Drilling new bolt holes through the 5mm steel plate on my adapted engine mounts, trashed a couple of drill bits already on just two holes. Can't remember, should the drill speed be fast or slow for drilling plate

Main thing is not to let the steel become hot, because it becomes hard.
then it will be almost impossible to drill.
I use WD40 to keep it cool.
Engine oil with a brush will do.

David

Hi

Bigger the drill, the slower the speed.

Put a bit of grease or oil on to lube it.

1/8 inch for pilot hole, then go in with the bigger one.

If the drills snapped, then you were probably pushing too hard. If they burnt out then you were going too fast

Regards

Chris

I forget who makes them. Might be black and decker, have a look at the 'bullet' range of drill bits. Not the cheapest, but they cut through so quick and easy. Drilled through 5mm plate in seconds with one. But won't work if you've drilled pilot holes

Steady pressure and drill speed to match the size of drill. If you are using a hand drill pulse the drill by switching on and off, as said use lubricant and do not let the drill bit run dry, if the drill bit starts to screech, the speed was to fast or lubricant ran dry,or both, either way the drill bit is toast.

may be down to quality of drill bits, ive previously used basic drill bits but recently brought a set of Dewalt HSS-G bits which are great easy through 1/4" plate

Normally, any HSS drill will do, as long as you are careful (see above). My Aldi ones are just fine.

Use a fine to cut a new edge on your dull drill.

Go slow and loads of lube.
I found a cheap 12v cordless drill with a wire rammed up its chuff and a 12v car battery on the other end rather effective. Ain't never going to stall with 350A of juice at its command and turns at low speed compared to a mains powered drill. Even now I occasionally resort to it when my mains powered drill isn't hacking it....

as said good quality sharp drill bits is the key. i was drilling 7mm the other day wit a poor enough bit at 13mm diameter took ages even with a 10mm pilot. then had two holes to do at 15mm, the bits i have for this hardly get used and there a good quality, took seconds rather than the minutes with the 13mm. Both times I was using 3 in 1 lube with silicon or is it ptfe, either way better stuff than wd40.

if you want calculate your spindle rpm cutting speed of steel is 30 to 38 meters per second, need to work out the average circumference your cutting as well for make any sense/use

I think you'll find thats meters per minute

Mick

Nice and slow with quite a lot of pressure, thick oil as lubricant too.

A rule of thumb for getting drill speed something like is that you should still just be able to see the drill form (i.e flutes) when its at the correct revs but this is quite difiicult to achieve with a hand drill. A common mistake is to run the drill far to quickly.

If I have to do any drilling by "hand" then a cordless is usually better than the mains drill in terms of rev control/speed.

If the chippings/swarf from the drilling comes off in nice long "spirals" then you have the cutting speed/feed spot on.

Just takes practice, especially with hand drills


[Edited on 25/10/09 by Nosbod]

Pilot drill with a small bit then use progressively bigger drills

Drilling a pilot hole isnt really neessary unless you are drilling a huge holes (20mm+) which you wouldnt want to try in plate anyway. Most of the holes we drill will be up to 12mm in diameter, all of which should drill easily into steel straight through if you are running at the correct speed and have a sharp drill.

Also you shouldnt need to use oil or grease to lube the drill if you are running at the correct speed.

Mild steel also doesnt work harden, and doesnt beome hard with excess heat (there isnt enough cerbon for it to happen). What generally happens when there is excess heat is that the corners of the drill soften and become damaged.

Basically there are 2 reaons you can bugger a drill

1. Running too fast
2. The drill is of poor quality or the wrong material.

The best HSS drills are made by Dormer. They arent cheap though, but will outlast any of the cheaper ones many times over.

General method for drilling sheet:

Mark hole using a centre punch. Make a decent sized dimple. Even better if you can then use a centre drill to make a better centre point for the drill to pick up.

As a rough guide for drilling mild steel:

1/2" drill should run around 400rpm

Speed is then linearly increased. So a 1/4" drill should run at double the speed. ~800rpm etc.

Remember drilling a large hole requires a lot of pressure, this is where peoples patience generally runs out and they run the drill too fast.


Just my 2p worth anyway

steel plate as in mild steel?

what diameter holeas this determines drill speed.

I use thos titanium nitride (yellow end) dormer drill bits - brilliant stuff.

pilot hole -with cutting oil then one or two more holes in increasing size.

note that once you reach about 8 mm ish, the drill flutes will tendto grab the metal so you can end up with an off centre hole.

remeber with big drills, you run at slower speed so the central portion is running at a much slower speed - hence the pilot hole to help with the cutting process.

Thanks guys, definitely think I was running too fast as I was screeching a lot(well the bit was anyway). It was the end of the day, after getting the Zetec in so I was probably rushing thing a bit.

Sound advice guys, thanks very much, bought one of the Black and Decker 'Bullet' bits (£9.99 incidentaly). Slowed the drilling speed and kept it well lubricated with some old 20W50 I have lying around (the Crossflow liked it), worked a treat, holes drilled no problem and bit is unmarked.