10mm holes in 8mm mild steel

[Sideways]

Step drills don't seem to have the issue.

That totally makes sense. Step drills - mine at least - don't have the "screw" that causes the problem. Personally I keep those for plastic and thin sheet only to ensure they always cut a very clean hole, and the steps of mine wouldn't handle 10mm plate unless I could get access from both sides.

 

[Sporky McGuffin]

That's a good point - I think my step drills might do 4mm at most.

 

[Alpha-Dave]

I think that I’m much more likely to get the drill to catch as it exits the material than any point during the main drilling, something to do with the material thinning, and the drill the screwing in to the remaining material. Therefore I often put a block of mdf or the offcut under the workpiece (but still in the vice), that’s also true for drilling thin sheet metal, but then I would prefer a hole-saw or punch depending on the hole size.

Edit: actually, the ‘worst’ catch I ever had was centre drilling a rod of ebonite (vulcanised rubber) for a pen blank; the drill’s heat softened the rubber, which caused more friction, more heat, etc and in a fraction of a second it had gone an additional couple of cm in to the blank, which the cooled and tightly held the bit. Took ages to separate the two.

 

[Jameshow]

I think that I’m much more likely to get the drill to catch as it exits the material than any point during the main drilling, something to do with the material thinning, and the drill the screwing in to the remaining material. Therefore I often put a block of mdf or the offcut under the workpiece (but still in the vice), that’s also true for drilling thin sheet metal, but then I would prefer a hole-saw or punch depending on the hole size.

Edit: actually, the ‘worst’ catch I ever had was centre drilling a rod of ebonite (vulcanised rubber) for a pen blank; the drill’s heat softened the rubber, which caused more friction, more heat, etc and in a fraction of a second it had gone an additional couple of cm in to the blank, which the cooled and tightly held the bit. Took ages to separate the two.

Worst material I have drilled is lead the drill went in and the lead heated and moulded around it and before I realised what was going on snap!!
Only when I continuously pulled out did it not heat up!!!

 

[Fergie 307]

Always put a piece of scrap wood underneath so the drill doesn't catch on the way out. You will get a much neater exit to the hole. And an old trick for drilling large truly round holes neatly in thin metal with a normal twist drill is to place a piece of linen or similar cloth scrap over the metal and drill through it. The piece of cloth wants to be about twice the size of the eventual hole. You just place it on the surface and drill through so the cloth wraps around the end of the bit as it goes in. No idea why it works but it does.

 

[AES]

Always put a piece of scrap wood underneath so the drill doesn't catch on the way out. You will get a much neater exit to the hole. And an old trick for drilling large truly round holes neatly in thin metal with a normal twist drill is to place a piece of linen or similar cloth scrap over the metal and drill through it. The piece of cloth wants to be about twice the size of the eventual hole. You just place it on the surface and drill through so the cloth wraps around the end of the bit as it goes in. No idea why it works but it does.

Well that's a new one on me, thanks. I must try it sometime.

 

[Sideways]

Edit: actually, the ‘worst’ catch I ever had was centre drilling a rod of ebonite (vulcanised rubber) for a pen blank...

Me too.
I melted a brand new drill into one of my first ever acrylic blanks. I didn't even try to separate them !
Lesson learnt

 

[Jameshow]

Always put a piece of scrap wood underneath so the drill doesn't catch on the way out. You will get a much neater exit to the hole. And an old trick for drilling large truly round holes neatly in thin metal with a normal twist drill is to place a piece of linen or similar cloth scrap over the metal and drill through it. The piece of cloth wants to be about twice the size of the eventual hole. You just place it on the surface and drill through so the cloth wraps around the end of the bit as it goes in. No idea why it works but it does.

I've sandwiched thin metal between two sheets of plywood and drilled through both!

 

[AES]

I've sandwiched thin metal between two sheets of plywood and drilled through both!

Yup, that works well too (and ditto BTW, for cutting out thin sheet metal on the scroll saw).

 

[baldkev]

Invest in some quality bits. Ive got bosch cobalt which are ok, and some very good irwin titanium bits. Also have some metabo hss ( not good )

 

[Beanwood]

I asked almost exactly this quetion on a mig-welding forum

Mine was actually drilling a 7mm blind hole in an arbor press ram, so I could cut an 8mm screw thread.

In summary - drop your drill speed right down (500 RPM?). Drill a small pilot hole (3-4mm sounds right) UNLESS you're using a good quality split point drill bit. It seems (And I tried it in order to prove it to myself) split point drill bits don't really like a pilot hole.

I also bought some CT-90, and honestly - it was worth the money in my view.

 

[Fergie 307]

That totally makes sense. Step drills - mine at least - don't have the "screw" that causes the problem. Personally I keep those for plastic and thin sheet only to ensure they always cut a very clean hole, and the steps of mine wouldn't handle 10mm plate unless I could get access from both sides.

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 ?

I think the problem is if you go from say 8 to 10 mm then all the cutting is being done at the very edge of the flute, this then becomes very hot, more likely to jam and ultimately blunts the drill. As a rule of thumb I would never drill the pilot hole more than half the size of the bit you intend to use to finish the hole, and probably a bit less of the material is very thick. So in this case I would agree with 4mm as probably the ideal size.

 

[Fergie 307]

Well that's a new one on me, thanks. I must try it sometime.

found this video of a guy demonstrating it.

 

[Jameshow]

Invest in some quality bits. Ive got bosch cobalt which are ok, and some very good irwin titanium bits. Also have some metabo hss ( not good )

I got 100 bits for £10 off eBay - never again!!!

 

[emlclcy]

i had lots of 10mm holes to drill in the top of a welding table i made so i hired a mag drill. it has a magnetic base and uses special cutters that drill the hole in one go with oil fed down the middle of the cutter. i was so impressed with it i bought it and have used it many times since

 

[MorrisWoodman12]

I got 100 bits for £10 off eBay - never again!!!

I was drilling stainless steel. Knew it would be hard going so bought a pack of drills from Homebase. Never again. Some of them even had the rake on the bit ground the wrong way.
Have drilled SS several times successfully since, just gone slow with plenty of cutting fluid.
Buy good, buy once.
Martin

 

[MorrisWoodman12]

found this video of a guy demonstrating it.

How can that ever work?

 

[AES]

found this video of a guy demonstrating it.

Well, I've watched it now. Seems to work very well, though I've no idea how/why. Must try it myself sometime (I actually do have a similar job coming up soon, will let you all know how I get on). Thanks.

 

[redhunter350]

Yep oldest struck in the book works every time, we used a small piece of fine emery cloth, also works if you are getting chatter with a countersink. Why ???? No idea it just does

 

[Jameshow]

I was drilling stainless steel. Knew it would be hard going so bought a pack of drills from Homebase. Never again. Some of them even had the rake on the bit ground the wrong way.
Have drilled SS several times successfully since, just gone slow with plenty of cutting fluid.
Buy good, buy once.
Martin

I was drilling bolt holes for a camper van 8mm each X 20??

I then went to 4/8mm cobat drill bits - fantastic!!