Very Thin Nutserts ?

[awemawson]

I have a problem making some sliding covers for a machine tool. The construction is in two halves made from 2 mm aluminium. One half was existing, the other had 'vanished' so I've never seen it. The existing one has an upwards joggle at the join, so I assume that the missing cover went under it. There are holes at the join with the upper cover having countersinks, so a csk screw can thread into the lower cover, but 2 mm aluminium is not strong enough for an M4 thread AND NOTHING CAN PROJECT BELOW

As the table of the machine moves, it pulls this pair of covers around, their travel being halted by upstanding 'kerbs' which catch on the downturns flanges on the covers. These kerbs are the same depth as the flanges hence nothing can project below the lower surface, and there is only 2 mm clearance at one point above the covers.

In the picture you can see the new cover I've bent up and the old one joining with two screw holes. I did try just tapping the aluminium, but with less than three threads in the thickness its far too weak.

Is there some sort of thread insert that I could strengthen the thread with within the thickness of the 2 mm sheet? Certainly no room for a conventional hank bush

Trouble is it is not just 'fit and forget' as these covers have to come off regularly for maintenance.

Any suggestions would be very welcome

 

[ajlelectronics]

Could you make them in stainless? Otherwise, thinking aloud... Drill a hole to the AF size of the nut, apply some epoxy and use a press to set them into the shhet?

 

[awemawson]

Excellent suggestion squashing nuts in, and seems to work really well. I used my 60 ton press but probably only 2-3 tons needed. OK I had to re-tap the nut - standard M4 nut is 3 mm thick - this one is now 2.3 mm thick having been tortured

Very many thanks - I think you've probably solved my problem

 

[Rocketman]

could you not use cage nuts?

 

[awemawson]

Sadly no room for cage nuts - the underside of the panel literally slides on another member

 

[brightspark]

Could you make them in stainless? Otherwise, thinking aloud... Drill a hole to the AF size of the nut, apply some epoxy and use a press to set them into the shhet?

what is shhet ??is it an abbreviation or a spelling mistake by the english teacher

 

[MattF]

Sadly no room for cage nuts - the underside of the panel literally slides on another member

Instead of compressing and retapping the nuts, could you not drill a round hole and then insert some outer knurled rod using the same method, then drill and tap that after the compression? You'd end up with a thread which wasn't hanging on by the skin of its teeth that way, and it should be grippy enough. Either that or use hex rod. I'd be concerned about the tenacity of that thread after compression and retapping, especially if it's going to be frequently dismantled. Only time will tell if it's a problem or not though.

 

[awemawson]

Matt you are right that's how it should be done, but they are big flappy panels to get onto the drilling machine.

What I'm intending to do is press stainless 'half nuts' into a round hole from the underside. As they are about 1.5 mm thick there will be a 0.5 mm ledge against which they will pull from above, and probably won't have damaged threads as they are harder than mild steel and won't get squashed so much as they are thinner than the panel. Half nuts are on order so I'll post a picture when they arrive and have experimented!

 

[hooblah]

Google hank bush.

 

[awemawson]

Google hank bush.

As per Post #1

"Is there some sort of thread insert that I could strengthen the thread with within the thickness of the 2 mm sheet? Certainly no room for a conventional hank bush"

 

[hooblah]

Ah sorry I didn't read that properly!

 

[Shox Dr]

How about welding a stud to the panel, so you fit the nut from the top. Apologies if I have misunderstood the OP question/requirement

 

[awemawson]

Upper panel has to be retained by counter sunk screws as there not only is a problem with things sticking out below, but also above

I'm having to use M4 x 4 mm stainless pozidrives - not many threads in them !!!!!

It's actually a pretty stupid design, but not too easy to change. This is a 1984 Fanuc Tapecut Model M wire EDM machine. Ideally as someone else suggested, I'd bend up new covers in 2 mm stainless that would take a thread, but although my Edwards folder will bend it, my guillotine won't cut it !

 

[Paul.]

I use self clinching nuts from RS for this kind of job, the M4 ones are only a couple of mm thick, and can be skimmed with a flap disc after fitting to make them even thinner.
http://uk.rs-online.com/web/p/self-clinching-nuts/0827647/

 

[Rig Pig]

Use a flute less forming tap, made for this type of work.

 

[awemawson]

Use a flute less forming tap, made for this type of work.

I thought that they raised a tube of thread on the far side of the panel? Thread has to lie entirely within the 2mm thick aluminium panel and hence aluminium threads (which are too weak - at 0.7 mm pitch there are only 3 of them !!!!!)

 

[awemawson]

OK Half nuts arrived - they are 2.09 mm thick so pretty well ideal, and as I thought, when pressed in the thread is not distorted and works fine without re-tapping

 

[awemawson]

So VERY many thanks to AJLElectronics who suggested pressing in nuts - it has solved my problem apparently entirely and is a useful trick to have up my sleeve in future. In practise using the AF size of the nut for the hole makes a pretty secure fixing - I did experiment going smaller and bigger but the actual AF isthe best compromise and needs no adhesive, being a good friction fit.