The alternative is to mark the hole, chain drill around it and then clean up with a file (or a flap disc in a dremel if you have one).
bah, few seconds too slow
Bonus picture of chain drilling
[Edited on 15/9/13 by iank]
Novice question this - how do I cut a hole in my 3mm steel pedal box to accommodate my brake master cylinder?
Is one of those 'saw blades bent into a circle - that operates in an electric drill' the answer? I guess they are called 'hole
-cutters'?
They aren't cheap - so it seems excessive to buy one to cut a single hole?
They are called hole saws. They do work, another good thing would be a "step drill" which is like a very large cone drill the steps up in
size the deeper you drill, however fairly expensive.
If you don't want to buy anything, even just a series of small holes drilled around the circumference of the big hole you want to cut out can
work and clean it up with a file.
Yes a decent bi-metal hole saw will do the job in a few seconds (drill nice and slow, with lubricant).
The alternative is to mark the hole, chain drill around it and then clean up with a file (or a flap disc in a dremel if you have one).
bah, few seconds too slow
Bonus picture of chain drilling
[Edited on 15/9/13 by iank]
If you do buy a hole saw, get a decent one, Starret is good. The cheaper ones vibrate like stink and give a very poor cut. A bit of lubricant always helps.
I have one of these, you can buy the arbour and saws separately. I
cut a 86mm hole in 4mm mild steel, it was slow, and I used lots of lubricant with a very slow speed.
One tip is not to cut all the way through, cut half way then turn the piece over and finish off. Also, I replaced the pilot drill with a steel rod,
this stops the pilot hole progressively becoming oval, before the saw self centres. 
I have good hole saws for the sizes I use most. These are usually Starrett. However, I bought a set of cheapy ones from Lidl and they've suprisingly good! One has just chewed eight 3" holes through 4mm stainless. Slow cutting speed with a few breaks to allow things to cool, and cutting paste. Ideal if you only need to make a few holes.
Slightly off topic but I have never had much success with hole cutters - the blade always comes loose from the pilot drill no matter how tight I clamp
it 
- what is the secret of stopping that from happening?
the step drills are magic!!!
Ivan, the large sizes use two pins to locate in the top of the saw unit rather than sinply butting up against the flange of the securing thread. In use this system can vibrate free with larger saws.
I used this adapted thing on the driller, with lots of lubricant and slooooowwww speed. But used it on ally not on steel. Not sure if it gets through
steel.
The nice thing is that it is adjustable to several hole sizes.
https://picasaweb.google.com/lh/photo/0qDmQd30_zaiAvEaM55o7dMTjNZETYmyPJy0liipFm0?feat=directlink
[Edited on 15/9/13 by HappyFather]
quote:
Originally posted by Ivan
Slightly off topic but I have never had much success with hole cutters - the blade always comes loose from the pilot drill no matter how tight I clamp it
quote:
I used this adapted thing on the driller, with lots of lubricant and slooooowwww speed. But used it on ally not on steel. Not sure if it gets through steel. The nice thing is that it is adjustable to several hole sizes. https://picasaweb.google.com/lh/photo/0qDmQd30_zaiAvEaM55o7dMTjNZETYmyPJy0liipFm0?feat=directlink
The Aldi kit is bimetal as good as Starrett and a fraction of the cost with 2 arbors and a good selection of sizes use mine for work the bonus is the
arbors will also fit starrett. Its finding a store with stock thats the problem as they arent currently on offer.
Cheers,
Bob
quote:
Originally posted by owelly
quote:
I used this adapted thing on the driller, with lots of lubricant and slooooowwww speed. But used it on ally not on steel. Not sure if it gets through steel. The nice thing is that it is adjustable to several hole sizes. https://picasaweb.google.com/lh/photo/0qDmQd30_zaiAvEaM55o7dMTjNZETYmyPJy0liipFm0?feat=directlink
Aka trepanning tool.
quote:
Originally posted by splitrivet
The Aldi kit is bimetal as good as Starrett and a fraction of the cost with 2 arbors and a good selection of sizes use mine for work the bonus is the arbors will also fit starrett. Its finding a store with stock thats the problem as they arent currently on offer.
Cheers,
Bob
Go slowly with lots of lub and if it starts smoking stop ASAP. Lots of breaks to cool the cutter and nice slow speed and jobs a good'un. I like Qmax type punches for sheet but they wouldn't do 3mm. 1.2mm stainless is the max I've tried with those fellas. Great for cutting holes in the ali sides for exhausts though- such a shame you have to cover the neat edges with trim for SVA/IVA!
quote:
Originally posted by liam.mccaffrey
the step drills are magic!!!
I'd second/third/what it is the step drills. Whilst they are expensive, they're also very versatile. As with all things though, they have their limitations. The main one being they can only cut as thick as the steps on the drill are, usually 5-6mm. Otherwise they're excellent.
We use starrett at work (offshore) and I've cut through over 25 mm plate with them taking my time. A good hole saw is worth paying the money for and as they say use the correct tool for the job. The easiest way is always the best. Or most of the time any way!
I'm not sure the OP has been pricing the right thing. I'm not Rockerfeller by any means, but I can buy 1.5" holesaws (decent ones) for
less than $5 (..about 3 quid?) which I think is pretty cheap actually.
I will usually evaluate tool purchases based on the time saving...I know it's supposed to be fun and not business but if I can save a couple of
hours for 3 quid then I'd say it's worthwhile...
I've seen this other threads too....spending hours to save a just few bob....but it's your time, your money..
Just my thoughts...
quote:
Originally posted by Alan B
I'm not sure the OP has been pricing the right thing. I'm not Rockerfeller by any means, but I can buy 1.5" holesaws (decent ones) for less than $5 (..about 3 quid?) which I think is pretty cheap actually.
quote:
Originally posted by Alan B
I'm not sure the OP has been pricing the right thing. I'm not Rockerfeller by any means, but I can buy 1.5" holesaws (decent ones) for less than $5 (..about 3 quid?) which I think is pretty cheap actually.
I will usually evaluate tool purchases based on the time saving...I know it's supposed to be fun and not business but if I can save a couple of hours for 3 quid then I'd say it's worthwhile...
I've seen this other threads too....spending hours to save a just few bob....but it's your time, your money..
Just my thoughts...
To be fair stuff like Starrett is quite expensive, especially when you have to buy the arbor as well, but there are plenty of lower cost versions that will do the job.
quote:
Originally posted by jps
Yeah - I did have a Google after i'd posted and realised that the Bosch ones that i'd seen in the local Kent Blaxhill (upwards of £30 each) were phenomenally expensive for some reason - perhaps they were for specialist application and I hadn't realised...