10mm holes in 8mm mild steel

[DigitalM]

Noob metalworking question from an intermediate woodworker...

I want to make some 10mm holes for bolts in some 8mm thick mild steel bar I have, for use as brackets. I've got a good pillar drill. I don't have a drill vice. Maybe I should invest in one of those.

Should I just go at it with a 10mm drill bit or get myself a step drill like I saw in a youtube video. I won't be making holes all day long for days and days (I need to make 8 holes), but I may need to do something similar in future, I just don't need to be buying top of the range and spending a fortune without good reason.

Any advice welcome, along with any product recommendations.

 

[bourbon]

The way I approach these jobs is to Put a centre punch where I need the hole, drill a smaller maybe 3mm hole Putting 3-1 oil on the flutes of the drill. Get the speed of the drill as slow as you can get it. then up the size to 6mm, plenty of oil again, then the 10mm. You will need a vice to hold it as it will have a tendency to snatch.

 

[Sideways]

I would pilot drill each hole with something like a 3 or possibly 4mm then push the 10mm straight through.
The 10mm has a fair sized web in the middle of the drill between the flutes. A pilot drill of about that size will make it much easier for the 10mm to go through and the pilot will also help to stop it from wandering off until the full 10mm diameter is cutting.

I've used the exact method to push 14mm holes through 10mm plate using a handheld drill.

 

[Alpha-Dave]

I would go centre-punch, then 4-6-10 mm standard HSS drill bits, with cutting oil. You can drill faster with the smaller bits, I would go ~1,000 rpm for 4 and 6, then closer to 500 rpm for 10 mm.

I would always use a vice for this sort of work-holding; if it grabs and swings the bar around at 500 rpm you may regret it quickly if you can’t move your hands out of the way in less than 0.12 seconds.

Sharp drill bits are a joy to use, dull ones are a hazard; either learn to sharpen on a grindstone with a jig, or buy cheap semi-disposable ones for a fresh-edge when you need it. I probably sharpen after 20-40 holes depending on what I have been drilling.

 

[Jameshow]

If you don't have a vice but some scraps of 18mm plywood or MDF you can lock the piece into plywood with small offcuts all-round screwed in with small screws, you can then g clamp or bolt the ply to your pillar drill table.

 

[bp122]

What has been said above.

Larger the drill bit you use, more chance of excessive heat build up, drill bit wander and a messier hole.

Just the other day I had to drill a few 8mm holes. It is in fact quicker and easier to do it in smaller steps than to gun it with a larger bit.

Also, easy to blunt the drill bit.

So:
1. Invest in a drill vice (worth it) or at least a drilling block
2. Use oil while cutting (use something with a long snout to reach the target area safely)
3. Do it in steps
4. Don't wear loose clothing /gloves etc
5. Debur the holes.
6. Don't forget eye protection (spiral scrap just flies off)

 

[Sporky McGuffin]

A drill vice is well worth having.

 

[--Tom--]

Without a vice clamp something to the table to butt the piece up against. Will stop it windmilling if the steel tries to catch.

4mm then 10mm will be fine, slow the speed down and use some cutting lubricant

 

[pe2dave]

Think of your fingers, bruised and cut (or worse) trying to hold on to some sharp metal that the drill bit grabbed?
As others, a drill vice (cheap / nasty / second hand) will reward you without you knowing it.

 

[Jameshow]

I'd get a couple of cobat bits too.

Makes for a much more than effective drilling experience!

 

[redhunter350]

Have a look at this clamp Axminster Drill Clamps a very useful tool instead of or in addition to a vice. One of my most used tools now some 50 years old ! As far as drilling it’s pretty much all been said, either use a pilot hole or thin the point and drill straight through with a HSS 10mm drill , buy a good quality set of drills from Dormer, Ghuring or similar, not all but many of the economically priced sets will not serve you well — false economy !

 

[MorrisWoodman12]

Yes to most of the advice above especially as slow as possible with the 10mm bit. I'd probably pilot with a drill just a little bigger than the 10mm bit's root so I guess about 4mm: that helps keep the 10mm centred. Plus it's often easier to drill 10mm halfway through then start again from the other side. Stops the horrendous snagging as the bit comes through.

I'd get a couple of cobat bits too.

Makes for a much more than effective drilling experience!

But proper 5% cobalt bits not just 'cobalt' described bits as this just a coating that comes off quite quickly. Personally I would simply use a 'normal' HSS bit.
Hope this is of some help.
Martin

 

[MARK.B.]

Excellent advice already given i would add that it is easier to drill the holes in your brackets before bending to the required shape . I have a 2" scar on my left hand that was caused by a chunk of metal not held securely by a vice or clamping in place trust me when i say it hurts A LOT, i was lucky not to have caused any permanent damage , i now have a vice and it get used every time

 

[DigitalM]

Thanks everyone! All very helpful. I'll get on with it!

 

[Sandyn]

Definitely agree, get a good sized vice which can be clamped to the drill table. Get good drills.
I normally use a centre drill to create the pilot holes. If you are drilling repeat holes in a line, centre the pilot drill on the first hole with the piece clamped in the vice, supported by a narrower bit of wood so you can drill through with the 10mm. Clamp the vice to the table, then re-check centre. In this way, it makes all the other holes already aligned in one dimension. My trusty drill chart says 600-1000 for 10mm in steel. I use cutting fluid or oil. I don't go up through the sizes. I find the possibility of drill snatch increases if you are drilling in small increments, especially with larger drills.

 

[sploo]

Largely just echoing others' comments, but agreed: work holding (i.e. a vice) is important (bits can "grab", and a work piece windmilling around on a drill press is really dangerous).

Don't get greedy with metal drilling; use plenty of lubricant (3-in-1 oil, or something specifically designed for the job e.g. CT-90) as it helps prolong bit life. Heat is a killer for drill bits.

Cobalt bits are great, and in smaller diameters they're not expensive.

Centre punch, then work your way up with 4-6-8-10mm bits.

You'll find that a sharp 4mm cobalt bit, with lube, will go through mild steel really easily, then the larger sizes are not too bad.

 

[Sideways]

This has been a popular thread so I'll risk deflecting it slightly to ask a related question.
I find when drilling larger holes into metal that working up through the sizes has a very real risk that a larger drill will grab. The bit will carve into the workpiece like a corkscrew and jam. For this reason I wouldn't drill 4,6,8,10 in turn. No need and actually more likely to cause a problem.

This is much less a problem if the work is in a vice and the job being done with a drill press but that isn't always possible or convenient. There are plenty of workpieces too big to fit in a vice or even be clamped to a drill press table. Other times when a hand drill is the only option.

The root cause is that the spiral of the drill bit is effectively a VERY coarse thread and given half a chance it will bite and try to screw itself into the previous hole. Clamped in a drill press you might be able to hold a drill back. With a hand drill or an unsecured workpiece, even a heavy or large one, you don't have enough control.

If a single pilot hole is used, around the size of the web of the bit, the chances of the large finished size drill digging in is very much less in my experience.

Has anyone else noticed the same issue ?

 

[pe2dave]

This has been a popular thread so I'll risk deflecting it slightly to ask a related question.
I find when drilling larger holes into metal that working up through the sizes has a very real risk that a larger drill will grab. The bit will carve into the workpiece like a corkscrew and jam. For this reason I wouldn't drill 4,6,8,10 in turn. No need and actually more likely to cause a problem.


Has anyone else noticed the same issue ?

Yes, though I think 2mm increments might make this effect worse (especially if you have a morse taper chuck?).
Yes, pilot (4mm?) then straight in with 10, though going back from the other side sounds like solid advice.

 

[Sporky McGuffin]

Likewise - I think it's also down to the wrong feed rate and rpm.

Step drills don't seem to have the issue.

 

[AES]

@Sideways. Agree with you in part. Myself, after a centre pop mark, I'd certainly start off with a centre drill (Slocombe) chosen to be approx the same dia as the web of the 10 mm drill. (If no Slocombe, then an ordinary jobbers drill with dia as per the web of the 10 mm final drill). Personally I'd never bother with going up in steps after the first drill (such as 4-6-8) as particularly with good quality modern drills (even "just" HSS), the edges of the swarf clearance spirals are quite hard and quite sharp and will "dig in like a screw thread" exactly as you describe).

If I may, I'd also point out that the term "big" when describing a drill is entirely relative - for a watchmaker, 10 mm is gigantic, to a ship yard worker, tiny. OK, those are ridiculous examples I realise, but for the average hobby shop with a pillar drill and a decent set of drills, anything up to about 14 or 15 mm isn't SO large, especially if only drilling MS. Provided the work is held securely - when possible, a drill vice as you suggest, otherwise take other steps, like a ratchet strap or something - and provided rpm is well down and feed is firm/steady and not excessive, and providing a lubricant is used, drilling 10 mm holes into 8 mm MS plate is "easy peasy" really. I can understand a newbie having doubts when first looking at a "thick" chunk of steel and a "big" drill, but with the above caveats, no problem really.

But YES, building "your own screw thread" as you describe above while drilling sheet/plate MS (especially the thinner stuff) CAN be painful on the hands/arms until! And do NOT try it on thin sheet ali - you become the inventor of the instant rotary razor blade. DAMHIKT!