Mill, boring large hole.

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Munty Scruntfundle

Established Member
22 Sep 2019
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Hi there.

I should have a mill in the garage in the next couple of weeks, woohoo! The project is going to need a large diameter hole in some Aluminium plate.

I'm new to milling so this is a 'winging it' project while I get used to the machine. So, I've been trying to gather some tools and knowledge.

I can find loads of information on how to use boring heads, it's not exactly complicated, however I can't find a single resource on using the horizontal tool mounting point, kind of like a fly cutter. Now I can see all the forces are suddenly going in the wrong direction along the tool, but I can't see why it would be a problem, it's only the same as a bar of a lathe. Should I use the same thumb rules as lathing, or is there anything specific to milling I should know?

I must buy a copy of the Machinery guide, but the price of one of those buys me 3 meters of material!

Thanks folks.
Reading your post it seems a little jumbled. Is it a flat bed mill or a vertical mill? Fly cutters i don't like, you have to go extremely slow with the speed and feed with them plus lots of coolant.
If you have a vertical mill you can get vices that rotate by a handle on the side, this will allow infinite hole sizes to be cut .
If it's a flat bed you will need an angle plate with the job mounted on the vertical face.

If you have not used this type of machinery before remember they can maim or even kill you. They are dangerous to use and i for one learnt about engineering in my apprenticeship with someone standing next to be.

Getting a mill by itself is the start, it's all the cutters, vices, clamps you need next. You will need tee nuts that you can make .
I'm guessing it will be a small mill as it will be in your garage using a single phase supply. Just go slow with it.
If you use the horizontal mounting position you will need to be able to run the mill in reverse unless you have a set of right hand boring bars (unlikely). You also need plenty of clearance underneath the workpiece to accommodate the boring head

Same rules as lathe work apply, you are working on a massive diameter so you need to take it really slow to keep the surface speed in the right range, I would also recommend very light cuts.

Boring large holes takes a long time, remove as much material as possible using other methods. Hole saws are great but limited to about 100mm. If you are cutting into plate then mark out the cut about 4mm undersize and cut out the excess with a jigsaw.