Forstner bit and aluminium

[Devmeister]

You may try using a piloted spotting mill cutter. I got one that spots a 7/8 in spotting operation using a 1/2 in shank. The pilot helps you line up the spot with the hole. What your doing here is a classic spotting operation.

 

[hawkeyefxr]

I have used Parafin on aluminium before, it's thin like water and oily at the same time. When you have a hole stablished keep it filled up with parafin.
You do not say what aluminium you are using soft or hard, like Dural. Soft with be the worst to machine.
When aluminium is machined the work area is drenched with a constant flow of coolant.

 

[starlingwood]

I did it. Happy with the result. The forstner bit is not in too bad condition actually, the point has gone but the cutting edges still sharp, not a great shame to replace anyway.

Here she is in her intended use.

And at rest for the next time.

 

[hawkeyefxr]

I want to do just this only i will be drilling a 10mm hole to accept 10mm acrylic tube ( I am making a manometer for balancing the carburettors on my bike). The ally will be 3/4in square bar and plenty of paraffin will be used.
Drilling sheet metal is always dodgy as the bit grabs the metal as it breaks through and spins the sheet making it an effective bacon slicer. Clamp it with at least two clamps and keep fingers well away. I will not be going all the way through the 3/4 bar just about a 1/4 inch deep.
My reason for making the manometer is that though there are plenty of vacuum gauge setups you can buy unless you go for big money the dam needles bounce about something rotten.

 

[J-G]

Drilling sheet metal is always dodgy as the bit grabs the metal as it breaks through and spins the sheet making it an effective bacon slicer.

In that case you have not secured the sheet correctly!

 

[Sideways]

Why on earth would you use a forstner bit to drill a 10mm hole in ally bar when 10mm jobber (i.e. ordinary twist) drills are so cheap in that size ?
You're cutting aluminium so almost any cheap drill bit will do, you don't need to pay skf dormer prices....
I'd have though that the small cost of the jobber was less than the agravation of resharpening a damaged forstner bit or risk of messing up and having to buy a new piece of alloy bar.

 

[Fergie 307]

I want to do just this only i will be drilling a 10mm hole to accept 10mm acrylic tube ( I am making a manometer for balancing the carburettors on my bike). The ally will be 3/4in square bar and plenty of paraffin will be used.
Drilling sheet metal is always dodgy as the bit grabs the metal as it breaks through and spins the sheet making it an effective bacon slicer. Clamp it with at least two clamps and keep fingers well away. I will not be going all the way through the 3/4 bar just about a 1/4 inch deep.
My reason for making the manometer is that though there are plenty of vacuum gauge setups you can buy unless you go for big money the dam needles bounce about something rotten.

Needle ones are carp. Get the type with the balls in a tube, i assume that is they type you are making.

 

[Fergie 307]

And have to agree with Sideways, use a proper bit. Forstner will be ruined, and cut a rubbish hole to boot.

 

[Dave Moore]

I want to use a forstner bit on a 10mm aluminium plate.

Is it OK to do?

I once used a mitre saw blade to cut a thin strip of aluminium but the blade got knackered. Since bought a blade suited for aluminium. I can't find such a comparison in terms of forstner bits.

A carbide tipped hole saw should do this and much better. We use them for stainless steel at work with better results than an ordinary hole saw. If it’s 10mm consider using a hss twist drill, you may need to reduce the angle but should be ok with normal. Ensure its well clamped.