Expanding Mandrel with Outside SupportFebruary 27, 2016, 2:21 pm
February 27, 2016, 2:21 pm
February 27, 2016, 3:42 pm
Sat August 15, 2009, 4:00 pm
Sat April 22, 2017, 6:56 pm
Being a CNC Machinist/Programmer is sometimes more than simply creating a program and machining the actual part, often times it is about creating efficient and accurate fixturing.
In this little project:
I had to machine rectangular cut-outs and drill holes through an already-turned steel ring. Then I had to part each ring to 4 equal pieces.
There were about 100 such rings that worked out to 400 pieces in total.
After drilling holes on an indexer I had to machine a fixture to hold my part through 2 remaining set-ups.
First half of the fixture consists of the expanding mandrel:
The work-piece would be mounted on it like so. A hole on the side is used to properly position it:
The mounted part already has cut-outs machined in the first op on the same fixture.
After slightly tightening the screw, the second half of the fixture is installed. It keeps the 4 machined pieces in place after they are parted from each other:
Then the screw is tightened even more until I can no longer turn the top half of the fixture by hand.
Both the lower and the upper halves are machined to slide-fit to the work-piece, so that when the mandrel expands it clamps the work-piece against the upper half.
By the marks on the fixture you can see where machining was taking place.
And yes, I accidentally machined my fixture by crashing a small end mill into it - MasterCAM did some weird stuff with rotating my toolpaths and messed up the g-code.
Unfortunately I forgot to snap a picture of the finished part.
But I think it is clear from the sketch how it should have looked.
This is one of those cases when coming up with a fixture takes more time and effort than programming and machining the part itself.
And its fun!