Cutting bolts into aluminium

[bowlingo]

Hi all,

I am trying to cut these bolts

http://www.toolstation.com/shop/Scr...Bolts/Roofing+Bolt+M6+x+100/d90/sd1670/p90926

into some 8mm aluminium sheet and I need to recess the bolt head only into the aluminium sheet. It is going to be used as a bracket (flat piece of aluminium sheet with 4 x M6 bolt threads coming down and the sheet fixed to the flat ceiling)

I have to make 8 of these and tried making one yesterday using these countersinks (16mm one)

http://www.toolstation.com/shop/HSS+Countersink+Set/p18880

I had a hell of a time trying to cut deep enough into the aluminium using a powerfull drill and a battery drill. I eventually got there but it took me over an hour to do 4 holes!

I am not sure if the countersink is correct? If not please can you tell me the best one for the job I need a 20mm countersink ideally as the 16mm is only just wide enough.

I already have the aluminium plates, bolts etc so I will be using the materials I already have (apart from countersink as they are blunt)

Thanks

 

[foxhole]

I simply use a larger hss bit to counter sink in ali a few seconds to do each hole, though I don't understand your post as the link does not show screws or bolts with countersunk heads.?

 

[bowlingo]

http://www.toolstation.com/shop/Scr...Bolts/Roofing+Bolt+M6+x+100/d90/sd1670/p90926

they are M6 100mm roofing bolts

I could use a drill bit but it would need to be about 20mm and I am afriad of going to far (8mm thick aluminium) and going through the other side....

What kind of countersink would be best for this? I am looking around Ebay but am not sure

 

[bowlingo]

Anyone tell me what the best countersinks are for alluminium please?

 

[foxhole]

The bolts are flat head not countersunk?

 

[bowlingo]

yes sorry flat head but need a hole within the aluminium plate to make the heads flush...

I have just bought this countersink

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=290602511580

Is this the correct tool for the job?

Thanks

 

[Burnerman]

What you are wanting to do is to counterbore rather than countersink the screw heads into the aluminium....however thats not too easy without a machine shop so a large HSS countersink bit is the way to go......drilll slowly with plenty of lubricant (WD40 will do) and you'll get there.
I've never come across a CSK without flutes though and can only assume that this will actually swage the material rather than actually cut it.
Of course, you could always get some CSK stainless screws to make things easier for yourself!
Cromwell tools do counterbore bits, but they are really for milling machines.
John

 

[cajar]

Countersunk bolt heads match the shape of a countersink meaning you dont have to remove any more material than neccessary.

To get your flat head bolt flush you will have to go much further than would be necessary with a countersunk bolt because the outer edge of the hole has to be the full depth of the head, which means of course the tip of the conical countersink is probably almost out the other side.

You're making things very hard for yourself for the want of a few bolts.

 

[TicklyT]

Personally, I would tap the holes in the ally, and screw pieces of M6 studding directly into it - no need to countersink or anything, just a 5mm drill bit and an M6 taper tap.

IME one characteristic of aluminium that makes it hard to work nicely is pieces of swarf cold welding to the cutting edge of tools.

A good supply of lubricant helps, along with an appropriate cutting speed (the average DIY power drill spins much too fast).

WD40, paraffin and turpentine all work well as cutting lubricants on aluminium, and keep the cutting edges of your drills or countersinks clean by breaking away any swarf that gets stuck to them. Bits of swarf stuck to the cutting edges mean the tool just rubs away by friction, overheating and drawing the temper of the tool, and getting more bits of ally stuck to it to boot.

Judging the cutting speed - usually a couple of hundred RPM is enough - and feed (pressure applied) to keep the countersink cutting rather than rubbing keeps things copacetic, and judicious use of the side of a screwdriver blade is usually enough to clean the cutter flutes if you get it wrong.

It is normal practise to counterBORE holes for the type of screws you linked to. That is usually done with a normal twist drill, and finished to a flat bottom with a 'D' bit

CounterSUNK holes normally accept countersunk head screws, which exactly match the profile of the countersink bit, not a bolt with a flat underside to the head.

Your choice of bolt is making life more difficult because roofing bolts have a larger head diameter than virtually any other type of bolt

 

[big-all]

as an aside if you are trying to countersink into ally to a specific depth
place a bit off steel under the ally countersink to depth
on the next hole drill until you pierce the ally position over the first hollow on the steel and a few turns will give you the depth without pushing to much
use hss or harder drill bits for a 20 second countersink