RTS 400 - control issue

[rljatl]

On higher settings it would behave erratically, jump around and stutter. 

Ok, let me say I am not doubting you but I am curious as to why this lack of power would translate into a jumpy stuttering machine.

Here's why from the Festool FAQ linked to by Alex above - I take this to mean the brushes do not make good contact and therefore the motor receives intermittent power.  Not really a power line problem, but I think you get the idea....the jumpiness is caused by the motor fluctuating during use.  Similar to a car engine with a bad fuel pump.  The car will buck as if it is starting and stopping.

"All Festool 120 volt power tools use brush-type universal motors with self-seating brushes. These brushes are serrated on the surface with narrow triangular grooves. The grooved texture of this surface needs to be worn down to the solid carbon substrate before the tool will reach peak performance. This is called the break in period. During this break-in period the brush takes on the same cylindrical shape that perfectly matches the curvature of the spinning armature, resulting in full contact. Some of our tools need to be run for as long as 10 hours before the brushes take on this shape and the motor develops full power. Your sander will be susceptible to power line fluctuations during this period and may not run at a constant speed."

 

[AlexThePalex]

I read the link in your post earlier (Thank you, I had never read this before) which has lead to the questions I have as to why lack of power creates a mechanical(?) problem.

It's all about overcomming the friction between the surface of the workpiece and the sandpaper. This requires a lot of force, that's why these small sanders run at 10.000 rpm. If you lower the rpm enough the sander will not have enough power to overcome the friction with the surface anymore, but come to a halt.

Now if the power fluctuates, one moment the sander will have enough power to overcome friction, and the next moment it won't. We're talking split seconds here. This makes for a very erratically behaving sander.

 

[Len R]

This is a very educational discussion, but the explanations offered do not address why my ETS125 required no break in period at all, and the RTS would need 8 to 10 hours to "calm down".

Thanks,

Len

 

[AlexThePalex]

This is a very educational discussion, but the explanations offered do not address why my ETS125 required no break in period at all, and the RTS would need 8 to 10 hours to "calm down".

I guess not all sanders are equally affected. Sometimes the break in problem is very apparent, and other times it's not big enough to be noticed. It's a lottery.

 

[oldie]

The ETS125 is a random orbit sander.  The RTS/DTS sanders are direct drive. 
Maybe the ETS pad has more momentum, thereby 'disguising' any reduced
power during the transistion period??  [unsure]

Richard UK.
(edit: replaced one word.)

 

[Scott B.]

I think this might be a matter of the RTS being larger than the picture frames being sanded.

It is always better for the surface to be larger than the sander. If not, hand sand.

 

[Rick Christopherson]

There is no need for any sander break-in. Not for the Rotex. Not for the ETS. Not for the RTS. There is nothing to be gained by it except for wasting 8 hours of your brand new tool's life. This myth started here on the forum because someone mistakenly believed that the Rotex drivetrain needed to be broken in, but somehow it has now morphed into the RTS sanders which are direct drive without a drivetrain. To put it to rest once and for all, it is now listed in the manuals.

[attachimg=1]

 

[oldie]

Agree with Scott B. 
Also reminded of comment made by Alex (I think) once upon a time. 
The RTS can, to some, seem a bit 'tippy' when moved side to side -
better to move sander in line with it's length - hope the way I expressed that
makes sense??

Richard UK
(edit:  My post overlapped with Rick's.  Must say that my RTS, DTS and ETS performed
quite satisfactorily from the get go - I wouldn't know if there was any improvement over time. 
If I bought another, wonder if now that I'm aware of this 'myth,' whether I'd perceive some initial 'power' loss?? [blink])
(2nd edit:  removed duplicated word)

 

[AlexThePalex]

Well, my brand new DTS400 was complete crap when I bought it. I already had the DS400 for a year and the RTS for 2 years. So I knew exactly how these sanders should work. The DTS was like a stumbling baby and I saw it come to life through use over the next two weeks. Two painful weeks, I might add. Now it runs very well.

And yes, that was me about the tippy RTS, the biggest reason why I don't like it very much.