Best tooling? Enlarge counterbores in Alum

[davo727]

Hello, I recently got a r7045 type mill , it has R8 type head and I want to be able to enlarge counterbores in aluminum. The holes are about 3/8 deep and one will be going from approx 1.35in enlarged to 1.45 and the second from 1.6 up to 1.80. The bottom edge of the holes must be square. Would like to have 2 seperate tools so I dont have to reset them to change sizes. Would very much appreciate any suggestions for adjustable and accurate tooling that doesnt cost a fortune. Thanks Dave

[snowshovelbmx]

A boring head would be able to enlarge those holes quite easily keeping them round and square. buying two of these would be quite expensive though you could try your luck at making two different offset boring bars seeing as these will be the only size holes you are doing and will not need adjustment.
chris.

[BobWarfield]

I would either buy 2 boring heads used off eBay--they're pretty cheap, or make 2 customer heads that are based on a fly cutter-like design.

The latter would involve machining a bar on a shank that has a position for the boring bar that is fixed at the appropriate distance.

Personally, I would purchase a couple of boring heads. The Criterion I bought off eBay cost $75 for a nice one used.

Best,

BW

[lerman]

Are these holes or are they true counterbores? A counterbore would be a section of larger diameter at the top of a hole of smaller diameter.

If they are true counterbores, it is pretty easy to make a custom tool to enlarge them if you have a lathe. Take a piece of steel and turn it to the diameter of the smaller hole. Then drill a cross hole through it in which you will insert a HSS cutter that extends to the desired larger diameter. Drill and tap an axial hole at the end of the tool to hold the cutter in place. When you are done, you will have a tool that looks and works like a fly cutter, but has a positioning "nub" at the bottom.

For the actual cutter, you might use a cutoff section of a half round drill bit.

I've made and used such a tool to cut a two inch diameter taper in an aluminum manifold. It worked just fine.

[davo727]

Hi, I guess they are just simple straight wall holes. They are the holes that hold the valve seat inserts in an aluminum head. I remove the stock small ones and need to enlarge the hole a little to allow me to install the bigger seats. Thanks for the suggestions. Dave