ROS finish problem

[ian]

I think in part the "cause" of the problem is working with rough sawn timber through to final finishing.

I think that before gluing the boards to make a top you should sand -- if that is your only option -- through to at least 120 to remove the saw marks and get boards of uniform thickness
then as the project progresses, you should aim to sand at least one grit finer as you complete each step.

However, unless you have a drum sander -- sanding rough sawn timber through to a finish ready surface has to be one of the more difficult WW tasks.

Almost certainly, your swirl marks are the result of not completely removing all the swirls from the coarsest grit you started with

[q9]

40 grit is really grinding, not sanding. The problem is really the cross cut wipes of the abrading surface are going to cut and tear deeper than you want and it will take a long time with a higher grade to get rid of them. Sanding with the grain will be better (ie not ROS) as those deeper cuts will disappear into the grain, but really you need to machine finish after sawing, jointer or thicknesser...

So my advice is change tools, or change grits. I'd never use 40 as a start to anything I wanted to look at.

[Shedhand]

I still don't understand the source of the problem. I can think of two reasons why this happens:
1) you sand all the way through the grits properly, but the final grit leaves swirls that you still see. I don't think this is possible, since you sand up to very high grits.
2) Somewhere in the process of sanding, when switching to finer grit you do not fully sand the marks from the previous grit. What helps me is after 320 grit ROS session, I go with 320 grit hand sanding along the grain until all the marks from ROS are gone. Then I continue sanding with ROS, and repeat hand sanding with the finest grit I reach with ROS.

G'day Ilya, yes I would love to be able to hand sand and hand plane for that matter but as I alluded to earlier, I have some very debilitating problems with my joints. Arthritis, Cervical bilateral ferominal stenosis, bi-lateral epicondylitis, carpal tunnel and a lumbar spine rapidly losing its discs. Everything is a pain for me but I decided to keep going until I can't. Hopefully the upcoming surgery will allow me to continue walk upright for a few years yet. And yes the "dark side" is much cheaper. Derek (Cohen)is my hero!

[mark david]

Hi absolutely, really coarse grits that a really going to a major problem, if you are using these to derss rough sawn timber, although have not come across this technique before but if you don't have a thicknesser or drum sander then you need some other method.Using bench and block planes will save you a lot of time and money in the long run.

I certainly don't recommend using anything coarser than 120 grit on any timber you want to give a sprayed or lacquered finish.
I am not a huge fan of using super fine grits either to be honest,if I am using jarrah or marri for instance I don't go any finer than 320 grit, I was even told by an experienced furniture maker that he didn even go beyond 240 grit on jarrah it is just a waste of time.

Pine is one of the worst timbers I have found for showing the swirl marks due to its softness and grain structure and have major problems with it after using coarse grits to remove old varnish

Hi Ilya, it's swirl marks from the coarser grits only, and probably the 1starting grit. The matte finish at that stage restricts being able to see them until you've moved right up to the polishing grits, when they can stick out like nads, as Sheddie says. I think the most important thing to do is give the job a really thorough inspection in oblique light after each grit up to about 120. That's a bit tricky and time consuming to inspect so minutely when you're doing a table or similar, but if not then a price is paid....

[FenceFurniture]

I was even told by an experienced furniture maker that he didn even go beyond 240 grit on jarrah it is just a waste of time.

Jeez Mark, I'm not sure if I want to buy any of his furniture then. This is the result of going up to 3000 grit (and no finish applied), which I definitely wouldn't call a waste of time.



Give the chosen finish the best start, I say. Perhaps he used 2 pack finishes, in which case he could get away with a much lower grit I suppose.

[mark david]

Yes I can imagine what kind of finish you you can get with a 3000 grit but basically you would be burnishing the surface, if you are not then going to apply any kind of surface finsish then then fair enough but its not like polishing a piece of metal, you still need a final finish to acheive any durability.

If you were going to spray or lacqeur the surface then you would probably not be able to tell whether it had been sanded to 300 or 3000 and is quite likely a very fine grit might even compromise the surface adhesion of any finish applied to it.

the last piece of furniture I made was sanded to about 240 grit and sprayed with Becker Acroma dm307 it still looks like wood and not a plasticky finish

Jeez Mark, I'm not sure if I want to buy any of his furniture then. This is the result of going up to 3000 grit (and no finish applied), which I definitely wouldn't call a waste of time.



Give the chosen finish the best start, I say. Perhaps he used 2 pack finishes, in which case he could get away with a much lower grit I suppose.

[LGS]

Hi,

There is an oil finishing method which requires hard burnishing. At 4000g the finish is sensational, at 400 it's a waste of time. The finish is highly resilient and is unaffected by heat, moisture and spills of food and the like.

As for not using anything higher than 240-320 on Jarrah, good luck to your mate. I strongly disagree.

Regards,

Rob

[mark david]

Each to his own of course, although I suspect the burnishing oil requires the burnishing at the application stage of the oil and not before.

Oil finsishes are known to darken significantly with age and are not to everyones taste.

Hi,

There is an oil finishing method which requires hard burnishing. At 4000g the finish is sensational, at 400 it's a waste of time. The finish is highly resilient and is unaffected by heat, moisture and spills of food and the like.

As for not using anything higher than 240-320 on Jarrah, good luck to your mate. I strongly disagree.

Regards,

Rob

[Evanism]

I've read the thread from top to bottom and I'm at a bit of a loss. My Festool ROS125 is nice with the dust extraction, but I've found over sanding does nothing but waste time.

I've found I'm under the pump for time, so I turn off the random function for 80, 120 and sometimes 180. I lift the tail of the sander to only just alleviate the pressure on the back of the pad (let's call it a 5 degree lift) and rotary sand at full blast. Farting around with slow speed makes no sense.

As far as movement, I move the sander in a simple snakes-and-ladders fashion with a 50%-ish overlap. I'd say it's moved about 7 to 8 seconds per 30 cm.

I then turn to random function on on either 120 or 180 dependant on the wood and do up to 240. I might note that the random function isn't really random if any pressure is applied. The disk just vibrates, it's only when the whole disk also rotates anticlockwise that it takes on a more hyper-detailed Spirograph-like function....any pressure and it's just vibrating in small circles.... Could this be your problem?

The paper is used to death before its thrown out.... For I have the poverty!

The disks are occasionally cleaned using the $5 Big Erasers that are grabbed as extra throw-ins when buying from Machinery Warehouse or Rockler.

Surprising that FenceFurniture experiences this, I'd regard him as the Sanding King. Those tests he did were exhaustive and very detailed. After 900km of sanding he should be the grand master!

Maybe burnishing up a scraper and finish with that? I love the finish a freshly curled scraper gives.

Has anyone ever tried finishing with some 0000 steel wool under the sanding pad?

[Ilya]

That is tough - hopefully you will get a chance to get a drum sander, this reduces the time and effort with ROS immensely. Definitely what you need.

G'day Ilya, yes I would love to be able to hand sand and hand plane for that matter but as I alluded to earlier, I have some very debilitating problems with my joints. Arthritis, Cervical bilateral ferominal stenosis, bi-lateral epicondylitis, carpal tunnel and a lumbar spine rapidly losing its discs. Everything is a pain for me but I decided to keep going until I can't. Hopefully the upcoming surgery will allow me to continue walk upright for a few years yet. And yes the "dark side" is much cheaper. Derek (Cohen)is my hero!

[Ilya]

Shedhand, I would imagine that you are not doing a huge number of project - maybe there is a forum member or a woodies club near you that have the drum sander that they can let you use?

[FenceFurniture]

Shedhand, I would imagine that you are not doing a huge number of project - maybe there is a forum member or a woodies club near you that have the drum sander that they can let you use?

Or at least a jointer.....

It is a pain in the butt to load up the car etc, but probably less than the aggravation from 40 grit. A six pack of something decent should do the trick.

[Shedhand]

Many thanks to LGS (Rob) for dragging his gear down to my shed and spending the time to show me what I was doing wrong. Very enlightening I have to say.
Cheers
Sheddie

[ian]

for the enlightenment of us all

what were you doing wrong?

[Shedhand]

for the enlightenment of us all

what were you doing wrong?

i simply wasn't spending enough time on each of the grits and sanding too slowly which caused the swirlies plus Rob demonstrated to me that starting at 80# or 100# with the Rotex was as coarse as needed even on a piece of rough sawn Blackwood.
cheers
sheddie.