Making a drilling jig

[Matty F]

I need to drill holes in steel clamps which are being bent by hand using a blowtorch. The clamps are to be bolted to poles. The dimensions are not that important, but clearly the holes need to line up so that bolts can be put through. I want to make a jig so that the holes line up. The clamps are being made by hand so the curves will not be that accurate. From past experience I know that dimension C will not be the same for all clamps. When the bolts are tightened up the clamps will bend to fit the poles. There will be spacing washers and lock washers which I have not shown in this diagram:

I think the jig should measure the distance from the bend to the hole (dimension B) while everybody else thinks I should measure between the two holes (dimension A). So which dimension should the jig measure?

[petek]

As the relative position ( i.e. dimn. A) of the holes is not critical, why not make the holes a bit oversize, or even slots, so that drilling them accurately is not important.

Trying to get an accurate, and by that I mean repeatable, postion for a hole from a bend of indeterminate radius and position would be difficult. Better take a location for the first hole on each piece from the end of the clamp and then locate the second hole in relation to the first.

Have you got a lot to do? Accurate marking out and centre popping the holes may be easier.

Pete

[Matty F]

But "locating the first hole in relation to the first" includes the width of the large curved part, which I have said will close up on the pole and change its dimension.

I already have a jig which I made last time that measures from the sharp bend, and I think that worked very well. The length of the flat part of each clamp will be different for each clamp.

Yes there are lots to be made. It is not possible to make the clamps in matching pairs since they need to be galvanised after drilling. It is not possible to label them. I want any clamp to be able to be used with any other clamp It's easy for me to put the holes anywhere, but the question is, where? I reckon that all the holes should effectively be the same distance away from the pole, so that the bolts are in straight. i.e. measuring dimension B only. I find it odd that nobody at my work seems to understand the problem. The problem is very evident when someone tries to put the bolts in and they are crooked.

[Mr Fuxit]

Make them in pairs and buy a set of number punches and mark them.

[Matty F]

1. I want to be able to swap the clamps around at any time in the future so I want all the hole positions to match.
2. After they are hot-dip galvanised the numbers will be too hard to read.
3. The way I want to do it is much easier and quicker.

I've drawn another diagram to show what I mean. The errors in the clamps are exaggerated to illustrate the point.

Note that the clamps will tighten up against the pole and any wrong curvature will correct itself. I want the jig to put the holes all at exactly 60 units away from the pole. Measuring from the end of the clamps will be the wrong thing to do. But why can't anybody but me see that?

[Rod]

I am convinced that any commercial product would use at least one slot (elongated hole) or rely on general slop. If the curvature isn't quite right, it will be difficult to get a screw to go from front bit through hole in back bit - especially if the holes are just clearance diameter. So the fact that it would self-correct when you tighten it up might be a bit lost as it won't, IYSWIM.

Have you thought of using standard scaffolding clamps? (Or other pipe clamps - if not scaffolding tube diameter.) Or at least looking closely at them?

[The Medway Handyman]

From the end of the clamp surely? Assuming all the flat bar stock is the same length.

[Matty F]

Because of the difficulty of bending the steel by hand while heating it red hot, the three bends will be in different places for each clamp. The small differences don't matter for appearance sake, but it does mean the flat part on the end of each clamp is a different length. Anyway I'm not doing the bends, and I know from past experience that they *are* all different. There is one constant dimension, and that is the one labelled 60 in this diagram, and that is what I am going to measure:

[Matty F]

The poles are cast iron and around 200mm diameter. There is nothing commercially available. We need to match clamps made 100 years ago. Other clamps that were recently made by professionals were very expensive and had to be redrilled.

[Mike Clarke]

For each pair why not just drill one piece first, positioning the holes by eye so they look right. Then use the first piece as a jig to mark the hole positions on the other half.

[Mike]

You'd probably get some good ideas from a different newsgroup.

news:uk.rec.models.engineering is full of many professionals and non professionals who'd not bat an eyelid at a problem like this.

Personally I'd make a pattern out of wood, have it cast, tidy up with an angle grinder fitted with a flap disc and then drill the holes accurately with a pillar drill.

[Andy Dingley]

This depends on the shear load afterwards. Crude location can manage with threaded bolts passing through oversize holes, typical work is plain-shanked bolts through accurate holes, hand-fitted non- interchangeable work for best load bearing drills undersize, then drills or reams each pair to fit once assembled.

I'd probably do it with a nice big, rigid drill press, then a sheet of thick plywood clamped over the table (same one I use every time) a straight guide rail (more plywood) along the edge and a pin sticking up to locate off the first hole.

[kb]

Would munson clips do the job ? e.g. from

[Matty F]

I will be using the metal jig that I made last time. I just hold it in the vice of a large drill press.

ensures that the holes on all clamps are the same distance from the bend, rather than from the end of the clamp or from the other hole. How odd that nobody seems to understand the crux of the problem.

[Matty F]

I'm effectively doing that with this jig:

clamps won't fit closely together anyway

[Mike]

Of course they do, you're just not asking the right people. Would you ask a weatherman to explain the offside rule? A rocket scientist to cook you an edible meal? A housewife to split the atom, juggle live hand grenades while ironing and still have the dinner ready for when her husband comes home?

You've said previously there are lots to be made. The clamps can be produced, easily. You're simply using the wrong manufacturing processes and sequences and approaching it in the wrong way thereby creating 'problems' when there aren't any. If you manufacture it a different way they can be knocked out in large quantities extremely accurately.

It might be an idea to define what you mean by "lots to be made". If you really do mean lots then the cost could be a few tens of pence per piece.

But.

You don't specify the quantities, the tolerances, the expected loading.

You might have made a very bad choice in materials, you might have made a bad choice in the qualities of those materials.

and maybe there lies one of your problems.

You can get the curves absolutely spot on, with the holes in exactly the right place ensuring that they are symmetrical and fully interchangeable.

And crucially as I mentioned above you're almost certainly not asking the right people.

news:uk.rec.models.engineering ^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^

or if you want the view of a heap of Americans

news:rec.crafts.metalworking ^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^

[Matty F]

I've already asked engineers. What I want is to ask people with practical experience in making things the old fashioned way with minimal tools, but more importantly, with common sense.

The clamps have to match the look of existing heritage clamps that may be up to 100 years old. A modern perfectly made clamp would look quite out of place. People keep answering questions that I have not asked. The only question I am asking is whether the location of the hole should be measured

1. from the right-angle bend (which I believe is the only correct way)
2. from the end of the clamp (wrong)
3. from the other hole (wrong)

I am not making models. This would be classed as heavy engineering.

[Mike]

You've missed the point entirely - again.

No it wouldn't, you could make a 'modern' clamp look exactly like an old one. People restoring buildings and those involved with historic engineering do this all the time.

If you manufacture it correctly the location of the hole will be accurate, from what I've read so far and particularly the type of questions you are asking on basic engineering drawing you are quite simply not manufacturing it correctly. Your process and sequences are almost certainly wrong. You would never 'measure' such an article as the correct manufacturing process and jigs would produce it precisely (or as inaccurately as you need to match the existing)

FFS! I'm not suggesting you go anywhere full of modellers, the places I mentioned are where a good proportion of professional practical engineers hang out, as well as people who routinely turn out jobs like yours in less time than you and a dozen others have spent posting to this thread.

There might even be some from NZ, there are certainly some from Oz and South Africa, Canada, Germany, Italy, Greece, USA, the UK and Ireland.

[Andy Dingley]

That's because you're making these, you're not the poor bugger who has to fit them.

Align the first hole off the bend by all means. Then align holes hole- to-hole, because that's how they'll jam when you're trying to insert the second bolt. Any slight inaccuracies in the hole-bend spacing will pull tight as you tighten the bolts.

[Matty F]

I'm not bending the clamps, so I have no control over that. They'll be bent in a forge by a blacksmith. I'm happy with the slight variations that result. I'm just drilling the holes, and I will be fitting them on the poles. As the bolts are tightened, the two right-angle bends will pull up to and touch the pole. The bolts will then be correctly at right angles to the pole, unlike all the other suggestions.