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LEGO Flattening Jig for Domed Stones

This is my LEGO Flattening Jig. It works very well. If I had a smaller stone, I would likely have tried a bunch of other stuff first (taping the edges, freehand, etc.) but with these monster stones, it was just too much. The doming on these 12"x3"x1" Arkansas Stones was pretty pronounced, and even after all the work I have put into them, I still have a long way to go.

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First, find yourself a nice FLAT base. The flatness of the base will determine the flatness of the stone. On stones this size, a single tile was not sufficient, and since I installed the tiles in our kitchen, there are not two of them in a row that are flat enough to span. Our flat top stove worked very well. We also have a glass-shelved TV stand that I had thought about. I first cleaned the surface as best possible, using a razor-scraper, water, and buffed it nice and dry. It's not perfect, but it's the best I could do with the tools at hand.
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The flattening jig relies on the flatness of the base and the incredibly tight tolerances of the LEGO blocks and LEGO wheels.
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Now just attach some w/d sandpaper to another FLAT surface (in my case a marble tile left over from kitchen renovations). I use binder clips to keep them in place, partly because I can never justify buying spray adhesive, partly because I had the binder clips in the stationary drawer :).
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Now flip that over and lap until your sandpaper/tile is riding on all the wheels. If the stone doesn't have a large enough flat area yet, shim the stone with some paper or card stock. I had a bunch of card stock and paper cut up, and was working to get the stone nice and flat. This jig is set up so that all the wheels ride in the same plane. That combined with the flatness of the tile give you a flat stone.

You will notice that the sandpaper/tile ride on AT LEAST four wheels at a time, and most of the time it is riding on six. This keeps the tile in a single plane. True, you only need it to ride on three at a time to keep it in plane, but four provides more stability.

I have found that adding some SiC powder on the surface of the stone when doing the lapping speeds things up. It prevents the need to swap out w/d sandpaper, and it really powers through the stone. I ran the rig dry, partly because it being wet would have made a big mess, partly because I was worried that water would alter the thickness of my shimming medium.

Suggested improvements would be a uniform thickness anti-slip mat for underneath. The jig wanted to slide around in use, so I added the hand hold you can see on the one the right side (it's just a cross bar to hold on to). I also found that it was best to put a couple sheets of paper under the rig, one on each end (not overlapping), to catch the SiC powder and stone dust. If you had a large rubber mat, it would do the same thing. I did my best to re-use the SiC as much as possible, since I had a limited supply to start out with.

I have put broad, flat areas on two stones this way. This one (a Translucent Black Arkansas) and a Black Arkansas. I thought that since both were flat, I could then put SiC between them and flatten away. I was wrong. It doesn't work like that. It wound up re-doming the Translucent Black, and cupping the Black (both very slightly). I guess you live and you learn. I'll be using the jig again to re-flatten the Translucent Black to the point where I can take over flattening them by hand, and to get the Soft and Hard stones well on their way to being flat also. Actually, I will be using it for their bottom sides also, and I'll modify it to use for the edges. These stones will give both large surface areas on the major faces, but also allow me to use them on edge as a long, skinny hone.

I have been thinking about how nice it would be to have a milling machine that could do the work for me :). After all this work to flatten the stones, you can bet your bottom dollar that I'll get some good use out of them :). I am purchasing more abrasive powders (both SiC and AlOx) to finish flattening them and polish them. By the time all things are said and done, it may have been less expensive to just buy flat stones, or pay someone to flatten them for me :). The good news is that the LEGO Flattening Jig cost me precisely $0, since I had the LEGOS on hand (got them for my daughter and I to play with).
 
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Wow. We need your mind working on something like global peace or market instability or a truly delicious frozen pie. Your talents are wasted on just flattening stones.
 

Steve56

Ask me about shaving naked!
Wow. We need your mind working on something like global peace or market instability or a truly delicious frozen pie. Your talents are wasted on just flattening stones.

No, he's obviously an engineer! I've had similar thoughts, but with tape and a smaller JNat stone. Presented with a large Ark, I'd probably use a lapidary option.

Cheers, Steve
 
Wow. We need your mind working on something like global peace or market instability or a truly delicious frozen pie. Your talents are wasted on just flattening stones.
I've been working on a truly easy french bread from a bread machine. The recipe that came with the machine has been hard to beat...
No, he's obviously an engineer! I've had similar thoughts, but with tape and a smaller JNat stone. Presented with a large Ark, I'd probably use a lapidary option.

Cheers, Steve
Yeah, I wanted to do this on my own if I could. Yes, I'm an engineer, was it that obvious?
Must be an engineer bc this is over engineered but cool
Over engineered? I'm not sure if I should take offense :).
You are hilarious and I respect you now and will forever do so!>
It's about time someone respects me... I'll try to not let it go to my head!
 
Yes, I'm an engineer, was it that obvious?

First sign was the complexity, when the task can be easily performed by placing the tile paper-side-up and the stone face down... pencil lines indicate flatness.
This also makes it easier to keep the paper wet.

2nd sign was the fact that you have more than one binder clip in your home :biggrin:
 
First sign was the complexity, when the task can be easily performed by placing the tile paper-side-up and the stone face down... pencil lines indicate flatness.
This also makes it easier to keep the paper wet.

2nd sign was the fact that you have more than one binder clip in your home :biggrin:
Well, it was kind of a joke. I figured a relatively complex system was going to be a give away. It was the simplest system I could come up with, using things I had on hand, to solve the problem.

Actually, I built the rig because the stones couldn't be lapped flat face down, I couldn't anyhow. The stones were rocking in both directions (very slight, but it was happening). After freehand "flattening" 2 stones and laying them face to face, it was obvious that they were not FLAT, just much smoother in the middle. This photo shows how far I thought it was flat (orange) vs. how far it was flat in reality (blue). This also explains why there is only a pencil grid out in the middle. It took a long time to get that blue circle back out to the orange lines! You can compare back to the second picture in the first post and see that I'm not making this up.
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Oh, and I can't take credit for the binder clips, those are my wife's. She used them a lot in college, and she was an English major. I do like binder clips though...
 
UPDATE:
So after using the LEGO Flattening Jig to flatten both the Translucent Black Arkansas, and the Black Arkansas Stones, I decided it would be much faster to use the SiC between the stones, since it would be working both surfaces at the same time. Since both surfaces were flat to begin with, my assumption was that they would stay flat. Well, guess what... The Black Ark dished, and the Translucent Black Ark was left domed, again...

While I was lamenting over my poor decision making abilities, I was thinking that I needed to use the Flattening Jig to flatten both stones again, then I would just use w/d over a tile with SiC powder. Before I got the Jig set up, I realized that I would not need to use it on the Black, since it was dished, thus providing a flat plane to start with. By the time I had the Jig ready to go, I had realized that I didn't need the Jig at all. I NEVER needed the Jig! I could use the SiC powder and a "narrow" stone to dish the Translucent Black Ark (very slightly) thus giving it a flat starting plane. I decided I wanted at least half the length of the stone to start with. Once again, a practical solution triumphs over an engineered solution. Here's a picture of what the pre-sandpaper stone looked like.
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You can see the narrow stone I used on the left (marble), and you can see where I clearly removed the shine from the Translucent Black. From here, I returned to 220 w/d with 220 SiC powder on a polished marble tile.

You can also see two more things. First, you can clearly see how far I thought I was with lapping. Second you can see what the 220 grit between the two stones can yield. What I had done here was used some 220 between the Black and Translucent Black, and I worked it until it stopped making any "crunching" sounds. I then timed it and proceeded to polish (with the slurry that was generated) for another 15 minutes, rinsed, dried, and had a very nice polished surface. The only problem was that the polished surface was not flat...

After several additional hours of flattening the Translucent Black on worn out wet/dry with 220 SiC powder, I have a flat surface all the way to 3 of the corners (well, I need to glue the paper down if I want it ALL the way to the corners), and just have to work that bottom left corner flat. I could stop now if I wanted to, but I've already come this far...
 
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