Plate cutting methods,Nibbler or Torch?

[robmill54]

I'm a first time builder in steel ( 21ft Mal Low tug) and have some fabricating expierence in metal, (non-boat),but extensive wooden boat building expierence. While I understand how to,and have used a torch before, I'm wondering if it would help with distortion issues to use a nibbler instead to cut out 10 gauge plate for the hull?
The nibbler I'm considering is the Makita JN3200 model which is rated for continued use in 10 gauge mild steel. The advantages seem to be a clean cut, clean edges, and since I plan to make full size doorskin templates for the plating, I would think that it would be more accurate to use a nibbler to cut to a line and not distort the plate.
This is a single chine hull with an easy shape and no compound curves.

Opinions?

[Brent Swain]

A torch shrinks the edges, a nibbler expands the edges , great for hollow sections like a clipper bow, but a headache elsewhere, especially on round bilged hulls ,where it does the exact opposite of what you need. It's also slower.
Plasma has made the nibbler largely outdated.
Brent

[lazeyjack]

I think th best way is with oxy /propane, ,
the tip it different, , usae JUST enough pressure to cut, it is fast and cheap
The torch tip is a two piece, more expensive than an acetylene tip
More heat, more buckling, especially with slow travel speeds If your plates are flat, pein the edges after cutting The steel should be wired brushed clean first, spose that's obvious

[BHOFM]

You can, depending on how big your original pieces are,
clamp a piece of angle on each side to use as a guide.
This also acts as a heat sink and prevents warpage.

I have also used a zig saw with a diamond blade.
Slow, but very accurate. And no edge deformation.

[waikikin]

Robmill, you might find that cutting discs in your grinder maybe the "best" way to go for you, a 9" grinder is pretty handy tool in steel boat building, when buying cutting discs get ones that are for stainless- the extra distance they cut is worth the little extra they cost + you change discs less often! Typically I would get around to 7 meters cut on 4mm plate however be carefull to never use them as a ordinary grinding disc by side loading them(Danger!) & also don't force the cut, let the disc float though the steel - like you are caressing a very beautiful but noisy! woman, also protect eyes, ears lungs & skin & keep bystanders & flammables & long/dry grass away. Very little heat distortion with this method & you can get a "blind" start or finish to a cut & with a lttle practice its easy to split a scribed line & all the grinding of edges except for easy removal of a sharp burr & some weld prep if required is done, the cut once the disc is engaged through the steel is generally self fairing. All the best from Jeff. & all the BS back to the joker that bagged my post, I call Bs on you for having no clue on what works in the real world & man up to your negative feedback.

[Landlubber]

Try a cheap Plasma cutter, plenty around now for less than $1000, my one can cut 6mm plate on single phase 240VAC

[robmill54]

Thanks for all the replys, I thought of the plasma cutter , but not a cutting disk. I have 240v available in my home workshop. The tug will be built under cover in my backyard. About a hundred years, or at least it seems that long ago, I was a millwright and so I'm comfortable with a lot of this, but I plan to take a welding class to refresh myself.
I can buy the Makita nibbler for about $200 US and just thought it might be overkill to go for a plasma cutter for a one off job. I suppose I could buy one used and then resell it after I'm finished withbuilding the tug.
I have a 9 inch grinder and will try the cutting disc method to see how that goes.
My plans for the tug are to build to a workboat finish , the craftsman in me however,demands that I do the best possible job that I'm capable of doing regardless of finish level.
Thanks again for the advise.

[Brent Swain]

The beauty of oxy propane is if you run out on a weekend, you don't have to wait for the welding supplies to open on monday. You own your bottle outright, no contracts, and you fit many times the propane in the bottle than you can get acetylene in an acetylene bottle. That is why the welding supplies try to talk you into acetylene. Economic self interest.
I found those $1 each Brico cutting discs from China cut more metal per disc than the far more expensive ones. I once had a race with my torch against a guy with a brico disc on a grinder, and the speed was roughly the same.
Brent

[alan white]

A very fine tooth carbide metal-cutting circular saw blade might be ideal. Expensive, but long-lasting. You can cut long curves with a circular blade.

They sell larger (14") carbide metal cut-off blades for about $150, so a 7" blade would be less.

[Brent Swain]

Have you cut a lot of steel with those blades? How much? Princes auto has one for $200 , but the saw is worm gear drive, which suggests that high torque, low speed is the trick.
Brent

[welder/fitter]

"Robmill",
As "Waikikin" suggested, a zip cut is a decent way to cut your plate, as would be a skill-saw with a metal cutting blade. Oxy-fuel will, of course, do the job, but - as Lazeyjack points out - use a small tip, still, some deformation is expected on gauge sheet. A nibbler is useful for cutting curved lines, but the cutting speed is extremely slow & few nibblers last very long when cutting thicker gauge sheet. The initial cost of plasma scares most people away, though it is of value if you anticipate other metal projects. Of course, you can always sell the plasma cutter at the end of your project.
Mike

[lazeyjack]

Originally Posted by welder/fitter

"Robmill",
As "Waikikin" suggested, a zip cut is a decent way to cut your plate, as would be a skill-saw with a metal cutting blade. Oxy-fuel will, of course, do the job, but - as Lazeyjack points out - use a small tip, still, some deformation is expected on gauge sheet. A nibbler is useful for cutting curved lines, but the cutting speed is extremely slow & few nibblers last very long when cutting thicker gauge sheet. The initial cost of plasma scares most people away, though it is of value if you anticipate other metal projects. Of course, you can always sell the plasma cutter at the end of your project.
Mike

unless you buy aTromphe which will bash through 8mm, but the noise is unbelievable
not seen you yahoo lately, hey found a partner
i think a good man on a torch will cut cooler than a carbide blade, you watch the plate glow with such a blade, also damned things are dangerous if you breathe the dust

[alan white]

Originally Posted by Brent Swain

Have you cut a lot of steel with those blades? How much? Princes auto has one for $200 , but the saw is worm gear drive, which suggests that high torque, low speed is the trick.
Brent

I haven't personally used a carbide saw on 10 guage steel, but have had it suggested to me as superior to the carborundum blades I have used on thick sheet metal. 10 guage is not too thick but it would wear out the dirt cheap carborundum blades quickly enough to be a bit of a hassle always changing them on a big job like cutting panels for a hull.
I'd agree low speed is probably better so I'd check my regular skilsaws for rpm ratings before buying the worm drive mentioned. Skil, Rigid, Makita, and Milwaukee all make good worm drive saws. Is the one you saw for sale a regular brand or possibly a Chinese knock-off? Seems pretty inexpensive for both blade and saw if the blade is also included.
Once the perfect rpm is decided, it might be better quality-wise to buy the saw and the blade seperately. And maybe you can use your existing skilsaw (which I assume you have) if it runs at the right rpm. Can't hurt to try.

[Wynand N]

Originally Posted by welder/fitter

The initial cost of plasma scares most people away....

what no one mentions here is that you need a decent compressor and water traps with it - 100lt tank with 7.6CFM pump unit at least to start with for a small plasma machine capable of 8mm max mild steel cut. (5mm stainless steel)

[Brent Swain]

Lack of adequate air means your plasma will crap out often. I once built a boat for a guy who didn't have enough air for his plasma. He'd go like hell,run out of air and have to wait , while I passed him with the torch. His compressor was not small.
The steel cutting saw I saw at Princess Auto a was a combination saw and blade as a package deal. I don't know the brand.
Brent