Large >5” hole in 24” long 3/8” aluminum plate

Gbalock · Jan 5, 2020

I turned a 6” x 0.75” disc with a 0.375 notch (the pivot). I now need to machine a hole in one end of a 6“ by 24” 0.375” aluminum’s plate to match the notch in the pivot. I’ll need a fairly close tolerance so that the plate rotates freely on the pivot without binding.

I have access (not mine) to a Bridgeport vertical mill and a rotary table.

So, what is the best way to do this? BTW, I am fairly new to machining.

Limy Sami · Jan 5, 2020

If both pieces are Aluminium and you want close tolerance and movement, ..I'd do a serious rethink as galling is big problem with alu on alu

MichaelP · Jan 5, 2020

I'm not 100% sure I understood what you need, but if it's a hole in the plate, and you don't have suitable dia. cutters (holesaw, etc.), using rotary table on Bridgeport to cut the hole with an endmill is one option. Cutting a smaller hole (with a hole saw, plasma, chain drilling, jigsaw, etc.) and increasing it with a boring head will be another option. Val-Cut trepanning tool, if you're lucky to have one, would be one more way to do it.

Gordon Heaton · Jan 5, 2020

For speed and simplicity, I'd lay it out, plasma cut, then finish with a boring head on your mill. What I'm not clear on is whether or not the hole you refer to is straight through, stepped or not through at all. Obviously, the plasma option will only work if at least part of the hole is all the way through the bar.

Reading it again, since the 'notch' is .375 and the bar is .375 thick, a simple through-hole is what you're looking for. Right?

A rotary table + endmill will work, but it is much more difficult to position properly and nearly impossible to get the smoothness (finish) you'd get with a boring head/bar.

Gbalock · Jan 5, 2020

Large >5” hole in 24” long 3/8” aluminum plate

Yes, the hole is straight through. What I’m making is a spherical slide rest for a Rose engine, so the amount of wear will be minimal. But, I’m looking for a fairly tight tolerance so that the cuts I make with it are repeatable

My one concern with the mill/rotary table combo is that I may not be able to swing the piece through 360 degrees.

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awander · Jan 5, 2020

So the "notch" in the disc is an annular cut, at 5" diameter, leaving 3/8" of the thickness of the disc at 6" diameter?

MichaelP · Jan 5, 2020

Gbalock said:
My one concern with the mill/rotary table combo is that I may not be able to swing the piece through 360 degrees.

If the hole is at the end of the strip, it can be a problem, indeed...

I'd cut a smaller hole with a holesaw and finish with a boring head (boring bar inserted into the side socket).

LKeithR · Jan 6, 2020

A drawing of what you're trying to accomplish would sure help...

DDoug · Jan 6, 2020

Gbalock said:
I turned a 6” x 0.75” disc with a 0.375 notch (the pivot). I now need to machine a hole in one end of a 6“ by 24” 0.375” aluminum’s plate to match the notch in the pivot. I’ll need a fairly close tolerance so that the plate rotates freely on the pivot without binding.

I have access (not mine) to a Bridgeport vertical mill and a rotary table.

So, what is the best way to do this? BTW, I am fairly new to machining.

Maybe you should have it waterjet cut out.

Gordon Heaton · Jan 6, 2020

digger doug said:
Maybe you should have it waterjet cut out.

A good option. Water jet is cheap but not all that precise, and you won't get a mirror-smooth finish like you can with a boring bar. Manual attempts to polish a water-jet edge will result in deformation of the arc.

as9100d · Jan 6, 2020

digger doug said:
Maybe you should have it waterjet cut out.

I second waterjet. Find a shop with taper compensation. We have an omax with a tiltajet and can get zero taper on 3/4" thick parts and typically can hold +/-0.001 all day long.

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art.h · Jan 6, 2020

Take your largest annular or holesaw in your mill determine a secondary diameter about your required centre that will place the edge of this cutter near your needed diameter then using trig. to place a series of over lapping cut out holes inside your required diameter. Finish to size with a boring head.

Hardplates · Jan 6, 2020

Gbalock said:
Yes, the hole is straight through. What I’m making is a spherical slide rest for a Rose engine, so the amount of wear will be minimal. But, I’m looking for a fairly tight tolerance so that the cuts I make with it are repeatable

My one concern with the mill/rotary table combo is that I may not be able to swing the piece through 360 degrees.

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Set the rotary up near the end of the table and swing the head over to it. Should easily be able to swing 24"

art.h · Jan 6, 2020

Another method if you wish to use rotary table. Ream .500 hole in your plate at desired location. Turn a locating plug to fit centre hole of rotary table with a .500 spigot to fit into hole in plate. Create a series of arcs to achieve required diameter by repositioning plate about the spigot to do the full cut out. If dim. is critical do under size a finish bore.

DDoug · Jan 6, 2020

as9100d said:
I second waterjet. Find a shop with taper compensation. We have an omax with a tiltajet and can get zero taper on 3/4" thick parts and typically can hold +/-0.001 all day long.

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With that tolerance on the hole (from the waterjet), you could machine a ring from steel, and press fit it in, for the wear & finish requirements.

mike 44 · Jan 6, 2020

You can do this with a router and 1/2" shank end mill. Make an accurate template from MDF or plywood. Install appropriate bushing in router that will ride against the template. Put center lines on the template and the work. Line up the marks and clamp. Probably cut 1/4" deep each pass. Some routers such as Porter cable 3 HP have 5 speeds. 8000 Rpm is the slowest. Possibly a speed reducer may be okay since routers have universal motors. You will be okay at high speeds but if you can reduce the speed to 2000 RPMS it would be safer. Move the router clockwise. After the hole is cut you can clean up the hole by reverse routing , also known as climb cutting. Climb cutting tends to pull the router away from the work and usually only used to clean up the cut.

mike

snowshooze · Jan 6, 2020

That is real-world stuf.

snowshooze · Jan 6, 2020

Honestly, we are a good bunch here. So many have helped me out...
Look, let one of us do it for you.
That is a 5 minute program, we could save you so much time.
If you were here, I'd do it for beer.
Mark

Bondo · Jan 6, 2020

I'd just use a jig saw, alum on alum is going to grab anyways. You should make some kind of bushing ring for the shaft.

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Large >5” hole in 24” long 3/8” aluminum plate

Plastic

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Titanium

Plastic

Stainless

Titanium

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Titanium

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Aluminum

Stainless

Aluminum

Diamond

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Stainless

Stainless

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