Advise needed

[Hillbilly]

Thanks for all your advice .
I will try to setup in the dividing head or see if I can find a 160mm holesaw [ I live rural so that may take time ]
Otherwise I will cross my fingers and try trepanning .

 

[Illinoyance]

Use a hole saw as near finish size as you can get. Remember that hole saws often cut oversize. Grind a tool bit to fit the cross hole in your boring head. Yes, you can use a square tool bit in the round hole. Finish to size with the boring head. You can use any size hole saw that will allow the boring head to pass through. The smaller the hole saw, the more boring you need to do.

 

[Asm109]

My experience is holes saws cut oversize sometimes by a lot. I would be 1/8 to 1/4 inch below finish size.

 

[OTmachine]

How about making a round wood template for a router with a guide bearing template. It would allow you to have a flat surface to locate the router on. You would have to make the template smaller by the diameter of the guide bearing if you were to cut on the outside. And I would think that a ring type template would be better, as you would guide on the inside edge minimizing your chances of cutting oversize. Just a thought …….

 

[Illinoyance]

Another approach would be to chain drill around the periphery, leaving enough material to finish with the boring head.

 

[Parlo]

A jigsaw through 5mm Ally will only take a few minutes.

 

[WobblyHand]

Make a circle cutter. They're pretty easy to make. I used one to cut 110mm holes in a steel box (for fans) and it all came out fine. The tool grind isn't complicated, just give it clearance on the three sides. I do recommend slightly more clearance on the inner radius as it's smaller. You should have no problem with aluminum, keep the RPM slow and use lubricant. The process and cutting is a lot easier than everyone is making it seem. With the circle cutter the hole is clean, you may not even have to bore it.