Best way to shape 4x4mm square hole in 3mm steel

[Tetsuaiga]

Hello,

I'm trying to work out how I can do this. I've done some research and it seems theres some expensive options like spending 2 to 3 hundred which I dont really want to do.

I think the other methods I came across were drilling a circular holes to start then using triangular, square or needle file to finish. I think I also read about an Arbor press, which you can get fairly cheaply but im really not sure what these machines are capable of.

Can anyone recommend methods?


Thank you.

 

[Cheshirechappie]

If you only have one, or perhaps half a dozen, to do, by far the most straightforward way is to drill about 3.5mm and open up with small files. Make yourself a small gauge to fit the hole to - a length of square bar may well do. If you're going into production and need hundreds, drill pilot holes and press a broach through - you'll probably have to have the broach specially made.

There are fancy ways of drilling square holes, but the kit is like hen's teeth to buy, so you'd probably have to make it yourself. For just a few holes, not worth the effort.

 

[Tetsuaiga]

Thanks. I dont have many to do so I think i'll try the filing method.

When you say use a gauge, would you make an indentation on the metal with it, say by hammering it to mark out the square on the surface?

Can you also suggest what kind of file to use? Like what shape file is best.

Thanks a lot.

 

[AndyT]

My experience of metalworking is pretty limited - the last thing I made was a little shoulder plane - but it was from 3mm mild steel and not difficult.

As CC says, keep it simple; it's probably easier than you think. This is how I would go about it.

Mark the square on the steel - go over it with a permanent marker then use a scriber to scratch the lines.
Drill a 3 or 3.5mm hole centrally.
Hold the work vertical in the vice, and use needle files, working horizontally. Use a "threesquare" file which is actually triangular in cross-section. Concentrate on just one side of the square at a time, cutting downwards. Keep the file horizontal. Rotate the work to cut each side of the square in turn.

Decent Swiss needle files are not expensive - cheap enough to make the really cheap Chinese offerings poor value. Do use a handle on your file - it will be safer and much more comfortable.

 

[Cheshirechappie]

Yep - can't add much to what Andy's said. Mild steel, especially something as thin as 3mm, is less of a filing challenge than you might think. A practice run on a piece of scrap would be a good move if you're a tad apprehensive or haven't done much metalwork before. Holding the workpiece firmly in a vice or whatever is a big help - you can control the file much better with two hands.

One tip, though - move the file fairly slowly. Many a beginner tends to assume that a high file-speed is needed - it isn't. With a needle file (about 3" of cut length) about two strokes a second would be top speed, and one stroke a second for precision work; it's easier to control what you're doing if you file slowly and deliberately.

By 'gauge', I meant a device to check the hole's size and dimension. File until the gauge just won't quite go in, then ease out metal a file stroke or two at a time until the gauge just fits nicely. It may help to have two - one 4mm x 3mm to check the first two (opposite) sides, then a second one 4mm square to fit the second two adjacent sides. How close and accurate a fit depends on the application, of course. If you just need clearance holes, the gauges may not be necessary - just file until whatever is to go through the hole does so.

Edit to add - I've just read Andy's link to his shoulder plane making thread, and it's well worth a look. Nice little plane, too.

 

[AES]

Being a not very experienced woodworker, but someone who has spents many hours filing metal, I agree 100% with everyone's points above, especially the "take it easy" approach.

An extra couple of tips, especially if using swiss files, is 1st, buy a fine brass wire brush (as used for cleaning suede shoes) and make sure you clean the file/s off, at least after making each hole, if not more often. 2nd, although not so common as on larger files, you can sometimes find the odd square-section swiss file with a safety edge (i.e. no teeth on one side).

Another thing to consider if you have a decent tool merchant nearby is too look for what's called a pillar file. This is just like anordinary hand file excet that it's much narropwer than a normal file. They come in different lengths with reduced widths in proportion so if you do find one, I guess a pillar file of about 6 to 8 inched long, in medium or fine cut will do your job nicely. Not terribly expensive either.

But again, do look for a file with a safety edge - though a triangular section file is probably the safest for you, especially if you cant find a pillar file with a safety edge. But with a triangular file, even a fine cut swiss file, DO go very carefully into each corner as the hole nears final size, otherwise it's VERY easy to "run into the corner" too far. Do NOT ask me how I know that please ;-)

A lot of people with little or no experience of filing find the thought daunting, but actually if you use a decent, sharp file, you'll find it cuts very well and much quicker than you imagined - sometimes too quickly! Go for it and enjoy it.

Krgds
AES

 

[AndyT]

Tetsuaiga - now we're all thinking about it, are you going to show us what you are making? :wink:

 

[bugbear]

If you're not confident of your filing accuracy to keep the hole parallel (3mm a deep enough hole for this to be an issue) fit a longer-than-usual handle to the file, say 30cm of dowel. A longer handle greatly increases angular accuracy.

BugBear

 

[AES]

Bugbear has a very good point. I was going to say it myself in my last post and forgot - a handle greatly improves your accuracy, especially when first starting out.

AES

 

[jasonB]

I doubt you will find a pillar file much smaller than 6mm and it will also be hard to find something small enough with a safety edge. All is not lost as it is quite easy to grind of one or the two opposite faces of a needle file or small square file, thats what I used for the 1/16"x1/4" slots in this linkage to take the wedges & cotters.

But you should be OK with a 3mm square needle file, just take your time

If you have a lot to do then a broach will make light work of it, at that size you don't need a proper press it could be done with the drill press of a chisel morticer, I've bought broaches from Steelmans in the past who are quite reasonable on price
http://www.steelmans.co.uk/?91,4mm-square-broach

J

 

[Tetsuaiga]

Wow thanks for all the help, its very kind. I'll go with the drill hole then, needle file while measuring method.

I'm not making anything very exciting at all, just a key to turn a zither pin for an instrument. You can buy then but it seems such a simple device id like to try doing my own instead.