Under cut guidance
Under cut guidance
(OP)
I am working on a design that when finished looks like a circular plate with T shaped stiffeners (like wheel spokes) 30 degrees apart. All the T stiffeners are oriented to run thru the center of the circle plate. The top (flange) of the Tees are 3 inches above the plate. This part to be machined from 7075 Al plate 4" thick. The T flange is 1.2" wide, has a .2" web, so I need to under cut .50" from each side to end up with the T shape.
What makes it complicated is all the other features that need to be provided. It's important to remove as much material as possible for weight reduction. Can someone give me pointers about cutting tools that can hog out the material between the T flange and circular plate? I'm looking for enough info to make the design producible, so data on cutter diameters and the related shaft diameter will help me layout proper clearances between features. thanks!
What makes it complicated is all the other features that need to be provided. It's important to remove as much material as possible for weight reduction. Can someone give me pointers about cutting tools that can hog out the material between the T flange and circular plate? I'm looking for enough info to make the design producible, so data on cutter diameters and the related shaft diameter will help me layout proper clearances between features. thanks!





RE: Under cut guidance
Bill
RE: Under cut guidance
Next choice might be stacked saws on a cantilevered spindle.
In both cases, you rough out the vees with a big end mill. Plunge cutting might be fastest.
Either way, you can't cut in to the center of the circle, so you have to leave that solid, or bore a big hole there. ... or EDM that area.
Don't be surprised if the big plate warps when you remove material asymmetrically.
Consider cutting T-slots in a thinner plate, and pressing in H-sections to form your fins. They can be mitered to meet in the center with no hole and no solid mesa.
Mike Halloran
Pembroke Pines, FL, USA
RE: Under cut guidance
Have you considered a weldment to avoid needing to core our a 4" thick plate?
Can you go with a cast grade of Al to minimise the warping Mike talks about?
Doug
RE: Under cut guidance
See attached for prelim idea of final part.
RE: Under cut guidance
I.e., your supplier will get some awards from his trade association, and you'll buy him a new Porsche.
In current form, the only way I can see to produce it is as a lost-wax casting to net shape, or damn near it.
The radii tangent to the webs at the bottom of the pockets are currently impossible; they must have the same radius as the T-slot cutter or larger.
...
Belay that; you can get in there and generate them with a really small ball end mill if you have a tilting spindle or indexing table.
Mike Halloran
Pembroke Pines, FL, USA
RE: Under cut guidance
These guys Link specialize in dificult 5 axis jobs. You could contact them for more detailed suggestions/quotes.
Doug
RE: Under cut guidance
We need to stick with the current shape for reasons that are too long and boring to explain, but I see your point about equal stiffness from taller ribs.
"The radii tangent to the webs at the bottom of the pockets are currently impossible; they must have the same radius as the T-slot cutter or larger."
Yeah, that's the aspect that causes me concern. I have .90 R where the short bosses transition to the vertical wwebs in the undercut area. Does that seem adequate?
There is an existing part made years ago very similar to this one. I only have photos to go by, but it did have bosses in the undercut area where access for an end mill is blocked by the tops of those T's. Not sure who made it and how $$ it was.
RE: Under cut guidance
RE: Under cut guidance
Or, it might be possible to mill it with tall fins and then bend them over into angles, but most of the alloys that machine well don't bend well, and conversely.
Mike Halloran
Pembroke Pines, FL, USA
RE: Under cut guidance
Looking at the length of those undercuts that is going to be one spindlely cutter and is going to sing at a nice high pitch and you will almost certainly need a few of them.
But if what I am assuming is correct and there is nothing I am missing then yes what you have is possible to machine, the cost on the other hand might make you sit up and draw breath.
RE: Under cut guidance
Yes that's what I'm thinking. to get .50 undercut with 1.75 cutter, it limits the shaft dia to .62
RE: Under cut guidance
Plan on using a high hook angle roughing end mill for roughing out the slots. You will have to watch the re-cutting of the chips. The best thing to do would be to have high pressure air blowing the chips out the of cut.
Distortion of the whole part may be a problem. You may have to rough machine the part and attempt some kind of a stress relieve and then finish machine. You are turning about 75% of the material into chips.
Good Luck on this part.
Bill
RE: Under cut guidance
RE: Under cut guidance