ROS finish problem

[Shedhand]

Hi all. Got a problem which i've had for ages but im ghetting fussy now and want to solve it. A couple years ago I had Festool ETS 150/3 ROS. When sanding the eventual xposed face of, say a table top, I noticed that from 40 grit up to about 120 the sander left little circles all over the surface. If I started at 40 grit on a sawn surface as the saw marks disappeared the sanding discs left their little circles behind and as i moved up the grits they got fainter but were still noticable in the right light. In the past I have just kept going up to my standard 2-3000 grit foams attaining a glass like finish. Howver when putting on wax or wipe on poly or even shellac the little circles become more visible. Now I recall some telling me to wipe the surface over with a tack cloth between grits which i always do but the little circles are still there. Time goes by, sold my tools when in need and now starting to get some good kit back together. I recently bought a Metabo ROS 150 GTHO or something (329 bucks so its reasonable quality) and I've been using it to sand a table top made from a very dense and colourful hardwood (its Eucalypt from Vic but don't know what brand - very purty tho ) my clamping is very primative as I also sold all my loverly Bessey Ks. I have 2x1500 and 2x1200 bessey pipe clamps so there was a fair bit of sanding to do to get the able top flat after gluing up. Started with the big ancient Elu belt sanding monster with 40 grit belt to rip the mountains off and got it reasonably flat using a steel straight edge and chalk marks to achieve reasonable flatness. Then got the Metabo to work. Started at 40 grit. Ughhh! barely made a mark on the deep scratches left behing by the Elu. Anyway I persevered in 20 minute bursts to give my stuffed shoulders some rest. The Elu marks are still evident but faint except now I have the problem of the little circles from the ROS with 40 grit disc. I kept at it and went through 60, 80, 100 and 120. Can't get rid of the circles. every grade up to 120 leaves them behind. Tack cloth and damp cloth between grits. What the hell am I doing wrong. Wipe on poly is damned expensive for a pensioner and nothing makes me more p#ssed off than putting the poly on the finished surface only the have these bloody little circles standing out like dogs nads. By the way, I've tried a million brands of disc (not quite but you get my drift) and the same with all of them. I'm connected to a dusty and I've tried various speeds for each grit. Nada! Any clues anyone.
Cheers
Sheddie back in the shed

[Kuffy]

I use a milwaukee ROS 150 E-2. its similar to your metabo, dual function random orbit at 3mm circles and 6mm circles. I use the 6mm orbit setting for roughing away the surface grits from 60#->180#, then ill set to the 3mm orbit setting for the finer grits for finishing. I usually finish with oils, and mostly I burnish them into the tops from 400# up to a finer grit until i'm happy with the sheen. The weight of the machine itself is enough, you dont need to add any extra weight via your arms/shoulders.

[DaveTTC]

Pedal powered lathe

EDIT Not sure what hapened here. this post was meant to go in a thread about a bike frame


Dave the turning cowboy

turning wood into art

[Ilya]

Hard to say really without pics, maybe you have too high standards. I have exactly the same Metabo by the sound of it. Just with each grit I sand until the circles of the previous grit are completely gone. There are, of course, new circles from the new grit, but they are fainter and fainter as you go higher with grits. Once I go to 1k grit, and then finish with oil, I cannot see any circles... What sequence of grits do you go through?

[Shedhand]

I use a milwaukee ROS 150 E-2. its similar to your metabo, dual function random orbit at 3mm circles and 6mm circles. I use the 6mm orbit setting for roughing away the surface grits from 60#->180#, then ill set to the 3mm orbit setting for the finer grits for finishing. I usually finish with oils, and mostly I burnish them into the tops from 400# up to a finer grit until i'm happy with the sheen. The weight of the machine itself is enough, you dont need to add any extra weight via your arms/shoulders.

thanks mate, but i never use pressure. I have serious arthritis and rotator cuff problems in both shoulders and just holding the tools is painful so I do most things in small bites. On the surgery wait list for a series of big deal spinal surgeries which will solve some of my problems but not shoulders yet.
cheers

[mark david]

Yeah, tell me about it!

Have had the same problem, first off 40 grit is way to coarse on almost any timber, maybe ok if you need to get rid of loads of paint or varnish you are better of with a minimum of 60 but preferably 80 grit to start with even 120 grit is pretty coarse and leaves bad swirl marks.you need to be meticulous going down through the grit grades 120 180 240 320 and so on.Realistically no amount of sanding with super fine discs will get rid of the marks left by the coarser discs if you try to rush it.

Be sure to regularly examine the discs as clogged portions can leave really bad swirl marks.
If you are starting out with machined timber I would generally not go any coarser than 180 to start with.

I restore a lot of low end furniture and regularly need to resand surfaces and dont worry too much about getting the best finish, usually the swirl marks are invisible until you apply a stain or finish and they magically appear.

Interestingly I have handled a lot of commercially mass produced furniture that has these swirl marks in the timber ?
What
I think the best advise is don't start with a coarser grit than you need too you will just spend more time trying to get rid of those marks.

[Shedhand]

Hard to say really without pics, maybe you have too high standards. I have exactly the same Metabo by the sound of it. Just with each grit I sand until the circles of the previous grit are completely gone. There are, of course, new circles from the new grit, but they are fainter and fainter as you go higher with grits. Once I go to 1k grit, and then finish with oil, I cannot see any circles... What sequence of grits do you go through?

If rough sawn - 40/60/80/100
Else
120/150/180/240/320/400/500/600/800/1000/1200/1500/foams from 2k to 4k.
Then wax or wipe on poly.

I do have high standards and get properly rewarded for it
cheers.

[Arron]

The Elu marks are still evident but faint except now I have the problem of the little circles from the ROS with 40 grit disc. I kept at it and went through 60, 80, 100 and 120. Can't get rid of the circles. every grade up to 120 leaves them behind

Yep, thats what I find - every grit 120 and over on an ROS leaves little spirals behind. I'm sure you could get rid of them if you sanded deeper with every grit, but if you have stuffed shoulders (me too) then who wants to do that ?

Realising this limitation, I use drum or big boy sanders up to 180 or 240 grit, then just a quick once over with 240 and/or 320 grit on the ROS, usually followed by 400 (just cos I like it, it plays no useful role in the finishing process).

240 grit doesnt leave spirals.

I think thats how these tools were designed to be used. Think cabinetmaking workshop - think efficiency - drum and stroke sanders for most of the real work, an ROS for just the finishing off. Trying to finish from 40 grit down on an ROS is an abberation. Possible, sure, but inefficient, not what they are designed for and you should treat your body with more care.

Regards
Arron

Ps. Nice fish in your avatar. Bluefin ??

[Shedhand]

Yeah, tell me about it!

Have had the same problem, first off 40 grit is way to coarse on almost any timber, maybe ok if you need to get rid of loads of paint or varnish you are better of with a minimum of 60 but preferably 80 grit to start with even 120 grit is pretty coarse and leaves bad swirl marks.you need to be meticulous going down through the grit grades 120 180 240 320 and so on.Realistically no amount of sanding with super fine discs will get rid of the marks left by the coarser discs if you try to rush it.

Be sure to regularly examine the discs as clogged portions can leave really bad swirl marks.
If you are starting out with machined timber I would generally not go any coarser than 180 to start with.

I restore a lot of low end furniture and regularly need to resand surfaces and dont worry too much about getting the best finish, usually the swirl marks are invisible until you apply a stain or finish and they magically appear.

Interestingly I have handled a lot of commercially mass produced furniture that has these swirl marks in the timber ?
What
I think the best advise is don't start with a coarser grit than you need too you will just spend more time trying to get rid of those marks.

Thanks mate, I start low on rough sawn stock as I don't have a thicknesser or jointer. If I have dressed stuff I start around 180 (hardwood) or 240 (softwood). I keep the Ros pads clean and pick the nits of the back of the discs.

[Shedhand]

Yep, thats what I find - every grit 120 and over on an ROS leaves little spirals behind. I'm sure you could get rid of them if you sanded deeper with every grit, but if you have stuffed shoulders (me too) then who wants to do that ?

Realising this limitation, I use drum or big boy sanders up to 180 or 240 grit, then just a quick once over with 240 and/or 320 grit on the ROS, usually followed by 400 (just cos I like it, it plays no useful role in the finishing process).

240 grit doesnt leave spirals.

I think thats how these tools were designed to be used. Think cabinetmaking workshop - think efficiency - drum and stroke sanders for most of the real work, an ROS for just the finishing off. Trying to finish from 40 grit down on an ROS is an abberation. Possible, sure, but inefficient, not what they are designed for and you should treat your body with more care.

Regards
Arron

Yes, I dream nightly about a big fat drum sander after a day finishing .treat my body better? That's what my surgeon said as he was booking me in for some heavy duty spinal work.
cheers mate.

[Arron]

Yes, I dream nightly about a big fat drum sander after a day finishing .treat my body better? That's what my surgeon said as he was booking me in for some heavy duty spinal work.
cheers mate.

Yes, I did realise you are probably not in the market for a drum sander at present - I was really just pointing out how these tools are really designed to be used, and why results might be sub-optimal if used in any other way.

I guess you missed my question about your avatar.

Arron

[FenceFurniture]

Yairs, it gives me the irrits too. There is a "sweet speed" at which to move the sander back and forth, and it's something to do with the speed of the orbit and rotation. Moving very slowly seems to be reasonably ok, and quite fast movement is better still (I'm using an ETS 150/3). So, I do the hog work with the first chosen grit, and then at the end of the grit I make sure I cover the whole surface with fast strokes and quite a few of them with the grain, not across it. If you think about it, the little swirl has to be elongated with a much faster stroke, and therefore more like a straight line.

I think that the sander speed (the machine speed) also has something to do with it, but I'm buggered if I know how to work that out. Someone like BobL may be able to calculate what's going on.

The problem is that with the coarse grits the timber surface is still matte so they can be damned difficult to see. Shining a light at just a few degrees off the timber surface helps to show them up.



Today I was working with Huon, and after getting swirls in much harder Blackwood a couple of days ago I thought I'd better try something different as it could be horrendous on Huon. On the Blackwood I had to re-do a whole corner after finishing at 3000. Didn't see the rotten little blighters until I moved the board "just so" under the oblique light.

I started with 80 to get rid of the ridges from terrible jointing the timber seller had done. In retrospect I could have started at 120 because they just vaporised at 80 grit. I'm too used to nasty hardwoods I guess. After the 80 grit I spent much more time with the 100, 120 & 150 than I usually do (I don't seem to get swirls from 150 up).

SUCCESS! There were still a couple of very small ones, but I'm afraid the answer seems to be spending more time with the coarser grits and increased sander movement speed (and the grit upper limit will depend on your sander and sander speed).

HTH
Brett

[Shedhand]

Yep, thats what I find - every grit 120 and over on an ROS leaves little spirals behind. I'm sure you could get rid of them if you sanded deeper with every grit, but if you have stuffed shoulders (me too) then who wants to do that ?

Realising this limitation, I use drum or big boy sanders up to 180 or 240 grit, then just a quick once over with 240 and/or 320 grit on the ROS, usually followed by 400 (just cos I like it, it plays no useful role in the finishing process).

240 grit doesnt leave spirals.

I think thats how these tools were designed to be used. Think cabinetmaking workshop - think efficiency - drum and stroke sanders for most of the real work, an ROS for just the finishing off. Trying to finish from 40 grit down on an ROS is an abberation. Possible, sure, but inefficient, not what they are designed for and you should treat your body with more care.

Regards
Arron

Ps. Nice fish in your avatar. Bluefin ??

sorry mate, missed the ps. From memory it was a foul day down around Tasman Island. I think we got 4 Yellowtail Tuna and 3 Bluefin. Kept one of each and put the big ones back. The yellowtail in the avatar was about 25kg from memory and we got a 40 kg bluey.
cheers.

[Ilya]

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.

[FenceFurniture]

I still don't understand the source of the problem.

Hi Ilya, it's swirl marks from the coarser grits only, and probably the starting 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....