[How do I?] 7" Diameter Alumimum 'shell' - Mill Or Lathe?

C

cowanrg

Registered
Registered
Joined
Aug 26, 2015
Messages
9
Hello everyone. First post! I have a bit of machining experience, but I'm still new to HOW to do certain things. I have a CNC PM30-MVL and a Harbor Freight 9x20 Lathe.

I need to make a 7" diameter 'shell' for a combat robot. It will be 6061 most likely. Since it will be spinning between 5k - 10k RPM, it needs to be pretty concentric. My biggest question is how big of a chuck can I use on my lathe? I have the basic 3-jaw 4" chuck and was looking to get a 4-jaw. I was originally going to chuck it on the lathe, turn the inside, then hold it from the inside, and turn the outside. But, it seems like an 8" chuck on my lathe is way too big.

Thoughts? I don't have the file on me, but it's essentially a shell/bowl that's 7" diameter, ~0.25" wall thickness. Thanks!
 
Ah OK. I've not used a faceplate before (I haven't done a lot of lathe work, just milling). How do you attach a workpiece to the faceplate?
 
Currently, it only has a couple of small holes in the middle. There is a center hole, but it's very small, M3 or so. Not enough for mounting. I could drill some holes in the top for mounting I guess. But I need to cut out the center of the shell, so they'd be in the way.
 
it depends on the part you are working on and what you are doing to it.

Here are some web photos that will give you some ideas.
http://homews.co.uk/LrgFPlateUse08.jpg
http://www.toolsandmods.com/images/lathe-chuck-repair-4.jpg
http://i20.photobucket.com/albums/b201/michael0100/DSCN8953.jpg
http://www.homews.co.uk/LrgFPlateUse05.jpg
http://www.homews.co.uk/LrgZEasyFaceplate17.jpg
http://www.homews.co.uk/LrgFPlateUse11.jpg
http://img.photobucket.com/albums/v156/jasonballamy/Fowler construction/PICT0001.jpg
http://www.rcdon.com/assets/images/6CI_Steam_Engine_0188.jpg

even after you turn it, you are still going to need to have it dynamically balanced. Even if you turned it perfectly concentric, the natural deviance in the stock would cause an imbalance issue at those kinds of rpms.
 
Yeah, I know I'll have to do some balancing after the fact.

The faceplate seems like the way to go, but mounting it might be a trick, since I can only handle 9", which doesn't leave a lot of room for mounting. Maybe this would be easier on the mill?

What if I mounted the puck to my table, milled out the inside cavity, then used a boring bar/head to get it concentric, THEN moved it to the lathe and clamped the chuck on the inside of the shell?
 
I would need to see what stock you are starting with and what the finished piece looks like to get an idea.

I would however say without a doubt, getting the inside and outside true to each other needs to be done on the lathe, and fixtured in such a way that it doesn't have to be demounted to switch between operations.
 
Stock would be just round bar stock, cut roughly to length (7" diameter, roughly 1.5" long).

I can't post images yet, but the end part would just be a cup essentially. 0.25" thick walls, and the top of the shell would be 0.25" too. There would be a couple mounting holes on top (nothing big enough to use for mounting) and a couple small grooves on the inside to key to the motor housing. I can post a solidworks file or screen shot when I get home. It's a really simple part, I just need to essentially hollow out a 7" diameter puck of aluminum and drill a couple holes.
 
cowanrg said:
Currently, it only has a couple of small holes in the middle. There is a center hole, but it's very small, M3 or so. Not enough for mounting. I could drill some holes in the top for mounting I guess. But I need to cut out the center of the shell, so they'd be in the way.
Click to expand...
Drill all your mounting holes, including at least two outside the finished OD.

Mount the blank on the faceplate via those outside holes.

Machine out the inside.

Without removing the workpiece from the faceplate secure it with screws through the inner holes.

Finish the OD (after removing the outer screws).
 
Last edited:
You must log in or register to reply here.
Back
Top