bar position.....

[eyecave]

:-Xjus' thought i would ask if any of you use an oversized bar on your rack and whether or not you used it in the second position or in the first?.... ;D :oalso.... :owhat about spacers?

[Sharon Faulkner]

No I don't use an oversize bar. I don't use spacers either. ;D

I know spacers have been a matter of debate in some circles, but I've caved with folks who always use them and seen them used on relatively deep (Fantastic for instance) drops without incident. So I don't necessarily see spacers as good or bad, but simply another vertical gear option for some folks.

[Rebel Rouser]

I was thinking of things to tell a newbie and looked up to see who posted this. Dan, you rascal... ;D No big bars, no solid bars, and no spacers. IMHO, spacers significantly contributed to if not directly caused a death. That goes way beyond 'just another gear choice' for me. Of course this is only my opinion and I could be wrong! What if I'm not? We will never know if we don't ask questions and parties keep such incidents from scrutiny. Kent

Dan are you baiting me?

[Tim White]

Large stainless steel bar with grove in #1 position. (home-made)
Spacers between #1 & #2 bars. They are shaft collars locked into place with set screws.
Standard 6-bar SMC rack (5 stainless steel bars)

This set-up works for me. NOT for everyone! i.e. inexperienced

I do not teach new vertical folks to use spacers...as a matter of fact I recommend they DO NOT!

BTW: I rappel MILES every year, and have for many years.

[Josh Babcock]

I use normal BMS bars in all positions except #2, which gets a thick BMS bar. The reason is simply to avoid burning my hands on short drops. The #2 bar has been proven to absorb more energy than any other bar. Since change in temperature is proportional to change in heat and inversely proportional to mass, the easy way to lower temperature for a given amount of energy is to increase the size of your heat sink.

You can do other things to increase the capacity of your heat sink, like use a material with a higher specific heat (e.g. Al at 900 J/kg*K vs stainless at 500J/kg*K). Of course, that option leaves you with a much larger bar due to the low density of Al, and it also leaves you with an Al plated rope.

The other factor, which comes into play on long drops where the temp gets high enough that the heat radiated by the bar allows it to reach an equilibrium temp, is to increase radiative surface area and surface exposed to convection. In other words, use a U bar instead of a round one.

Josh

[macaver]

I've used spacers after my first year on my SMC 6 bar stainless rack. & I've yet to experience a problem with them. But with newbies that are learning on racks (after some experience with 8's), I've been careful to remove them if they're going to use mine and to tell them to get at least a year's worth of good use i.e. once or twice a month on drops of more than 50 feet to get the full feel of the rack and it's properties. Then I tell them if they want to put spacers on then to do so and still be very careful til they are used to the lesser amount of friction at the beginning of a drop.
My spacers are made from the plastic tubes that at the end of cash-register or fax paper rolls and cut to 9/16th to accomidate the standard (caving) rope. These are cheap (free if you know store managers) and are easily replaced.
I've heard the cons of spacers and can appreciate where they're coming from. They are indeed not for everyone, I agree, but used properly and with common sense they're not as dangerous (IMHO) as (some) folks say they are.
My rack and I have enjoyed 35, 000 + feet of vertical experience together with spacers and probably will try for another 35K.

[caverat46542]

I have used spacers on all my Racks for 8 years now. If I did not, with my light weight, I would not be able to get down.

I have used my Rack from soupy to stiff rope and still have a smooth ride.

I have never had any problem with speed with my Rack using spacers.

[Brian Roebuck]

The use of spacers may have a lot to do with how well your rack is "tuned". By that I mean how easy is it to slide the bars up and down etc. I have read things about this in "ON Rope" as well as heard it talked about. Basically one uses a file to shape the holes in the bars just enough to allow free travel while on the rack frame. I have never done this to my rack and occasionally it seems hard to use and can pinch the rope pretty hard between the first two bars.

Any comments from the vertical pros on this idea?

BTW Josh - I enjoyed your correct engineering analysis of heat transfer and conduction as applied to rack bars. Nicely done!

[Josh Babcock]

Thanks Brian.

I was also introduced recently to a technique that really improves how easily bars slide and equalize under tension. One of my grotto members regularly polishes her frame with emory cloth. You have to do this regularly, since even the smallest imperfections seem to create resistance to bar movement. Blindingly simple, but I had never seen or thought of it before.

Josh

[guanonoggin]

<Beavis> He he he, Uhhhh he said "polishing her frame" he he he <Beavis>

Dude that sounds like a righteous idea though. If you can't like move the bars really easy it would make it totally hard to control the speed. So who else does stuff like this? I've never done any work on my rack at all. It just works like it is.

Chucky

[Rebel Rouser]

I was taught that the bars, when positioned on rack should slide freely when the rack is inverted. This can be accomplished by manipulating rack frame (less desirable) and by filing hole in bar larger(more desirable). I say less desirable for the frame manipulation only because the frame should be fairly close to correct width to start with. Small amounts of friction in the frame/bar relation will compound itself when the rack is in use. kent

[tagkaver]

i use a large bar with a groove as my first bar, and use no spacers. i have done up to 1200' rappels with this set-up with no problems.