A bit wider... but how much? Drilling template, one round, one elongated hole

[pe2dave]

A mounting bracket to go on wood / brick wall. Has two holes (horiz or vert).
3.5mm screws. 30mm long.
Question: By how much should one hole be elongated to make it easy for an average
DIY person to fit without straining the bracket?
Hope the question is clear. Trying to cater for masonry drill catching a flint in the mortar, or
poor marking on wood.
It's a bracket for mounting a security camera.

 

[Sideways]

I don't think there's a good answer to this without getting a dozen random diyers to drill a dozen holes apiece, and measure their efforts

How about a 3:2 ratio ?

 

[Spectric]

Answer is to do the job right first time, elongating holes is just evidence someone cannot mark up and drill holes in the right place. The way I approach jobs like this is:

If wall is pebble dashed then this can be more difficult but lets assume a flat wall. Place bracket on wall and mark one of the holes with a felt pen, using a hammer drill and small bit start the hole at very low speed keeping on the mark and square to wall. Using this hole as a guide put the bracket in place and mark the other hole and drill like before. Now drill out to final size to suit a wall plug, I only use nylon Fischer plugs and then tap plugs in holes and fit bracket.

Pebble dashing can be another story, a right pita at times depending on the type of dash used.

 

[pe2dave]

Answer is to do the job right first time, elongating holes is just evidence someone cannot mark up and drill holes in the right place.

I'm doing this to get a commercial company to cater for more customer skill levels.
'do it right' isn't helpful when you have little skills?
Hence my question, to make it easier for newbies.

 

[pe2dave]

I don't think there's a good answer to this without getting a dozen random diyers to drill a dozen holes apiece, and measure their efforts

How about a 3:2 ratio ?

So 4.75mm 'long' to 3.5mm wide?

 

[Sideways]

Gotta try something...

 

[Spectric]

The answer is to work on the skills, working round a lack of skill is just de skilling and getting people to do a job right has to be a good thing.

 

[Duncan A]

Do as is commonly found on window blind brackets. One vertical elongated hole and one horizontal elongated hole. At a guess I'd say the holes are about twice as long as they are wide.
Duncan

 

[--Tom--]

Being supplied a bracket with slots instead of holes is much more user friendly - so good idea. I’d go for 2:1 drill two holes side by side and file away the web to leave a slot.

 

[pe2dave]

Do as is commonly found on window blind brackets. One vertical elongated hole and one horizontal elongated hole. At a guess I'd say the holes are about twice as long as they are wide.
Duncan

I like the idea. I've only one bracket (plastic) to play with. Two 'extended' H and V sounds ideal.
I think I prefer 'twice' as long as necessary, except I'd run into the raised part.
I'll pass that one on though, tks @Duncan A

 

[Sideways]

The answer is to work on the skills, working round a lack of skill is just de skilling and getting people to do a job right has to be a good thing.

My spirit level reads vertical to 0.05 degrees. I defy you to consistently drill holes into breeze block at that level of precision hand held. I feel a little chuffed if I get them better than 99.8 degrees.
Maybe don't buy a digital spirit level - so easy to read and no fooling yourself you got it right when you didn't

 

[Spectric]

I feel a little chuffed if I get them better than 99.8 degrees.

What can help is a block of hardwood, mine is Eroka with a hole drilled through it on the drill press, now with the wood on the wall it gives good support to get the holes drilled consistantly. Using a digital level, especially with a beep function can cause more problems than it solves, with just a good Stabilla bubble level and with the bubble " appearing " dead central then try your digital level and more often than not it will not be bang on. But because we now know it is not bang on we tend to try to get perfection when for years we were satisfied with just the bubble.

 

[gcusick]

Answer is to do the job right first time, elongating holes is just evidence someone cannot mark up and drill holes in the right place. The way I approach jobs like this is:

If wall is pebble dashed then this can be more difficult but lets assume a flat wall. Place bracket on wall and mark one of the holes with a felt pen, using a hammer drill and small bit start the hole at very low speed keeping on the mark and square to wall. Using this hole as a guide put the bracket in place and mark the other hole and drill like before. Now drill out to final size to suit a wall plug, I only use nylon Fischer plugs and then tap plugs in holes and fit bracket.

Pebble dashing can be another story, a right pita at times depending on the type of dash used.

Or, as we say, “If I were you, I wouldn’t start from here.”

 

[simonridout]

It becomes more difficult with a random stone wall. I often have to chose the stone carefully, sandstone is good, flat granite hard drilling but ok, rounded, river washed stones difficult as the drill will skid sideways and of course avoid the lime mortar. Often the answer is to fit a wood backing piece and then fix the bracket to this. If the wall is rendered it becomes much more challenging!

 

[pe2dave]

My spirit level reads vertical to 0.05 degrees. I defy you to consistently drill holes into breeze block at that level of precision hand held. I feel a little chuffed if I get them better than 99.8 degrees.
Maybe don't buy a digital spirit level - so easy to read and no fooling yourself you got it right when you didn't

Please read the OP? I'm trying to improve a design for (rel to you) numpties so they can do it easily?

It becomes more difficult with a random stone wall. I often have to chose the stone carefully, sandstone is good, flat granite hard drilling but ok, rounded, river washed stones difficult as the drill will skid sideways and of course avoid the lime mortar. Often the answer is to fit a wood backing piece and then fix the bracket to this. If the wall is rendered it becomes much more challenging!

And @Spectric make this suggestion. Fair enough for a DIY bod.
Hardly applicable to those with 5 tools at the bottom of the kitchen drawer?
I'm trying to include those as 'customers' who can cope with a better solution.

 

[Austin Branson]

On difficult wall surfaces, I use a centre punch to get the drill started in the right place.

 

[HappyHacker]

I have installed many hundreds of bits of equipment where the manufacturer expects three or more holes to be drilled into the mounting surface to accuracies less than a mm and therefore commend your attempt to make it easier. It does not matter how good ones drilling technique is there is always a stone etc to throw the drill off on at least one of the holes.

The easiest option is to do what many manufacturers do is to make each hole about three or four times the diameter of the screw. Then supply screws whose head is smaller than the hole. Don't supply any washers so the user has to make a special trip to go and buy some unless having been caught out by this before they have boxes of every washer size going clutter up their storage. From experience the washer size that you want to cover the hole, fit the screw and be small enough to get into whatever space has been left around the hole has been removed from the stash by the borrowers.

As has been suggested the best option is two elongated holes at right angles with possibly another pair at 45 degrees if space allows so that there are options for which to use. Many electrical back boxes have excellent examples of this.

And to answer your question I would make them at least three times longer than the diameter of the screw and probably four times. Allow for larger screws to be used in case the substrate is complete crap and the original screw/plug does not work and a larger one is required. I once tried to drilled a six mm hole into plastered breeze block I got hole about six inches in dia. it was not breeze block but something with the consistency of Wheetabex but not as strong. The usual problem is for the hole to hit the morter between courses and some cheapskate has "forgotton" to add any cement so even Fischer plugs don't grip.

 

[Spectric]

It does not matter how good ones drilling technique is there is always a stone etc to throw the drill off on at least one of the holes.

I think this issue is often down to the hammer drill used and the material being drilled. My cordless Makita is good on softer materials but not brick or concrete so is then only used for making the initial indent to locate the hole. For holes in the harder materials I use an old Hilti T22 which has a nice slow hammer action that delivers a good impact wheras the makita is like a woodpecker on speed and the Hilti just can work all day without fuss. I have had so many people who have asked me to drill holes for their curtain fixings, there drill just does not touch a concrete lintel and in the process wanders to make a mess yet a good drill just does it with ease.

 

[Spectric]

Often the answer is to fit a wood backing piece and then fix the bracket to this. If the wall is rendered it becomes much more challenging!

One of the more challenging types of wall is dot & dab plasterboard, or some walls in new builds that move if you even faart on them let along try to hang something on it. Years ago an architect pointed out that the close coupled toilet was to stop having a heavy cistern hanging on the wall and transfer the weight through the pan into the floor instead, good fun when someone wants a traditional style bathroom where the toilet has a flush pipe or even jharder a high level cistern.

 

[Spectric]

Hardly applicable to those with 5 tools at the bottom of the kitchen drawer?

The weekend warriors who mess up jobs at the weekend and then want us trades in asap to put it right and it ends up costing more so if in doubt or lacking the tools then just get it done properly.

The other solution is to go back before we had cordless drills and use a rawl plug tool, just hit and twist so a nice slow process and accurate, I can remember forty plus years ago using one of these to fix dozens of backboxes and conduit drops .