Thread: ETS 150 sander going off course due to the "jagging" phenomenon

Posted in wrong forum. Moved to right one!!!

Thanks for that Brett (TTS). I may give you a call at some stage.

I also have a thread running on FOG, and was urged to do a few tests to try to eliminate as many factors as possible. The results of that were as follows:



Ok, have done a few tests.

The 17 hole disc was 220 grit Rubin 2 (brand new out of the drawer), and what I refer to as the microhole disc is a Jöst 220 grit (brand new out of the drawer). it has a couple of hundred or more holes that are 1½ to 2 millimetres in diameter. The back of it is only very marginally softer than the Rubin back.

I sanded four different pieces, with and without dust extraction (either full suction or off). The DE made no difference at all.

Using a "Hard" pad on the sander.
Sander speed just less than 5.

Results are:
The original piece of hardwood (4½" wide so the sander overlaps the edges by 3/4" each side) - same face as the previous 8 kilometres
microhole disc - smooth ride (with and without DE)
17 hole disc - moderately rough ride (with and without DE)

That piece of timber does not have lumps and bumps, just a bit of cupping from all the previous sanding.

The reverse side of the hardwood - straight out of the thicknesser - flat as a tack
microhole disc - smooth ride (with and without DE)
17 hole disc - much rougher ride (in fact quite difficult to control the sander - seriously) (with and without DE)

Piece of softwood (Mango root) - straight out of the thicknesser - 10" wide
microhole disc - smooth ride (with and without DE)
17 hole disc - moderately rough ride (with and without DE)

10" wide piece of MDF
microhole disc - smooth ride (with and without DE)
17 hole disc - moderately rough ride (with and without DE)

As I slowed the speed of the sander down the ride did become a bit smoother, but was still not the same as the microhole discs where the speed made no difference - smooth all the way.

Changing to the "Soft" pad and using the same discs and timber pieces:
This diminished the roughness of the ride quite a bit. I will only show results for the 17 hole disc (microhole was tested - all smooth).
The 8km face of hardwood - noticeable, but not too bad
The flat face of the hardwood - quite noticeable
Softwood - only barely noticeable because i was looking for it - nothing to complain about
MDF- only barely noticeable because I was looking for it - nothing to complain about


So, after that:

• I know that the hard pad exacerbates the rough ride quite significantly. Yesterday I changed to a brand new hard pad - identical rough ride.
• Hardwood exacerbates the rough ride
• Dead flat hardwood results in an even rougher ride (hard to control the sander - came close to out of control at one point)
• Dust extraction power makes no difference at all

I may get to the bottom of this tomorrow. I'm going to a mate's place and he has the same sander. I will take with me the same piece of timber that has been the most problematic, my sander, and the testing discs that have been jagging. If his doesn't do it then clearly my sander has a problem - if his does it as well then I think I can be assured that there is nothing at all wrong with the sander - or we both have faulty sanders (highly unlikely).

Originally Posted by FenceFurniture

So, after that:

• I know that the hard pad exacerbates the rough ride quite significantly. Yesterday I changed to a brand new hard pad - identical rough ride.
• Hardwood exacerbates the rough ride
• Dead flat hardwood results in an even rougher ride (hard to control the sander - came close to out of control at one point)
• Dust extraction power makes no difference at all

Based on your summary here's my explanation.

a) A hard pad would not flex as much as a softer one so even the slightest tilting during movement of the sander will tip the sander onto its outer edge more than a soft pad which would lead to greater jagging. Tilting a softer pad will still distribute the contact area across the disc so that the forces generated are not as uni-directional.
b) Hardwood V softwood is probably the hardwood having higher friction which exacerbates a)
c) flat hardwood just allows the sander to make even more contact with a smaller point on the rim and skate off more easily.

The same thing happens with large rotary floor sanders and polishers

Originally Posted by BobL

Based on your summary here's my explanation.

a) A hard pad would not flex as much as a softer one so even the slightest tilting during movement of the sander will tip the sander onto its outer edge more than a soft pad which would lead to greater jagging. Tilting a softer pad will still distribute the contact area across the disc so that the forces generated are not as uni-directional.
b) Hardwood V softwood is probably the hardwood having higher friction which exacerbates a)
c) flat hardwood just allows the sander to make even more contact with a smaller point on the rim and skate off more easily.

The same thing happens with large rotary floor sanders and polishers

That's how I see it at the moment Bob, but there is only one way to eliminate the sander being the problem. In talking to that mate this morning he seems to think he had a similar problem sanding some Jarrah a while ago.

In keeping with your thoughts re floor sanders, I fooled around with putting pressure more towards one side and then the other as I went left and right. This did create less jagging but would be very difficult to do every stroke all the time, and even more fatiguing. It also caused points where the sander skimmed across the job too easily (reducing the abrasion of course) and this would no doubt be due to varying the pressure.

This would not be a desirable way to sand.

One other factor that I'm not if I mentioned before: the jagging can be become less as the disc gets more used/clogged.

Something that might be worth knowing. A few months back FF tried to hard burnish his work bench. This involves a considerable amount of wet and dry sanding. I assume he used the ETS 150/3 to do this. Was there any rocking and vibration from the sander then?

I wasn't using 17 hole discs for that.

Ok, this morning I took my sander, the same discs that I have been using, and the piece of hardwood to another workshop for comparison with another ETS 150/3.

I'll let the other chap make his observations (which may not be for a while due to work commitments)..

Today I received a Klingspor backing pad "Medium" to suit Festool sanders. It is slightly softer than the Festool "Hard" pad, but nowhere near as soft as the Festool "Soft" Pad.

I tried about a dozen different papers on the three pads (an aggressive 80 grit, 5 different 120 grit, 3 different 180 grit, a 220 grit, and a 320 grit.

The Festool Hard pad jagged in the same way as previously reported (unpleasant).
The Festool Soft pad was much more friendly (also as previously reported).
The Klingspor Medium pad showed slightly less jagging than the FT soft pad, and significantly less then the hard pad.

Overall the jagging was not as bad as previously with the very same abrasive discs (on the FT hard pad), and this would be because the discs are becoming more and more worn out. I observed this over the course of the testing - I referred back to my notes and in most cases where the jagging was present it became smoother as the disc usage went on.

I will do some more tests using brand new discs.

It would be interesting to see how a Klingspor "Hard" pad performed (in fact I thought that was what was coming).

As an aside, I noted that the K pad had more dust on the pad itself than the FT pads, and the 17 hole discs had fairly significant dust on the back of them, as opposed to being almost totally clean when they come off a FT pad. The dust was collected around the central 60mm of the discs.

While pottering around, something occurred to me.

A sheet-sander will shoot off in some direction if it's 'rolled' slightly in one direction or t'other, so one edge bites more than it's opposite. How far 'n fast depends on the degree of 'roll' AND the grit size, wear, etc. of the paper...

What if the disk on a ROS is skewed so it's plane is not perpendicular to it's axis? eg. it had been dropped on one edge of the disk? Because the disk rotates as well as oscillating, the direction it wants to shoot off will also be rotating, causing circular 'jags.'

In use, the disk will want to sit flat on the wood and the body will want to precess at a rate governed by the disks rotation speed. It may manifest as a slow vibration. Holding the body tightly to prevent this, will cause the disk to no longer lie flat, thus jagging. The natural impulse to such a jag would be to hold the body tighter, which would make the jags worse!

Sound reasonable? Easy enough to check whether it's valid reasoning or not... just get Brett to try again with the same grit on the same piece of wood: one trial holding the ROS as usual and the other using the ol' "just guide it along with two-fingers method." If there's any validity to my reasoning, any differences should be quite apparent.

Then again, all the turps & paint fumes I've been breathing lately may just have loosed the unicorn-riding goblin in my head again.

Skew, that's very much in line with Bob's floor sander theory.

I have actually just held the sander by the power lead and let it do it's thing, and is still occurs. Can't really say if it was any worse or not because I couldn't "feel" it.

Moreover, that wouldn't explain why the other sander also did it in exactly the same way (although it did have my hard pad on it). But I've also changed to a brand new hard pad (Festool) and it was exactly the same.

And then we have the Klingspor "Medium" pad (marginally softer than the FT hard) giving a better ride than even the FT Soft pad (which was much smoother ride than the hard pad, but still noticeable).

So, thanks, but it appears to be inherent in the Ft pad I think. I have narrowed it right down I believe.

Just waiting on the other sander operator to make his observations.

Have you tried contacting the Festool Owners Group? I believe that there are a few Festool employees on there and they may well be able to help you resolve what seems like a very unusual problem.

Here is a link to a video that I just took.
https://dl.dropboxusercontent.com/u/...agging0005.AVI

I have others, but haven't uploaded them at (this point anyway). The first disc is Festool Granat 320 on a piece of MDF, the second is a Jöst 320. They were both as good as new - had only less than a minute running time from some previous vids that I took.

So, am I to be believed now? Or am I capable of some other magic feat when I'm not even touching the sander, and with both hands clearly in view?