Thread tapping

Uncle Petey · 21 Sep 2014 at 05:57

Could anyone advise on what exactly I would need to tap M4 threads into ~2mm box section steel or aluminium?
I get lost when looking at tapping kits and stuff tbh

I don't have a drill press, just a regular drill and a workbench. Could I just do it by hand without power tools?

Meridian · 21 Sep 2014 at 08:27

You need a tapered M4 tap and a tap handle. And yes, you can do it by hand. Make sure it's a tapered tap, not a bottoming tap - the one you want will have no thread at the bottom, and a full thread at the top, with a steady taper between the two (hence the name). Remember: wind until there's resistance, then wind back. Wind forward until you get resistance, etc. Make sure the tap stays vertical - that's going to be hard on such thin metal.

But...

M4 seems a big thread to put through 2mm of material? You're only going to get about one turn to two turns to grip surely?

R B Customs · 21 Sep 2014 at 08:37

It's such a tricky thing! Generally taps for aluminium are not suitable for steel and vice versa, it going to come down to testing it on a bit of scrap.

I've been drilling a lot of 12mm deep, m6 blind holes in aluminium bar, but also tested 3mm sheet and these work great http://m.ebay.co.uk/itm/271512518957?nav=SEARCH

The traditional twin flute straight taps can be testing to use, especially trying to fingers a decent one so I'd recommend buying them individually rather than in cheaply sets.

The one I linked to is yellow band which iirc is for aluminium. There's different colours though.

Makhaira · 21 Sep 2014 at 09:50

I'm with Meridian, you're not going to get much grip on M4 in 2mm - you'd be better bolting through it to be honest.

Uncle Petey · 21 Sep 2014 at 18:25

Thanks chaps

I kind of just picked M4, but it's not absolutely necessary that I use that size. Any other size recommendations that would be more suitable are welcome

ED: Duh, M6 has been recommended..

Bolting through is not really an option for me, as this is for a planned scratch built case using 1" box section framework and I plan to attach the panels (and other bits) by screwing them into the frame.

I'd prefer to use aluminium as it'd be a fair bit lighter, but it would work out a fair bit more expensive, so steel is still in the running if it makes a difference.

Too Tall · 21 Sep 2014 at 18:48

Do you have a drawing or somthing of what your trying to make?

wazza300 · 21 Sep 2014 at 18:51

wouldn't self tapping screws work?

Uncle Petey · 21 Sep 2014 at 18:56

Too Tall said:
Do you have a drawing or somthing of what your trying to make?

Yeah, I have a couple of sketchup designs, but I probably won't be going with either of them as it stands, so that may not help much.

There is no real load bearing required for the parts I want to attach to the framework if that helps. It's just the weight of 5mm Acrylic sheet, some of which may be large-ish at 5-600mm.
There may be a couple of spots where bolting through it would be fine, but for most bits it's not an option.

@Wazza
No idea mate

Too Tall · 21 Sep 2014 at 18:58

Good quality tap and die sets aren't cheap. But you can get a draper tap and die set on the rainforest for around 40 quid. Get some cutting compound too.

How thick is the material you're looking to put a thread in?

Uncle Petey · 21 Sep 2014 at 19:32

If I used steel box section, around 2.5mm wall thickness.

Makhaira · 21 Sep 2014 at 19:45

Could you rivet it instead?

Uncle Petey · 21 Sep 2014 at 19:49

Not really. Panels need to be easily removable.

Too Tall · 21 Sep 2014 at 19:49

If its not load bearing then I'd use the smallest thread you can get away with. At 2.5mm you won't get many threads cut on a larger size.

Uncle Petey · 21 Sep 2014 at 19:57

Aside from a couple of large acrylic side panels, there shouldn't be any real weight on the screws, so M3 or?

Too Tall · 21 Sep 2014 at 20:10

I'd give it a bash on a bit of scrap and see how you get on.

Uncle Petey · 21 Sep 2014 at 20:17

Yeah, I could just order a small section of steel to test with.

That brings me back to the original question of what to get?

I seriously know nothing about this kind of thing...

JBuk · 21 Sep 2014 at 20:21

Do you need it threaded? Could you not get a nut behind and have a clearance hole?

Edit: just seen you can't

Another option is to weld a boss in or behind the structural parts then drill & tap into that

Uncle Petey · 21 Sep 2014 at 20:26

I did think of that actually. It would work for some parts, but not others.
Threading really would be the easiest and most flexible way.

JBuk · 21 Sep 2014 at 20:32

Does it need to be box section? Could you use angle plate with a thicker profile allowing for a few more threads

Uncle Petey · 21 Sep 2014 at 20:40

Possibly, yes. Would also help with shrinking the overall dimensions I suppose.

I went with box section as I don't have a massive selection of power tools or a workshop etc, and was just going to have them cut to size and popped together using a variety of these.
All I'd then need to do is tap the required threads and screw on the panels, plus a few L brackets for various bits.
Welding or cutting metal that can't be done with anything more than a nibbler or jigsaw isn't an option here.