[SRT Mike]

I had asked previously about cutting lathe jaws, but the part I am working on now, I will need 2 setups to cut it right.

The 2nd fixture it will be basically a cylinder with a hole halfway through the center, and I will finish cut the whole length of the exterior into a cone shape, so I'll need to hold it on the ID with custom soft jaws.

I know you're supposed to load the jaws as they will be when they are actually used, but how the heck would I do this for an ID chucking setup? Is it OK to just close the jaws on themselves and cut my shape? If not, how is it done correctly?

[Geof]

How about close the jaws on something and turn a small step on the end; about 1/4" long from the tip of the jaw.

Now make a ring the correct size so that when you open the jaws with the ring on the small step they are positioned correctly for turning a larger step the size for your workpiece ID.

Then as a final step grip something again and face off the small step.

[SRT Mike]

I was thinking about that Geof but every time I was thinking to do it that way it seemed to be a fair bit of work and my lazy gene kept kicking in and saying there must be an easier way

The only other issue is that the ID of the part I will be grabbing is only 1.5" so the end diameter is going to be pretty small, meaning max OD on said ring would be 1.5 and maybe... 1" ID (I'll need some meat left on the jaws to make them hold tight enough to machine) - That's only 1/4" of material to hold the jaws so I'd be looking at doing it from steel, I'd think... and all my tooling is for aluminum pretty much. If I just clamped down on a 1/2" rod for example and bored my diameter, is it a big no-no given I am maching on ID clamping but I will use the jaws in OD clamping? If the difference is small I may do it that way but if it's important to bore while they are under opening pressure then I'll try the ring idea and see how I do.

Hey while I am at it, and since you know just about everything Geof how in the hell are you supposed to use those boring stars/cam things? Like these...

http://cgi.ebay.com/4pc-STEEL-CAMS-S...QQcmdZViewItem

If the link doesnt work look at item #290173657214 on eBay. I got a set but I am stymied! Near as I can figure I put it against the chuck and then install the jaws after it's in place.... then... rotate it so that the jaws touch it before they close? Problem is because it's rounded, as the jaws start to close on it, it just rotates and doesn't stop the jaw movement. There is a slot in the center - is it designed to be braced somehow to prevent rotation? There were no instructions and I haven't seen anything online about how to use them, so I'm guessing here

[Geof]

...it seemed to be a fair bit of work and my lazy gene kept kicking in and saying there must be an easier way ....

Hey while I am at it, and since you know just about everything Geof how in the hell are you supposed to use those boring stars/cam things? Like these...

I have a lazy gene too; and I find it is more active these days than forty or so years ago. Or at least I find it difficult to put in 12 and 18 hour days now.

Don't I wish I knew just about everything but then maybe not, the fun is in the learning. I don't have the foggiest idea how you would use those star things. I guess if there was some sort of key or stop to go behind one jaw???

[307startup]

Those cams are for the jaw spacing you want to cut the soft jaws at, they go to the rear of the soft jaws, mounted on a mandrel. Since they are ramped like cams, you can figure out just about any od or id you want using just the four sizes. You turn the mandrel by hand while measuring the spacing with a set of calipers or t-handled ID snap-gauges. Once you get the size you want by adjusting the hydraulic or pneumatic pressure for the chuck (measure, twiddle, remeasure, twiddle some more), you can "clamp" the chuck and bore or turn the jaws to size. The problem is, they are only good for 3 jaw chucks, otherwise you end up with the largest diameter being the only diameter you can choose. They aren't the greatest thing in the world, but if you really like gadgets, I guess they are ok.

[star-turn]

Hi Mike,

you may get away with the 'lazy' way, but you will incurr some run-out, thts ok if you are just doing a non critical cheapo job.

if you can not go smaller think bigger!!!

clamp on your 1/2" bar and turn your jaws to minus .020" of your component say 3/4" long then turn a bigger diameter for a ring - turn this minus 0.030" of the rings bore.

remove bar clamp on inside of ring, skim jaws .010" you now have size turned jaws and the step in the jaws acts as a back stop.

ST

[Geof]

....remove bar clamp on inside of ring, skim jaws .010" you now have size turned jaws and the step in the jaws acts as a back stop.

ST

And if you make the ring step diameter smaller than the end of your part you have room to run the tool off the end and do a small back chamfer to take the rag off.

I have to admit star-turn's suggestion is more elegant than mine.

[SRT Mike]

Hi Mike,

you may get away with the 'lazy' way, but you will incurr some run-out, thts ok if you are just doing a non critical cheapo job.

if you can not go smaller think bigger!!!

clamp on your 1/2" bar and turn your jaws to minus .020" of your component say 3/4" long then turn a bigger diameter for a ring - turn this minus 0.030" of the rings bore.

remove bar clamp on inside of ring, skim jaws .010" you now have size turned jaws and the step in the jaws acts as a back stop.

ST

Great idea - I think I will give that a shot! Thanks!

[star-turn]

Geof - you made my heart go all fluttery!!

ST

[pepo]

At work we use banding like you use on a pallet. At home I use hose clamps,big ones are cheap and you can put them together and theyre adjustable of course. Yes your chuck is more than strong enough to bust the clamps if you over do it.

[bearclaw]

Question:

When I have a part I will be chucking on the ID to machine the OD I will cut the soft jaws using OD-grip while chucking on some stock material bar lying around. I will cut the jaws within .01 to .02 Then switch the machine to ID-grip for my part. I have been told recently this is wrong by another machinist that in order to cut properly if you are chucking on ID then you have to cut using ID-grip. Whichever grip you are using for the part the jaws MUST be cut with the same grip. But another shop I worked at they used od-grip and cut the jaws for gripping on ID. Now are both ways right?

[Geof]

Think about it logically. The jaws on a chuck always spring slightly when they are tightened onto something, this springing is a combination of taking up any clearances in the jaw slides and closing mechanism and any elastic deflection. For best accuracy you want the loading on the jaws to be as close to identical during boring, or turning for ID clamping, as the loading is when the jaws are gripping the work. This means you grip something with OD clamping for boring and ID clamping for turning jaws. And, ideally, the loading should be toward the front of the jaws because in use that is normally where the loading is. This is why a boring ring is the best approach. It is held by means of plugs put on the bolt counterbore so the loading is right at the fron of the jaws.