"Crack-in-a-Box" novel device for jam training

The thread on that fingerboard crack machine prompted me to post up a few pics of something I built recently. It's a variable "crack" in a box. It's portable, and I've brought it out to the crag (well, as far as the parking lot) for crack newbies to get a first exposure to various jamming modes. I found it's much more effective to spend a couple minutes of ground school with this than futilely yelling up "Put you whole hand in...no, deeper. Now, cup over your thumb. No, not like that. Your THUMB" and the like, which typically is not very successful for folks who have never encountered a vertical crack in their (typically short) climbing career.

What it is - a simple wooden box with two concrete "pavers" and a variety of wooden blocks of various thickness. The pavers come in various sizes; mine are about 7.5" square. I can vary the crack from tips to hand-fist stack.

The device isn't a substitute for a true crack machine like some folks (and a few gyms) have, since you can't actually climb it. But getting a solid enough jam to be able to lift the box (about 10 pounds) off the floor is nominally a "good jam". And being able to demonstrate this and then have the student try it themselves is something I found very helpful to newbies building their fundamental skillset. Hell, even I learned something about stacking this way (as with all jamming I suppose, there are some subtleties to doing it well).

Crack box

hand size jam

thumb stack

hand-fist stack

Yeah, but can you use it to teach new climbers how to place trad gear at the gym?

That's actually pretty awesome! I've taught crack climbing classes in the past and always seek out a variety of ground level cracks for students to sample. This would be useful in an overkill sort of way.

Reminds me of DMM's "crack boulder"

youtube.com/watch?v=b8gyEly…

Top notch man that's pretty clever. I might have to partner something like this up with my Kent Pease book and step up my crack game.

I like it!

That's fantastic.

You could reasonably add more weight to the bottom to make each jam "harder" to do.

(I like this too)

Isn't it funny that a lot of times it's not what you say it's how you say it? This is nearly identical to that elegantly engineered but tragically impractical gym "cam accepting crack" training thing that guy pitched a couple months ago. Approaching people as a suggestion or possibility rather than (what I took as) arrogance and ignorance goes a long way!

LongRanger wrote:That's fantastic. You could reasonably add more weight to the bottom to make each jam "harder" to do.

I can make the crack flare outwards (or inwards for that matter) by putting a shorter shim in the bottom (so the pavers aren't parallel). Just a 1/4" shim in the bottom makes that thumb stack jam a lot harder.

With a strong enough box and a tight pairs of pavers, I suspect you could bolt a pair of these to the wall to provide for deadhangs and pullups.

One unexpected thing as I was playing with this box: I realized that I tend to stick my right (dominant) hand in to find out how best to jam each size. When I finally started using my left hand, ha! I am so much less effective on that side.

To hang it up on a wall put 2x4 at the ends or something strong enough to hold the pavers in then open the side so you can slide them in place.

It's totally brilliant. I love the feedback you would get from doing the crack, "wrong" - everything falls out! I can imagine trying to work your hand in the right position while the box is on the ground, trying to make everything wedge in correctly. What a great learning tool.

You could glue sharp pebbles/crystals to the pavers to simulate the misery that is that kind of crack.

Gavin W wrote:Yeah, but can you use it to teach new climbers how to place trad gear at the gym?

In a sense, yeah.

I used a wood clamp for the same purpose so that I could practice jams in every size and also match each jam to a corresponding cam size.

Ryan Hill wrote:That's actually pretty awesome! I've taught crack climbing classes in the past and always seek out a variety of ground level cracks for students to sample. This would be useful in an overkill sort of way. Reminds me of DMM's "crack boulder" youtube.com/watch?v=b8gyEly…

That is completely pointless test though because that isn't realistic on how gear is fallen on. A smooth slow pull isn't the same as a fall on gear.