Tapping Aluminium extrusion

[Web Goblin]

3539
Hi all,
I thought i would make a start on my router build but have hit a problem already.
Tapping the aluminium extrusion wasnt as easy as I thought it would be. Normal straight flute taps are no good for this because the hole is not completely surrounded by material. As you can see it doesnt work vey well.
Looks like I will need to wait till I get back to work on Wednesday to get some spiral flute taps.


Ian

[M250cnc]

Hi Ian at least you didn't break a tap.

My guess is there are special screws for the extrusion that self thread, this will make life very easy.

Phil

[Web Goblin]

Phil,
gave up with it as soon as I realised the tap was moving off course. Thats a good call on the self threading screws. I will give the supplier a call after the holidays and see what they have. The holes are 10mm so it will be a 12mm bolt. They will also have to be 50mm long so that might be a problem but I will find out.

Ian

[Jonathan]

Could you grind a non-cutting cylindrical portion on the end of the tap the same diameter as the pilot hole? That should ensure the tap stays on center.

[Jonathan]

Had another idea...could you make a mild steel bushing piece that fits on the end of the extrusion with a tapped hole over where you want to tap. Clamp it to the end then try tapping it using the tapped hole to guide the tap initially? Hope that makes sense!

[Web Goblin]

Jonathon,
thought about that one last night but I would need to get it accurate. Flat bar bent to a right angle with a 12mm tapped hole, then G-clamp the long bit to the side of the extrusion. I have already machined the linear bearing guide blocks which will be bolted to these sections.
Ive had a look on the suppliers website and they say they have self threading core screws but dont give any lengths on them and they are still on holiday. Also they would need to be cap screws. I think a spiral flute tap would be easier once I get one.
I just hate having to wait on things.

Ian

[Jonathan]

Also they would need to be cap screws. I think a spiral flute tap would be easier once I get one.
I just hate having to wait on things.

Can you get one with a left hand thread so the chips fall down through the extrusion? Might be too expensive.

Edit: I meant left hand spiral...

[Web Goblin]

I think left hand spirals only come in left hand threads. Cant be sure about that but I have only seen spiral flute taps where the directin of spiral matches the direction of thread. You have just reminded me of something I came across a few years ago. It was a tap alignment tool to keep the tap straight. Cant remember where I saw it though.

Ian

[Wobblybootie]

KJN and Hepco do a series of self tapping 'core screws' for their extrusions. http://www.aluminium-profile.co.uk/acatalog/Aluminium_Profile_Core_Screw.html For the 45 X 45 I used, the central 'hole' is 10mm but it is not a 'plain hole' ... more like a star washer. I used 12mm dia and about 30mm long with a size 50 Torx head. They are designed to join profiles together at 90 deg. To build a T, you would drill a 10-11 mm hole through the centre of the cross piece, the screw is slid along the lower slot of the cross piece until the head is visible through the drilled hole, bring up the vertical extrusion and the screw is screwed into the central hole. The Torx bit being inserted through the drilled hole. A very secure fixing but if the end of the extrusion is not absolutely square then the 'joint' will not be.