Need to make a big hole in Aluminum plate

[pineyfolks]

The hole in the steady rest is only for clearance. You could mill a square or hexagon hole in it and it'll still work fine. You're using the fingers to center the workpiece.

 

[whitmore]

I have a small rotary table. What about mounting it so that I could turn it under the mill head, and cut with an end mill?

Yes, that'd work; you'd want to start by making the lathe bed-base part, affix the plate to it, and use the lathe to
drill an accurate center hole, to use in centering the work on the rotary table.

I've considered making a rest that takes a press-in ball bearing race, so I could make adapter inner sleeves
to slip-fit a future project. If there's a junkbox of big bearings, removed for preventive maintenance,
this can be justification for doing a really accurate circular aperture for your project.

 

[stupoty]

I was under the impression that a hole saw cutting that deep in aluminum was a problem. But that does look like the easiest solution. I have several hole saws already but hadn't really considered using one because as I said I thought it was somehow an issue.
I guess going slow and lots of cleaning out of chips would work and might be the easiest set up.

I some times drill from both sides on thick parts , depends if the chips are nice and leaving the hole.

theirs an rpm chart from starreett to give a guide to speed ,
http://www.starrett.com/docs/other-downloadable-resources/hole-saw-speed-chart---bulletin-194.pdf

 

[Dabbler]

This is old school, but it will give you your large hole. A steady rest will have to be cut in half anyway, so:
1) use layout blue to the preferred diameter - sounds like 3" is your best target....
2) make your halving layout and cut with a band saw.
3) continue to take cuts on the band saw until most of the hole is taken out
4) file finish - after all this is just clearance.....

 

[P. Waller]

What was the issue that turned you off of that method?

I suspect that chip control was an issue as there is no way to evacuate the chips from the top, this will involve a good deal of pecks.

If indeed one wants to use a hole saw for this purpose make it act like a bandsaw where the chips pass through, drill several through holes where the cut will be and the chips will exit through them clearing the blade, you will find that this approach makes using such a tool almost easy.

Like so.

 

[P. Waller]

As to the size that will pass though a steady you are only limited by the diameter that will allow you to build it and fit on the machine ways.
Often you will have to turn the ends of a part that will not fit through the spindle yet is short enough to hold in a chuck on one end and the steady on the other, make it as big as possible.

This part would not fit through the spindle but was less then the 100" long would that would fit in the machine, also make it as big as possible in the event that the OD is a finished surface that requires the use of a cats head.

 

[homebrewed]

It seems one apparent limitation of the rotary table approach is the disk you're making in the cut, which could jam once it's free. But you don't need to do it that way. Your follower will have some holes in it for mounting the finger adjusting mechanisms, right? Place them first then use them to mount the plate to a sacrificial piece of plywood. Mount that on your RT. Drill the center hole as big as you can, then enlarge the hole by stepping the RT over and milling with your end mill. It will be -- sorta -- like a boring head setup. Keep on stepping over and rotating/milling the piece until the hole is the size you want. You probably want to do conventional milling, not climb milling, with this setup.

 

[Silverbullet]

I to wouldn't just cut the three inch hole, I'd go as big as the piece will handle and leave enough room for the adjusters . And yes I'd start from the bed up , base , ring , adjusters, . Cutting the hole shouldn't be a problem , I'd drill holes close together and near the diameter size . I'd either jig saw by hand or trepan it in the lathe. But your rotary table for you sounds best and yes go from both sides . You can mount it with a sacrificial piece between the part and table to support the size.

 

[Charles Spencer]

This is old school, but it will give you your large hole. A steady rest will have to be cut in half anyway, so:
1) use layout blue to the preferred diameter - sounds like 3" is your best target....
2) make your halving layout and cut with a band saw.
3) continue to take cuts on the band saw until most of the hole is taken out
4) file finish - after all this is just clearance.....

I like it! I think that's the approach I would take.

 

[kd4gij]

The one I made for my 12" crafts lathe will hold 4 1/2: stock.