Drilling 20mm holes in 10mm plate

[scott brunsdon]

So I've got 8 of them to do - some structural steel for my latest DIY renovation.

Had to go and buy a 20mm drill bit - boy, that was expensive.

What size pilot hole would be best? I would hate to bugger my new drill bit.

Scott

[denrep]

I guess for us Yankees that's about 13/16" in about 3/8 plate.

If this is field work, a slugger bit would probably be better than a twist drill, because of the catch at break-through.

Otherwise if you have the power to turn the twist bit, you only need a pilot hole large enough so that the bit's tip, between the flutes, drops and allows the cutting edges to make contact.

Good Luck

[DesertRider33]

20mm is about 3/4". 10mm is about 3/8".

When I drill big holes like that with regular drill bits, I do them in 3 or 4 steps, starting small and working up to the final size. I buy extra long bits in the smaller sizes so I can use the drill press at the same table height for all the bit sizes so the chuck stays centered over the hole throughout the process.

[scott brunsdon]

Thanks. I'll give it a go both ways. This is going to put my Chinese made drill press to the test - I never expected it to last as long as it already has anyway.
Scott

[Sandy]

I think millimeter holes are a lot harder to drill than regular holes too. :)

[scott brunsdon]

Definitely harder. And we're upside down as well.

Hey, what's a 'slugger bit'?

[Sandy]

Hey, what's a 'slugger bit'?


Slug cutter bit. Annular cutter style. Precision hole saw.

[scott brunsdon]

Hmmm. Didn't see them down at the local hardware store. I bet they're expensive.

[Sandy]

Hmmm. Didn't see them down at the local hardware store. I bet they're expensive.

When your buying individual bits, like I do a lot, pricing is unpredictable. But yeh, they can seem pricey. Large diameter twist drills take a lot of torque to turn tho or you're doing the multiple step thing. Annulars can pay back for those that do a lot of holes.

[MarkBall2]

I think millimeter holes are a lot harder to drill than regular holes too. :)

She said she liked it harder................and upside down.................

[tom37]

I don't think I have posted since I first registered, sorry but there is tons to read.

I just thought I would throw this out there. I bought a 1" bit called the Brute. So far its drilled 30 plus holes. A few in 1/8 a bunch in 1/4 and just a couple in 1/2", with no pilot.

It sorta resembles a hole saw on steroids.

Good luck and have a great day.

[denrep]

No doubt that a quality bit pays for itself.

I had a project with about a dozen 3/4" holes that had to be punched through three layers of rusty steel, using a mag-drill.

I was so dreading the miserable task, expecting to break and burn bits, that I bought three brand new drill bits, the most expensive bits in stock at an industrial tool supply. I'll check the brand tomorrow, if anyone cares.

Ended up completing the job with only one bit. The first bit cut all the holes like butter, rolling off two giant curlicues as it cut, and it was still sharp when drilling the last hole.

. . .And we're (drilling) upside down as well. . . .
True, but at least on most holes the chips fall away from the cut. :p

Good Luck

[DDA52]

Any chance you can ever get a mag drill...jump feet first. They will make short order of that little job. Probably take 15 minutes total...maybe 20 if it takes a while to set up and clean up. I drilled 80 some odd 11/16 holes today with a mag drill in under 2 hours...including all the layout. It was only 1/4" thick and each hole only took about 15 seconds or so to drill. Mag drills rule!:cool2:

[mrmikey]

These are good, http://tinyurl.com/lqdgh2 take less power and make a nice clean cut, Only downfall of them is vibration will kill 'em when they're carbide tipped.
The actual slugger bitt that Denrep mentioned http://tinyurl.com/lo7fdf .......Mike

[scott brunsdon]

I thought I would have a go at the holes when I got home from work yesterday - on warm evenings I like to head out into the shed with a beer and muck around with some small stuff.
So I did 3mm holes, then 10mm and then 20mm. Easy.
I would like to get one of those slugger bits one day, though.

[tom37]

These are good, http://tinyurl.com/lqdgh2 take less power and make a nice clean cut

This is the same bit as the Brute bit I referred to in my previous post. I can only offer what I have experienced, and even in my under powered tiny drill press it cuts wonderful.

[metalmeltr]

use lots of cutting oil

[kb0thn]

I had to field modify some structural steel work last month. 1/2" holes were drilled about 1/4" off. So they ended up getting enlarged to 7/8. 8 holes per skid and 4 skids. And half of the holes were right through weld (not my design!). No power available, so 18 volt cordless drills were used.

After some mulling, I bought a 7/8" Irwin Uni-bit for $40 (Alaska prices, ouch!). I did about 20 holes (5 drill batteries) before the customer wanted to try it. He then ruined the drill bit on the second hole. For drilling mild steel, you need to remove the heat with the chip. So go fast and push hard and you will get a blue chip coming off. Stop and feel the drill bit and it will only be moderately warm. Problems occur, as my customer learned, when you dwell on the material and work harden it.

You need a fairly powerful and high torque drill to do this with a big cutter. The 18 volt cordless just barely did the job. I personally run 28 volt Milwaukees and they do pertty well. I would not recommend the feed as hard as you can technique when using a normal twist bit. At it tears through the drill will attempt to break your arm. I had a miserable evening last night trying to hole saw 4.5" holes in aluminum.

-Jim