Author Topic: BMS Micro Rack question  (Read 2005 times)

Offline AlexR

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BMS Micro Rack question
« on: July 23, 2021, 10:17:28 pm »
tl;dr: Can the BMS micro rack with hyper bars be used on 9mm without packing extra toilet paper

Long term user of the old style Petzl Stop here, still really like it for sport caving (rigging) and a series of shorter pitches, but it's really not ideal as a "commuter" descender of long pitches to a dig. Two bobbins and one handle in purely for that dig so far, and eventually I won't be able to get my mitts on spare parts any more.

Tried the new Petzl Stop, absolutely hate it. Not an option. Could get a simple or Petzl rack. But I really like the idea of a stainless steel rack, especially the BMS short frame micro rack with dual hyper bars. No idea if it's useable on 9mm though; sent OnRope1 a customer query, no reply, sent one to Carroll Bassett (BMS contact person), no reply.

Bit of a long shot for a UK forum, but does anyone have any experience with the above descender?

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BMS Micro Rack question
« on: July 23, 2021, 10:17:28 pm »
Warmbac

Offline Fishes

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Re: BMS Micro Rack question
« Reply #1 on: July 23, 2021, 10:41:49 pm »
I moved from a stop to racks over 30 years ago and generally find they are much better on longer pitches. I've used racks hands free when combined with a leg rap quite a few times when doing shaft surveys etc. and I find them very versatile. The only issue I've had is on pitches rigged by a stop/simple user where they often rig too tight at rebelays which can be a real pain in the ass.

I've generally used racks with 10 or 11mm rope. On 8mm pushing rope I found it helped to put a 6th bar on a 5 bar rack. On 9 you might want to close the bars closer together with a spacer rather than putting an extra bar in.

I'm not sure that helps but it might give you something to think about.

Offline rsch

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Re: BMS Micro Rack question
« Reply #2 on: July 23, 2021, 11:24:00 pm »
Good timing with your question, I am planning some experimentation tomorrow along those very lines to figure out an answer for myself.

If I don't post again, you'll have a definitive answer :o

Offline Cantclimbtom

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Re: BMS Micro Rack question
« Reply #3 on: July 23, 2021, 11:29:30 pm »
...Tried the new Petzl Stop...
Each to their own but how odd. I've used the stop for 25 years or so, I really thought Petzl would mess it up like they did to so many other bits of kit (like croll with the nasty plastic catch) but you know what, on **thinner ropes** I think the new one is better, I was all prepared to hate it, but to my surprise.... Plus the new one has stainless bobbins not soft alloy so shouldn't wear out anywhere near quickly (I never liked the fact you could replace the bobbins, the very first drop on my very first ever rope access job, many years ago, the stop "exploded" thank goodness for the shunt rope, that was a real "welcome to the industry" experience - the new one can't have the nuts fall off and come apart). Agreed that > 80m they become a pain. On a fat fuzzy 11mm the new ones may be unworkable, just use skinnier slicker ropes :)
I think your solution is replace your ropes more often not replace you ab device. But each to their own..
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Offline PeteHall

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Re: BMS Micro Rack question
« Reply #4 on: July 24, 2021, 01:56:59 am »
Bit of a long shot for a UK forum, but does anyone have any experience with the above descender?

I have one and I love it. Very nice to use on anything between 9 am 12mm.

As it's quite short, I find it very easy for technical SRT  however you will still find you have a bit less height to play with at rebelays than with a stop. As the rope enters at the top, your body will be lower relative to the anchor than a stop or simple, where the rope enters at the bottom.

That said,  it's much nicer to abseil on and you soon get used to it, you may just need to tweak you cows tails or footloop/ safety cord a bit to get all the lengths working right together.

Final point to remember with a rack is that due to the large attachment hole, it is quite easy to accidentally cross load it across the gate of whatever you've attached it with. This tends to happen if you feed some slack through to pass a squeeze, then put your weight back onto it in an awkward position. This could and would easily break a carabiner, sending you to your death, so please make sure to use a large maillon which can be safely loaded in any direction. It's a bit more faff, but it's an easy way to reduce your risk of an untimely demise.

If you don't know what I mean, attach your rack to your harness with a snap gate and see if you can remove it without operating the gate with your hand. The same thing can happen with a screw gate, which will open just the same under load and it can happen while you are caving. Also note that this applies to any descender with a large attachment hole, such as a figure of eight.

Offline tamarmole

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Re: BMS Micro Rack question
« Reply #5 on: July 24, 2021, 08:12:45 pm »
I am currently using a BMS short micro.  It is an excellent bit of kit, strongly recommended.  Works really well on gritty dig ropes.

I tend to use mine on 10mm or 10.5mm.  Might be a bit fast on 9mm.

Offline Cap'n Chris

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Re: BMS Micro Rack question
« Reply #6 on: July 24, 2021, 08:32:44 pm »
Tried the new Petzl Stop, absolutely hate it.

IMO the new Petzl Stop is abysmal. So it's nice to hear it's not just me. Yay.

Offline rsch

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Re: BMS Micro Rack question
« Reply #7 on: July 25, 2021, 04:13:00 pm »
Long-term old style Stop user here also, not used to using a rack.

BMS Single Hyper-Bar Short Frame rack rigged as pictured on clean, dry Beal Spelenium Gold 9.5mm

Didn't get a chance to do multiple different or longer pitches, stuck to one simple 20m pitch with one deviation. Alternated between using just the rack and using the rack with a Raumer Handy braking krab. Using the Handy felt unnecessarily slow, just the rack in this config felt more controlled and smooth in descent than a Simple. Felt secure enough to go hands-free on lock to mess about adjusting deviation with no resulting drama.

Needs further experimentation but on first play, I like it.


Offline AlexR

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Re: BMS Micro Rack question
« Reply #8 on: July 25, 2021, 06:38:36 pm »
Thank you all for the input, I expected this to be a dead thread but what a great surprise!

I've bit the bullet and bought the descender, as you'd expect postage and import tax made up a very significant part of that purchase. Now I'll just have to wait until it makes it here. It was Pete Hall's post that made it in the end, I just wanted someone's opinion who had used them on 9mm, too.

Actually I'm one of those bastards guilty of rigging too tight for racks, when changing the permanent rigging around the Vortex pitches in Peak Alastair gave me an earful for this - so I dutifully changed it. Might get better at this in the future  ;)


Final point to remember with a rack is that due to the large attachment hole, it is quite easy to accidentally cross load it across the gate of whatever you've attached it with. This tends to happen if you feed some slack through to pass a squeeze, then put your weight back onto it in an awkward position. This could and would easily break a carabiner, sending you to your death, so please make sure to use a large maillon which can be safely loaded in any direction. It's a bit more faff, but it's an easy way to reduce your risk of an untimely demise.
An excellent consideration Pete, thanks for this! Though I dislike maillons this is solid advice. Might see how it plays with a BD Gridlock, too.

@rsch: Excellent to see that your experiments weren't terminal ;)  I'm sure such a switch requires re-training of engrained manoeuvrers, so very good to hear you're getting on well with it on first acquaintance.

@Cantclimbtom:
As you said everyone's experience varies; I personally cave on 8.5mm and even the route to the dig is currently rigged with 9mm after some ****er cored my 10mm that was on it previously. Simple reason being I'm not made of money and managed to get my mitts on new 9mm at a good price. But I digress. I tried the new Stop on this very 9mm, and had the jerkiest, most unpleasant descent I can recall. Yes, I'm not used to the device, but you'd think that at some point on those three long pitches I would have found a way to make it work.
The ropes to the dig are kept as clean as feasible, e.g. I have a bucket of water and brush at the bottom to wash off the vast majority of mud & grit before going up. I suspect one of the worst abrasives is actually the aluminium oxide straight off the descender. No matter the rate of wear, in the long term spare parts for the old style Stop will run out.


I will most likely continue using my (old Style) Petzl Stop together with the BMS descender, hopefully I'll like it enough to switch completely for sport caving as well as digging & exped use.
For anyone else considering the new style Petzl Stop, I strongly recommend you try before you buy. Very nearly bought one, and would have been seriously annoyed if I did. On paper it looks good, and with further practice I probably would be able to tame the jerky descent. The handle, though. I found pulling it put my body in a really awkward position where I needed to engage my core a LOT more than with the old style Stop - here squeezing the handle naturally keeps you upright and close to the rope.

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Re: BMS Micro Rack question
« Reply #9 on: July 25, 2021, 08:03:25 pm »
I've been using a Kong Banana with custom stainless bobbins and a Raumer Handy for at least four years now, on a weekly or more basis, and I only just flipped the bobbins last week, so that's pretty good wear, as they didn't really need flipping yet, but I'd rather they stay roughly circular! The original aluminium ones were wearing visibly - as in, leaving grey streaks on a clean rope, so the tip-off on the stainless was a godsend - I would have binned it ages ago based on the ally bobbins.

I'm certain I could handle a rack though, and I almost did get one until I found out about the stainless bobbins, and it's been so pleasant using these that I just haven't made it yet. But out of interest, there's one thing that's puzzled me for ages, which Pete mentioned earlier - why can't a rack be bottom-loading like a bobbin descender? So the rope goes in at the bottom, up the bars and then out the top? Obviously with the bar layout flipped too. I'm trying to think of a reason why it wouldn't work, but I can't think of one other than too much friction. I'm sure there must be a reason, or they'd all be like that!

Offline PeteHall

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Re: BMS Micro Rack question
« Reply #10 on: July 25, 2021, 08:07:51 pm »
there's one thing that's puzzled me for ages, which Pete mentioned earlier - why can't a rack be bottom-loading like a bobbin descender?

Very simple answer to that. In that configuration, the bars would be pushed together by your weight and it would lock itself. That's basically how you lock a rack, pulling the down rope over the hyper-bar (or top of the frame), squeezing the bars together and increasing the friction.

To go faster, you drop your controlling hand down and it allows the bars to space out, reducing friction, to slow, you pull your hand up (or run it over the hyper-bar), the bars squeeze together and you slow down.

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Re: BMS Micro Rack question
« Reply #11 on: July 25, 2021, 08:17:28 pm »
But if the bottom bar were fixed, like a bobbin, wouldn't the others above it be loose enough? Actually I guess as soon as you apply force to the tail of the rope, it'll just crush them back down again. Fair enough.

Offline PeteHall

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Re: BMS Micro Rack question
« Reply #12 on: July 25, 2021, 09:01:03 pm »
While we are on the subject of racks, I'll take the opportunity to share my rack collection and a few thoughts on each.

I borrowed a couple of racks from a friend a few years after I started caving and after trying them out at an indoor training venue, I instantly knew they were the descender for me. Next time I was in Inglesport, I bought the only rack they had, a Petzl.

https://www.inglesport.com/product/petzl-rack-descender/

It didn't take me long to realise that the long frame made free-handing re-belays incredibly difficult, despite the beautifully smooth descent, once you got going and the ability to use a double rope.

I took the rack in to my university engineering workshops, cut it off and threaded the ends of the frame, allowing it to be used inverted and reducing the overall length by about a third. After the original Petzl bars wore down too far, I machined new bars from mild steel in the engineering workshop and those bars are still on it now . My friends kindly christened this the "death rack".


This rack proved to be absolutely fantastic, it's short and great for technical SRT. The mild steel bars have excellent heat dissipation and I've never had issues with it overheating. The width of it allows it to be used with double ropes, which means you can do a pull through without a knot at the top and if managed right, this pretty much guarantees that it won't jam up when you pull through. I have one rope in each hand, running over the appropriate leg, keeping both down ropes completely separate for the entire descent, I then release the "back" rope and step away from the bottom of the pitch with the pull-down rope, so there is no chance that the ropes will come close to each other and twist together as can happen when they are joined by a knot at the middle, as is the case for a single rope descent pull-through. Just make sure to tie the bottom ends together before descending to prevent one running faster than the other and running off the end of one before reaching the bottom!  :o

The only problem I've found with this rack is that because it is short, it needs a thin rope. Anything over 10.5mm is a real struggle to get down...  :wall:

Next in my collection is the BMS Micro-Rack. This was a gift from an American caver who visited his wife's family in the UK every year and having seen my "death rack" the year before, brought an American rack for me next time he visited. being slightly longer than the "death rack", it is much better on a thicker rope, but being a rack, the bars are all free to move, so it's just as good on a thin rope. As stainless steel has poor heat dissipation, the bars are hollow, which seems to do the trick, but I do still wet my ropes before use and have never had issues with overheating. This became my rack of choice for everything except pull-through's, as being narrow, it can't be used on a double rope.


The great thing about the stainless steel is that it has excellent wear resistance and despite a lot of use on muddy ropes, the bars have very little sign of wear even after several years use.


One day however, while cleaning my kit, I noticed a hairline crack in the pin on the hyper-bar; on closer inspection, I realised that it was cracked right through. It struck me that this had created a knife-edge right next to the loaded rope and it wouldn't take much for this to slice right through the rope!  :o
I'm not sure how it happened as I don't remember knocking it and I've not heard of this happenening to anyone else, so perhaps just a freak accident, but worth keeping an eye out for on any rack with a similar design:


My final rack is a Kong Rackong, purchased from Starless River at Eurospeleo (though I notice Tony doesn't seem to stock them any more) as my MBS was out of service with the cracked pin at the time. To use, it's almost identical tot he BMS micro-rack and in that regard I'm very happy with it. The key difference is that the bars are aluminium (or alloy?) so better heat dissipation and hence solid not hollow, though this does not affect it's use. Despite this, I'll not be recommending it; the bars are so soft, I pretty much cut through them during the course of Eurospeleo. I've barely used it since, so the below is basically from one weeks caving:


If my "death rack" was about 10mm longer, or my BMS wide enough for a double rope, either would be pretty much perfect. As it is, I need to swap between them depending what I'm doing (which being Mendip based is pretty much no SRT at all for the last 2 years!).

Finally, here are the three together for a comparison on length. Not much in it, but you really notice it on a thicker rope!

Offline Fjell

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Re: BMS Micro Rack question
« Reply #13 on: July 26, 2021, 09:14:18 am »
I managed to severely bend the eye on a Petzl rack by misloading it under body weight. That was my second rack and I called it a day. I have done a 160m drop with a Stop on dry rope, so I don’t see the need in general. I use either a Stop or Simple with a Handy. It’s just easier, and you are then rigging for others who use the same.

I tend to think for most people that racks are best paired with the rope types and rigging styles they were designed for (cable with no rebelays). I have a vague unease  that a micro rack (ie hyberbar) and 8 or 9mm might lead to the odd stimulating moment. Also those hollow steel bars will get toasty, right?


Offline andrewmc

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Re: BMS Micro Rack question
« Reply #14 on: July 26, 2021, 10:09:52 am »
Actually I'm one of those bastards guilty of rigging too tight for racks, when changing the permanent rigging around the Vortex pitches in Peak Alastair gave me an earful for this - so I dutifully changed it. Might get better at this in the future  ;)

As a Rig user, where no spare rope is needed at all to lock off (even for me on my 8mm), I have to be careful not to rig too tightly for Stop users :P but then the shortest rebelay is the safest (provided it's long enough that people don't get hung up in it, which is far more likely than a resin anchor failing)...

The ropes to the dig are kept as clean as feasible, e.g. I have a bucket of water and brush at the bottom to wash off the vast majority of mud & grit before going up. I suspect one of the worst abrasives is actually the aluminium oxide straight off the descender. No matter the rate of wear, in the long term spare parts for the old style Stop will run out.

This is a good thing about the new Stop - once everyone's switched over to a descender where the wearing parts are made of stainless (rack, new Stop or whatever) fixed ropes will be less full of abrasive aluminium...

Offline aricooperdavis

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Re: BMS Micro Rack question
« Reply #15 on: July 26, 2021, 01:51:35 pm »
I've been using a Kong Banana with custom stainless bobbins [...]

Custom stainless bobbins, eh? Do you have any more info? Starless offer "special" bobbins but it doesn't say that they're stainless - are these what you mean?

Offline AlexR

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Re: BMS Micro Rack question
« Reply #16 on: July 26, 2021, 01:54:27 pm »
I believe Tony sells them, the word stainless is not mentioned but heavily implied.
They look to be solid, so not sure how good heat management is; the bars on the stainless rack descender are hollow for this reason.

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Re: BMS Micro Rack question
« Reply #17 on: July 26, 2021, 02:56:46 pm »
They are, and yes, they are solid SS, making them very heavy compared to an alluminium-based unit, but they wear so slowly and the descent is so smooth that I don't really care - the rest of my kit is as light as possible to offset this! They're much faster than ally though, and that's why I use a Handy. Once you find the sweet spot it's lovely. Bloody scary on 8mm though, especially the top pitch of Titan. That wasn't my idea...

Can't say I've ever worried about the heat, but obviously wet ropes would always be preferable! One of the first bobbins I bought wasn't quite machined properly and the groove was slightly off-centre, so I didn't install it and it was replaced for a perfect one. The only thing to watch obviously is the nut coming undone if it's not tightened up properly after installation - it has a little collar on it to allow the front plate to keep swinging, so it's non-standard.

Offline Rob

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Re: BMS Micro Rack question
« Reply #18 on: July 26, 2021, 03:37:17 pm »
Only just spotted this thread. I have used a BMS Micro since 2009. Love it. No probs on 8.6mm for me. I only use one hyper bar.

Alex, where did you buy from? I need to order some new bars but struggling to get online sellers shipping to UK.
The end is where we start....

Offline AlexR

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Re: BMS Micro Rack question
« Reply #19 on: July 26, 2021, 03:47:53 pm »
Pretty much the reason why I fudged around so long Rob, all American sources I looked at didn't ship to the UK, I even considered having it shipped to Germany only for my parents to then send it over to these fair isles.
Originally I was just going to ask somebody headed over the pond to bring one back, but first a certain knight being rescued out of a wet hole drove up US insurance costs for cavers, and then there was something about a pandemic or whatever. So this has been over 2 years in the making.

Only source I now found is a US climbing shop via ebay, but they don't sell individual bars.
 

Offline PeteHall

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Re: BMS Micro Rack question
« Reply #20 on: July 26, 2021, 05:18:54 pm »
I have caving contacts and relatives in the US who may be able to help if you know anywhere that will ship within the US?  :shrug:

Offline AlexR

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Re: BMS Micro Rack question
« Reply #21 on: August 09, 2021, 10:56:52 am »
The BMS rack went on its first trip yesterday, and I'm impressed!

Got a smooth descent, lock off feels secure even free hanging with 60m of fresh air underneath yourself, and it's all intuitive really. Given that I've never used a rack before now it went pretty much as well as it could have. You need more rope for a lock off than for a stop, but if there's very little rope you could simply wrap the rope over the hyper bars until the rope underneath you is tight - meaning you won't be going anywhere in a hurry.

There is only a marginal time difference between threading the rack vs a Stop, and again that's with a descender I'm completely unused to. After a good few trips I expect the rack to be the same, with the added benefit that it can't catch on the carabiner like the free plate of the Stop is somewhat prone to do.

Started playing with the position of the bottom bar for speed control, I think with a little more use and experience this should really give excellent fine tuning.

No use for the hyper bar on 9mm rope, I tried using the descender on cord down to 7mm for a lark (at home) and think you could actually descend this safely. Well, as safe as 7mm will ever be.

An added benefit of the hyper bars is that you'd struggle to suicide rig it as it gives the rack an obvious right/ left, i.e. correct side facing you or not.


There is only one single thing I dislike: Found I couldn't really pull rope through it, when using a Stop I like to get rid of any slack at rebelays, but that's just personal preference.

Although it feels hefty, the micro rack is actually slightly lighter overall than a Stop + Raumer.

Offline alastairgott

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Re: BMS Micro Rack question
« Reply #22 on: August 09, 2021, 11:19:02 am »
There is only one single thing I dislike: Found I couldn't really pull rope through it, when using a Stop I like to get rid of any slack at rebelays, but that's just personal preference.

If you’re using stiff or thick rope, (which incidentally I know you don’t :) ) it’s hard to pull through slack anyway. So no difference for older insitu stuff :)

Offline Stuart France

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Re: BMS Micro Rack question
« Reply #23 on: August 09, 2021, 08:11:59 pm »
What a display of UK caving engineering talent there is in this thread.

If you don't like the Stop then the answer is simply to make your own.  Here's mine made with lightweight titanium bars and titanium nylock nuts.  It takes the standard Petzl bars which seem made of pretty hard alloy.  Aerospace grade alloy right-angle blocks form a top V-shaped brake that suits different rope diameters, and the bottom link is to krab the harness.  Weight is about 350g similar to the old Stop.



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Re: BMS Micro Rack question
« Reply #24 on: August 09, 2021, 10:05:30 pm »
That's fantastic, especially the brake block - like having the Handy krab built-in.  :clap2:

Offline AlexR

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Re: BMS Micro Rack question
« Reply #25 on: August 10, 2021, 09:48:34 am »
If you don't like the Stop then the answer is simply to make your own.

That looks like the ticket! I assume as the groove doesn't see much load on it abrasion there is negligible? Do you see any accelerated aluminium corrosion due to the Titanium? I suppose there is little difference in the electrode potential between Al-Ti and Al- stainless.
Did you ever consider making Titanium bars? Titanium tubing is commercially available, though the required wall thickness might be an issue - and I wouldn't bloody like to bore round stock on the lathe, I hear it work hardens like an absolute bugger.

Coincidentally I did think about machining a top part with some sort of groove like yours under the incorrect assumption that I wouldn't get enough breaking power off the BMS rack on thin ropes. After my tests I'm confident you could safely descend the sketchiest of ropes, so not needed.

Offline PeteHall

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Re: BMS Micro Rack question
« Reply #26 on: August 10, 2021, 11:12:51 am »
I wouldn't bloody like to bore round stock on the lathe, I hear it work hardens like an absolute bugger.

I believe you are correct. We once did a job at a jet engine factory (on the water treatment plant) and had to walk through the machine halls to get to where we were working. The engineers were very happy to show us what they were doing and explained how much of an absolute twat titanium is to work with. You have to get it just right, first time, or it has to be scrapped and re-processed from scratch.

Offline Stuart France

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Re: BMS Micro Rack question
« Reply #27 on: August 10, 2021, 09:15:08 pm »
There are no stainless steel or other ferrous parts in my rack - it's all made of Al / Ti.  My previous descenders were all racks based on stainless steel U pieces with a pigtail on one end for the krab.  The rack bars became unobtainable, and it was quite heavy, but otherwise no complaints.

The main problem for hobby constructors is getting hold of the metal stock.  I got the aerospace grade Al angle from the USA.  A friend over there bought me a couple of hobby lengths of 12" in different sized materials and sent them over here.  The long Ti bars which were already threaded at both ends and the titanium nuts came from a specialist motorbike outfit in the UK.  The ready-to-go rack bars made by Petzl came from Inglesport and I felt these were really well designed and likely to be available as spare parts for some years to come, although I have stocked up on them.  It can all be disassembled easily with one spanner and any worn part then replaced.

The advantage of having the V-shaped brake slot dead centre is that the rack is not pulled to one side when the brake is used and there is none of this left-handed-right-handed nonsense.  I'm a left hander in a mainly right handed world.  The wear on the V slot is minimal as the brake works mainly by the 'wrapped up' shape that the rope adopts when the V is used.


Offline traff

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Re: BMS Micro Rack question
« Reply #28 on: August 11, 2021, 07:57:24 am »
It always makes me laugh when I see 'aerospace grade'. No such thing. A grade of aluminium used in the aerospace industry would perhaps be a better description. I'm no expert but having built my own aircraft I'm very familiar with some of the grades used, some of which would be totally in appropiate in this application. Eitherway it's readilly available in the UK, you just need to know what you are asking for.

Offline AlexR

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Re: BMS Micro Rack question
« Reply #29 on: August 11, 2021, 08:56:28 am »
Well, "aerospace grade aluminium" just sounds better than "Look, the guy in storage mixed up a load of 2011, 6061 and 6082, would take too long to find out what's what, can't we just sell it all under one label?"

Joking aside, given the considerable differences in wear between e.g. the Kong and Petzl racks if I were a betting man I'd say Kong used 60xx (because it's cheap) and Petzl 70xx (because it's hard).

@Stuart:
I understand there are no ferrous metals, but in terms of their position in the galvanic series titanium is comparable to stainless, and galvanic corrosion between aluminium and titanium does definitely occur - ask people with posh titanium fixtures holding down aluminium masts. Though I suspect it won't be an issue under "standard" caving environments.

Offline Stuart France

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Re: BMS Micro Rack question
« Reply #30 on: August 16, 2021, 12:55:57 pm »
Well, I thought 'aerospace' was clearer in this context than '6061-T6'.  It all arrived adorned with bar coded sticky labels in 2ft lengths.  Sorry to disappoint, but there were no mixs-ups in the warehouse.

I bought several sizes to experiment with but the stock I eventually used was 1.25x1.25" equal leg, 0.1875 thick, and 0.125 between-leg radius.  The legs with the paired holes for the long titanium bars were shortened to 1.125".  The reason for imperial meaurements is that I bought from USA after failing to find a UK supplier selling in less than industrial quantities.

I've tried various lengths for the long titanium bars and settled on 210mm including 25mm of threads at both ends, initially.  The top angle in the final rack was later fitted with 4mm thick half-nuts underneath (rather than use full nuts which are 10mm thick) and the resultant 6mm excess thread then poking out of the topmost nuts was removed.  I then notched the top fixed Petzl rack bar to accomodate the half nuts so that it sits flush with the top angle to avoid leaving a gap.

The only noticeable wear so far is on the Petzl rack bars, and that is consistent with level of use.  I thought the angle pieces might need periodic replacement (i.e. the V-brake at the top and karabiner hole at the bottom) but they show no significant wear.   There is no corrosion and it is of course stored in a dry place.  Incidentally, I'm not aware of any commercial rack designs that use only a single metal.  The M10 nuts and long bars are the same titanium material.  The 6061 angles are clamped by paired Ti nuts on both sides.  So the 10mm holes through the angle pieces for the M10 bars are not threaded - this is deliberate.

Used it this weekend in some mines and I'm very happy with the smooth action, the speed range from fairly fast to dead slow and precise locking off to do rigging.  What else is not to like?


Offline AlexR

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Re: BMS Micro Rack question
« Reply #31 on: August 17, 2021, 10:22:29 pm »
Well, I thought 'aerospace' was clearer in this context than '6061-T6'.  It all arrived adorned with bar coded sticky labels in 2ft lengths.  Sorry to disappoint, but there were no mixs-ups in the warehouse.

Sorry Stuart - my comments on aerospace grade Al weren't meant to be a swipe at your choice of metal or identification, just a reflection of my dislike of "aerospace grade aluminium" by people selling a product, as it's inherently meaningless.
But as someone who has had trouble sourcing 7075 T6 in smaller quantities I sure understand the struggle in getting your mitts on certain materials.

Incidentally, I'm not aware of any commercial rack designs that use only a single metal.

The BMS rack I asked about in this thread and have now bought and used is all stainless steel. The manufacturer BMS does not disclose which type(s) of stainless, and if you wanted to be pedantic it could be pointed out that the components are probably made of different stainless steels.


BMS micro rack preliminary wear and handling

I've now used the BMS for 360m of descent (completely on rope). 180m on 9mm, 180m on 10.5mm. It handles both diameters really well, on the 10.5 you're starting to run out of space for locking off, but it's just about enough to pass a loop between the bars.
The wear on the bars is already visible, this is for pretty clean but not pristine ropes. Spent a thrilling half hour or so taking some measurements, mean wear is 0.135mm.* The wall thickness varies between 2.80 - 2.88mm. The bars can be flipped, but you also don't want to wear all the way through a bar on either side, so for argument's sake let's say the maximum wear before retirement is 2.80mm, meaning you'll get 7.5km of descent on clean-ish ropes. More if you predominantly cave in nice clean washed Yorkshire potholes using freshly washed ropes.

Althought I keep a log of all my caving, I didn't write down when exactly I replaced parts on the Petzl Stop. As an extremely rough ballpark under comparable conditions the top aluminium bobbin was good for maybe 1.5km, and the stainless steel handle one for 3-4km.


Info of use to absolutely no one:
The bars on the BMS can visually be identified as straight seam welded pipe. There is no benefit to using seamless here, so good price choice. Deviation from roundness 0.12mm +/- 0.02mm.

*mean wear over all bars compared to averaged measurements of ODs. Don't ask me about the uncertainty, there is enough overanalysis here already.

Offline tamarmole

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Re: BMS Micro Rack question
« Reply #32 on: August 18, 2021, 07:00:44 am »


Incidentally, I'm not aware of any commercial rack designs that use only a single metal.

The BMS rack I asked about in this thread and have now bought and used is all stainless steel. The manufacturer BMS does not disclose which type(s) of stainless, and if you wanted to be pedantic it could be pointed out that the components are probably made of different stainless steels.

[/quote]

I designed and a mate built me a BMS clone; we used 316 stainless throughout.  The bars were Schedule 40 316 stainless tube which has a good wall thickness.

 

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