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Sanding small flat surfaces so they stay flat Answered


I'm trying to sand fairly small wooden objects that are about 1/2"x1" and sometimes a little larger. I often find that one side is thicker than the other or the corners are no longer perpendicular.

I am trying various techniques, like taking a chunk of 2x4 and wrapping it sandpaper and then vice it to my workbench. Then I rub the object against the paper block. That is getting better results. 

I've read that some people use spray-on adhesive to secure sheets of sandpaper to a granite top and that it is supposed to work well.

There are a few instructables that explicitly talk about sanding and I've read many of them. They advocate a bunch of techniques.

I'm wondering what other folks have had success with.



If you have more than one piece and want all to be the same and flat:
Make a box like frame where you can adjust one side with screws to press your blocks together.
The side walls should be slightly lower than your blocks.
Add your blocks, put a little pressure on the srews and tap the blocks down.
Increase the pressure so the blocks stay secured.
Now you can move the entire frame over some sandpaper, preferably glued or clamped onto a flat surface.
When one side is finnished open the srews, turn your blocks and repeat the process.
Do it six times and you should end up with very even and flat blocks.
Using a frame for small parts makes sure you don't wobble the part you are sanding.
It is very hard to keep even pressure without increasing the pressure towards to outside of small parts.

This is a really interesting approach. I think I can do this one pretty easily too by milling out a custom jig for each part and then aligning a common vice for each one. Great idea! Thanks


Hi, thanks for commenting. I haven't used a sander like this... yet. The object is very small and the sander seems like it can take a lot of material off very quickly. Is there a way to limit the amount of material it removes?

I realized that it is probably easier to see what I'm doing then to guess at it. I'm trying to sand smooth the sides of some home-mode wooden lego. The process for making them will leave a the sides a little rough and so they need to be sanded smooth.

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Those look amazing andy. How did you make those? Theres got to be some type of jigging involved.... A wood finish would protect and smooth out the wood, linseed oil, tung oil, danish oil. THe finish of your choice thinned with mineral spirits. For the harbor freight sander you ca buy up to 240 grit in the store for the disk part elsewear it can be gotten up to 1000 grit. A machine sander is going to be faster and more precise than a hand sander. If you buy a disk sand sander you may have to put a second table top on it that is closer to the disc due to the small size of the pieces but such a table could then include any custom wooden stops you wanted to add. When finishing wood floors, to get the smoothest finish possible, the finish may be apllied and the floow wet sanded with a fine grit at the same time, making a slurry that fills small gaps. At the stae your at the liquid finish itself may be enough to fill the small gaps/roughness, but if not you could try finishing with a finish slurry made from finish spirits, and the finest wood dust you can manage to create. Be careful not to breath too much sanding dust or you can get the woodworkers flu. See my dustmask ible if concerned. God bless it I keep makeing typos and then having to retype portions of this message when i try to fix them because I dont know how to change from typeover to insert. Have you seen the lego quatros? Theyre discontinued by theyre basically the double of duplos. I always want to extend the concept. Lego Ochos....Lego diezyseises. (16's)

Thanks, I'm building an ible with detailed instructions on how to make them yourself. Actually, I have 2 archetype lego's done and am working on a third.

I use a CNC router to make the legos and make several bricks at a time.

I have tried a number of finishes, some parts with better with different finishes. Like flat-top plates look amazing with aerosol lacquer. I was thinking either linseed oil or shellac as the finish.

I, um, have a full face respirator because I work with other aersol's, paint thinners and sanding at 180+ grits. Plus it makes me feel a little like darth vadar.

My current sanding process is to use really strong double sided tape, like nitto p-02, and apply a piece of 180 grit to a piece of mdf and then secure it to a fence. It is OK, but I would really like to refine the process. I'm usually just trying to clean up some tearout or something slightly worse.

The wet sanding is interesting. I've read about it but never tried it and this would be a good test. Would you suggest applying linseed oil and then immediately sanding with like a 600 grit? Or something different?


I would imagine the tops are cnc'd and then they blocks cut with a saw of some sort. Is that right. What saw cuts makes the square block cuts? To avoid tearout on something small like that you could use a sacrificial piece of wood clamped to the piece you are cutting so their is no possibility of tear out because instead of being able to tear out at the end the blade just starts cutting into the sacrificial piece. An of course the thinnest, finest tooth blade or bit will be the least prone to large tear out.

Ive not done a lot of sanding. 120 is all the higher ive ever seen the benefit of going to for anything ive done.

If the spray lacquer is not too thick of a finish to effect the assempby of the blocks. I would think thinned polyurethane would work, or any thinned all in one stain/sealer. The linseed is not a sealant like lacquer, it wont give a polish, the blocks will still get dusty, also definately thin the boiled linseed oil to at least 50/50. It will be easy to add another coat later, oil improves wood as it improves leather, it's idiot proof but not permant and you dont want to go too heavy or it will take forever to be not oily.

I would go with thinned boiled linseed oil. Its cheap, its naturalish, as wooden legos are naturalish, and it will lubricate the blocks slightly. What was rough before will be softened by lubrication rather than sanding away the roughness.

Wet sanding wont have the same wood filler effect with linseed as it would with poly or an all in one finish. I think tung oil does harden to a plasticlike, almost poly state. I'm not sure though, Ive only read that.

I really think your doing too much with the sanding, one tends to ocd ones own work, forgetting that the awesomeness of wooden legos trumps the slight roughness. I agree with caitlins Dad that you are probably applying uneven pressure with your fingers, I agree with you that or more square sanding block without twists would help. And I agree with me that a power sander would help to limit the need to push with force the workpieces into the sansdpaper, relying instead on the precise force of the download rotating disk sander, barely pushing the block up against it, and agree with you that some jigs or stops would restrict the unevenness of apllied force resulting in the slant or non flatness.

There's a lot there!

I actually cut them with the CNC machine, not a saw. Lego bricks have very tight tolerances and are measured in the sub-millimeter range, like 0.8mm is a standard unit of measure. The 2x4 brick you see is 11.4 x 31.6 x 15.6 mm. The dimensions have to be precise so that the brick will have a snug fit with regular lego bricks. I get pretty close results, but I can't get it perfect and that's ok. The last 5% to perfection is really not worth the level of effort.

I'm very much in the experimentation phase for finishes. The flat top plates need a different finish because they are almost perfectly smooth. I make 3 blocks per batch and try a different finish on each one until I'm happy with the results.

I'll spend some time at Home depot and try to find some floor paste wax. I also have some bee's wax and I'm wondering how that would work since it is commonly used to seal butcher block counters. I have this stuff that is a combination of bee's wax, carnuba and orange. I'm testing that right now. The finish won't last forever, but I can always refinish them too.

You made a great point about the focus being the lego and not the finish. That is the rub :) , lego is tough to make, really time consuming to design the archetypes and come up with a reusable toolpath for the cnc machine. The finish is fairly important because the lego themselves look a world more beautiful when they are finished.

Here's an interasting instructable about wax sealing.


oils, waxes, poly, they can all be mixed together into a super potion with spirits I believe. Theyre a spectrum. Of course the waxes need melted but heating any finish helps it soak in better.

Something about legos is theyre multicolor. you could get a nice multicolor affect by putting first more or less amounts of stain on the blacks.

I had no idea they were compatible with regular legos. Thats an impressive precision, considering that the legos themselves rely on the slight bend in the complex inside plastic walls of the lego bricks. Are yours three hole only connectors or mimic the actual lego connectors? That would be wild.

A wax finish you would need to remove all the wax for more to adhere, plus Id think the wax would mess with the precision, a harder wax like carnauba less so. I bet your blocks are smooth enough that you could use car wax. It's carnauba based I'm pretty sure.

All this lego business really has me wanting to make some legos. I dont have a cnc, and no coding knowledge. I'd be in the realm of the Maxi legos. I dont know your setup, but have you tried any blocks in the Duplo range? A larger block wouldn't need to be as precise.

The ible is interesting. They mentioned something called otter wax though and I may try that out since it is already mixed. I've used the double boiler technique for a bunch of food related things. I'm hesitant to use it for anything else though. Still, interesting idea.

I spent some time at home depot and picked up tung and danish oil. I love experimenting. I agree that part of what makes lego's great is that they have a lot of colors. I am right now working with only basswood, which mills OK, but not great. I picked up some red oak and poplar to see if they come out better. Consequently, I can go with one finish method if I am working with multiple types of wood or I can just apply multiple finish recipes to a bunch of basswood blocks.

Check out the photo below. They are fully compatible with standard lego bricks, mini's and other odd bits. The brick you see here was finished with the beeswax and carnuba mix I mentioned earlier. The bricks are very close to lego spec. The bottom of the brick is exact. The top of the brick has slightly too narrow knobs/studs because of a tolerance issue when I was milling them. I think I have corrected the problem, but we'll see in the next batch. I usually have to make two prototype batches before I have a repeatable process.

The Othermachine CNC mill uses bits as small as 1/100th of an inch. This brick used 1/8, 1/16 and 1/32 flat mill ends. It takes nearly 2 hours right now to make a batch of three bricks.

All the CNC design work is done in a CAD application and then I use the CAM component to set the paths the machine will follow to make the brick. There is no code involved, but there is a lot of messing about with measurements and setting the feed and speeds so the mill can carve out the brick cleanly and without damaging the bit.

I can't actually make the larger bricks with my machine. The othermill has a small build area. You need to move up to a larger machine to make the big bricks, however, some of the larger machines are much less precise. The othermill was meant to carve out circuit boards. However, it can be used to do a lot of other things too.

beeswax - 1.jpg

That you copied the actual bottom of a lego, out of wood, blows my mind. Do you have a picture of that?

These are the brick types I have created so far. From right to left: 2x4 brick, 2x4 plate, 4x4 plate (lego doesn't make one of these). Getting the 2x4 brick to work lets me create any variant of a wide brick. I should be able to knock out the next generation tomorrow.

The 1xN bricks are different and that requires a new design. A 1x1 is also different from the 1x2. But it I can make a 1x2 then I can make a 1x3 or a 1x4 or a 1x8 for that matter.

I would have made the knobby plates but my stock got water damaged.

legobricks - 1.jpg

Those look great! I can hardly tell by the picture, it's not quite close up enough. You probably already know this since you said exact copy, but I'll mention it just because it took me a while to figure it out, do your blocks like the one on the very left have those lines on the edges like this block in the picture I'm attaching here. There's twelve lines total. Those are the 80's style block design. Those lines are part of the connections. Its harder to see how they work with the smaller blocks. I have the jumbos so its very clear. I am wondering how well those lines stand up to the compresssion of the connection in wood vs plastic, the wood being spongier and not springing back as much, I dont know if that is a factor that needs accounted for in measurements.


Thanks, I'm very happy with how they worked out too!

The bumps and the support connections are indeed missing from my bricks. I am not clear on the purpose of the bumps and I wonder if they are to enhance the strength of the connection, to make bricks easier to detach, or a cost savings measure because it lets you make thinner walls and use less material. I'm curious what the real reason is for the bumps and supports.

Real Lego bricks are almost totally hollowed out. I'm pretty sure that they use the very least material possible to cut costs. Slightly thinner walls would require some kind of bump to make up for the missing material that used to secure another brick's studs/knobs. I mean, they are probably saving a relatively insignificant amount of material on a single brick, but maybe the savings of 20 or 30 bricks provides enough material to make a new brick. They make a lot of bricks every day.

My version of the bricks leave as much material as I can. I remove just enough material so that the bricks will lock together and no more. For me, any extra time milling is time that could be spent milling another brick. Also, every cut causes wear on the mill ends, which is a cost too.

I'm not trying to get this to scale to a level of real manufacturing. I am trying to keep the wear on the mill ends to a minimum.

For the sake of science I dissected a duplo block. A picture says a thousand words. Hopefully the two thousand here are in focus enough. I am in agreement with you on the cost saving theory. That is why commonly those supports are added in manufactured plastic pieces, but in legos they serve another purpose. You can see in the picture the green bumps pressing against the yellow circle. The yellow circles are jammed in between the hollow green circles and the bumps.


Would you mind if I used the photos in the ible? I think they demonstrate a great point.

BTW, the ible is more than just a description of how I made the bricks. It is a detailed description of the original bricks with drawings, plans and a lot more. My hope is that others can take the info and make both existing and entirely new types of lego. It is sort of growing into a small book. :)

Not at all would I mind. I would be happy to have contributed! My hope is that there will one day be legos to build the world out of, that building can be done as much by the average person as the expert builder. I'll be making those type of legos. (Hopefully someday, for now you're on the doing side of things but I'm right there with you on the hoping side.)

Hi, those images are great. Here comes the thousand or so words. The photos do a great job of showing the bumps securing the knobs to the center columns and forcing a tight fit.

The thickness of a regular lego is ~1.15mm while the thickness of the bump and wall is ~ 1.5mm. The wall thickness of my design is ~1.4mm. The center supports on mine are slightly thicker too. Mine are the old style brick and do not have the bumps. Yet both bricks work well together.

On a lightly different note, I made another batch of bricks and the updated cutting and finishing process worked pretty well. Though there is a bug and I'll have to do another run.

I cut the bricks, sanded them with 80 grit paper to get rid of some of extra material. I made an error between the top and bottom cuts that separate the brick from the stock. I then sanded it smooth, really smooth, with 400 grit (I wore my respirator and have a dost collection system right nest to where I was sanding). Finally, I used a clear/natural danish oil. The danish oil produced a really interesting finish. I'll post some mages later today of the difference between various finishes vs. the danish oil finish. Hands down, the danish oil is the best. However, I took too much material off the sides and it resulted in 1-2 mm gap so the blocks do not sit flush against each other. I've since adjusted the milling process to leave 1mm on the sides to allow for light sanding.

There is a positive to the extra stock being taken off. I stacked the bricks together and then sanded them all at once. I had a much better grip on the bricks, they were all square and they all look exactly the same.

The oil really enhanced the look of the brick. You can see details that none of the other finishes cam close to bringing out. I would like a more glossy finish, but these look really good already so I'm reluctant to push my luck!

I was wondering how the danish oil would work out. I've just read about it, never tried it. I'll pick some up to try. At the hardware near me they sell it it in various colors from natural to dark. If you're sanding and danish oiling, you might give the wetsanding a go, the wet coming from the danish oil. I think the sanddust, danish oil mixture would act as a wood filler to fill pores thereby increasing gloss at each stage of sanding. In that way you could maybe skip a lower grit and instead fill in to that level of smoothness by wetsanding with a higher grit. I remember reading that the gloss effect in Danish oil comes from tung oil, as long as the finish doesnt fully cure between coats it is more forgiving than a polyurethane, so you could probably use it as multiple stages of sanding. Maybe for more gloss too you could get away with adding polyurethane or another glossing finish thinned down to a very thin consistency to push the gloss layer gradually as high as it can go in successive coats once the danish oil is cured. I think it would adhere to the danish oil. Sanding to improve adhesion might be a backpedal there. Not sure.

*I meant I can hardly tell if they have the 12 lines, not about them looking great, that is clear in the picture. Sometimes I dont read over before hitting the button to comment.

As a side note regarding machine size and precision. There are plenty of wonderful CNC routers and mills out there. I'm a bit enamored by the shopbot's but I have no idea if this is something the machine can handle. A shopbot is not cheap, but you get a lot. Then there are the real CNC machines. The enthusiast CNC machines can work with a lot of materials but they all stop short of anything ferrous. So no steal, iron, etc.

The major CNC machines can carve through steel and have coolant systems. But they start at $10k (Tormach) and that is just for the basic machine. You still need tools, coolant and a darn good circuit breaker. :)

Also i was just thinking, wow, 600 grit wow. I think you could achieve the smoothness of that by sanding much rougher, no over 240, and then rubbing the blocks with floor paste wax to fill in the pores. Thats something else that would be worth a shot. Should be no more than six bucks or so for a can of enough wax to do about 1000 blocks.

Thats a tricky one indeed, I use a sheet of sandpaper on a window pane, moving the object in a fig8 pattern as well as rotating it frequently to keep things square.

Does the window pane flex? It would seem like this approach would cause the center of the object to be a different thickness than the edges.

It will if the pane is large and you press hard, I use a gentle touch on 4mm thick 200mm square panes.

I used this technique to match a heatsink to a cpu, both were flattened individually on the glass pane.

I see what you mean. At 4mm thick and only 200mm square, the pane remains rigid and has no ridges, cups or twists like a wood block. Think 1/4" lexan would be about as good?


3 years ago

There's an old boat building technique, utilizing sanding blocks of certain length that are recessed in the middle. With that construction, they "self compensate" on convex curves, so the sanding surfaces on the ends are always tangent to the hull. Different length blocks would be used for tighter radius hull curves.

You could modify this technique for flat work--make a sanding stick that has a single, flat "working end" with sandpaper. The other end would always stay in contact with a flat surface "guide" (a board clamped to the workbench, for instance). So the plane of the sanding stick would always be flat, if the guide is flat.

Of course, this would require that the work be clamped somehow in a vice, etc. If you have the type of vice that's flush with the workbench surface, that can be used as your flat guide...

I follow using the sanding stick, the guide, but I'm not sure how the work and the sanding stick make contact.

I sort of think that you are talking about vicing the work down and running the sanding stick over it. The stick would follow a groove and possibly a top cover that keeps it from wobbling vertically while letting it move freely horizontally. Does that sound right or am I missing the point?

One end of the stick/block is in contact with the work, the other end rides on a flat surface--so long as both remain in contact, the working angle of the "business end" cannot change (well--not much, anyways). If the stick is a board (has some width), and rides on a flat guide, the sanding surface cannot rotate side-to-side, either.

It's "self compensating" like a plane--the longer the plane body, the more "true" the work becomes as you plane. The body of the plane prevents the blade from following the contour of the wood, so it takes off the "proud" parts first--the high spots.

Make any sense? I'm not sure... Maybe a pic will help?

Five minute drawing / scan--help any?


Ah! Now I see what you mean. This is a pretty interesting way to get a consistently flat surface. This looks easy enough to set up. I'll give it a try and let you know how it goes.

Hmmm, seems your technique of holding the piece may be off and not using equal pressure to sand. Maybe you ought to use finer grits to get down to the line. Do you constantly check the work up to the light as you sand down? Do you have a steel straightedge or square to put up against the surface to check? It's the same process when you try to hand plane a wood edge too. Good luck.