Cutting steel to size

[Nicholas FarrParticipant @nicholasfarr14254]

Posted by andrew lyner on 13/05/2019 20:45:43:

but a grinder won’t do circles.

Hi Andrew, not strictly true. You can cut a disc with an angel grinder by starting with a square the size you want your disc (or slight bigger if you need to tidy up) mark the disc out on the square and then cut a straight line at 45 degrees on each corner so that it just touches the circle that you have marked. once you have the four corners cut, you can then cut two more straight lines each side of the corner cuts you have just cut and again just touching the circle you have marked after that you can do the same on each side of those you have just cut. You will come to a stage where you have a knobbly circle and the high points can then be flushed down to the circle line that you marked, using a flap disc. It's a bit long winded though and you need to have a good hand/eye coordination and keep the disc perpendicular to the metal, but it can be done. Of course, if you can get most of it cut by this method and can then trim the final diameter on the lathe all the better.

Regards Nick.

[not done it yetParticipant @notdoneityet]

Posted by Nicholas Farr on 14/05/2019 00:35:10:

Posted by andrew lyner on 13/05/2019 20:45:43:

but a grinder won’t do circles.

Hi Andrew, not strictly true. You can cut a disc with an angel grinder by starting with a square the size you want your disc (or slight bigger if you need to tidy up) mark the disc out on the square and then cut a straight line at 45 degrees on each corner so that it just touches the circle that you have marked. once you have the four corners cut, you can then cut two more straight lines each side of the corner cuts you have just cut and again just touching the circle you have marked after that you can do the same on each side of those you have just cut. You will come to a stage where you have a knobbly circle and the high points can then be flushed down to the circle line that you marked, using a flap disc. It's a bit long winded though and you need to have a good hand/eye coordination and keep the disc perpendicular to the metal, but it can be done. Of course, if you can get most of it cut by this method and can then trim the final diameter on the lathe all the better.

Regards Nick.

Perhaps Andrew should have qualified his statement and explained that angle grinders can only cut angles and cannot cut in circles. Ie, they can only cut straight lines.

Of course, even then the pedants amongst us might well have pointed out that a straight line is, in fact, part of a circle (of infinite radius). You just can’t win, on the simple specifics, with some.

Perhaps you have the time to make an infinite number of cuts (all at a tangent to the circumference desired), in order to produce a circle. Most of us don’t, as it would take a very long time.

[JasonBModerator @jasonb]

Nice simple circle cutting jig here

And before the comments that you need ahole in the middle this one has promise, just don't wear nylon trowsers or cut through the wire.

[andrew lynerParticipant @andrewlyner71257]

I love that magnetic clamp!!

An angle grinder could work for large radii and many / most discs would need a central hole. However, if I rough cut a circle – either by stitching or with many straight cuts, I still would need to clean up the edge which could tax the poor little mini. This is why I wanted to do it on the (replaceable and cheap) pillar drill.

I was even considering an auxiliary / temporary replacement drive to power the lathe at lower speeds (an extra motor to fit the spindle – extended) but that sort of approach can easily be open ended and demand more and more complication.

I haven't read any serious comment about the cheap and cheerful flying cutter idea. I don't want to chuck away my money, even if it's less than $10 so I though someone here would have tried it once and either rejected the idea or thought it worth while. The advantage would be that the resulting circumference would be pretty clean.

But I now have the disc I needed for this particular job so I will worry again next time round.

Thanks for the comments guys.

[JasonBModerator @jasonb]

I've only used the single point type cutters on brass and even then I tidied up the disc afterwards in the lathe. Back in the day they were often used to put holes in old galvanised tanks and usually driven with a hand brace so they do cut holes in steel.

[not done it yetParticipant @notdoneityet]

Isn’t the OP only wanting bits up to 40 mm in diameter? Cutting, then grinding with an angle grinder would work but I very much doubt Steve would master cutting a ~40mm circle with the set up shown above.

Like trepanning – again easier for a new starter to trepan larger diameters with shallow grooves, but not so easy for the smaller ones, particularly deeper, in thicker metal.

[Nigel Graham 2Participant @nigelgraham2]

I take off the worst of the "teeth" with a file or angle-grinder before machining a stitch-drilled edge, to reduce the hammering effect on the poor machine and tool.

Cutting thin metal with an angle-grinder or a jig-saw is a bit quieter if you sandwich it between a couple of sheet of gash plywood or similar, with the under-sheet just clear of the cut, the upper a bit further back to be clear of the grinder. I did say "bit quieter"… These power-tools are noisy enough as they are!

[SillyOldDufferModerator @sillyoldduffer]

Posted by andrew lyner on 13/05/2019 19:44:52:

I keep finding the need to cut discs out of 5mm steel (I bought a lot of 100mm square offcuts for pence and I am using them where I can).

I tried the circular cutters that come in a set. One was fine and I managed a 65mm diameter hole in some 6mm sheet (also from the offcuts place). I used plenty of cutting fluid and put my toy pillar drill on the minimum speed. It worked fine because I took ages and ages over the job. The 85mm version just wouldn't touch the steel, despite the oil and slow speed; annoying.

So I tried a 2mm HSS parting tool and it actually worked but it was at the limit of the mini lathe capabilities. The belt kept slipping and graunching and I imagine the spare will soon be needed. Not the best technique although it gave a result eventually.

I was wondering about trying one of those Adjustable Circle Cutters. Some have on blade and some seem to have two blades. But they are sooo cheap that I cannot believe they would do anything substantial.

Apart from the "I wouldn't;t start from here" answer, is there a way forward?

A number of good answers already, especially from Jason, but I'd comment this is a variant of the classic and often very difficult hobby problem 'asking too much of the machine available'. In this example, although the job can be fitted physically, both pillar drill and mini-lathe lack the power and/or rigidity needed to hack through that much metal. The larger circular cutters are a particularly big ask.

The way to approach it is to find ways of reducing the amount of metal removed. Chain drilling works by making lots of small holes over a longer time, trepanning by allowing a single point tool to attack a small area of metal. Or you can use a brutal tool like an angle grinder to chop off as much as possible before tidying up on the lathe.

Faced with the problem of making discs from plate, I'd chop the corners of the plate to an octagon with the angle grinder, then super glue the octagon to a mandrel in the mini-lathe, and turn what's left to a disk. This reduces the work done by the lathe into its comfort zone.

But! I think using scrap to make discs is more trouble than it's worth. As you've spotted, it really isn't the best place to start. A better solution is to buy rod that will fit in the lathe without needing loads of tedious pre-processing. And buying new metal avoids another potential booby trap; a surprising number of alloys do not machine well. After several painful experiences I now avoid random scrap, instead buying alloys intended to be machined. It saves a lot of time and trouble.

Last comment, my single most useful workshop purchase was a cheap bandsaw. Hand sawing is good for small items, but otherwise nothing but boring time wasting hard work. Metalwork is much more fun when you can get on with it. Don't despair. I started small and gradually built up the machines and metal over several years. Not flinging money at my workshop was interesting in its own way and taught me many tricks. But I made a lot of mistakes, got frustrated, and the floor is still bloodstained…

Dave

[andrew lynerParticipant @andrewlyner71257]

A band saw. Yes, I was looking on eBay the other day and I'm waiting for one to turn up, locally. There will be the pr

m of where to put it in my tiny shed but a few things could go to the tip and we wouldn't miss them.

Most of the saws that are on sale are for wood, though. Grrr,

[andrew lynerParticipant @andrewlyner71257]

I located (locally) and bought a Clarke 4 1/2 inch bandsaw on eBay and, once I sorted out some lunatic mistakes the seller had made in originally assembling it out of the box, I am really impressed with what it does. It chews slowly but surely through all sorts of materials and leaves a terrific finish. As people have mentioned in other posts, you just leave it to get on with the job and it turns itself off when finished. Brilliant and only £127 !! (including a new spare blade)

[Jeff DaymanParticipant @jeffdayman43397]

That's a great result Andrew! congratulations. Price paid sounds like a great deal.

[Howard LewisParticipant @howardlewis46836]

I have a 4 1/2 inch Warco Bandsaw, probably a clone of the Machine Mart ( Clarke ) one.

The bearings on the wormwheel shaft were separated by a very thin wall tube. this eventually broke up and worked its way through the lower bearing and oil seal. Whilst replacing the bearings and oil seal, a thick wall brass spacer was made up. Since then, no more problems. At the same time, the back of the gear was skimmed to remove enough of the teeth to prevent them rubbing on the gearbox casting.

Some time ago, in E I M, I think, a design was published for a blade tensioning device. Basically, it was a clock, clamped to the blade to measure the extension as tension was applied. I made one, and since then have had longer blade life, and very little problems of the cut being curved (Excessive downward pressure will accentuate this )

It is worth spending time ensuring that the guide rollers are set correctly, and that there is no excessive clearance in the Idler pulley, (and that the surface on which the blade rides on the pulleys does not run out.

Once fettled and adjusted, it is not a bad machine, for hobby use.

Howard

[Enough!Participant @enough]

One thing that I wasn't happy about on my 4 x 6 bandsaw when I got it was the grounding. The incoming connection was grounded to the chassis at the point of entry. The motor, however, is mounted to the moving part and the only ground connection between them was mechanically through the pivot.

I jumpered it on mine with a heavy ground braid.

I've had my bandsaw for many years now and it may well be that current models have addressed this issue …. wouldn't hurt to check though.

[andrew lynerParticipant @andrewlyner71257]

My bandsaw seems to be a mixture of good and bad quality construction and design. Where it really counts – the nice chunky frame and pulleys are reassuring and also the general 'band control' features seem fairly substantial. The electrics are a bit screwed-on as an afterthought and I will look into the grounding – thanks. The stand, the vertical cutting elevation control is a bodge and the bent tin legs and table are a joke. When I took the unit off the back of my truck, at home, half the screws had come out and everything was bending alarmingly in my arms as it neared the ground. A few extra spars and even a bit of tack welding might improve it all.

A lot quieter to use and more predictable than the old angle grinder.

Edited By andrew lyner on 24/05/2019 23:03:00

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