Successful drilling

[bertterbo]

So, lets say you're wanting to drill a 13mm hole into 20mm thick Bright mild steel on a bench top drill press.

My approach for this has generally been :

- Centre punch a mark to guide the drill
- Have the piece clamped in a vice, but have the vice loose on the table so it can find it's place as the drill centres on the mark
- Sometimes use a centre drill for the first hole if I want it to be very accurate
- start with 6mm, then progress through 8, 10, 12 and finally 13mm.

However, the problem I find is that when you go to use the next size drill bit, it often doesn't cleanly centre in on the previous hole. The wings of the drill catch, and you get a lot of vibration. For the larger bits this can be really bad as they're so long and can flex. The same problem applies if you use a centre drill. The wings catch.

So, clamp down the vice to the table you say? ... well, I tried that too. But the problem there is that as the drill bit diameter increases, the drill gets longer. And so to remove the drill to change it, you have to move/lower the table, losing your positioning. So whilst its more stable, the wings are still likely to catch as its unlikely to be correctly centred.

Having done some research on this, I have discovered that you're actually not really supposed to use a centre drill (which are actually designed for the live centre on a metal lathe, love learning new stuff!), but instead, a spotting drill. A spotting drill has a much larger angle than a centre drill, 120 degrees vs 60 degrees. So the wings on a standard drill (135 degrees) are much less likely to catch.

So, the question is, if you were going to drill the hole described, would you start off with say a 12mm spotting drill? and then go through 6, 8, 10, 12. Or ... go straight to the 12mm drill? or something else?

 

[imageel]

I'm not a pro, and am sure others who are will chime in however I find that unless you are increment drilling there is a tendency to catch since you inadvertently apply more pressure on a small area, however as the diameter goes up, so does the torque required to cut cleanly.
Paradoxically if as you move up the sizes then keeping the rpm the same can work to your advantage if well lubed, since it allows you to take shallower cuts requiring less torque from the drill.
I've drilled all sorts of steel like this, right up to some particularly difficult 22mm stainless steel rod when I was fabbing a fancy kitchen pot hanger.
With this material to be able to cut clean semi-circular butt ends I ended up purchasing a carbide tipped Starret hole saw
TBH if you don't drill steel regularly then you really need to have a play with the rpm and feed-rates to get a feel for things and obviously have sharp tooling.
Variabilities in the types of steel you are using obviously impacts the technique too however again my strategy would be to have a try on a waste piece 1st so as to get a feel for what is going to work best, and sometimes adjust the cutting lubricant (or not use any) - I usually try either WD-40 or paraffin are good to try, or even turps
Good luck!
Ed

 

[J-G]

I usually try either WD-40 or paraffin are good

!!!! SO wrong !!!!

Paraffin is good for Aluminium but not Steel - WD-40 is not a lubricator!

Cutting Fluid is probably the best but any 'oil' would do - or possibly nothing depending upon the grade of steel.

 

[Inspector]

I watched the machinists drilling both manually and with the CNC mills. They would spot with a bit bigger than the final size just deep enough to leave the hole slightly countersunk when final drill size was done, de-burred in other words. Then if they didn't drill to final size right away would do the first small bit, 6mm in your case, then final size with the second. If the hole was threaded the spot drill was deep enough to allow for a de-burred hole when that was done with the machine too. Coolant was normally flooded onto the part unless on the big radial drill in which case they either used coolant or a cutting/tapping fluid appropriate for the material squirted on with a spray bottle or oil can. No kerosene or WD40 of any kind in the plant.

Pete

 

[dzj]

I'd go straight to the 12mm. Your drill bit should be sharpened in one of the ways in which the 'chisel'
part is reduced as much as possible.

 

[Dalboy]

I try to centre drill first the use a drill large enough to make a hole slightly larger than the centre flut on the next size I use which in you example I would go for something like a 3mm then straight to the 13mm if a very accurate hole is needed then I would do this different as I would use a drill one size smaller than the final hole and then ream(Metric would be 0,1mm increments not 0.5mm)

 

[porker]

!!!! SO wrong !!!!

Paraffin is good for Aluminium but not Steel - WD-40 is not a lubricator!

Cutting Fluid is probably the best but any 'oil' would do - or possibly nothing depending upon the grade of steel.

From the WD-40 website...

Myth: WD-40 Multi-Use Product is not really a lubricant.

Fact: While the “W-D” in WD-40 stands for Water Displacement, WD-40 Multi-Use Product is a unique, special blend of lubricants. The product’s formulation also contains anti-corrosion agents and ingredients for penetration, water displacement and soil removal

 

[imageel]

!!!! SO wrong !!!!

Paraffin is good for Aluminium but not Steel - WD-40 is not a lubricator!

Cutting Fluid is probably the best but any 'oil' would do - or possibly nothing depending upon the grade of steel.

As I stated I'm no expert, however anything that provides some cooling and whatever WD-40 is determined to be does help - heck back in the day folks regularly used plain water to aid cooling/chip removal...
/Ed

 

[TRITON]

Stepped drill bit ?. or am i missing something here.
https://www.screwfix.com/p/erbauer-...VC57tCh21VQ6cEAQYASABEgJxEvD_BwE&gclsrc=aw.ds

 

[Ttrees]

There you go, my 40 pound pillar drill is the bees knees now.
Very silly and lazy that the manufacturers haven't used thicker columns,
which would lend itself to having a slot milled up the centre, with swinging sprung pin
for when you want to do this...
i.e near every time, practically.

Some reading or watching might inspire some workarounds,
which might include the table "indexing" off the wall (with cleat so you're not smacking the table off concrete)
or....a huge timber square which clamps to the bench instead.


https://www.ukworkshop.co.uk/thread...-boring-what-angle-to-make-jaws.135568/page-4
Tom

 

[clogs]

Firstly using a center point /start drill in a pillar drill will end in tears unless it's a decent/ professional jobby…..u'll end up snapping the tip eventually…
they like a drill/ mill with noslop on the main shaft…..
I reg drill heavy plate over and above 13mm in a pillar drill….
my procedure is center punch , then a 5mm pilot hole and then straight to the finished size….I do use coolant coz it's n stock for other machines…
I recommend cobalt drills for those with diy drills….they take all the knocks u don’t always need a load of coolant and hardl ever need sharpening….they cost around 25% more than standard HSS…

If I need super finished accurate holes they get done on the mill…..
most pillar drill just ain’t up to it….

 

[Inspector]

Stepped drill bit ?. or am i missing something here.
https://www.screwfix.com/p/erbauer-...VC57tCh21VQ6cEAQYASABEgJxEvD_BwE&gclsrc=aw.dsView attachment 155969

The OP is drilling through 20mm thick material per the first sentence of the first post. Step drill bits are meant to drill sheet metal.

Pete

 

[Fergie 307]

Agree with Clogs and the others who small pilot hole, then straight to the finished size. If you still from day 12 o 13 mm then you are only using the very edge of the bit. This will catch, rapidly overheat and blunt the drill. You need to bolt the vice to the table and use some sort of cutting fluid, just vegetable cooking oil will do if you haven't got anything else. Make sure your drill is set to an appropriate speed. If it's the normal diy variety then probably the slowest speed. Cobalt drill is a good call, well worth the extra money. And as Pete says step or come drills are specifically for sheet. Try and use one of these on thick material and you will get yourself into a world of trouble. Bright mild is a nice easy material to drill, so providing your drill is a decent quality one, and sharp, this should be fairly simple even with a little diy drill press.

 

[Ttrees]

Regardless of the bits used, the fundamental issue is with the changing of the size drills.

Most of the ubiquitous machines made for the last donkeys years, don't have enough travel of the quill to peck a hole and swap out to a large bit without moving the table.

They also don't have a table with a raising knee like on a mill, and that looks a bit involved and possibly troublesome if using linear bearings and a bottle jack or motor.
That would do the same job, as in keeping the work centered.

Easiest bodge is something rigid and parallel with the column, so you can swing the table over until contact, then tighten the lock.
(whilst letting it do it's thing, no lateral pressure required against the stop)

Tom

 

[DRC]

So, lets say you're wanting to drill a 13mm hole into 20mm thick Bright mild steel on a bench top drill press.

My approach for this has generally been :

- Centre punch a mark to guide the drill
- Have the piece clamped in a vice, but have the vice loose on the table so it can find it's place as the drill centres on the mark
- Sometimes use a centre drill for the first hole if I want it to be very accurate
- start with 6mm, then progress through 8, 10, 12 and finally 13mm.

However, the problem I find is that when you go to use the next size drill bit, it often doesn't cleanly centre in on the previous hole. The wings of the drill catch, and you get a lot of vibration. For the larger bits this can be really bad as they're so long and can flex. The same problem applies if you use a centre drill. The wings catch.

So, clamp down the vice to the table you say? ... well, I tried that too. But the problem there is that as the drill bit diameter increases, the drill gets longer. And so to remove the drill to change it, you have to move/lower the table, losing your positioning. So whilst its more stable, the wings are still likely to catch as its unlikely to be correctly centred.

Having done some research on this, I have discovered that you're actually not really supposed to use a centre drill (which are actually designed for the live centre on a metal lathe, love learning new stuff!), but instead, a spotting drill. A spotting drill has a much larger angle than a centre drill, 120 degrees vs 60 degrees. So the wings on a standard drill (135 degrees) are much less likely to catch.

So, the question is, if you were going to drill the hole described, would you start off with say a 12mm spotting drill? and then go through 6, 8, 10, 12. Or ... go straight to the 12mm drill? or something else?

I use Starrett hole saws they are reasonably accurate enough for my needs for the last 30+ years.

 

[J-G]

From the WD-40 website...

Myth: WD-40 Multi-Use Product is not really a lubricant.

Fact: While the “W-D” in WD-40 stands for Water Displacement, WD-40 Multi-Use Product is a unique, special blend of lubricants. The product’s formulation also contains anti-corrosion agents and ingredients for penetration, water displacement and soil removal

WD-40 Multi-Use is not the product that is normally referred to when anyone specifies it as a means to lubricate.

 

[bansobaby]

Pilot drill no bigger than 6mm, straight to 13mm, going up a few mm at at a time just ruins your drill bits, speed slower than you think (about 600 rpm) and slower than a lot of drills will do. Rule of thumb for mild steel about a foot per second surface speed, but varies hugely as there are lots of different steels.
Use lubricant if possible, cutting fluid preferable, but again there are many different ones. As said above vegetable oil is ok, WD40 a total waste of money for this job.
If you are getting it right you will know by the swarf.

 

[HamsterJam]

my procedure is center punch , then a 5mm pilot hole and then straight to the finished size….

This is what I was taught to do about 40years ago. (Centre punch, pilot, then final size).

 

[Spectric]

@clogs is the right way, small pilot and then drill to final in one go with the workpiece and drill all clamped down. As you drill larger holes then reduce the drill speed and for accurate marking use an optical centre punch. For super precise holes you would need a mill .

 

[throbscottle]

I've never heard of drilling a large hole in small stages. Pilot then full size is what I was taught and have always done.