Thread: Metabo Duo Thoughts?

What price are the new turbo Duos over there? Waldo reported that he had used both the duo and the new turbo duo and thought the new one was far better. No mention of fine scratches though. What are you using at the moment and what final grit paper are you using? Dry or wet sanding?

I use a metabo duo and it is a very good tool. On fine setting gives avery good finish and on the courser setting pretty well hogs off the material. Only fault is the lack of any indication of what you are set on when you pick it up.

Haven't had any problems with the Metabo Duo Turbo leaving any fine scratches, it's oscillating action negates this problem and going through to finer grits naturally gives a better finish.

As a point to demonstrate this I sanded down a cheapo pine bed or my daughter, even at only sanding at 240 grit I had no swirls in pine. I went from 240, 320 and 400.

Sounds promising Waldo
The new model isn't available here ( Japan ) so hoping the old one is a ripper! I've heard a lot of good things about it.

I'm using two festool sanders shock horror, yes I have been getting scratches with them (half sheet, and ro150)
I've never experienced this problem to such a degree before (my previous sanders were Makita's).
I've tried everything to rid the work of scratches, and haven't succeeded (vac control, different paper, I sand up to #400, going through all the grits, motor speed, slow controlled motion, keeping the sander flat etc etc...) I have quite a bit of experience woodworking, and the sanding that goes with it, and I'm sure my technique isn't the problem.

I read an article recently that said some brake pads on ROS's restrict the random movement of the sander, and that's why some scratch more than others
Cheers

Hi all,

i have found during lots of practice hours that scratches in the finish can be kept to a minimum by watching:
1. the quality of the abrasive
2. the wear and soiling of the abrasive
3. the working pressure on the abrasive
4. the ways of getting rid of debris and the soiling of the machine
5. the vibration of the machine

1. when you would examine sanding paper under a microscope, you would see a mass of sharp rocks of reasonably similar sizes, glued on paper or linen. This is not like a smooth brick or cobble road, but rather like a raked surface of sharp pointy pebbles. The points sticking out the most make the deepest scratches, until they wear or break off. Points sticking out also transfer more of the working pressure from the machine through the sanding paper to the workpiece surface, than the more receding points around protruding points do.
Furthermore, like individual hairs letting loose from cheap paint brushes, abrasive grains can become unstuck from sanding paper. The cheaper the paper, the cheaper the glue and the munfacturing process, the sooner the grains may let loose. High pressure and vigorous handling will break out grains even more quickly. Loose grains will roll between the abrasive surface on the machine and the workpiece. They are real pressure points and bite hard into the workpiece and are often responsible for the deepest scratches.
You will probably have heard the theory that you can stand on two layers of glass without breaking them, when their surfaces are clean and the pressure is divided. But you can easiliy break the glass when a grain of sand is trapped between the panes, concentrating the pressure on one point, like a glass cutter does. So a good quality brand of abrasive materials will provide a strong bonding of the grains and a more careful grain gauge selection (making sure that most grains are e.g. truly 120 gauge and not somewhere between 110 and 130). Cheap paper looks like sticky paper sprinkled with grains. More expensive paper or linen looks like a layer of grains smothered in bonding material, a bit like peanuts covered in chocolate.

2. worn abrasives loose their bite, because the sharp points on the rocks are broken off or rounded, as it were. To get some more effect out of that particular piece of sanding paper, many people resort to heavier leaning on the machine, making the grains bite better into the material because of this pressure. Sometimes i'm amazed how long folks can keep this up. You hear minutes of sanding going on without a break, with just that same tired piece of paper. It must be dull as an eggshell and dollars worth of service hours are pressed out of an expensive machine to save some cents on sanding paper. There is a lot of friction heat and because the scraped off tiny wood curls are reduced to specks of dust because of loss of bite, the paper clogs and clumps of compacted wood dust accumulate between the grains. Once in a while these clumps also let loose and they are squeezed and rolled between the sanding plate and the workpiece. That can't possibly give quality results.
Fresh sanding paper with biting grains has a distincitive shshshsh-sound, which can be heard clearly when the machine itself is not too noisy. When the bite wears off, so does this distinctive sound. A stroke with the palm of the hand along the grain surface will also tell if the grains have gotten blunt and smooth.
The bite can be prolonged somewhat by holding a fine steel brush against the grains while running the machine. This will loosen accumulated debris and freshen up the grains a bit. This works one time only, after that it's time to replace the paper.

3. for most sanding machines, the machine's own weight is enough pressure on the abrasive material. 1/3 sheet orbital sanders are somewhat in the region of 150 to 300 Watts and weigh 1 to 2,5 kilo's and 1/2 sheet sanders have 300 to 600 Watts and weigh 2,5 to 4 kilo's. There is a clear relation between these figures and sizes. Palm sanders could manage with 100 Watts, but daily real world applications have shown that, when firmly gripped in a fist, these machines invite to "get on with it" and are often treated fairly vigorously, so they are rather fitted with 200 watt motors. Random orbital sanders have complex motions and can have much more abrasive effect in some settings, so they also have heavier motors (450 to 750 watts). A belt sander with a contact surface of abrasive belt of about 110 x 160 mms, moving with 250 to 400 metres per second, needs a 1000 Watts plus motor to pull the abrasive along between the workpiece and their own weight of 6 to 9 kilo's.
The grain bonding of abrasives seems to have been optimized for this philosophy. Higher pressure on the machine will result in larger forces on the grains and glue, which will pry loose the grains sooner. Just as a loose tooth; when wiggled it can be wrenched out of its socket sooner. In the Netherlands, dikes along choppy waters are often reinforced by stones. When a few stones are pried loose, the sand around and under them will be attacked and more stones will be loosened. When the first one is gone, the ones around it are compromised. On a cheaper grade of sanding paper used vigorously, bald patches without any grains can sometimes be seen. Those are areas where the grains have all been pried loose; even the glue has gone. Many of these loose grains will have generated scratches.

4. getting rid of the debris between the abrasive material and the workpiece is therefore important. Punctured sanding paper and suction holes in the machine's base plate are an ideal way of achieving this. Powerfull suction is also a real help. Regular users of sanders will know that machines with built in dust suction fans will soil themselves. However good dust seals in ball bearing are claimed to be by manufacturers, ball bearings in dust laden air streams are known to fail sooner or later, by lubricant being sponged out and dust working its way in. Machines with vac attachments, drawing away dust through channels far away from well insulated bearings and drives, are still the most reliable and durable solutions. With loose grains and clumps of debris sucked away as soon and effectively as possible, there is far less chance of scratching. Should dust suction not be available, then regular time-outs are handy. Sand a bit and stop to brush clean the surface and continue sanding again for a bit, etc. Every tiny bit of sharp dust that is removed before it can roll and scratch, is a bonus. A clean sanding machine is always a good start. You are bound to compromise your results when you take the risk of grinding the dust cakes gathered on the machine from previous jobs, into your current workpiece. I clean my sanding machines with compressed air, after every job no residue it left from the material that has been worked on. Clean machines are also a greater pleasure to work with.

5. i have found that vibrationfree running of a sanding machine results in a steadier and less bouncier interaction between the abrasive and the workpiece. A cheap rattly sander shudders and thumps along, a steady sander slides along. This is easier on the paper and the wrists and less agressive on the wood grain.

Long story, that's always my weak point. But after that, the conclusion can be brief. It doesn't necessarily have to be a Festool or a Rupes or a Metabo, but it helps if the machine is well built and vibrationfree and if it is used with a bit of care. Use good quality abrasives, do not wear them down to a minimum and always keep the workpiece and the tool clean. Change paper a bit more often, do not force too much effect out of it to gain a few cents. And choose the right moments to change from 120 to 180 to 240 to 400 grit. If need be, you can even do the final stage with a cork block manually. This whole story has saved me many a scratch over the years. My favorite machines are the Makita belt sanders, the Elu MVS47 and MVS71 orbitals (now DeWalt 636), the medium size Festo orbital sanders as well as a Fein and Rupes type, the old 150 mm Festo ROS but also the Metabo 475 Watts ROS, the Milwaukee and Festool RS400 palm sander and the Fein triangle sander. All these machines run marvelously and steady as tanks, and the ones i own have done so for many years.

regards

gerhard

Thanks Gerhard,

I've made a few of the mistakes you've mentioned. That's good info.

Regards, Kev

Excellent post once again Gerhard

Thanks Gerhard! You're a wealth of knowledge!

I've been using festools paper, among others.
I don't sand with downward force, but the swirling remains I've followed all the recommendations from festool. As I said before, this is the first time I've had the problem this consistently. I'm wondering whether the random movement isn't so random I've pretty much come to the conclusion, it must be the sander and thus, I'm looking for something else
Thanks!

Good morning undie, I have Metabo ROS too and I think it is a great machine.

Afternoon Wongo

WonGo, have you noticed and swirlies on the table tops you've made (I know you've made a few)
If I Put a light next to the table and move around it, looking at different angles, I see the swirlies. My wife even noticed them, on a door panel, for a commissioned cabinet I'm building...she's given me the word, to get it sorted I don't want to go back to the old 5" Makita, although it didn't create all these swirlies.

My Orbital half sheet pigtails, but I think they all do a bit (maybe not rupes).
cheers!

Yes, I have made a few and I am making a couple at the moment.

I have never noticed any scratches (pig tails??) on the surface. Sometimes if I was really picky I would finish it off by hand.

I will have a look at the tables at home tonight and report back.

I inspected a couple of desks, coffee tables, hall tables and cabinets tonight. There were deep pencil marks made by the children but nothing by the sander.

So it is good to go undieused.

Wongo, thanks for having a look
Sounds like it's got to be a Metabo then
The new type isn't here yet (if ever) , but the old Duo sounds good
When I bought the ROS I have now, I hesitated and nearly got the Metabo...should have went for that by the sounds of it.
Cheers for the help!

Great input Gerhard!
I have a Bosch PEX400. Still learning to use it properly but so far I like it.