CNC Random Orbit Sander

[krtwood]

This is an idea I've had kicking around for a while but hadn't gotten around to trying.  The mount I came up with is dead simple and it kind of works.  Okay, most situations no matter how good the cnc is at moving around a sander it's not going to be as efficient as doing it yourself.  But the use case I see is somebody batching out end grain cutting boards that take a lot of sanding.  If you've already got a cnc and two sanders it's kind of a no brainer to spend less than an hour and use parts you probably already have and let the cnc do the bulk of the coarse sanding for you while you do the rest.  It doesn't have to work perfectly in that scenario.

 

 

[wtnhighlander]

Very interesting. Great 'out-of-the-box' thinking!

[wdwerker]

 Fun approach to automating a boring task !

Hooking up the dust collection hose & using full suction might stabilize the wobble. I've also found my ETS-150 doesn't dance near as much as the Bosch sanders I used to use.  Only drawback is they recommend using much less suction on RO sanders to reduce the heat which wears out the $45 velcro pads. 

[krtwood]

3 hours ago, wdwerker said:

 Fun approach to automating a boring task !

Hooking up the dust collection hose & using full suction might stabilize the wobble. I've also found my ETS-150 doesn't dance near as much as the Bosch sanders I used to use.  Only drawback is they recommend using much less suction on RO sanders to reduce the heat which wears out the $45 velcro pads. 

I had an ETS 125 in the past and I would put that Bosch very close to it ergonomically.  I always had problems with the Festool leaving swirl marks that got progressively worse.  No problems with the Bosch.  You can see in the video when I put my finger on it the movement goes away and it runs smooth and I'm not putting any pressure on it, just touching it.

I wanted to start without the hose because balancing the weight of the hose as the cnc moves around is a problem.  I think a 90 degree elbow right off the sander would do the trick but didn't have one handy.  I'm thinking some foam weatherstripping between the sander and the bracket would help a lot.

It's amusing how many people are suggesting to put a lot more weight on it or angle the springs so they pull it down.  Great way to burn up the pad! 

[Chestnut]

38 minutes ago, krtwood said:

I had an ETS 125 in the past and I would put that Bosch very close to it ergonomically.  I always had problems with the Festool leaving swirl marks that got progressively worse.  No problems with the Bosch.  You can see in the video when I put my finger on it the movement goes away and it runs smooth and I'm not putting any pressure on it, just touching it.

I wanted to start without the hose because balancing the weight of the hose as the cnc moves around is a problem.  I think a 90 degree elbow right off the sander would do the trick but didn't have one handy.  I'm thinking some foam weatherstripping between the sander and the bracket would help a lot.

It's amusing how many people are suggesting to put a lot more weight on it or angle the springs so they pull it down.  Great way to burn up the pad! 

Yeah the ETS 125 and ETS 150 are worlds different sanders. I bought the old ETS 125 before they beefed up the motor and released that Pro 5 LTD as the new ETS 125 I returned it 24 hours later. The old ETS never seemed to sand without pigtails. The new one is better but still isn't in the same reality as the ETS150. I use the new one only when the grit is 180 or higher, below that it just doesn't have the power.

It seems like you system doesn't need weight as much as it needs dampening. Like a shock on our car absorbs the oscillating forces generated from the springs. Our hand stops the sander from oscilating the same way you see here. There is a lot of research that goes into these different systems and their dampening. If your curious look up mechanical Q there is also electrical Q but that doesn't really apply here.

[krtwood]

Version 0.4 is perfect.  Just need to teach the cnc not to linger in the corners.

 

[lewisc]

If you do another test, could you put some pencil marks on the timber? This would show how well it sands.

[Chestnut]

Sanding something bigger might help with the corner rounding problem too. Your corner area to board area is quite high with that board. Interesting use though.

[krtwood]

I've got a laminated 2x4 bench top that's about 28"x24", or at least it will be once the last 2x4 is dry enough to use.  Too big for the drum sander so this will be a perfect real world test, as long as I have enough z height to do it.

[wdwerker]

So I'm guessing your drum sander isn't open on one side ? You have a CNC, look around for a shop with an open sided or bigger drum sander. 

But if you start with 40 or 60 grit paper that ingenious rig just might pull it off for you. 

[krtwood]

It's a 10-20 so it wouldn't be able to reach the middle.  I have it set up as close to parallel to the bed rather than up at the end so it would leave a ridge if I did something wider anyway.  I don't do many full furniture size projects so big things test my little shop.

[wdwerker]

I would run it through my 19/38 for you but the freight would be ridiculous .   Your shop is set up for multiples of small goods. It seems to work for you. Bigger jobs just get harder as I get older so I see the appeal. 

[krtwood]

Somebody gave me a link to this slightly more advanced version

 

Btw, I did use it to sand the top for my power carving bench.  It worked out pretty well, though the top has some slots in it and I kind of forgot that it requires some skill to move a ROS over open spaces and not catch an edge.  Which it did, and boy does 80 grit take a bite out of spruce on edge with a lot of pressure on it  Part of the reason for making the bench was so that I wouldn't power carve into my workbench, so I wanted something I didn't care if it got all gouged up.  But I wanted to be the one to gouge it, so I fixed it.  Once I filled in the slots with some blocks it went fine.  Though it did throw the paper off the sander at one point.  I put the paper on with it already mounted in there and I guess didn't give it enough of a smack to fully engage the hook and loop.  So a bit of a problem to walk away from it while it's doing its thing and come back to find it destroying the sander pad instead of sanding.  But the pad is still okay, thankfully.

[Dion]

I've been thinking about exactly this kind of thing to reduce the tedium of finish sanding large panels.

As for the wobble, I connect my vacuum to my Bosch 5" ROS and it doesn't wobble at all. I just let the weight of the sander (plus whatever suction the vacuum creates) do the work, using my hand only to guide it in the X and Y direction. This has the added benefit of maximizing sandpaper life. For flat panels I won't even need a Z controller. I've found twelve passes at 6 inches per second with grits 100, 150, 220 gives me a perfect surface ready for color and topcoat, though I still hold the workpiece up to the light after each grit to make sure the scratches from the previous grit are gone.

[wtnhighlander]

@Dion, I'd like to know what abrasive you use that let's you get by with 6 ips passes!