Drilling and tapping holes and general metal working tips

[Gackt]

As the title suggests, I need some tips on accurately drilling and tapping holes, specifically in aluminium. I've made a few practise attempts, with the results usually being quite dismal. I've only got a bottom-of-the-range clarke bench drill to work with (of dubious accuracy, me thinks).

The main problem, after marking out and centre-punching, is getting the bit accurately over the mark, it always seems to go off-centre no matter how much time I take setting it up. Also, I find it's hard to stop a tap going wonky when starting off. Any help other general tips would be really appreciated.

Come on lads, help out a noob in distress.

Ta people.

[spacemonkey]

As the title suggests, I need some tips on accurately drilling and tapping holes, specifically in aluminium. I've made a few practise attempts, with the results usually being quite dismal. I've only got a bottom-of-the-range clarke bench drill to work with (of dubious accuracy, me thinks).

The main problem, after marking out and centre-punching, is getting the bit accurately over the mark, it always seems to go off-centre no matter how much time I take setting it up. Also, I find it's hard to stop a tap going wonky when starting off. Any help other general tips would be really appreciated.

Come on lads, help out a noob in distress.

Ta people.

Start with a centre drill on your punch mark.... Works for me!

[Gackt]

Spacemonkey, I'd heard of using centre drills before but haven't been able to find any locally. I'll see if I can grab some off ebay. Thanks.

Zakalwe, I haven't used any lubricant so that probably explains why my holes look somewhat ragged. Is it possible to use something house-holdish like wd40 or is that not recommended? Haven't heard of ally soap before, where can you get it from?

Another problem (I know, problems, problems) is that when I tighten the vise, the jaw pushes the workpiece up slightly on one side, cause the bit to at an angle throught the piece. I got round it by only just tightening the vise but I don't feel comfortable doing this as it's not very secure. Is this just my vise being cheap and poo? Is it better just to clamp the piece directly to the table?

Thanks for the advice lads.

[750 Gixxer]

As the title suggests, I need some tips on accurately drilling and tapping holes, specifically in aluminium. I've made a few practise attempts, with the results usually being quite dismal. I've only got a bottom-of-the-range clarke bench drill to work with (of dubious accuracy, me thinks).

The main problem, after marking out and centre-punching, is getting the bit accurately over the mark, it always seems to go off-centre no matter how much time I take setting it up. Also, I find it's hard to stop a tap going wonky when starting off. Any help other general tips would be really appreciated.

Come on lads, help out a noob in distress.

Ta people.

Sound like you are starting with to big a drill or the drill bit is`ent sharpend correct or just cheap shitty drill bits. For lubrication use household alcohol, might be called rubbing alcohol it`s the stuff they use in hospitals for disinfectin things, you get the idea. WD40 can also be used, better than nothing.

Good luck

Martin

[blow_away]

All golden advice as usual

Don't forget to check your speeds and feeds

http://www.tapdie.com/html/drill_regrinding.html

This site has loads of other info that may be helpful, just keep practising

[speedzephyr]

Spacemonkey, I'd heard of using centre drills before but haven't been able to find any locally. I'll see if I can grab some off ebay. Thanks.

Zakalwe, I haven't used any lubricant so that probably explains why my holes look somewhat ragged. Is it possible to use something house-holdish like wd40 or is that not recommended? Haven't heard of ally soap before, where can you get it from?

Another problem (I know, problems, problems) is that when I tighten the vise, the jaw pushes the workpiece up slightly on one side, cause the bit to at an angle throught the piece. I got round it by only just tightening the vise but I don't feel comfortable doing this as it's not very secure. Is this just my vise being cheap and poo? Is it better just to clamp the piece directly to the table?

Thanks for the advice lads.

Most drill vises will lift the jaw unless its a real expensive one, you could use a "lock down" milling vise they pull the jaw down with 50% of the clamping pressure, If you put 500lbs of clamp force on a part the moveable jaw has 250lbs of down force, Pretty sweet! Extremely expensive. Just buy a milling machine they usually come with one.

For drilling try to get some "135 degree split point" drill bits they walk much less and drill like a bullet. And if you get some tap/drill lubricant make sure it can be used on nonferrous metals.

[Gackt]

Thanks for all the advice, lads, it's really appreciated. Made me see how many mistakes I was making. Ah well, practise makes perfect.

[intra]

Four-facet drill sharpening for the win.

[billysbones]

Centre punch first. Then use very small drill bit and work your way up through the sizes slowly, if you need to be really accurate. If you need a 12 mm hole, make your second to last drill bit an 11.5, so you are removing the minimum amount of material on your fianal cut. As the size of your drill bit goes up, your drill speed should come down. I was told as a rule of thumb to use 300rpm per inch of drill bit. so if you want a 12mm hole use 600rpm. there or thereabouts, anyway.

as for tapping, thats a bit of a black art that comes with practice, but using a square as mille suggests is a top tip. do not get impatient, and keep turning the tap backwards to break the swarf off.

As zakalwe said, always use lubricant for both drilling and tapping, and it sounds as though your vice is shite.

good luck, and let us know how you get on.

[2 smokes 4 ever]

Centre punch is the wrong thing to drill accurately placed holes

Accurately mark the hole centre, then scribe a box around the cross hairs forming the centre so you get a box the same size as the hole dia

Then as you drill you can see if you are in the right place as the hole should approach the 4 sides of the box equally

If its going out of position, push/pull on the work piece as required and you can actually move the position of the hole, so long as the full dia of the drill has not be reached.

This was demonstrated to me on my apprenticeship, and it does in deed work

The lecturer got us to start a drill in the one corner of the scribed box, and he moved the positon of the hole by pushing on the work piece til it was spot on in position.

Centre punching is for bodgers

As for tapping, 1.5 turns then 0.5 turn back to break the swarf chips

Use a 1st taper tap, then 2nd tap then, plug tap if tapping a blind hole

Lubrication a must (parafin)

Tap must be sharp for use in Al

[billysbones]

Centre punching is for bodgers

Thanks for your very diplomatic comment there!

He's right gackt. ignore all the rest of us with our time honoured, ham fisted bodgey method, and go with a method that nobody else in the known universe has ever heard of!!

I'm not saying that you are wrong by the way, but surely the centre punch method is the simplest way, given that the guy obviously has quite limited resources/access to equipment. (No offence intended, gackt)

by the way, you don't say how you can so accurately scribe such an accurate square on your workpiece so.....er accurately.

[intra]

Centre-punching has also been pushed upon me quite hard in my apprenticeship by the plethora of tradesman I have worked with, not to mention the 15 years previous I spent working with my father, a tradesman of 45 years. It sounds like it would be easy for someone to fuck up marking out their box man.

[Coose]

Centre punch is the wrong thing to drill accurately placed holes

Accurately mark the hole centre, then scribe a box around the cross hairs forming the centre so you get a box the same size as the hole dia

Then as you drill you can see if you are in the right place as the hole should approach the 4 sides of the box equally

If its going out of position, push/pull on the work piece as required and you can actually move the position of the hole, so long as the full dia of the drill has not be reached.

This was demonstrated to me on my apprenticeship, and it does in deed work

The lecturer got us to start a drill in the one corner of the scribed box, and he moved the positon of the hole by pushing on the work piece til it was spot on in position.

Centre punching is for bodgers

As for tapping, 1.5 turns then 0.5 turn back to break the swarf chips

Use a 1st taper tap, then 2nd tap then, plug tap if tapping a blind hole

Lubrication a must (parafin)

Tap must be sharp for use in Al

Eh? Rubbish - you'll never get an accurate hole position by "pulling and pushing" the workpiece! A drill is not designed or capable of cutting with the edge of the helix, just the tip. The drill will follow the point at where the tip has started to cut or will drill an elliptical hole if the workpiece is moved.

Accurate centre punching is the only way that you can centre a drill, unless you're using a slot drill but then you'd be using a milling machine and not worrying about centre punching!

Coose IEng MIET (time-served mech. eng. with the MOD)

[2 smokes 4 ever]

Eh? Rubbish - you'll never get an accurate hole position by "pulling and pushing" the workpiece! A drill is not designed or capable of cutting with the edge of the helix, just the tip. The drill will follow the point at where the tip has started to cut or will drill an elliptical hole if the workpiece is moved.

Accurate centre punching is the only way that you can centre a drill, unless you're using a slot drill but then you'd be using a milling machine and not worrying about centre punching!

Coose IEng MIET (time-served mech. eng. with the MOD)

Coose, Ask any toolmaker and you'll be corrected

I always thought like you did, uptil my engineering apprenticeship, and I was shown the error of my ways

I suggest you try it before rubbishing it

Yes centre punch is fine for construction industry, and low accuracy work etc, but as the thread starter has said, they always end up off centre when he does it

The scribing of the box allows you to see if the drill has wandered from the intended position as the cutting edge will hit one of the box sides before the rest and hence indicate that you are no in the correct position

For high accuracy the above method is the correct way - only works with a pillar drill , you can't do it with a hand held DIY drill.

Scribe and a rule is good enough to get accurate lines if you're careful

2Smokes (Time served engineering apprentice) and that means hands on, not a theorist.

[tootall]

Quality centre punch and start small and work up. As (nearly) everyone else has said. Never had to (or seen done) scribe squares and all that.

Tootall qualified and time served mechanic and then HNC mech & prod engineering working on race car engines

[Coose]

The first year of my apprenticeship was spent in the college machine and fabrication/sheet welding shops. We worked to a tolerance of +/-0.1mm, so if we were out by more than this we'd have to start again! Therefore, accurate marking and mounting of the workpiece was the key, along with keeping your cutting tools (drills in this case) in good condition.

So, to drill a hole once and once only requires: -

• accurate marking and punching,
  
• using decent quality, well maintained drills
  
• correct mounting of the workpiece,
  
• selecting the correct drill speed,
  
• start with a small drill and work up to the desired size.
  

Simple as that!

[billysbones]

The first year of my apprenticeship was spent in the college machine and fabrication/sheet welding shops. We worked to a tolerance of +/-0.1mm, so if we were out by more than this we'd have to start again! Therefore, accurate marking and mounting of the workpiece was the key, along with keeping your cutting tools (drills in this case) in good condition.

So, to drill a hole once and once only requires: -

• accurate marking and punching,
  
• using decent quality, well maintained drills
  
• correct mounting of the workpiece,
  
• selecting the correct drill speed,
  
• start with a small drill and work up to the desired size.
  

Simple as that!

what he said

again, i'm not saying you're wrong cos i've never tried it. Then again, I wouldn't, cos it goes against everything i've ever been taught.

billysbones electrician (and all round good egg. well, at least everyone says I'm all round) and no-where near as qualified as others who have posted here.

[2 smokes 4 ever]

Some of the responses on here indicate why engineering is dead in this country

[billysbones]

Some of the responses on here indicate why engineering is dead in this country

yes. you're absolutely right. we are ALL wrong and you are right.

[billysbones]

2Smokes (Time served engineering apprentice) and that means hands on, not a theorist.

It sounds to me like you ar punching over your weight here. There are an awful lot of VERY qualified people telling you that in their experience, (Which counts for a lot more than engineering apprenticeship alone) that you are wrong.

Please do not misunderstand me. I served an engineering apprenticeship too, then spent 20 years collecting experience in multi skilled maintenance work, but still recognise when somebody MORE qualified and experienced than myself has something to say.

As you will no doubt notice from my previous posts, I STILL do not say you are wrong, but I don't understand how you can drill an accurate hole in a workpiece which is not securely fastened down, and you are actively trying to move about, and as such, you cannot guarantee that it is square-on to the drill bit.

Think your arguments through a bit before you basically insult the knowledge and experience of just about everyone who has bothered to post on this thread, with the sole purpose of trying to offer help to someone who has asked for it.

[Coose]

Some of the responses on here indicate why engineering is dead in this country

It wasn't the responses on here that killed it, it was the Prime Minister from 1979-1990 but that's another story....

[jollygiant]

When I mounted an alarm on my Escort 1.3GL, I tried drilling holes through the bulkhead panel to mount the siren bracket using wood drills. After blunting my drills, I at least had a dent where each hole needed to be so I hammered a 6-inch nail through to make the holes. Bit of wobbling about and the holes were big enough for the bolts.

Who says engineering's dead?

Used that technique a few times my self

Esp when battery's flat in my drill

[VeeTeeArr]

If I have to cut a thread using a tap I'll try (if possible) to bolt a steel plate, with a nut of the correct thread welded to it, onto the work piece. Centring the nut over the hole with the correct size drill bit. This helps hold the tap upright and always helps feed the tap into the work piece.

VTR(zero years engineering) 22years HGV mechanic and bodger

[Sidkinky]

Bloody amateurs, the lot of yers. Use a bigger hammer, innit?

Sidkinky - hitting things with bigger things for twenty+ years.

[intra]

I'm kind of curious as to how you scribe a square to suit something like a 2.5mm pilot hole to be honest. My vision is 20/20 and I'd struggle.

Edit: Are you talking about witness marks man? Marking your diagonals across the point of the hole to be drilled, griding a V into a power hacksaw blade to make a solid scribe, scribing a circle the size of your desired hole around the hole centre and then centre punching where the four lines of your diagonals intersect with the circle you scribed? That method still requires you to do a centre punch for your hole centre. I've been thinking about what you said and it's all that I can really come up with that I've seen. Most workplaces are against it though because it makes the job take 3 times longer than it would if you just did a centre punch.

[2 smokes 4 ever]

It sounds to me like you ar punching over your weight here. There are an awful lot of VERY qualified people telling you that in their experience, (Which counts for a lot more than engineering apprenticeship alone) that you are wrong.

Please do not misunderstand me. I served an engineering apprenticeship too, then spent 20 years collecting experience in multi skilled maintenance work, but still recognise when somebody MORE qualified and experienced than myself has something to say.

As you will no doubt notice from my previous posts, I STILL do not say you are wrong, but I don't understand how you can drill an accurate hole in a workpiece which is not securely fastened down, and you are actively trying to move about, and as such, you cannot guarantee that it is square-on to the drill bit.

Think your arguments through a bit before you basically insult the knowledge and experience of just about everyone who has bothered to post on this thread, with the sole purpose of trying to offer help to someone who has asked for it.

It is not an apprenticeship alone but followed by 20 years in engineering

How do you accurately bolt the work down in the first place?

Luck more than judgement I'd say.

If its not in exactly the right place then the drill bit will try to drill the hole in the wrong place

The purpose of scribing the square is to allow you to see if this very issue - ie the hole being drilled will 'hit' into one of the scribed lines before the others and hence you'll know you're off centre, and slight sideways pressure will correct the error

Fine, all those who have rubbished it

You carry on doing it your way - I ain't that bothered

I know the above technique works, to allow a correction to be made when the hole doesn't drill in to the correct place as wanted.

Without the box around CL of the hole, you have no idea if the drill is still on centre one the centre punch mark is gone

I didn't dream it up - It was taught to me by 2 college lecturers during the first 12 months off the job training at college on my EITB apprenticeship.

A centre punch alone is not enough, as the thread starter has found out, for accuracy

milliemillie - ah yes but how many of these 15000 can drill an accuratly position hole?

Your average Civil Engineer doesn't prsses any toolmaking skill does he?

If your employers are increasing in size and scope every day, then they must be the only ones in the country, seeing as the rest of us are in recession. Nice work if you can get it, and this country is dead as a engineering powerhouse. Toolmakers are going to the wall on a daily basis, seeing as most press and mould tools are now made in China.

[2 smokes 4 ever]

I'm kind of curious as to how you scribe a square to suit something like a 2.5mm pilot hole to be honest. My vision is 20/20 and I'd struggle.

Edit: Are you talking about witness marks man? Marking your diagonals across the point of the hole to be drilled, griding a V into a power hacksaw blade to make a solid scribe, scribing a circle the size of your desired hole around the hole centre and then centre punching where the four lines of your diagonals intersect with the circle you scribed? That method still requires you to do a centre punch for your hole centre. I've been thinking about what you said and it's all that I can really come up with that I've seen. Most workplaces are against it though because it makes the job take 3 times longer than it would if you just did a centre punch.

The scribed square is sized at the larger hole, not the pilot hole

Scribed CL's for the hole, then 4 lines to form a box at the diameter fo the final hole size

ie 10mm dia hole, box at 10mm sq. No diagonals, no tools, no grinding, just a a scribe and a rule (or surface table and height gauge which allows for higher accuracy)

It doesn't make the job as long as having to do it again though does it

Measure twice, cut once

[Coose]

If you don't use a centre punch your drill WILL wander....

[Mr.Pigdog]

Hello there!Aeronautically trained(m.o.d.)a few years doing both military and civil heavy maintenance of aircraft and couple of years as a driller for the m.o.d. before that,now thankfully a motorbike mechanic!!Never heard of this scribing a square malarky before and would give it a try but have reservations--i think surely scribing a 'crosshair' would show any drillbit wandering?A square would surely be open to more scope for mistakes?suppose you use an engineers square for it too??i worked with a old boy that happened to be a lecturer on motorcycle mechanics-He was a prime example of all theory not enough practice and wouldnt listen to anyone elses advice-didnt last long in the real world anyways.

Only a fool thinks he knows it all.I've always found that you can indeed influence the positioning of the hole being drilled slightly by angling the drill-but you can only do it slighty and have to straighten up sharpish whilst its in the pilot hole stage-removed countless amounts of rivets from aircraft panels this way without damaging surrounded structure.Just get an old lump of alloy and practice lots i reckon as you get a feel for whats going on with it i find

[Gackt]

What is this beast that I have created? lol

Buy yourself a small engineers square and use this when tapping holes to ensure that as soon as the tap has bitten it is square.

I take it you have a set of 1st, 2nd and final cut taps ?

I have a square so I will give that a go, thanks.

The tap and die set i have is very basic. The taps are tapered slightly so I'm guessing these are 1st.

Centre punch first. Then use very small drill bit and work your way up through the sizes slowly, if you need to be really accurate. If you need a 12 mm hole, make your second to last drill bit an 11.5, so you are removing the minimum amount of material on your fianal cut. As the size of your drill bit goes up, your drill speed should come down. I was told as a rule of thumb to use 300rpm per inch of drill bit. so if you want a 12mm hole use 600rpm. there or thereabouts, anyway.

as for tapping, thats a bit of a black art that comes with practice, but using a square as mille suggests is a top tip. do not get impatient, and keep turning the tap backwards to break the swarf off.

As zakalwe said, always use lubricant for both drilling and tapping, and it sounds as though your vice is shite.

good luck, and let us know how you get on.

Tis very shite indeed. Thanks for the pointers.

I'm not saying that you are wrong by the way, but surely the centre punch method is the simplest way, given that the guy obviously has quite limited resources/access to equipment. (No offence intended, gackt)

No offense taken, billybones. There are holes in the ground in the middle of the artic tundra that have better equipped workshops than me.

Despite my knowledge being rudimentary (at best), I am somewhat wary of the method described by 2 smokes 4 ever. Please note that I am not insulting your experience or techniques but, to me, it doesn't seem like a good idea to put any kind of side load on a drill bit which wasn't designed to take it. I'm also dubious about the effectiveness of pushing and pulling on the work to centre a hole that's already gone off-centre. Having said that, I do appreciate the input.

I think another cause of my inaccuracy woes is the chuck on my drill press. It seems to have a fair amount of lateral movement in it, maybe between 0.5-1mm, which I'm sure isn't helping at all.

What I'm going to do (along with taking on-board all your good advice) is to invest in a new drill press (maybe an axminster, or if anyone can recommend something good for the £100-150 mark) and some quality bits. I may just save a bit longer and buy a small mill, as this is something I've been very keen to learn for a while.

For the record (if anyones bothered), I'm attempting to make some adapter plates to mount some gilles VCRs on my ickle cagiva raptor 125 (why? why not, says I) out of 12.7mm 6082 plate.