Sanding Pressure and Technique?

[onocoffee]

I've seen a couple of videos where Sedge was talking about extractor pressure as it relates to sanding. My take is that Sedge recommends setting the extractor to the lowest setting to "break surface tension." I really don't know what this means truly. I just have been following along in the vein that others know better than I do.

This summer, when I was using a friends ETS EC 150/5 connected to a Rigid vac, I did notice some swirls (after finishing, of course). This I've been attributing to "too much" suction and have been keeping my own CT MIDI I on the lowest setting. But is there anything "bad" about this?

I'm wondering because I've been rough sanding (P40 Rubin 2) some 3/4 underlayment plywood that has been out in the elements for the past six months and it's covered in dirt, grime and kinda black oxidized. I've been sanding it just to clean that off. My plan is to use the ply to make rolling carts for shop equipment and then stain it dark so you really won't notice imperfections. I'm using my ETS EC 150/3 but have noticed if I pump up the vac to Full Blast, it will remove the grime a bit more quickly. Are the downsides of this (full blast) mainly swirl marks (which would be unsuitable for fine sanding)?

Thanks!

 

[Lincoln]

I find just over half suction is the right balance between avoiding swirls but maintaining dust extraction.

 

[makpacman]

That's a project moving up my list quickly. The downsides of too high suction for me have been swirls and/or difficulty controlling the sander depending on the material.

If we're talking full sheets of ply and the job's going much faster, that sounds like an acceptable tradeoff given the project. One which I'll keep in mind in fact.[wink] Also, I'm usually able to remove or lessen swirls with a very quick pass or two on the proper setting. Might still be shaving time, even doing that.

 

[bobtskutter]

I have a Rotex 125, ETS125 and DTS400.

If I'm sanding old, dirty, damaged material I use the Rotex with the vacuum at maximum and an 80 grit disk.  Because I want to clean it up quickly with minimal dust, I'm not worried about swirls.

If I'm sanding a finished workpiece I use the ETS with the vacuum set lower, by opening the vacuum breaker valve on the Festool hose, and 120/180/220 grit.

The DTS400 is used for awkward situations (corners) with the vacuum at the lowest setting.  This sander likes to stick to the workpiece if the vacuum is too high.

My ETS125 has little holes in the top of the sanding pad to limit the amount of pressure on the workpiece.

I get the worst swirl marks from the Rotex on soft material.  The Rotex is also very "jumpy" on soft material.
The ETS125 kinda glides over the surface.
The DTS400 is hard to control if the vacuum is too high.

Regards
Bob

 

[hdv]

I recently extended my workshop and from that had a number of left-over underlayment sheets. Just like you, I planned to use them for cabinets and stuff like that in the shop, where you wouldn't be bothered by the lesser quality of underlayment compared to regular ply [1]. I my case I built lots of systainer cabinets from the underlayment. I sanded the faces and edge-banded the front edges that were visible. The result isn't bad at all.

However, when I was sanding them I noticed something: the surface of "modern" underlayment has a lot of deficiencies. The surface veneer is cut much more roughly and the wood itself is much more prone to tear-out of larger strands of wood, not just fibres. This results in places where you'll see lots of peaks and valleys in the surface following the grain (sorry, I don't have a better way to describe it, but it is not just a roughness of the surface). When sanding you'll find that in such places your sander will be much harder to control due to the increased loss of suction through those "valleys" compared to the better spots. This difference increases when you turn up your vacuum. Making it even harder to keep the speed and pressure constant during sanding. For rough sanding with course grids that won't be too much of a problem, but when you get to the finer grids I would definitely turn down the vacuum. Not just for the swirls, but also to make the whole business of sanding such large surfaces a bit more pleasant. Your sander will jump around a lot less. It will also mean you have to spend less energy yourself.

Sorry for the long-winded answer. Just thought I would share my experience.

[1] Which has gone down a lot in the last couple of years, by the way. I compared it to some pieces I still had left from when I built my workshop about a decade ago. What a difference!

 

[peter halle]

Years ago when Festool had their End User Training classes they would demonstrate what they thought at the time was the best approach to achieving the optimal compromise between suction and sanding performance.  It went basically like this with a finish sander:

1. With sander going turn extractor to max suction.
2. Listen to sander rpms - they should have dropped
3. Slowly turn the suction down and listen to the rpms increase
4. When the rpms just reach their max that is what they considered optimum.

At that point your sander should basically glide over the surface and the user is pretty much just guiding the sander.

Time has passed since those classes and perhaps there are different ways but this is the approach that I use except for edges where I too will use max suction for edges narrower than the pad and paper.

Peter

 

[onocoffee]

Thank you all for sharing your experiences.

[member=66485]hdv[/member] The underlayment I'm using is definitely as you described of modern ply - peaks and valleys is a good description. It is very much "rough terrain" on some surfaces. One of the cuts I'm going to use as a top, which I would like to be a little smoother, so I'm planning on borrowing a friends RO150 to take it to task.

[member=1674]Peter Halle[/member] - I will try that technique of listening to the rpms. I have found that the ETS EC 150/3 at full speed, with the lowest suction on the CT MIDI I, truly glides on the surface while producing great results.

 

[woodferret]

Pressure down on the pad eventually wears out the bearings.  There are makerspaces full of sander killers because of this.

 

[Sparktrician]

 

You might want to watch this video in which Larry Smith talks about swirl-free sanding.  And as Sedge often says, "Let the tool do the work!" 

 

[onocoffee]

[member=7493]Sparktrician[/member] Wow, that was a good video. Didn't realize you could use Rotex mode the entire way. Thanks!

 

[leakyroof]

[member=7493]Sparktrician[/member] Wow, that was a good video. Didn't realize you could use Rotex mode the entire way. Thanks!

  I've never used my Rotex Sanders this way, but Warner Contruction member swears by it in some of his posts years past. As far as vacuum, sanders, swirls... The grit of the Abrasive you're using, the grain of the wood you're sanding, is it open pore or tight pore,  those too are needing to be taken into account for how much Vacuum to apply/allow with your Extractor.