on heat. It's bad for the wood, bad for the paper, and it's a function of sanding pressure more than frequency of contact, though I suppose at super high rates of speed there would be no chance to dissipate some heat between rotations of the piece on the lathe. Of course the speed would create a higher airflow, so ... well, let's not get hung up on it.

 

[Brian Hahn]

The sandpaper industry probably has lots of data for effectiveness vs surface contact speed. I doubt that they will ever share it in the detail you're asking for. And remember that different woods respond differently to sanding. It can get real complicated real fast.

I've got to agree with the others. Do whatever works best for you.

As MichaelMouse said, "let's not get hung up on it."

 

[Steve Worcester]

Lets look at this also.... (more the result of power sanding than hand sanding)

One of the enemies here is heat. Heating the wood we will agree is bad, and heating a hook and loop disk is bad. Higher rotational speed, (not surface feet per minute) increases friction and in turn heat.

The other issue is that across grain and in between annular rings, are varying densities of wood (early wood and late wood) as you increase the woods rotational speed, you cannot as easily maintain proper surface contact and will more likely get a more uneven surface because the pad will start to "jump" off of the rings. Sand a softer wood bowl too much and you will feel the grain pattern.

 

[George Guadiane]

Here's MY 2 cents:
I have been using oil (mineral/olive) to power sand with for a while now. At first I was concerned about finish bonding, but this SEEMS to be a non issue with shellac AND water based poly (so far).
The oil seems to keep the heat down, along with the dust. It also seems to show the flaws. The idea of skipping a few grades/grits to check my progress is one I will use for sure. I did crack the bottom of a box once by building up too much heat before I started using common sense and oil.
The growth rings thing is real, but when I get down to the final grits, I lower the rotation speed and also sand, BY HAND, with the grain to eliminate most, if not all of that.
Anyway, this is another "cat," and if you get that ideal finish, it is properly skinned.

 

[Ken Grunke]

Being at the age where arthritis is becoming more and more noticable, I'm always on the lookout for ways to make sanding as fast as possible. But still, I turn the speed down for spin-sanding, and turn the lathe off to sand with the grain even though sometimes it can get a little painful. My own scientific studies have proven to myself, and on occasion in front of a group, that a speed a bit too fast can have me sticking my fingers in my mouth to cool them off--ouch that hurts! I should have a pail of water within reach. Has anyone tried sanding with just water?

 

[Russ Fairfield]

If you are trying to start an argument about sanding speed, forget it. We all do what works for us. If you have tried sanding slow and it didn't work, then don't do it. If you haven't tried sanding slow, then you can't say it doesn't work.

Heat is a reality. Scortching, casehardening, heat checks, cracking, and burnishing the wood surface, explosions of the piece in the lathe, melting glue lines in segmented assemblies, melting velcro pads, burning our fingers, and a few other adverse things are all realities of getting the wood and the sanding medium too hot. Controlling or eliminating these problems is more important than how fast you are spinning the wood or the sanding disc.

 

[waltben]

Speed of what?

I didn't see anyone writing about wood surface speed, only lathe RPM - which is meaningless in this thread. A 3" diameter piece can turn at 1,000 RPM for sanding at a 'moderate' to 'fast' surface speed, but try doing that with a 12" diameter piece. I usually sand at the highest speed I can handle, as I want to get it done as quickly as possible without checking the wood or burning my fingers. On a pepper mill body this can be up to about 1,500 RPM, but on a 14" bowl, it won't exceed 400 to 500. Don't have time to do the math, but that's the point. I also sometimes skip to a high grit to look for scoring that I've missed, but then go back to the grit I was at (usually around 120 to 180) and then go all the way up to 1,500.

 

[Jake Debski]

After reading all the replies to Phillip's post, seems to me there are lots of ways to get there from here. Just choose the one that works best for you.

 

[pfduffy]

Sanding speed

Thanks to all who contributed ideas and suggestions. I learned some new ideas and have to note that the sandpaper gurus did not contribute. But then, it was the weekend and they were all fast asleep in their beds. Philip

 

[Steve Worcester]

I learned some new ideas and have to note that the sandpaper gurus did not contribute. Philip

I am almost offended by not being considered a sandpaper guru :cool2:

 

[n7bsn]

I am almost offended by not being considered a sandpaper guru :cool2:

emmm, when he posted that I thought.... but Steve posted

 

[john lucas]

I don't know what the definition of a Guru is but when it comes to sanding I listen when Steve or Russ talk.

 

[pfduffy]

sanding speeds

OK, Steve, you have been a guru a long time. But Russ, there was never any intention of starting an argument, but now you have, so you are no longer a guru. I think the question still stands; any manufacturer of abrasives done a study? NO? Well, that tells me they like to sell their products but can't seem to invest a dime in the customers. Funny how the world is like that these days. Philip

 

[MichaelMouse]

I think the question still stands; any manufacturer of abrasives done a study? NO? Well, that tells me they like to sell their products but can't seem to invest a dime in the customers. Funny how the world is like that these days. Philip

They already tell you how to use the paper. Don't press, and use multiple grits to avoid the temptation to do so. Pretty simple.

As to speed, it's not in the friction equations, and sanding speed varies from hand sanding at ten strokes per minute to 25,000 orbits, so it's probably true that it doesn't make a difference. You can verify that pressure makes heat with bare fingers if you have the inclination.

As to the problem of end versus face grain, harder latewood versus early, and my personal favorite, white punky spalted versus nearly sound, the same thing that keeps the heat down also does them best. Sand with a touch not a press. My solution is to help my arm and wrist (no "limp wrist" comments, please) by resting my sanding handpiece on the toolrest as if it were a lathe tool and letting the wood come to the grit. With the disk rotating at one speed and the piece at another, I can sand up at collective speed, or down at subtractive by choosing nine or three o'clock. Noon is best for removing gouge ridges.

 

[George Guadiane]

I think the question still stands; any manufacturer of abrasives done a study? NO? Philip

If that is a SERIOUS question, try contacting some of the manufacturers... It seems unlikely that their representatives and/or scientists are hovering our boards waiting to answer the question you raise. :cool2:

 

[Steve Worcester]

Controlling or eliminating these problems is more important than how fast you are spinning the wood or the sanding disc.

I have to say that I would greatly respect and agree with Russ on this... and the reality of his sage advice is that you work with what is effective for you and find that out by your own trial and error. Even if there was some sort of scientific evidence to back any manufacturers findings, I would still be a sceptic and have to try it for myself. (And I do)

I have seen some magazines do tests of abrasives by cutting wood, weighing it, using pressure measurements and times and weights again to see how effective different brands are at removing material, but is still comes down to trying what works best for you. Just like any types of reviews or studies, your proverbial mileage will vary.

But as for the arguments comment, bring it on. The diversity and opinions of forums are what makes it fun and why we (as moderators and participants) put our time into it. Oh, and the camaraderie (and beer).

 

[Michael Kuehl]

On smaller pieces(3"-8") I will sand with coarse grits up to 1600 rpm briefly. I don't do segmented turnings, so I can't comment on the effect on glue joints. However, an advantage to sanding at, say, 400 rpm is that if there has been wood movement, the sanding will more likely also be able to hit the "low" spots.

 

[Bill Boehme]

who has done a scientific study of the effectiveness of abrasives of various grit sizes as a function of speed?

Without a doubt, all of the major manufacturers such as Norton and 3M have done massive amounts of research. Their research is driven by the need to have a better product than their competition. Will they share it with the world? Duh -- no.

I should point out that the question that you have asked despite its request for "scientific research" is NOT the type of question that scientific research is directed towards -- you are actually asking for a product evaluation ("effectiveness" is a marketing term) when it is used in a certain way. Research focuses on issues that are considerably more technical in nature than your question.

Bill

 

[Bill Boehme]

I learned some new ideas and have to note that the sandpaper gurus did not contribute.

Or, perhaps you weren't listening!

Steve, old pal, sorry that you had to find out the truth this way. BWAHAHAHA

Bill

 

[Brian Hahn]

The type of wood is an important factor

This weekend I was power sanding identical pieces made from four different species of wood. The size, shape, speed and sandpaper were identical for all pieces, and the surface being sanded was about 80% air (multi-axis off-center turning). Everything was fine until I got to 320 grit. The cherry glazed and loaded the paper almost immediately. The black walnut, elm and butternut sanded just fine.

So there is a real shop test, complete with a "lab report". :cool2:

 

[Michael Kuehl]

Brian- What was the speed at which you were sanding?

 

[Brian Hahn]

Brian- What was the speed at which you were sanding?

The piece was spinning at 500 rpm, the minimum speed on a Jet mini. The piece's radius varied from 1 1/2" to 2 1/2". The sand paper was slowly moved by hand across the face of a backing block that was fixed in the tool rest holder, so that on each rotation the piece hit a slightly different section of the sandpaper.