What's new
What's new

Max RPM

Circuit 1

Aluminum
Joined
Nov 14, 2015
Is there a basic rule of thumb to use to determine the max rpm for a material size? I realized there are a lot of factors to consider like type of material, material size, soft jaw material and size. I have a job to do that is 6" diameter aluminum 6" long. The jaws are 3" tall aluminum and I'll grip about 2". Can anyone give me an approximate max rpm for that type of job. I have only done smaller parts in the lathe and so it really hasn't been an issue.
I try to be very conservative because I don't use the lathe that much and most of the parts are one off. But I'm not really sure where to even start.
As always any input is appreciated.
Thanks!

SQT-10M T-Plus Control
 
On our QT20 with an 8" chuck @200psi pressure I might go 1750rpm for the spindle clamp. Even being aluminum a part that size is going to tear the door off if it comes free. Be careful facing because when you get to X zero the spindle is at max programmed RPM and your surface speed is zero and the insert is just pushing the material off. On jobs like this I will take a clean up cut on the OD to remove any wobble which will eliminate most unbalanced vibrations. If there is a hole in the part I will drill that next so i don't have to face to center. Start out conservative and move up from there. This part being basically 6" by 6" you shouldn't have to be too worried.
 
That information helps.
Thanks!

Also another quick question. As I mentioned I'll be gripping 2" and my chuck is somewhat worn. How much taper should I cut into the soft jaws?
 
If your lower jaws are sloppy in the chuck body, you should measure how bad it is.

Put an indicator on your chuck, close it with only a little pressure and a slug of something stopping the lower jaws.
Next, increase to your running pressure and grip something at the end of those top-jaws.

You'll get an idea of how much "lift" or "rock" each jaw has. Use the number from the worst one.
Too much pressure and you're also measuring the flex in those 3" aluminum jaws.

That gets you an axial measurement the way I'm picturing it (they way the wear allows slop to happen).
You can use two indicators, one on the bottom jaw (radially) while the other is on the top jaw (radially) to get the radial difference reading directly. You'll have to zero both indicators and subtract one indicator from the other.

I may be over-complicating things, but that's the way I would approach it.
 
SQT 250 holding on .750 length in a 10in chuck drilling and turning no problem at 3000RPM and thats not even pushing it.
 
How much taper should I cut into the soft jaws?

Just enough, but not too much.

If you bore your jaws straight, can you get a feeler gage in between the material and the
jaws? If not, then you only need a bit..

My chuck is old, and when I'm holding on a bar, full length of the jaws, I need about
.002" taper(diameter) per inch of jaw depth.. More than that and I end up only getting
a good bite on Z+ edge of the jaws, and that's just as bad as only grabbing at the back.

If I'm only grabbing on a small bit of material, say 1/4", I might go .005 or .006 over
that 1/4".
 








 
Back
Top