For an upcoming project I want to cut a half round slot into a block of aluminum. The purpose is to support a 2" diameter piece of 6061 tubing in a lighting boom setup.
Is that something the Haas can do ?
I think I can see how to do it on the Bridgeport ( ball end mill and a lot of passes after some annoying math… )
Is there a better way that I’m missing ?
The blocks need to be about 12 inches long, and I do need two of them, so a lathe operation might make sense, but I’ve never bored a hole that large that deep with a lathe before.
Pondering further - get the blocks for both pieces, face them, then rough out the slots on the bridgeport.
Then bolt them together, slotted sides inward, and cut out to round on the lathe.
Problem is that would be a 12" x 4" x 3" block of aluminum. ( made of two 12" x 2" x 3" blocks bolted together ). Is that workable ? 12" hanging out from the face of the chuck seems like a lot.
Better way and more accurate would be to use the rotary tables. The advantage is you can cut it circular, but a first roughing cut that makes it slightly undersized, then slowly open it until it where you want. You should be able to get within a couple thou doing it slowly. If you have the tube, mic it so the hole you makes matches it’s size. If you need a clearance fit, you can test it. If you need an interference or really close fit, keeping increasing until you are there.
The hole you make will probably be more round than the tube/bar, so take at least three measurements at 120 degrees apart.
If the part is narrow enough to fit in the Curt vise 12" x whatever that vise takes, mount the vise on the rotary table and you won’t need a sacrificial piece under it, just make sure it clears the parallels.
Use the hydraulic lift table to position it just slighty next to the Bridgeport table so it slides off easily. The table with the cross slides is heavier but will give you more control.
Using a rotary table use a regular end mill. The offset from the spindle center is the desired hole radius less the cutter radius. Just make multiple passes going deeper each time till you’re through. Do the final pass nice and slow with lubrication and you should get a good wall finish. If there is space, have the cutter do that final pass with it about .500" ~ 1.000" past the bottom, the flutes of the cutter will be sharper further up the cutter so you get a cleaner finish.
This video shows him cutting a a half round out the edge - move it inboard all the way and it would be a circle.
I should note that high precision is not required here. I plane to line the half round part with a thin piece of rubber and then make some clamps to bolt over the pipe.
The object its to be able to change the angles of my light booms, so there will be pivot bushings underneath as well.
A redesign may be in order. 2" deep blocks would be a LOT easier than 12". More parts to make - 2 or 3 per side, but again. Much easier.
What is the size of the finished part? It’s 12" thick, but how wide and long.
We don’t have any mill cutters that will go 12" deep, Haas or Bridgeport, our adjustable boring bars aren’t that long. I’m not sure we have a boring bar 12" long for use on the lathe - that is stout bar to not flex that far out. @BobKarnaugh suggestions.
The general rule of the ratio of cutter diameter to depth is about 6:1 max, so you’d basically need a 2" diameter cutter to avoid excessive flexing. 4:1 is more commonly recommended.
Your best shot will be the lathe if you can get the material onto the chuck and get a boring bar that over 12", closer to 15"-16" becuase you’ll need the extra length to mount in tool holder.
Initial plan was 12" long, 3 " wide, and 2" thick. Hole along the 12" axis.
Rethinking now that perhaps making a pair of 2" long, 3" wide, 2" thick supports, and a brace to connect them together might be much easier. I could make them in pairs on the lathe or the rotary table on the mill.
How long is your boom? How much weight? What is wall thickness of tubing?
Just asking, I’ve got an 8’ long boom with a light on on a 6’ stand. It uses a steel steel tube about 1.0 in diameter. The upright support is 1.875" steel. This is how it is put together, may give you some ideas.
The boom will need that wide plate as it will be experiencing a lot of leverage. The upright is all downward force and simple clamping action makes it work.
First photo shows the 1" boom attached to the 7" torsion plate that gets clamped to control the tilt. The knob at top locks bar in position in terms of length. Second photo rotated 90 degrees and shows how this is attached to the 1.875" upright steel bar.
Not sure of wall thickness, but would guess .250", they don’t flex.
The red plate you see has strap attached to it that goes down the center of the upright and has a counterweight inside. The upper piece has pulley it goes over.
My booms are 18 ft long. 40 pound counterweight on one end, and about 20 pounds of lights on the other. The current support is a pipe that sits over the light stands ( 13 foot crank up ). I have aluminum plates bolted to that with U-bolts, then 2 more u-bolts to attach the boom to the plate. The pipe extends up another 12-18 inches. I run a steel cable across that and out to each end of the boom to take up some of the load. The boom center of mass is about 1/3 of the way towards the middle from the end with the weights.
The reason for the redesign is that the new hotel has higher risers than the previous ones. So I want to get the lights ( LED stage lights ) up higher. The existing design doesn’t allow for angle changes. It also places the load slightly off to one side. That is putting unnecessary torque on the light stands.
I’ll see if I have a picture when I get home tonight. We’ve used these for several years at FenCon. I didn’t have access to good tools when I built them. I think I can do better now.
