Basic metalwork

[Boulevardier]

Are there minimum bend radii for various gauges of aluminium sheet?

Mike

[Diabolical Artificer]

Been doing a lot of this metal fettling recently, it aint as easy as it looks to get good results. Ali sheet over 1mm ish is a nightmare to bend, you won't bend 2mm without a brake unless you use an angle grinder to score a line on the bend, and it has to be deep.

0.75mm ali is easier, I use a stout pair of scissors and a brake to bend, a brake makes all the difference.

Steel is easier to bend, though harder to drill.

Drilling big holes, you need a variable speed drill, I use my big variac. If your not careful you'll burn out your clutch in a cordless driver.

Marking out is where the skill comes in, I find it very hard to measure, mark and drill two holes accurately, though my eyesight is a bit iffy. So a good 16" ruler/angle is a good idea as is a pair of dividers and also a vernier.

You can use an angle grinder with thin cutting discs to cut sheet, a guide is a good idea, but it can be done by hand, once you get started, then file to size.

Lastly stock ain't cheap, a 2mm ali sheet costs about £70 - 1m x 2m, though your local scrappy might have off cuts cheaper.

Here's a good video on bending - https://www.youtube.com/watch?v=FyXpCPVOr8s I still say it it isn't easy to get very good results, without a lot of experience/teaching and a good workshop; a garden shed with a vice is not adequate. If you have more money than time I'd buy.

Good luck, Andy.

[Radio Wrangler]

Effectively, yes, but I've never seen tables of them. The minimum radii below which a bend is weakened depends on the particular alloy and also upon the surface finish. Linishing, and the direction of the sanding can seed the starts of cracks, so the grit, depth and orientation of sanding plays a part.

Bending metal hot allows it to deform in a plastic way without tearing.

The temper of metal, affected by any heat treatment or previous work-hardening gets in on the act.

Practically, it's easiest to fold a sample to the proposed radius and look at the surface on the outside of the bend with some good magnification.

David

[John M0GLN]

I've not had a great deal of success with chassis making using folding machines, the results were never quite as good, the folds never as sharp etc as the commercial ones.

If I have to make a chassis or cabinet for some gear now I usually use flat aluminium sheet and aluminium angle section, both of which can be worked quite easily at home by the methods suggested in the previous posts, but if I have a lot of cutting or there's stainless steel sheet I take it to a local sheet metal shop where they will cut it up for a nominal charge.
One advantage of the sheet and angle method is if there's a lot of changes to be done the flat chassis sheet can be replaced with another whilst keeping the rest of the framework, and if needed the chassis can be a number of plates for various sections of the circuit. With regards to the aluminium angle sections the mitred ends can be very easily trimmed after sawing with a bench disc sander.

Some aluminium sheet and angle sections I've bought were anodised and won't provide earth connections unless the anodising is scraped away locally.

I generally fasten it all together with stainless steel self tappers, I've attached a couple of photos showing the last thing I made, it's a matter of taste but I think it looks good for this particular type of equipment, if it was going in the lounge however I'm sure a creation by forum member 'David G4EBT' would be far more acceptable.

John

[Radio Wrangler]

Commercial metalwork rarely uses traditional folders. Most usually bends are made with a large press pushing a male Vee shaped tool into a female Vee shaped tool. The piece to be bent is sandwiched between the two. The folds are neat looking and come out to a fairly accurate 90 degrees. Appropriate lengths of tooling get fitted together to make folds for boxes where the other sides have to be cleared.

For thick ali, i cheat and cut each face as a flat piece, jig them together and weld the corners.

David

[woodchips]

If you can afford it, look at the Sheet Metal Machines sold by Clarke, Warco etc where you have a folder, guillotine and roller all in one machine. I bought the 12" version about 20 years ago, used it once to roll some sleeves for an excavator pin so had to be curved over the whole length. Worked very well, I was impressed.

I have a simple 24" folder you can have. I ended up buying that sheet metal system sold by RS, the bench press with lots of tooling, replaced everything else. Did spend, over the years, something like £2000! But neat sheet metal work is seriously hard to do without the right kit, a couple of bits of angle iron in the vice doesn't cut it.

The idea of the Vee folder is that it presses the metal into the Vee, there is no spring back, makes a sharp corner.

Don't forget that to make a box you need to cut the Vee former to the length of each side of the box to get inside. A simple folder, like mine, uses some saw slots to achieve the same effect, not really!

If you fit a vice then mount it so that your elbow, with the arm folded up, is at the same height as the jaws on the vice. You can then actually use it to hacksaw. You will find most benches are several inches too low.

Cone cuts are the way to go, forget drills over about 3-4mm. Don't buy one of those drill sets, 1mm to 10mm with about 200 drills for £30, crap, you can have mine.

If wanted I have a set of Q-max cutters, 5/8, 3/4, 7/8 and 1" you can have. New, never used, replaced by the RS bench press.

Might even sell the sheet metal machine, but weighs 50kg to not a postable item!

[mark_in_manc]

> I went over to a plasma cutter and there's no going back.

There was nearly no going back for me a few weeks back - I was using one on a big piece of 1" plate and concentrating so hard on getting a nice edge I didn't notice I had set the lab on fire. My shoes were smouldering a bit too. Watch where the burning snot is going

I just fixed one of those Chinese guillotine / press-brake / bending roll machines at work. Someone had chewed the teeth off the bending roll gears by going for it with too thick a sheet. I liked it - perhaps I should have persuaded someone to scrap it instead, and then I might have rescued it from the skip...

[joebog1]

Originally Posted by Bazz4CQJ

I have to be the 'spectre at the feast' here. The first time I bought boxes for radio projects was ~50 years ago; anyone recall the 'Universal Chassis' made by Home Radio Mitcham? I've done quite a lot of metal work and I'm reasonably well-equipped, but I've rarely managed to make a box (with a lid) which was of the same standard as a something made on a production line. Getting all the folds in just the right place at just the right angle, eludes me. But I don't need to do it very often, so the level of skill does not increase greatly. You can spend quite a lot of time making a box, which when it's finished, doesn't quite meet the standard.

Of course, this has not been a problem until recently, as it was possible to buy aluminium boxes and chassis at reasonable prices. Maplins used to have a good range. Sadly, such project boxes don't seem to be made in the UK any more. People like Mouser offer quite a comprehensive range of imports, but at a price.

So my current strategy is that if I need a metal box that will be going inside another box (and won't be seen) I may well make one. But if I'm looking for the external housing of a project "of significance", I will put my hand in my pocket and buy a commercial product.

B

Bazz has it in one!! There are several things here that I can add two bobs worth to, as well!! NICE boxes are made with a "PAN brake" NOT a press brake. A press brake can leave marks where the "channel" part causes the sheet metal being bent, to drag along the edge making scratches that are hard to fix. A small press brake is pretty easy made, and there are designs on this, and other fora with similar interests. Hole punches are good, but mainly suitable for "thinner" metal. Step drills are good, but really need a drill press to deliver the power and control required when the holes are large.
WEndyMott, also uses good ideas, as I make many boxes and pieces of tests equipment exactly as she describes.
Lastly, if you electronics deserves a really nice cabinet/box buy one!! There are thousands available from Asia, that you just cannot beat for quality. Its cheaper to buy a Chinese box already finished with laser accuarcy, supplied with all holes tapped EXACTLY square, and to perfect thread engagement depth, screws supplied with options such as black oxide finish, or stailess steel for pennies extra. To buy stock is expensive and MOST vendors wont deal with a one man band needing two 6" X 12" squares of flat sheet. A single black oxide screw of 1/8" or 3mm diameter can be as much as five bob. A box of 200 is about 12 quid or $25 here in Australia. Nuts and washers/ spring washers add extra. Then to polish or paint, add timber sides for a bit of bling. The list goes on.

I no longer have a big workshop, but I do still have boxes made for me by a local plumber that makes air conditioning ducts , and is quite geared up to do such work.
He welds all corners together using a TIG welder to a standard that almost looks cast in, and requires a few strokes only with a fine file, to produce a box that would take me about 3 or 4 hours to make my self. TO the approximate same standard, but involved about 5 grands worth of SECOND hand equipment to achieve. We still have painting/polishing or electro plating to finish off. 30 quid for a small box, 50 quid for a medium-ish one, and say 100 quid for a large one, but smaller than say a 500 watt transmitter will require.

Just my take, and I do accept all the previous advice givven here by some very talented builders, and ingenious ideas.

Best wishes to your efforts
Joe

[Diabolical Artificer]

" I went over to a plasma cutter and there's no going back. " Oooh, posh. Is it one with controllable XYZ? Helps if you don't set fire to yourself though : )

Angle sounds a good plan to join flat sheets, a lot easier than bending. Thought of that but didn't fancy all the screwheads on the surface.

I have a couple of bits of kit in the shed that look like prototypes or even small run type things. They were some sort of video/VHF something or other. They are built in modules built into a frame work that is a sort of mechanno for big lads (not Dexion). There are ali extruded struts, with pre drilled holes at regular spacing's, corner brackets/clips etc. The finish is very good, but guess they don't make this anymore. Something like it would be perfect for us fettlers and meddlers.

Andy.

[dseymo1]

If you want to use the 'sheet and angle' method but to avoid visible fixings, adhesives can be just as effective provided they are carefully used, with correct surface preparation etc. If they can stick aircraft together with Araldite, it's good enough for an equipment enclosure!
Of course, if screening or earth continuity is important, that needs to be addressed.
I've mentioned here before that a scrap caravan can yield enough lighweight ali sheet to keep anyone going for years, but fairly large offcuts are also often available from maufacturers of signs, sometimes attractively anodised.

[Argus25]

I know the topic is "basic metalwork" but once you get the tools and start working the sheet material you will soon master the art or drilling, filing, bending of different materials and you will find how much easier it is to work with aluminium rather than steel.

The real challenge though comes later. The true art of metalworking is not a lot different than surgery, it's about getting the job and processes you want done to the materials with minimal or no collateral damage to the surfaces and having finished edges.

When you file an edge for example the filings want to get between the panel surface and the surface you are holding or clamping it to putting multiple marks on the sources. It pays to have a layer or two of sticky plastic tape on all the exposed surfaces, to be removed after the work is done.

A dial caliper is very useful for measuring and making location marks like cross hairs on aluminium. When starting holes on the location use a sharp scribe to create a small indent and start the hole with a 1mm drill in a hand chuck (pin chuck) and then move to 1.5mm for an initial pilot hole in the drill press, and the larger hole less likely will be off centre from where you wanted it.

After filing edges these can be further smoothed with emery paper. For a flat edge a sheet can be placed on a table and the panel edge run along that, this also works with polishing compounds on a stretched cloth to improve an edge finish. The inside edges of filed holes can be smoothed by wrapping emery paper around the curved surface of a file.

When drilling holes it pays to approach the size you want in 0.5mm steps, the final bur around the hole is less and it pays to use a proper bur remover or countersink tool to remove the burs, as doing it with a large drill held in one hand gives a messier result.

Step hole cutters are good, but if a large number of steps are used, and the material is not well clamped, the holes can drift off centre. Be aware of the effects of clamps on the surfaces.

Metal bending machines leave marks on surfaces too and these can be prevented with tape. A vise's jaws can leave bad marks, so it pays to bend up some aluminium liners for the jaws and a layer of tape can help on those too.

Some people are more interested in the function of the object created, rather than its physical appearance or surface finish and often in the rush to complete a project less attention is paid to the fine details. But I can promise you that if you take the time to attend to the fine details, to make excellent edges on cut surfaces and any holes you make and take the time to precision mark and place the holes, and protect the metal surfaces, you will then be very proud of what you make and have something that works well and is beautiful too.

[emeritus]

Araldite certainly bonds well to Aluminium. In the early 1970's I built a mains unit for my EL3302 in a scrap small chassis that had several circa 1/2" holes, presumably for potentiometers and toggle switches. I stuck strips of masking tape on the inside over the holes, filled the holes with Araldite, sanded the outside smooth once it had set, and spray painted it matt black. It is still sound more than 40 years later. I used the original 2 hour curing stuff, 6/- (30p) for a pack at the time. Hopefully the formulation hasn't been changed for the worse: I note that the instructions no longer recommend it for repairing crockery, although I used the old stuff for reparing a broken earthenware casserole lid that my mother used in the oven for years.

[Radio Wrangler]

Originally Posted by Diabolical Artificer

" I went over to a plasma cutter and there's no going back. " Oooh, posh. Is it one with controllable XYZ? Helps if you don't set fire to yourself though : )

Chance would be a fine thing. Haven't got space for an X-Y table so it's a hand-held one. I run it against a straight edge, or make an over-sized tamplate to allow for the size of the shroud.

A quick zizz with a flap-wheel and it's ready for TIG. I use air for mild and stainless steels, and have a spare argon bottle for aluminium.

When being taught welding at Rolls-Royce, we were outside practicing oxy-acetylene cutting on some old engine test stands. One lad was cutting, shade 4 goggles on, concentrating, and he set the grass of the banking alight. The instructors stopped us telling him. When his overalls caught fire, one instructor doused him with a bucket of water as the other shut the bottles off. They explained that this way he'd never forget it, and neither would we. We all really understood the importance of a fire-watcher.

The more powerful the tool the more trouble you can get into and the more quickly!

David

[Jon_G4MDC]

High tech stuff happening here!
Does anyone recall the Goscut 2000 Nibbler?

I have always wanted one.Obsolete just as soon as I knew about it.

I used one for tailoring proper Issigonis Mini panels but it was not mine.
Some aviation snips I bought working on similar principles - just metal manglers.

Looking for the original!

[dseymo1]

Yes, I have a Goscut, and even use it occasionally.

[MotorBikeLes]

Years ago my pal cut the floor out of a 2.4 Jag using a Goscut. He got through more than one. He bought a Citringham welder to put it back in. not very pretty.
I bought the welder off him about 35 years ago, but gave it to a pal recently when I bought an inverter welder instead. I still have a Goscut, but also a couple of rather more robust tools to same basic design.
David's plasma cutter caught my eye, so I looked at them on "the auction site". Immediately made me think about my inverter welder, a Parweld XTS-162.
I suspect there will be a simple mod to achieve this. Any comment RW?
Les.

[Radio Wrangler]

Mine's an R-Tech bought new. Their prices are pretty decent and their equipment is much better than the super cheap Chinese stuff.

I find I can sometimes alternate quickly between welding and cutting, so having separate machines is best. The welder, though is an ESS ATG211. Very posh. Power factor correction for when you want to really express yourself. It'll o down low and stay smooth enough to weld coke can aluminium. The antenna ast on my gable is welded thick wall sluminium scaffolding tube. It welded that in a single pass.

I've made radio chassis and cabinets by cutting flat plates claping and welding. The bead can be made very smooth, or you can do the sort of stacked coins that make cyclists breathe faster(looks unprofessional to me!)

David

[TrevorG3VLF]

Tin snips made like scissors will result in a bent sheet however a tool is available which cuts a narrow strip out of the sheet, leaving both sides flat.

I bought a nibbler at a boot sale and was told it needed a very powerful drill to drive it. I dismantled it and found the bearing was half a thou over one inch. I contacted the maker to find the correct size but they had moved to Australia. They airmailed me parts and a spare cutter and anvil, all free of charge.

[ms660]

I use a jigsaw for cutting aluminium sheet and a compound miter saw (my woodworking one) for cutting aluminium profiled stock.

Lawrence.

[ajgriff]

There seems to have been much discussion here about some pretty esoteric pieces of kit with little mention of such essentials as the vice and a selection of hammers. It is so important to have a decent engineers vice with integral anvil, securely fixed to a solid bench, and to keep it in good condition. The same applies to hammers which should have their striking surfaces smoothed and polished on a regular basis.

Personally I wouldn't be without off-set (left and right) tin snips with long handles for steel work. These allow sheet material to be cut without distortion to the work piece itself. It's only the waste that gets distorted when the snips are used properly.

Good quality examples of these items are obtainable second hand at very reasonable prices. These are often better made than newly produced versions. Sometimes they will need fettling but, for me, that is all part of the fun.

Alan