Thread: How To Drill Accurately Located Holes in Inside Radius of Angle Iron?

Originally Posted by ozheat

I typed out a lengthy reply but the browser crashed, so I thought a diagram would be quicker.

Use 2 scrap pieces of flat/angle and clamp to your drill table to act as a guide.

To find hole centres between 2 holes.
Measure the outside edges of the 2 holes and then simply subtract one hole diameter assuming the 2 holes are the same diameter.
eg. the mesurement of the 2 outside edges are 227mm and the hole diameters are 6.5mm The centers of the 2 holes will be 227mm-6.5mm= 221.5mm

Hi ozheat,
If I am measuring hole centres from two previously drilled holes of the same diameter, I measure from one edge to the corresponding edge on the other hole. It saves having to subtract one hole diameter.
Another way is to get some rod the same diameter as the holes and machine points on them. Insert them in the holes and measure across the points. This method works for holes of different diameters.

Phil

I'd just like to add some further considerations for some of the other methods mentioned.

I also thought of using the tube to which the angle iron will be attached and using this as a drill guide. However this would require the V-blocks to hold the angle iron and secondly there will be a gap between the bottom of the tube and the inside corner of the angle iron to where the drill point has first contact. If there is any tendancy for the drill to "wander" it could snap the drill. It would be different if it was a flat surface that was being started on. It might work but tread carefully at the start.

Ian, thanks for the thumbs up, but using the wood takes away the locating properties of the jig. Normally jigs are made with hardened bushings for the drill bit so that the jig holes are not gouged out by sideways forces. The locating slot is much better in the flat steel bar so the locating holes are hard against the point where the holes will be started. Any tendancy for the drill to wander (move sideways) would just eat the wood away then the drill may snap when it bends.

Eddie I was thinking of something like that.

I have some pipe with an ID the same as the OD of this stuff and 3mm thick walls.

It seemed to me I could use it for a jig for drilling the pipe.

Now thinking of your idea I see I could use it as a jig for drilling the iron, too.

I could weld some sides on it and weld overturned angle under them so's it'd be at the right height and there'd just be enough room to slide a new workpiece in under there.

And I've been thinking and I'm not sure about what's so good about 'V' blocks? I mean I can see the usefulness without doubt - but can I make a perfectly adequate block out of a few pieces of angle iron stuck together in the way I'm proposing there?

All you have to do is mark out your centres and centre punch the outside corner and drill the hole, if it still trys to wander put a small drill through first it is that simple

Hi I would just like to say I agree with what beefy says ,but a further Idea

would be to make a good fitting steel dowel that will fit the holes in the pipe

that are already drilled, they don't have to be long then predrill the dowels with a smaller drill that would most likely stop any wandering and taper off the end of the dowels and this would make shore that you are centered in
the internal of the angle Iron, clamp up and drill pilot hole,then drill correct hole.

Cheer's Eddie

Originally Posted by BobL

V blocks are incredibly useful gizmos, you won't regret having one on hand.

Or Two....so you can support a long round object for machining.

I had to make a 'Bench Block' at TAFE, 30 years ago...didn't know what I was going to use it for..but I've used it quite a few times. Similar to a Vee Block, but has different size holes in it so you can drill right through a job.

got to admit I don't understand the steel dowel thing?

I finished up having to get it done before I could get a satisfactory method organised.

So what I did was put a 'template' piece of angle (that is, already drilled and acceptably straight holes) inside the next piece. Ground the angle away so's it would fit into the radius. So's one is nested inside the other. Sharp angle down. Inside radius looking up.

Then the two together clamped in my drill press vice alright. It held both of them at once.

So then I took the 1/4" drill down through the template and into the workpiece.

Just making a starter 'pit'. Because I couldn't guarantee the work was level in the vice.

Then I took the template piece out, levelled up the work with a spirit level and drilled.

Not a very satisfactory way of working for production of many pieces but it got the job done.



In future I'll try beefy's jig, especially after I get the spotting drill and the end mill I've ordered.

I think it is a bit hard trying to make a bit go straight down through a sharp angle but I'm no engineer or any kind of tradie nor even experienced home handyman, really. We'll just see how it goes.

I could grind a land about there easy enough, the job doesn't require the back of the angle remain sharp.



In fact the job doesn't require the holes be through the angle at all.

I chose that because it looked to me to be theoretically the best location to put bolts that are going to hold a rod or tube into an angle bracket.

The angle supports from two side and the bolts draw it right into the angle.

But for this application which is very light - frame for a shade shed - I think it would be easily strong enough if the bolts went through one of the sides of the angle iron. In fact I'm sure of it.

So the next one I'll give that a try. It'll be a damn sight easier to do I reckon.

But just a fraction out and one side of the tube will get no support from the angle - it will be getting all support from the bolts themselves, until the bolts give a little and it bears on the angle.

All a lot of nonsense, there's going to be no such forces acting on this thing and if there were the tube would give way like tissue paper.

Ha. The whole thing is incredibly badly designed. Brackets immensely too strong for the tube and designed (hole position) wrongly. But that's because " I'm no engineer not even a tradesman....". etc

I do thank everyone who's taken an interest and helped out with suggestions.

Thanks.



p.s. following that line of thought: rationalising the design - it doesn't even need to be angle iron, I guess. 2mm steel would be stronger than the pipework. I could have made it out of 2mm steel strip, or even 3mm perhaps.

Next time I might try to do more design thinking before I charge ahead.

Originally Posted by abrogard

Next time I might try to do more design thinking before I charge ahead.

Yeah, but it's amazing how much thinking time can go into one little operation. Easy and fast once we know how but before that, the skins worn off your finger from scratching your head.

I'm glad you started this thread because it made me realise I didn't have an instant answer if I ever need to do it. I've mentally noted your angle inside angle method too.

Keith.

Yep. Sorry I screwed up the thread so badly.

It got all mixed up between:

(1) how to mark out and drill two holes in 25mm angle (the question I asked)
and
(2) how to continue from there making more....

What I was raving on about on my last post was how I'm 'making more', wasn't it?

Which wasn't the question. The question was how to make the first one.
And though I didn't do it I think the best way to mark out and drill (the actual question) the very first one, the 'template' is beefy's (keith's) jig.

That creates the template. That's what it's all about.

Continue making them from there more or less as I have done - nesting one (the template) in the other - but using a V block instead of my cumbersome time consuming spirit levelling.