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  #21  
Old 09-08-2017, 07:06 PM
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digger doug digger doug is offline
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I usually don't need to light the propane, then hold it against the plate to add oxy.
I just turn on both propane and oxy approx. to what I think is right, then use
the spark lighter, then adjust from there, the flame already attached to the tip correctly.
"Hot starting" is the term.

As far as machine torch usage, the larger machines usually run (5) regulators.
Preheat fuel & Ox, cut Ox, and "running heat" fuel & ox.

The computer switches from preheat to "running heat" by solenoid, to lower
the preheating flames once cutting to help retain the top edge of the cut.

Cutting thick plate means slow speeds, and with a large preheat to get started,
once cutting, it has a tendency to melt over the top edge of the cut line.
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  #22  
Old 09-08-2017, 07:48 PM
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Quote:
Originally Posted by BukitCase View Post
Also, from this
http://www.wilhelmsen.com/marine-pro...ne-vs-propane/

quote - "Cutting

Propane can like acetylene be used for cutting. If you cut with acetylene, you normally put the tip of the inner flame cone on the metal (1mm from the plate surface). If you do the same with propane, you will be waiting for a long time. If you raise the torch so that the outer flame cone is used the preheat process is started faster. Propane releases only a small proportion of heat in the inner flame cone (less than 10%), so most of the heat in the flame is located in the outer cone. Acetylene releases almost 40% of its heat in the inner flame cone. "

More on the above link... Steve
This!
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  #23  
Old 09-08-2017, 07:50 PM
AussieTom AussieTom is offline
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The top edge will only melt over noticably if the pre-heat is too high or travel is too slow, or both. Correct size tip selection and settings matters, regardless of what your cutting. After the initial setup, the CAM sortware should prompt the correct variables.

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  #24  
Old 09-08-2017, 08:04 PM
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Quote:
Originally Posted by AussieTom View Post
The top edge will only melt over noticably if the pre-heat is too high or travel is too slow, or both. Correct size tip selection and settings matters, regardless of what your cutting. After the initial setup, the CAM sortware should prompt the correct variables.

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....Uhm yeah....in the real world it is a real problem, hence the money spent
on 5 hose set-ups.
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  #25  
Old 09-08-2017, 08:55 PM
AussieTom AussieTom is offline
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Pretty sure im in the real world, hard to tell though. I didn't refute the '5 hose setup', ive never seen one, but that doesn't mean there not available or good. My experience is with three line torches, even on the biggest machines. Fuel, pre-heat oxy and cut oxy. In the version of the world i live in, its not a problem with properly set up CNC machines. Still a problem doing it manualy. Not very often i need to do a manual cut in plate thick enough for it to be an issue.

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  #26  
Old 09-08-2017, 10:07 PM
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Matt Shade Matt Shade is offline
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Quote:
Originally Posted by AussieTom View Post
Something is definatly not right with the setup. You need to start with the fuel slightly lower and bring the oxy in, then increase them both, otherwise the flame will jump off the tip. But thats fairly obvious once you do it. Maybe your bottle pressures were way out? Or like doug said, wrong tip. I have never seen anybody set one just with regulator pressures like was suggested above, seems like an odd approach.
As far as consumption goes, the rule of thumb here is 3 "G" size oxy the 1 40kg LPG. We do use big heating torches alot, and all the cnc profile cutters and pipe cutters use the high speed tips, which consume more oxy than the standard ones.

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If you're referring to me, I didn't say you adjust it entirely from the regulators, I said you adjust your flame with the oxygen after your fuel valve is wide open. It's easy to barely crack the knob on the propane and then tweak the oxygen to get a pretty blue flame but it will take a week to make a cut (which is what most guys claim is the problem with propane).
You have to drive a propane tip hard. Open the valve a little and light it. Add a bit of oxygen, add more fuel, add more oxy, add more fuel. When the fuel is wide open and the torch is singing to you, tweak your oxygen for the proper flame and go to work. The regulators get set at the prescribed pressure for the tip your are using and left alone.

Smith Equipment demonstrates it in this video, adjusting the flame starts around 5:45
https://youtu.be/f2amO0T3vkQ
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Last edited by Matt Shade; 09-08-2017 at 10:16 PM.
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  #27  
Old 09-08-2017, 10:56 PM
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Quote:
Originally Posted by digger doug View Post
once cutting, it has a tendency to melt over the top edge of the cut line.
The melted edge is from an oxy rich flame,IMHO.
All pantograph and cnc flame cutters use propane, and cut a very clean edge, some of it is speed, but correct flame set is also part of it.

I see Aussietom mentioning high speed tips. I read up a bit on laminar flow and the bigger the tip the nicer the cut in thin metal. I normally use a #0 tip for everything up to 3/4", but if I want a nice cut, I put on a #3 tip for 1/2" and up. Plasma has spoiled me, though.

The oxy stream starts to get bushy in a short distance in a 0 tip, compared to a #3 because a 3 is designed to keep that stream together for a 2" and keep straight.
The laminar flow characteristics of a tip is why you keep oxy at 35psi and the propane at 5psi. I find when working scrapping, the scrap cutters always set for 60-70 psi and wonder why the cut looks like an alligator attack and the flame is hard to set.
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  #28  
Old 09-08-2017, 11:55 PM
AussieTom AussieTom is offline
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Quote:
Originally Posted by Matt Shade View Post
If you're referring to me, I didn't say you adjust it entirely from the regulators, I said you adjust your flame with the oxygen after your fuel valve is wide open. It's easy to barely crack the knob on the propane and then tweak the oxygen to get a pretty blue flame but it will take a week to make a cut (which is what most guys claim is the problem with propane).
You have to drive a propane tip hard. Open the valve a little and light it. Add a bit of oxygen, add more fuel, add more oxy, add more fuel. When the fuel is wide open and the torch is singing to you, tweak your oxygen for the proper flame and go to work. The regulators get set at the prescribed pressure for the tip your are using and left alone.

Smith Equipment demonstrates it in this video, adjusting the flame starts around 5:45
https://youtu.be/f2amO0T3vkQ
That would work fine i suppose, and is probably the technicaly correct way to do it. That being said, thats not how anyone ive ever seen does it. Fuel is set at roughly 400kpa (60psi), oxy in the colour bar that corresponds with what your doing (welding, cutting or heating). Then light and adjust. Takes 5 sec and gives perfectly accaptable results, good enough that nobody ever bothers to find the literature and do that. Just so doug doesnt jump down my throat about it, the big profile cutters are a different story. They only use flame cutting on material over 30mm. The regulator pressures are still static, im just not sure on what they are set at.

Seems like alot of things i was taught at trade school. There is the "correct" way to do it, and there is the way that everyone actualy does it.

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  #29  
Old 09-09-2017, 02:53 AM
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Wolfram Wolfram is offline
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Quote:
Originally Posted by digger doug View Post
Sounds like you didn't switch to the 2-piece tip.....
No -- I used all the right tips and equipment. Just couldn't seem to make it run right.

Quote:
Originally Posted by AussieTom View Post
Something is definatly not right with the setup. You need to start with the fuel slightly lower and bring the oxy in, then increase them both, otherwise the flame will jump off the tip. But thats fairly obvious once you do it.
Indeed, it was.
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