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I am trying to build a simple bench using wood and steel for the frame. The frame is made of square steel tube (25 mm, 1.5 mm wall thickness) which has to be cut to length. I have recently purchased an angle grinder (meaning I am a complete beginner with it) and using a cutting disk was able to easily cut through the tube. However, although the cross cut was straight, the cut in the vertical direction always seemed to lean outwards. I removed the excess material using a grinding disk (fortunately the cut had excess material).

Is this the typical way of using an angle grinder to make cuts? Am I doing something wrong? And how do I get more precise cuts?

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    Everybody has heard "practice makes perfect" but almost nobody wants to do it in practice... ;-) – Ecnerwal Feb 27 at 19:00
  • How precise is precise? Nearest 1/8th or 1/16th or 2 thou? – Solar Mike Feb 27 at 19:08
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    if you can leave excess on each cut, cleaning it up later is the best hope for results that look beyond skill level. – dandavis Feb 27 at 19:12
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    @SolarMike Good point. At the end the frame just has to look square. I’ve been assuming within a millimeter is good enough. Wrong? – Andrew Doble Feb 27 at 19:14
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    I'd make a jig to hold everything at exactly the right angle. You'll need wood working experience. Hickory is a nice tough choice for building interfaces to power equipment. – Wayfaring Stranger Feb 28 at 0:40
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What you're describing is just inexperienced workmanship. You did a guillotine cut, like you would saw through a piece of wood.

A better plan would be to use masking tape wrapped around it to designate the cut point, then cut through each face individually.

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    Thanks, this is helpful and yes I have been treating this like wood. I still have a number of cuts to make so I’ll try out the approach you suggested,. – Andrew Doble Feb 27 at 19:05
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    It's also much safer to cut in the way that this answer suggests. Much less chance for the blade to get wedged at an angle and explode if it never goes in very deep. – Jehan Feb 28 at 20:49
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    So I finished the work off using the technique suggested. The cuts were much better and nearly square. Just needed to grind them a little to have very clean and square surfaces. – Andrew Doble Feb 29 at 16:46
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If you'll indulge me a second, I do have a different take

I am trying to build a simple bench using wood and steel for the frame.

If you're working with wood, you can buy metal cutting discs for miter and circular saws (example). These might be tools you already own and they might get you the square cut you need without having to fiddle with the manual sloppiness of an angle grinder.

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If this is something you will do often, you can get an angle grinder holder that will allow it to function like a miniature chop saw. You can make your own, or you can buy a pre-made one, but they all have the basic idea of holding the grinder steady along the plane of the cut and allow it to pivot up and down to make the cut.

This will limit you to cutting fairly small stock, but can make the process quick and easy if you need to do multiple cuts or accurate miters.

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    amazing how much one can fill with weld if the mitre gap is a bit wide... – Solar Mike Feb 27 at 19:52
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    If you build one of these, the most critical thing is that the pin on which the holder pivots must be perfectly parallel with the rotational axis of the tool. I have a Horror Fright miter saw that isn't, and it's impossible to make a straight cut no matter how the fence is adjusted. – StackOverthrow Feb 28 at 17:12
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What I usually do when I'm cutting pipe depends on how square it actually needs to be. If it's going to be bearing against a surface, or if I'm threading the end of it, flatness is very important.

If I can, I usually design things so that the ends of pipe don't need to be perfectly square, because that reduces work for everyone -- but sometimes it can't be avoided.

The general idea of cutting in from multiple parts of the edge is good. One good tip, if you want to be really precise, is to start the cut (without going through) at a few different places and slowly go in until you've got a decent groove in the material -- then you can start biting through the edge of the pipe and follow the groove that's already there (scribed lines and pencil marks can be hard to see and impossible to feel).

In order of increasing precision and effort, here are some ways to mark out such a cut:

  1. Just start cutting from one point and go through to make a square cut (this requires pretty advanced skill to do properly)

  2. You can mark a line and just trace it around the pipe freehand (quick but not very reliable) -- this requires some skill but not anywhere near as much

  3. You can use one point, and then hope that you are able to wrap tape / scribe a line / etc at precisely 90 degrees to the pipe. This doesn't always work perfectly, but it will get you close

  4. If you want it to be very precise, you can measure the distance from the other end of the pipe using a height gauge or a measuring tape or whatever) to two or three points around the cut. Then connect the lines using tape, or scribe them (or both!)

  5. If you are obsessed with getting the cut perfectly flat, you can spray some layout fluid (Dykem, Prussian blue, etc) and then use a straightedge to scribe the line by rolling the pipe. This requires a non-trivial amount of setup, and is really not necessary unless you require an extremely close fit

When I am cutting anything with an angle grinder, I leave a good bit of space (maybe an eighth-inch to a quarter) between the cut and the final dimension -- the cutting wheel itself has a thickness, and it is not always easy to see small deviations while you're still in the cut.

Remember -- you can always go back afterwards and grind off more material from a part, but you can never go back and grind off less material -- unless you are a welder, but that is a different story ;)

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    Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know the details of contributing here. – Daniel Griscom Feb 28 at 13:15
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When I'm working with square or rectangular stock, I'll typically mark my cut with a soapstone on all 4 sides and follow my line on each face. This will get me within about a cutoff wheel's thickness of where I started, which I am going to fill with weld anyway.

Anytime I'm looking for a mostly square cut in round stock, I'll roll the round stock while keeping the angle grinder in the same place.

BTW, if you're welding the frame and also new to that, grind a bevel where the metal meets to aid in getting the weld all the way through the thickness of the metal. This really helps if you have a cheap-o starter welder.

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I fully agree with Harper - Reinstate Monica and a lot of what Tungsten Wizard say show heaps of experience. one tip that can help as well is to wrap a piece of paper around the stock (tightly) so that both sides of the top of the paper line up. Run any marker around the stock and the resulting line will always be square and consistent. This works for Square stock round stock and angles in any material.

  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know the details of contributing here. – Daniel Griscom Mar 1 at 13:13

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