Shop Tip: How to Make A Sacrificial Center
Sometimes my laziness tries to get in the way of doing things properly. For instance, there have been numerous times where the proper way of approaching a setup would be to turn the piece between centers. For me that means removing my 3 jaw chuck so that I can fit a MT#4 dead center in my spindle.
I don’t know why, but I’ll spend 20 minutes trying to figure out an alternative setup rather than spending 5 minutes removing my 3 jaw chuck.
Then one day at GEARS in Portland someone asked me why I just don’t turn a sacrificial center and use that in my 3 jaw. Great idea!
The principle behind a sacrificial center is simple. It’s a center that can be re-chucked and re-turned to ensure that it’s perfectly centered. Whenever you need to turn between centers you simply chuck the sacrificial center in your 3 jaw chuck, set your compound at 30
° (60° included), and shave off a few thousandths to ensure that it’s turning concentric.
It’s simple to build, but since this site is geared toward absolute beginners I’ll include pictures and directions below. The next time you need to turn something between centers, you’ll think twice before removing that chuck!
The Process:
First, find a piece of scrap steel an inch or so in diameter. Turn a shank down to about a half inch in diameter and at least an inch long.
Part off the piece leaving 2 to 3 inches of length on the larger diameter. The longer you make this portion, the more sacrificial cuts you’ll get out of it before you need to make a new center. Flip and re-chuck the parted-off piece.
Set your compound at 30° (60° included) and cut the center to a point in several passes.
You’re done once your center has a nice point to it.
Whenever you need to turn something between centers, re-chuck your sacrificial center, set your compound at 30° (60° included), and remove a few thousandths to ensure that the center is perfectly concentric along the axis of rotation. That’s it!
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Tags: Shop Tips
November 2nd, 2009 at 8:09 AM
Great idea. But how do you get the part to spin without a lathe dog? I’m still new at the hobby and I believe I got the exact same lathe as you…Grizzly 0602. Will the pressure alone exerted by the tailstock keep the part spinning during cutting operations?
November 2nd, 2009 at 10:54 AM
Hello fellow G0602 owner!
Yep, you’re right. If you use a live center in the tailstock the dead sacrificial center would spin the part, but you wouldn’t be able to take much of a cut (if any). You may be able to polish the part or use a toolpost grinder, but that would be limited to the amount of contact made between the dead center and the part. More contact = more friction. So you’re right, you would need a lathe dog to “turn between centers” as the post suggests. But that’s fine, let the leg of the lathe dog ride against the chuck jaw (instead of riding in a slot on your faceplate). Just be careful that the lathe dog doesn’t slap back and forth between the chuck jaws.
The reason a lathe dog isn’t shown in the pictures in the post is because I’m using the between centers setup in another useful way – for accurate setup. Sometimes you need to set the angle of the toolpost very accurately. Or you need to line up your tailstock to turn a long taper (or for that matter, you need to put the tailstock back to centerline after using it to turn a taper). One easy way to do this is to use a 12″ test bar that is held (without spinning) between centers. Then you can use a dial indicator attached to the cross slide (in my case via a mag-base) to sweep the test bar. If you move the dial indicator back and forth along the 12″ bar, you can get the tailstock set perfectly to zero.
In my case, I needed a way to duplicate the angle on a Morse taper, so I set the dial indicator up to sweep the taper. Once I had a zero reading across the entire length of the taper I knew the angle of the compound was set correctly. Harold Hall goes over using a “between-centers test bar” in his book, Lathework A Complete Course. He even goes into another useful technique, which is to set your cross slide at a very slight angle (like 1mm in 100mm) so that advancing the compound .02mm only advances the tool 0.0002mm toward the workpiece. This allows you to take very light cuts when you’re trying to ease up on a finished diameter where precision is a must.
To go back to the beginning, if you’re interested in turning a part between centers without using a lathe dog, Frank Ford made a really neat “Lathe Drive Center“. It gets away from the sacrificial center idea, but it’s a really nifty project all on its own. Here’s a picture of it.
Sorry for the long-winded response. I hope you’re enjoying your G0602 as much as I am!