[s2jesse]

Any good rule of thumb for work holding when it comes to 3 / 4 jaw chucks. For example I have 1.25 aluminum round stock protruding about 4" from a 3 jaw chuck on the 4th axis. What is the rule of thumb for how much should actually be "IN" the chuck. Ie how much should be left for gripping.

Milling is medium aggressiveness.

[tmarks11]

The only rule I know is that the ratio of length extending to diameter shouldn't exceed 3:1 without using a center (or a steady rest).

Obviously this is just a point of departure...

I was turning some 3.5" stainless today on my lathe, and I cut off a 3" piece to work with. No way I was going to stick all 12" in the chuck and let it rip. The thought of what 30 lbs of stainless could do if it came loose at 460 rpm....

[GLCarlson]

Depends on how fast you can duck.

In this case, a length equal to the jaw gripping length (1+ inches), since you're machining with a 4 inch lever arm and with any kind of heavier cut. My approximate rule of thumb is "as much in the jaws as the distance from jaw face to cutting edge". And, generally, not less than a quarter inch no matter how close or how fine the cut. That works about half the time; the other half, loud noises or bad words.

Put another way: if you think it's too little, it is. If you're trying to economize on material use, remember the cost of an ER visit.

[nitewatchman]

In a case like you describe, I like to machine dogbones or a piece of stock sufficient to make two parts plus stock to allow the two to be sawn apart.

We are currently machining Barrel Cams in our 4th axis. The stock is 2" dia. 1144 Fatigue Proof (C30-C34) and the part is 2-7/8" long. Stock is cut 6" long and centered on both ends in a manual lathe. Stock is chucked in the 4th axis full depth of the jaws with the end against the face of the chuck. Parts can be machined like this but we now add a tailstock to improve finish and minimize chatter in corners hence the center. A helical groove 3/4" wide and 1/2" deep is cut with a 210 deg duration along with timing flats. Part is then unchucked turned end for end and second part machined, Dogbone is then sawed in two and the ends finished.

Nice part that sell for about $100 requires about 45 minutes as there is a complex detail on one end of the part and there is a counterbored hole through the part. Making double end parts maximizes stock and gives the greatest chucking lengths.

gary

[MichaelHenry]

I've turned 3-1/8-in diameter brass and aluminum on my my Clausing 12x36 manual lathe, holding the 1-3/8-in long stock in a 4-in 5C pot collet by only 1/8-in and never had a problem with that. The stock was turned down to 3-on OD and faced to length on both ends at about 800 rpm and taking 0.050-in cuts. On the Tormach 15L I've turned a piece of 2-1/2-in OD x 9-1/2-in long aluminum rod unsupported in the 3-jaw chuck as an alignment checking exercise. About 1/2-in of stock was gripped in the jaws and the part was turned at 500 rpm with shallow cuts. Got too close to the shoulder on one pass, the bit dug in and the stock popped out and dropped into the chip pan. That was more uneventful than I would have expected but it was a one-time exercise that I probably won't repeat.

[CadRhino]

Gary, sounds like you still have your Tormach. I thought you got a Brother or Hass.

In a case like you describe, I like to machine dogbones or a piece of stock sufficient to make two parts plus stock to allow the two to be sawn apart.

We are currently machining Barrel Cams in our 4th axis. The stock is 2" dia. 1144 Fatigue Proof (C30-C34) and the part is 2-7/8" long. Stock is cut 6" long and centered on both ends in a manual lathe. Stock is chucked in the 4th axis full depth of the jaws with the end against the face of the chuck. Parts can be machined like this but we now add a tailstock to improve finish and minimize chatter in corners hence the center. A helical groove 3/4" wide and 1/2" deep is cut with a 210 deg duration along with timing flats. Part is then unchucked turned end for end and second part machined, Dogbone is then sawed in two and the ends finished.

Nice part that sell for about $100 requires about 45 minutes as there is a complex detail on one end of the part and there is a counterbored hole through the part. Making double end parts maximizes stock and gives the greatest chucking lengths.

gary

[nitewatchman]

I do!

I still have it and I am extremely happy with it. Last year or so it has been seeing a steady diet of Ductile Iron castings (nasty stuff to machine) and has been chewing them up and spitting them out. Sales return on the castings in 10X or 12x the purchase price of the machine. A Hass would definitely do a better job but the 1100 does okay and is a lot less to purchase, maintain and repair. Except for having to replace a couple of steel fingers on the ATC due to wear, a set of axis bearings and a set of spindle bearings it has been pretty trouble free. Doing the math on just the castings, the ATC has changed 100,000 tools.

Machine now has a tilting fourth axis, full enclosure, auto lube, PDB, ATC, Series 3 upgrades, toolsetter probe, PathPilot, High Speed Water Cooled Spindle.

gary

[mountaindew]

Any good rule of thumb for work holding when it comes to 3 / 4 jaw chucks. For example I have 1.25 aluminum round stock protruding about 4" from a 3 jaw chuck on the 4th axis. What is the rule of thumb for how much should actually be "IN" the chuck. Ie how much should be left for gripping.

Milling is medium aggressiveness.

I use a 5c collet and holder for very small parts in my 4th axis. Works great! And I can hold onto less then a 1/2" of material. Also moves the material out away from the very big 8" super spacer 4 jaw chuck.