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MG MGB Technical - Cutting sheet metal

In the past you guys have given me good advice on tools. SO I have another question. I am looking to cut sheet metal anywhere from 22ga to 18ga possibly even 16ga.

I am kind of confused about the difference in an air nibbler and an air shear.

Can anyone explain the 2.

Thanks
Bob
bsf Fowler

I just thought of somthing. What would be better AIR or Electric cutters. I do have a 7HP 60gal compressor

Thanks again
Bob
bsf Fowler

Bob, I'd suggest using an air nibbler instead of a shear. I'm aware to two types of shears, one cuts like a pair of scissors and distorts the metal, the other cuts a 14/" section from the metal and curls it up in front of the tool. This tends to get in the way of the user and must be clipped off at times. The nibbler acutally cuts small bites from the metal and leaves a clean 1/4" gap behind. Down side for both tools is to start them in an existing panel you must drill a fairly good size hole. For close tolerance work you could also use a cut off tool to start the slot and an air body saw to cut with. For the hobbiest the tools available from such places as Harbour Freight or Cummins do a pretty good job for very little money. Since you already have a compressor using air tools will be more cost effective than buying electric versions. (No need to buy a motor with each tool)
One more thing, the nibbler will make a little tighter turns than the shear and on the model sold by Cummins Tool the head can be rotated so that the tool body doesn't get in the way of obstructions. I just finished replacing the floor pans on a B using these tools and they worked well for that type job.
Bill Young

Bill Thanks for your advice. Yea I think I will go with the AIR tools. I have been pricing them and I can buy 2 air cuters for the price of one electric. Both with a 1 year warenty and its only $7.00 each for another year on the warenty. SO I think I will buy both a nibbler and a shear.


Thanks
Bob
bsf Fowler

I use an air shear for my projects. It cuts very quickly and cleanly. Never tried it on anything but flat sheet but I don't think it would do very well. For anything with a shape I use a cutoff wheel in an angle grinder or die grinder.
Mike Polan

I work in a sheet metal shop, we use air die grinder with thin cutoff wheel for everything, it is easy to be precise, slower than shear, but more handy. Makes sparks though.
Greg
Greg

I prefer an electric 4" or 4 1/2" grinder with a thin cut-off wheel. Burrs can be cleaned quickly with a file, and the cutting action is fast and precise with no distortion ever. The speed is always correct, as is NOT the case with air tools. They are also cheaper than electric shears, but you pay dearly for good wheels. The other good thing about a grinder is that you can shave small amounts from the edge if you didn't cut enough off. You can't usually do that with a nibbler or shear.
Jeff Schlemmer

I have a hand cutter called a monodex. Works fine for tyhe amount I do.
S Best

Hi,
I just purchased one of these from Harbor Freight, it really workd well.
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=46681
Regards
Tony
Tony Bates

I purchased both a nibbler and a shear. Both AIR. Each for about $60 form Northern tools. And I got a 2 year warranty on each for $7.00 they both seem to work well. The Shears are faster and I think will cut thicker metal but I can cut more difficult patterns with the nibbler. I do have several die grinders also but I seem to get a straighter line with the cutters. (That’s most likely just me).

Now I have to learn how to weld sheet metal. I have a wire welder and an oxygen/acetylene set.

Any advice on this?


Thanks for all your advice. It has always helped and is always appreciated.

Bob
bsf Fowler

Bob, the wire welder will be the most used type for general body work. Oxygen/Acetelene welding is almost an art form. Getting the flame mixture correct for good welds is tricky and it tends to impart a lot of heat into the work which will tend to warp sheet metal. Read as much as you can about these forms of welding, talk to other welders, and practice, practice, practice before you start on your car. Burning a hole in a piece of scrap is just learning, burning a hole in a quarter panel and then warping it when welding up the hole is also learning, but a lesson you don't want to learn. Bondo will hide a multitude of sins, but the price you pay is having to redo the work in only a few years as my midget shows. ;-) Good luck !!
Bill Young

Bob, don't waste your time trying to learn to wire weld without gas - it's more difficult and the welds will look like sh*t. If you haven't done it already, many wirefeed welders can be converted to MIG for < $200 and it's well worth it - night and day.

Couple of hours practice with the MIG and you'll be able to weld body panels up pretty easily.
Mike Polan

I am picking up a bottle for my welder next week. Up until now I have been using flux core. I have been getting some good welds with it but I went to a friend’s house and used his and you are right solid wire with a gas bottle gets a much nicer weld.

I have been told by some people to Mig weld the sheet metal and others say to braze it. I have a sheet of 18ga sheet metal I will be cutting up and practicing on. I will try both methods to see what works the best.

I am a computer Geek and welding is a learning process for me right now.

Thanks for your advice
Bob


bsf Fowler

Bob, forget brazing when working on body panels. My experience has shown that something in the flux or alloy seems to repel body filler. It will seperate in that area and fail. If you're using lead as a filler brazing will work fine, that's the way the old time body men worked the cars back in the 30's, 40's, and 50's. For using modern epoxy fillers stick with welding for best results.
Bill Young

I second that, brazing works really well in some applications but I don't use it for bodywork. With brazing you really should lap weld which means extra finishing. With MIG you can butt weld using many tacks to control the heat and there's very little distortion. Another disadvantage of brazing is that once you do it, you're stuck - you can't weld near the braze without a lot of cleanup.

I think I read somewhere that brazing is making a comeback, but in a strange form (spray deposition?) on exotic metals used a few some modern cars.
Mike Polan

The other point about brazing of course is that of strength. A welded joint is far superior and carried out properly will equal 100% of parent metal strength. Besides brazed repairs are not acceptable for MOTs. Brazing was once used to flush joints between panels but this is perhaps better achieved using lead.
Iain MacKintosh

The biggest thing I found that helped my MIG welding (also being a computer geek who learnt welding myself!) was an auto-darkening helmet. They are well worth the money I found.

As for cutting, I agree with Jeff. I also use an angle grinder with very thin cut off wheels for cutting sheet steel. You do go through the thin wheels fast but cutting is easy and quick and pretty precise for straight cuts.

Simon
Simon Jansen

Yes I also like the auto-darkening helmets. I bought my son one and I find myself using his more than I use mine. I also like a full face lenses. I can see a lot better than with a small lens.

Thanks
Bob
bsf Fowler

Years ago I tried to learn to gas braze well enough to do body work for myself. I practiced on the bench. The sheet metal always was warped and it did not seem to be strong enough. Later I purchaced a Hobart Handler wire feed with co2 argon gas. I was amased at how easy it was to learn and how good the results are. You still have to be careful about warping the long flat panels but it can be done. I have restored 3 cars since and worked on other owners cars. Replaced: rockers, floors, quarters, fender patches, trunk patches, etc. Don't bother with brazing.

For the cutting tools I have a nibber and air die-grinder with cutoff wheel. I rairly take out the nibber.

Don
Don

My personal favorite for cutting sheet metal is an air powered hacksaw. I probably use that tool more than any other. It'll cut through metal up to 16 ga like the proverbial hot knife through butter. It'll cut metal up to 1/4" thick if you're patient.

The replacement blades are rather expensive, but I get around that by buying regular hack saw blades and snapping them into two or three pieces. They fit perfectly, and work just as well as the regular blades as long as you are not cutting a sharp radius. For those, I do use the small replacement blades, expensive though they may be. As small radius cut will only be a small portion of your cutting, the extra expense is not too bad.
Dan Masters

Auto darkening helmets are available on e-bay for about £40 - with free welding gloves.
C Linn

This thread was discussed between 28/07/2005 and 04/08/2005

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