Compound orientation when internal threading

[mickri]

Needed to turn an internal thread for the adapter that I am making. Hadn't done that recently so I watched Mr. Pete's video (#186) on internal threading. He shows to have the compound point towards the tail stock. Also watched Halligan142's video on internal threading and he also said to have the compound pointed towards the tail stock. This required the threading bar to have an extremely large amount of stick out from the compound and there was a massive amount of flex as I cut the thread. I didn't remember having the compound point towards the tail stock the last time I cut an internal thread. Happened to be looking in the MOLO and the MOLO said to have the compound pointed towards the headstock when cutting internal threads. That's my recollection of how I had cut internal threads in the past. The threads worked either way.

Who's correct? Mr Pete or the MOLO?

 

[mikey]

How about neither. Just use the cross slide for your depth of cut.

 

[darkzero]

Doesn't matter which side the compound dial is pointing as long as the compound angle is correct when using the modified flank method for feeding. Either way wouldn't matter, really it's the tool post position & reach depending on the size of the part.

Also accessibility reaching the dial. Some people like the dial in the front on the headstock side cause it's easier to access. Others like the dial on the tailstock side on the backside cause the dial will be reading the correct direction when infeeding. More math, more risk for mistakes.

If it's not a coarse thread you don't need to use the modified flank method, just use the cross slide for feeding as Mike said. Me, I almost always use the modified flank method for feeding. That's how I learned & I'm just used to it. I only use the cross slide to feed for the final passes.

I don't use any of the positions mentioned. I use my compound in the same exact position as you would for external threading. I use internal threading bars upside down cutting on the backside of the bore. I like to do things unconventionally.

BTW, what is MOLO?

 

[mikey]

MOLO = Manual Of Lathe Operation

BOZO = Me ...

 

[tjb]

MOLO = Manual Of Lathe Operation

BOZO = Me ...

Funny. Wrong. But funny.

 

[Technical Ted]

I think of it this way... if you set your compound to let's say 29 degrees, you want to line up your compound so you are feeding into the side of the threading tool that is doing the majority of the cutting. So line things up so the screw pressure feeds the main cutting edge into the side of the thread. If you think of it this way, it doesn't matter if it's a right hand or left hand thread, or if you thread on the far side with your tool upside down... I always follow this rule.

Ted

 

[mickri]

Thanks for the replies. Really cleared things up for me. Next internal thread I am going to try the backside with the tool upside down.

 

[Illinoyance]

You want the compound oriented so it feeds parallel to the trailing flank of the tool, less a half degree or so. That is a pretty universal rule for flank feeding. If you are one of those who prefer plunge feeding the position of the compound is irrelevant.

 

[Superburban]

You want the compound oriented so it feeds parallel to the trailing flank of the tool, less a half degree or so. That is a pretty universal rule for flank feeding.

Agreed. I also was taught to have the flank side being the side towards the tail stock, so the cutting tool is cutting towards the chuck. Putting most of the cut on the flank, can let the material push the compound forward, by any backlash your setup has. The compound lead screw, and the main lead screw is pushing to the left, and the majority of the cut is one the right, also trying to push the tool to the left. Maybe a better way to explain it is the forces from the cutting operation, should always be opposite in direction to the forces the lead screw is putting on the tool.

Like most things in life, there is more then one way to skin a cat. The results are determined by the tools, material, machine rigidity, and the month you were born. Best thing is to try different methods, and do what works for you.