Aluminium extrusion drum sander!

[Prostheta]

An idea that I've had floating around my head has been to make a fairly compact drum sander for finish sanding and thicknessing. In general when doing precision woodworking, I have relied heavily on precision machinery. Over the years I've seen a number of DIY drum thickness sander builds on YouTube and various forums, all with varying degrees of accuracy, reliability, complexity and the other factors that need considering. Since I am dipping my toes into building various things using aluminium extrusion at the moment, I figured that this would be an interesting way to progress the idea.

I've decided on a few key aspects already based on what I've seen working successful for others. Primarily, these are the method of dust extraction, the way the workpiece is advanced through the machine plus auxiliary functionality like a Sand Flee. Check out this breathless goober for more info on that bit....

 

[Prostheta]

The fence on the Sand Flee also looks like a nice way to joint wood....

The purpose of this thread right now is as a way to collect my thoughts, and rattle them around seeing what suggestions, ideas and improvements come from collective input. Everything is intended to be made from commonly-available aluminium extrusions, leadscrews and other parts that are easy to source from the homebrew CNC and 3D printer market. Those have exploded in popularity, and in general parts are eminently affordable if one looks in the right places.

A choice I am yet to make is in regards to the table adjustment. One common setup is four leadscrews on corners, with height adjustment made on one and transferred around all four via a chain link. Another is for the table to raise/lower on one side with the opposite being hinged, thereby altering the distance between the bed and the drum. This is simpler in many ways, however it does add pressures to the maximum length of workpiece that can be comfortably passed through; straight and on a level is far easier in that respect.

[Prostheta]

Making a drum sander that is open-sided was considered, but I think an entirely-enclosed type would be better for structural purposes. Having the drum mechanism hanging out in the wind requires a lot of gantry stiffness, which often expresses itself through size and weight. I'd like the end product to be something that can be a picked and packed benchtop machine rather than a permanent fixture. On that basis, a maximum drum width of about 40cm seems adequate for the sort of work I do. Finding a drum as a part for an existing machine would be useful, especially if that drum has a built-in tensioning mechanism for the media. Sandpaper stretches, especially over the runs needed by drum sanders, and adhering paper to a DIY drum is not ideal for a number of reasons. I'd like to aim for tenths of a mm accuracy and the ability to adjust the lift mechanism to that accuracy also. Not too problematic in principle.

[komodo]

I didn't even know these existed! Concept is interesting, it's like a table saw vs a radial arm saw.

At first, I was with you wondering how you could build one, and then I watched that video. That dude started going and my eyes slowly turned into pinwheels and there was a brief loss of consciousness. When I came back to my senses, my wallet was out and the confirmation screen said I had ordered 5 units, 50 rolls of different grits, and a whole bunch of extras.

[Prostheta]

HAHAHAHAHA

Yeah, he's got some sort of screen-time mental issues that's for certain. Man, does he speak like that at the dinner table or in the bedroom too? Yeeeeee--ikes.

The idea of the Sand Flee can be incorporated into a drum sander by having a table over the top of the drum with a cutout that exposes the top of the drum whilst underneath it has a rolling bed like a typical thickness sander.

In all fairness, I'm not reinventing the wheel and I'm aiming for what Stumpy Nubs made but constructed from lightweight aluminium:

 

 

I would rather have two motors running the drum and bed rather than a manual advancement mechanism. It makes for a more consistent surface finish without divots across the width when the piece dwells too long or burns when you let it sit/stall. Also, the ability to bolt together and adjust an extrusion-based machine should allow it to be fine tuned if/when it requires. Plywood is heavy, and even though many machines benefit from mass for stability and strength, I think a machine that isn't doing truly demanding work can be made a little leaner.

[curtisa]

I had seen the Sand-flee some time back and always thought it would be impossible to get a flat surface out of the finished timber passing over the exposed drum. The two halves of the table are not at slightly different heights like you'd see on a jointer - the infeed table being lower than the cutting head is what defines how much wood is removed, but the outfeed table being at the same height as the apex of the rotating cutter is what is used to define how flat the cut is. The easy improvement to the Sand-flee would be to make the table in two halves to set the heights appropriately and remove the risk of sanding in divots or a wavy surface.

Not sure how I'd feel running something over the table held by the flat of my hand with a drum of sandpaper whizzing away underneath at a couple of thousand RPM either.

[Prostheta]

Exactly. Shimming the outfeed bed height would be crucial. A safety lamb leg isn't difficult, paper is safer than cutters. I've only ever almost jabbed a finger in a jointer once. Once.

[komodo]

Oh man, I was watching when I saw a girl put two fingers into a jointer in high school. PTSD right there buddy.
Have we ever had a workshop accidents post? Probably a healthy thing to have. My worst by far has been hand tools, and usually used stupidly in a rush.  One sent me to the ER when I cut my finger with a Swedish carving knife, right on the inside of my middle finger joint as deep as you can. yeesh. 

I love the idea and simplicity of the Sand Flee with the improvements by @curtisa.  Can't wait to see what you do Carl.

[curtisa]

7 hours ago, Prostheta said:

paper is safer than cutters

Still, I reckon the potential for a pretty nasty friction burn, abrading the outer layer of skin from your palms or a pinch where the drum meets the forward lip of the opening would be enough to make me want to engineer some additional safety tweaks into the basic idea of the Sand-flee. Some kind of self-retracting cover perhaps?

Another thing that might be worth considering is limiting the maximum depth of cut so that the workpiece doesn't get ejected straight back towards you if it catches while you're feeding it

[Prostheta]

The extraction hood would cover most of the exposed bit. At least, that's what I was originally thinking. In Sand Flee operation it would still need extraction. Perhaps partially revealing the drum or similar might work. I imagine that it would present a convenient method of cleaning the abrasive with a rubber stick. A work in progress. My son is over this weekend so I'll start drafting ideas In CAD during the week.

[Andyjr1515]

A drum sander/thicknesser has been on my wish list for a long time but I've always struggled with accommodating the size and weight of most of the commercial offerings.  I'll be watching this thread with interest. 

[Prostheta]

I'm wondering whether it might be feasible to use a brushless motor, since they're more compact. But yes, trying to reduce the footprint and making it packable is a big plus point.

[MiKro]

1 hour ago, Prostheta said:

I'm wondering whether it might be feasible to use a brushless motor, since they're more compact. But yes, trying to reduce the footprint and making it packable is a big plus point.

Are you thinking DC or AC brushless? Either would work. Advantages of each need to be considered though? The DC would give you more torque at a fixed speed for less $$$, Whereas the AC would give you 3 phase with adjustable speed and torque. Cost is always a factor though as the AC would be more expensive.

Just my 0.02 cents.

MK

[Prostheta]

Sure, there's plenty of pros and cons. I thought it was that AC could provide more torque (on demand via electronic control I presume) but DC is more efficient, compact and cheaper. This isn't a heavy-duty application, so I believe that DC is the way forward. Simple as necessary but no simpler.

[MiKro]

21 minutes ago, Prostheta said:

Sure, there's plenty of pros and cons. I thought it was that AC could provide more torque (on demand via electronic control I presume) but DC is more efficient, compact and cheaper. This isn't a heavy-duty application, so I believe that DC is the way forward. Simple as necessary but no simpler.

Yes using a VFD  for AC or similar type of ESC  which you could use for DC if a brushless DC 3 phase motor,  AC will keep the torque a constant as well but within limits. again expense here AC vs DC.

If using DC brushed motor, Using a type of DC Variac with PWM will keep the torque constant as well and much cheaper. Something like a router control will not work as it only lowers voltage and the torque deceases as the voltage decreases in an AC system which I am sure you are aware of.

mk

[Prostheta]

Drum sanders only really need torque to get moving or to maintain speed under load and even then there isn't much to power through. A small 1,0-1,5kW table saw motor should do the trick easily. No need for extraneous electronics like a VFD or ESC. If anything, that would be something one might consider for a power feed bed than the drum and even then I think it's excessive for most use. Like I said, a simple DC brushless motor should cover all bases without complication. A soft start would be nice, but hey.

[MiKro]

I agree, just giving you options.

Looks like a cool project. I like that you are using aluminum extrusions and plate. much beefier.

You can always make a small circuit using a start cap that should give you that soft start to control the inrush current.

 

MK

[Prostheta]

It should also keep things from pranging up the electrics on the same circuit as our house....

[ADFinlayson]

Jointing the figured stuff was my first thought with that thing, looked pretty cool until I saw the price. 

[ScottR]

On 9/26/2020 at 8:41 AM, komodo said:

That dude started going and my eyes slowly turned into pinwheels

Reminded me of the Oxy Clean dude before he OD'ed  and finally got quiet.

sR

[Prostheta]

Before committing to any specific sizes or dimensions, I need to establish the things I can't control such as the size of the motor, the drum (if I buy an off the shelf part) and conveyor bed (again, if a standard part). Everything else will be built around those constraints. Admittedly, I could go 100% own-made however I do like the idea of a tensioned sheet around a roller. So many people go the PVC drum route, and even though that will always be an option I'd rather arrive at that same conclusion via as an independent conclusion. One avenue I have been looking at is to extract via the drum itself, using an open abrasive medium such as an Abranet variant. Unfortunately, I don't think that they come in anything other than a hook and loop backing, which increases flex and conformity. It would 100% require being tensioned around a drum and even then the centrifugal force of the media around a spinning drum alters potential depth of cut. Not ideal.

[komodo]

Be careful Carl. The longer you throw ideas around, the more likely that guy is going to show up on your doorstep to convince you that the Sand Flee is the best option. My guess is that he would stick around for quite awhile, eating your food, getting muddy boots on your couch, wanting rides everywhere, staying up to all hours of the night and never shutting up about the Sand Flee.

[Prostheta]

46 minutes ago, komodo said:

....getting muddy boots on your couch....

Kind of like the Rick James of slapchop-esque tools you don't need?

[komodo]

AHAHAHAHAHAHAHAHAHAHAAAAA Chaaaaaahlie Maaaaaarphy ahahahahahaha

Cocaine is a helluva drug.

[Prostheta]

Definitely one of the all time classic comedy sketches ever!