The idea for this project started with inspiration from Cy Whitling,
in his blog post on his ultra-light frankenbinding
made from a Ski Trab toe piece and an ATK heel.
Part of the key to Cy's success riding tiny bindings on much bigger (and more fun) skis comes from the use of a freeride spacer, a simple block between the heel of your boot and your ski, compensating for the lack of power transfer in the heel of a tech binding.
Unfortunately, many people using DIY spacers are using static spacer, which introduce a significant amount of friction into the binding release system, which could significant increase the risk of a knee or leg injury.
While many people justify the use of a static spacer by positing that tech bindings were never safe to begin with, I think we ought to think about maximizing the tradeoff between safety and performance in any individual design decision. As such, adding a sliding mechanism in the free ride spacer is an obvious thing to do, and there is no scenario where you can justify using a static one due to the low cost and effort involved in using a sliding one.
This project aims to provide a simple open design for a free ride spacer which anyone can order/build themselves, specced to their specific boot/binding combo.
One key feature of my spacer is having an ultra-low stack height of 6.5mm, which is crucial for compatibility with ultra light tech bindings such as the ATK hate route heel used here.
The design of the spacer is ridiculously simple and easy to manufacture.
There is a low profile aluminum base, which is mounted to the ski with two M5 screws. These machine screws are not really meant to be drilled into wood, but they are easily available, and not load bearing so it is fine for this use.
Then on top sits a POM plastic piece, which offers a low friction surface to slide on the polished aluminum base.
Finally, a simple elastic band holds the piece in the center, while allowing it to slide out of the way in a release situation.
This whole setup weighs under 26 grams 
Note that I have updated the files and render with a new version that should be cheaper to manufacture and save some weight, but I haven't actually built this one as my previous version is still working fine.
Any CNC service can be used, but JLC CNC is what I used, and tends to be the cheapest.
To order, first measure your stack height with your boot+ binding combo, and then select the spacer file with a stack height greater than, but closest to your measured height. It is fairly easy to sand down the plastic spacer to get a perfect fit, but hard to add material later.
If you are handy with CAD software it should be easy to modify any of the spacer files to get a perfect fit, note that the base adds 2.5mm on top of the height of the spacer, which is accounted for in the file names, i.e. 6mm spacer = 2.5mm base + 4mm pad.
Then go to JLC CNC, or any other machining service, and upload the spacer.step file + the base.step file.
For the base use these settings, (make sure you add the drawing.pdf file below the roughness option!):
| Parameter | Value |
|---|---|
| CNC file | base.step |
| Qty | 2 |
| Material | Aluminum 6061 |
| Surface Finish | No |
| Tightest Tolerance | ISO 2768 medium |
| Smallest Roughness | Ra1.6 |
| Threads | No |
| Sub-assembly | No |
| Product Desc | Aluminum Alloy Rectangular Plate |
For the spacer use these settings:
| Parameter | Value |
|---|---|
| CNC file | spacer_(pick size).step |
| Qty | 2 |
| Material | POM(White) |
| Surface Finish | No |
| Tightest Tolerance | ISO 2768 medium |
| Smallest Roughness | Ra3.2 |
| Threads | No |
| Sub-assembly | No |
| Product Desc | Plastic Irregular Board |
Now you should be all set to order!
Each spacer uses 2x M5 flat head screws, and about 10cm of 2mm shock cord.
The spacers will likely not fit out of the box, as it's hard to dial in the tolerances without ordering a lot of different spacers. Make sure you order on the tall side, and then just sand down until you can just barely pull a piece of paper out from between the boot and spacer without it ripping. You also might need to lightly sand some plastic off the edge of the spacer to make sure it has enough clearance to slide freely in the base.
Then just measure and drill two holes (4.2mm), and screw in the base with epoxy/wood glue in the holes. I would try to put this spacer in the middle of where your heel rests inside the boot, though it shouldn't matter too much. I would also recommend applying some machine grease (chapstick works fine in a pinch) between the base and spacer to reduce icing and friction.
Finally, just insert the spacer and loop the shock cord through and tie it off.
Now go skiing!
I personally have this spacer setup with a ski trab toe and atk haute route heel mounted on a pair of line vision 108's, and it has performed great with over 2 seasons on them so far, with the "din" set at 9.
I think a lot of people would be surprised how well these light bindings perform with a spacer like this. With the elasticity in the trab toe combined with this spacer, I pretty much never lock my toe unless I am skiing in a no fall zone, and have been able to charge bumpy icy snow without a prerelease ever happening, as well as dropping some moderate sized cliffs and landing backseat. Though I will note that I am not the biggest person out there at 170lb, so bigger folks should take my experience here with a grain of salt.
These bindings held up great for this icy and exposed decent of the south face of Mt. Hood (toe unlocked for all but the very first part over exposure, where I would have locked any binding I was on).