Bobcat Owners - "blocking up question"

Started by Redhotsal, May 28, 2009, 01:51:35 PM

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Redhotsal

Bobcat owners....
A friend I know has had a load of trouble with their Bobcat - it seems to "clog up" even after a few minutes use and she has to keep stopping to clean it out. As far as I can make out she isn't doing anything odd or wrong - and she spent a day happily using my minor burner without any technical issues. She also bleeds out the hoses at the end of the session so it doesn't seem likely that the gas has settled and caused a problem.
Have any of you ever come across this sort of thing - or does it seem likely that she has a problem with that particular torch? She's running propane and oxycon. I  have very little experience with Bobcats so thought I'd ask on here.
Many thanks
Sal

garishglobes

Is it new? Mine used to spit out a bit of carbon, but I heard somewhere that this was a "settling down" issue... certainly, after a few weeks, it stopped and rarely spits at all now. I do find I need to run a good oxidising flame with it. It doesn't like waffy or very reducing flames for very long at all - if I run a 'cool', waffy flame I tend to give it a bit of an oxygen blast afterwards to clear things out again. Don't know if I'm meant to, but it does seem to help.
The bobcat does put out a hot flame, so if she was used to a Minor she might be running it a bit cooler than it likes??

julieHB

Hi, just to back up what Emma says, it sounds like your friend runs a slightly reducing flame all the time. This will cause build up of carbon unless the "fingers" are 1cm or so long (basically full power with one oxycon). It is very important that your friend does not run a small reducing flame for long, this will initially cause the glowing specks on the face of the torch (carbon), but can over time cause overheating of the tubes, which can ruin the torch.

I was quite confused for a long time, having only seen Manda's Minor in the flesh, and seen how the neutral flame "should" look. I would say that on the Bobcat you hardly see any yellow at the tip of the flame fingers when it is running neutral.

If you want a small flame just make sure you turn the propane down enough.

I got this advice from GTT, after I enquired whether I could adjust the flame down without ruining the torch. Since adjusting my propane down a bit I have had no carbon build up at all.

HTH  :)
Julie xx

                           My Webbie - My Flickr

beadysam

I agree with everyone above.  One good tip though, turn on your oxycon and just let it run through your torch for 5-10 mins to settle down and bed in.  I find if I do this I get a much more stable flame throughout my session, and rarely if ever, have to adjust the torch.

HelenV

Hi,

I have the same problem with my Bobcat - I`m glad its not just me!

I spoke with Sean @ Off Mandrel who said this does happen if you are running the flame too low - which I was.

I need my Oxycon as close to 5lpm as I can get, and this stops the problem.

I also find that as I work, if this happens I can brush the carbon away with a little wire brush from B+Q which gets the candles all back to full size again - how safe this is I don`t know but it stops me from having to stop, turn off the torch, bleed the lines, clean it and restart.

Apparently the Bobcats like as much 02 as you can give them, and reduce the propane. My candles are 8mm ish, with no yellow tips and I find this works well.

Hope that helps!

Helen x

www.helenvanekdesign.co.uk
www.etsy.com/shop/helenvanekdesign

julieHB

Helen, when I asked the specific question to GTT whether it was possible to run a small flame I got this reply:

My question:

"I have heard from somewhere that one can ruin the Bobcat by
adjusting the flame down to a pinpoint to make fine stringer work - is
this correct? For this reason I always keep a rather full flame. But
then I read on some forums that the beauty of the Bobcat is that you can
adjust the flame quite a lot. It certainly would make some work a lot
easier :-)"

GTT's answer:

"Hello Julie,
What you have heard is not true.  You can run many flame types as long
as you watch for any sign of the flame overheating the torch.  You need
to watch for any specs or tubes starting to glow, this indicates that
the torch is overheating or carbon is starting to buildup.  Nothing on
the face of the torch should ever glow.  The only flame type that will
cause carbon or glowing is a short soft flame.  If you want to run a
soft flame the candles in the flame must be kept at 3/8" or longer, this
will insure that there is no carbon or overheating.  If you want to use
a smaller flame, back the fuel down and adjust the flame with the oxy
valve.  Our Bobcats can get a good small flame by adjusting the fuel and
oxy down, just watch for carbon or glowing and adjust accordingly."


Since then I have adjusted down the flame many times, with no specks at all - so, the key bit is to decrease the flow of propane enough!
Julie xx

                           My Webbie - My Flickr

HelenV

Thanks Julie, thats really helpful. I`ll try it tonight.

I`ve only had my Bobcat for a few weeks, and it took me until 10 days ago to actually get it lit properly!

Hopefully the carbon will settle after I have used it a bit more. Out of interest, how long are your candles normally? I wonder if mine are too small.

Helen x

www.helenvanekdesign.co.uk
www.etsy.com/shop/helenvanekdesign

Redhotsal

Wow, well thanks everyone for the replies. Sounds like it's not an isolated problem and it also sounds like the Bobcat doesn't like a small flame.

Have to say that the old minor burner doesn't care at all what flame it gets. If you had a slightly dodgy oxycon which wasn't chucking out enough oxygen - and one of mine can be a bit tempermental - it looks as if it could be problematic if you are running a Bobcat?

So, what's the big advantage of the Bobcat as compared to the Minor Burner - cost? ease of use? Not sure I would want to recommend one to any of my students unless you guys love the Bobcat for other reasons?

julieHB

Quote from: Redhotsal on May 28, 2009, 06:38:11 PM
Wow, well thanks everyone for the replies. Sounds like it's not an isolated problem and it also sounds like the Bobcat doesn't like a small flame.

Have to say that the old minor burner doesn't care at all what flame it gets. If you had a slightly dodgy oxycon which wasn't chucking out enough oxygen - and one of mine can be a bit tempermental - it looks as if it could be problematic if you are running a Bobcat?

So, what's the big advantage of the Bobcat as compared to the Minor Burner - cost? ease of use? Not sure I would want to recommend one to any of my students unless you guys love the Bobcat for other reasons?

It doesn't mind a small flame, Sal, it minds a small reducing flame (for a longer period).  :)

I chose the Bobcat over the Minor due to:

1) I got it at sale price, making it the cheaper option  :)
2) It came recommended because it is sooo quiet, and burns very, very cleanly.
3) From what I understand it can burn hotter than the minor, and one can do some boro work, certainly if upgrading to 2 oxy's.

On the downside, it needs to be sent to the US for servicing, and obviously cannot take all kinds of abuse like the minor, which has a reputation of reliability. I think the Bobcat was designed to be used with bottled oxygen. It works fine with one oxycon, just as long as you know that the neutral flame will look different from the Minors. Hmm, maybe I have just found what needs to go on this years xmas list??  ::)

I am very much looking forward to hearing reviews on the GTT Cricket, which I think was designed for low pressure oxygen. When George comes home from vacation maybe she'll give us a report  :)


Helen, my flame is about the same as yours, when running the oxycon on 4.5 l/min. If I get impatient and want to melt something fast, that doesn't mind a bit of reduction, then I do turn the propane up a bit - at that flame size (candles 0.9cm +) you will not overheat the torch.


Julie xx

                           My Webbie - My Flickr

Kaz

I have had a play on George's Cricket and thought it was a cracking torch - even on one oxycon it was red hot!
Kazx
She's made of real glass. She got real real emotion. But my heart laughs I have that same sweet devotion!

garishglobes

I'd have to say, I adore my Bobcat :) It isn't just the colour, honest - for me, it is definitely the heat, and the fact that I could quite easily melt a fairly decent sized piece of boro with one oxy, without too much of a reducing atmosphere. It is easily adjustable, and Julie is right - it runs just fine as long as you don't spend ages with a reducing flame, which you wouldn't want to anyway.