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

I use a centre drill to start the hole to eliminate wandering..

I'd like to see a photo of the job and the marking out on the piece of angle iron?

Cheers,

Simon

Here's a drawing of the job - original back of the envelope thing - there's the angle iron acting as a bracket and a 1" pipe that fits it.

There's two 1/4" holes go right through the angle iron and the pipe to take 1/4" bolts to secure the pipe to the iron.

All the pipes will have holes at the same distance. So the angle iron holes must be accurately distanced.

But more importantly the angle iron holes must be perpendicular or at least in the same plane else the two bolts won't go through the pipe. One will go through centering the pipe that way and blocking the second.

That's the meaning of the dotted lines in the bottom drawing.

Ditto they must be 'in line' because the pipe can't angle to meet an out of line happening.

I'm getting it done but it seems to me I'm doing a hell of a lot of work to do it. If I had a couple of hundred to do it would get me down a bit.

What's a 'centre drill' ? Does that just mean drill a pilot hole? Well I try to do that but I'm saying my centre punch starting point is inaccurate anyway.

I just added a couple of pics. You can see what I'm making and you can see how I mark out by putting the template piece on top of the workpiece. I use a triangular file to scratch the location. Then I can file a land and always have that scratch crossing it to show me the apart distance location. I just need to find the centre then, for my centrepunch. I typically punch, file, punch, file, etc... because it punches off centre and I'm not satisfied.

So it is all too slow, too many hassles, too inaccurate...

How would they do it in a machine shop?

Google 'centre drill' (or center drill), also used to be called slocomb drill too I think.
They are a very short stubby drill with a built in angle for a lathe centre but in this application don't wander as much.
To do this I'd mark the hole centres using a height gauge and either put a flat on the angle and do it on the outside or mark on the inside. The radius will help you stay in position.
Centre punch before drilling as that will help.
If this was being done in a production setting it would be done a little differently - chances are there would be hardened bushes in a flat bit of steel with the centering V for the tube at the rear of the jig.

Michael

I'd use a V-block held in a (preferably cross slider) vice.
Aligning the chuck to the inner inset of the V on the V-block using a long thin piece of rod or bit.
Remove rod or long bit and insert the angle iron into the V-block
Use a centre drill bit to reduce bit wandering to start hole
Replace with longer bit to finish job.

An alternative to using a centre bit would be to use an especially shortened 6 mm bit.

Abrogard, have you got any hold down clamps for your drill press table. I'm conjuring up a possibility having just read about your problem but it requires hold down clamps.

Plus a thickish peice of flat steel bar and a couple of stout nuts and bolts.

As for a centre drill this would require sideways stiffness in your drill press to counteract any wandering the drill wanted to do. It may work, it may not, but in any case you'd still have to get your centre punch marks dead on, which is what you are having problems with anyway.

Keith.

I like this centre drill. I didn't know they existed. I think I'll get some. They look good.

And a 'v block'. I just have a little vice on my drill press table and I've been catching the angle in there, with the arms up and the 'v' down - trying to centre the drill in there the way that's been mentioned.

Not having a 'v' block means I make errors in levelling the angle in the vice. ('vise' for USA, I think). So the hole gets drilled out of line. I get around that by widening it but I don't like it.

A 'v' block is exactly what I want.

So the plan here is I don't mark laterally on the angle iron because the drill will be self centred by pushing down into a movable workpiece.

But I have to mark longitudinally - and how am I going to do that? Put a template piece on the inside, I guess. Specially drilled with small holes wide enough to take say a 1/16 centre punch. Centre punch a timid hole just for location. Centre up the drill by pushing down into the 'v' watching for alignment with this little hole.

Then drill.

O.K.

No, I don't have any hold down clamps. I just saw them for the first time on some googled pages. They might be good to have, too.

I make do with my ordinary 'F' and 'G' clamps.

Abrogard, here is a sketch I've just done. Right click on it and save it to your computer so you can view it in Windows Picture Viewer or whatever. It's the first time I've uploaded a picture to the forum so I've got a bit more to learn to get it full size. The corner drag handles don't work here so I can't increase its size.
Anyway the first thing you need to do is drill your 2 holes accurately in the flat bar at the positions show. The flat bar only needs to be 5-10mm past the edge of the 2 holes. Now grind out a couple of mm depth between these two holes stopping 5-10mm short of the holes you've just drilled. Now for the most difficult bit, with a hacksaw lined up on the dotted line shown (i.e. across the centres of the holes), carefully cut a slot about 1mm deep. This slot will locate the jig on the edge of your angle iron. If the hacksaw slot is not wide enough then carefully use a triangular file to open it a bit. The other 2 larger holes are for the adjusting nut and bolt.
Your drilling jig is ready. The 2nd picture shows how it will be used. If you don't understand any of it, let me know and I'll see if I can explain better. Another point is after you've drilled the first hole, put a nut and bolt through it to temporarilly fasten the jig to the angle iron so it can't slide along once the drill is removed. Then you can move it into position to do the 2nd hole. The hold down clamps I said you need will need to press down in the middle of the jig and the adjusting nuts are used to get the jig perpendicular to the drill bit (= parallel to the drill press table). You could use double nuts so once it's adjusted you can lock the nuts in this position.
JIG SKETCH.jpg

Here are some V block on evilbay, this is about as cheap as you will get, the seller has listed a heap at once....there was a guy that i bought some from that kept putting them up on ebay every now and then, they were $20 plus post i think. NEW "ECLIPSE" Cast Iron Vee Blocks Made in ENGLAND | eBay

Good luck

I like the jig. I've got confidence in it. I will use it. Thank you.

When the centre drills arrive I've just bought I'll use it with them. Until then I'll try using it with my ordinary drills. Would you say go for the full 1/4" straight off or make the jig with a smaller hole in it and use a smaller drill?

Which way round is going to find it easiest to go down through the edge of the angle iron?

Or should I file a land on it before putting it under the jig, do you think?


Thanks for the link to the 'v' blocks. I looked around and they aren't cheap, are they? And we must add postage, too.

I will give it a think: am I going to be needing that kind of precision that only a 'v' block can supply? and I'll look at the results of this job, see how it turns out with my present tools (and this new jig).

You want rigidity so use the full size drill with the jig. Filing a flat land is probably a good idea.

If you use centre drills in the jig then the jig will need to be extra thick because the body of the centre drill is some distance from the tip. Due to the very short distance between the bottom of the jig and the top edge of the angle iron, a normal drill should do fine.

Don't use thin steel for the jig, you want plenty "meat" to support the drill without the drill edges cutting the jig hole away. Normally jigs have hardened steel bushes but this is just a make up on the spot jig.

Hope it works out for you.

Keith.

Hi you havent said wether the pipe is available to be able to use it as a templet,if it is do as Bobl said clamp the pipe to the angle Iron and v block in the vice,after centering the v block and drill, drill through the previousl drilled holes in the pipe making sure that you have the centre of the holes over the centre of the angle Iron,use a drill bit the same size as the pipe holes and drill down to just make a mark or drill right through and take the chance you will damage the v block.you will have an acurate hole in the right place,hope this helps,

Eddie

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

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