Off centre turning in a 3 jaw chuck.

[Gas_mantle]

No probs 

Mind you there are 1 or 2 out there who do enjoy the fiddly bits of this hobby that the rest of us hate !

Personally I can't stand making 1 off jigs and mandrels etc but some guys seem to love it.

[zeeprogrammer]

Mind you there are 1 or 2 out there who do enjoy the fiddly bits of this hobby that the rest of us hate !

It just points out that there are many facets to any hobby. Some facets are more interesting to some people than others.
It's the same argument as 'do you enjoy the journey or the destination'?

I'm not into tool making although the occasional jig is pretty interesting.

As we all already know, (and I apologize for saying the obvious) whatever makes it fun and enjoyable.

[gerritv]

Since I guess I started some this later commentary by saying I used a shim to offset in a 3 jaw., no I am not lazy nor am I afraid of truing stock etc in a 4 jaw. For a small offset I looked at the 3 jaw and determined it was not a risk or problem. A large offset, yes I agree the grip would be a risk and issue. But 0.030 is not much.

Gerrit

[Flyboy Jim]

Another 2 cents....

With a dial indicator (mounted mine through a aluminum block that bolts to the cross slide with a t-nut, allows for really quick zeroing by moving the cross slide), centering up the 4 jaw takes me less than a minute. Once one axis is dialed in, the second one goes really quick. For offset eccentrics, I just center it, then offset one axis the amount needed. After a few times, the process becomes second nature. Its confusing which way to move which jaw the first couple times, gets easy quick.

If making lots of parts with same offset, I could see making a jig with the offset built in like you guys have shown so no adjustment part to part is needed.

Chris.........I remember seeing you do this on your Double Acting Twin Beam Engine build when I was first getting started. I just assumed that was how it was done with a 4 jaw chuck, so did the same thing. Really easy to set up that way. Then when I added my "Marv inspired pump center" it added even more versatility to the process.

Now that said.........I can see the benefit for understanding how it can also be done with a 3 jaw chuck. It certainly adds to the knowledge base.

Jim

PS: It's interesting to see how we all approach this hobby. At this point, early in my machining journey, I'm still really enthralled with the set up and process of making parts. If suddenly I end up with an engine that runs, that's just the frosting on the cake. I can see where, further down the stream, the end result might end up being more of the focus.

[10KPete]

When I was a young lad, an old machinist explained it to me thusly:

"A machinist makes chips. If he makes the chips correctly he has a good part left over."  Joe Bonney

Then I heard this from another machinist, in the same shop, when a designer brought him a drawing: "Don't tell me to 1/2" ream the hole! I know how to make holes! Tell me the diameter and the tolerance that's needed!!"

Later on, another old machinist said this (he was from Portugal):

"You got no set-up, you got nothing"  Paul Machado

I'll never forget those guys, and many others who guided me early on.

I don't think it matters much how you skin the cat.....

Pete

[Lew Hartswick]

Marv's humorous post is about the truth for me. A good example is the post on Burr puzzles. I was intrigued by the idea of  making the parts.
But after I made the soft jaws and developed the technique of making the cuts etc. the finished device is just more collected junk.  I'm not into engines at all the machining that is interesting.  Just the other day someone wanted me to make a few "flywheels" of different moment of inertia to demonstrate the change in current / acceleration of a DC motor, the resultant "trip back" through  my college physics book, Sears and Zemansky, and the resultant integral math was just GREAT!!!   :-)
   ...lew...

[mklotz]

...Just the other day someone wanted me to make a few "flywheels" of different moment of inertia to demonstrate the change in current / acceleration of a DC motor, the resultant "trip back" through  my college physics book, Sears and Zemansky, and the resultant integral math was just GREAT!!!   :-)

Next time, Lew, just ask me...

http://www.homemadetools.net/forum/flywheel-inertia-analysis-48288#post68898

[Lew Hartswick]

...Just the other day someone wanted me to make a few "flywheels" of different moment of inertia to demonstrate the change in current / acceleration of a DC motor, the resultant "trip back" through  my college physics book, Sears and Zemansky, and the resultant integral math was just GREAT!!!   :-)

Next time, Lew, just ask me...

http://www.homemadetools.net/forum/flywheel-inertia-analysis-48288#post68898

BUT it was such fun doing it with the old text from 1955 and even following the integration .  I was "intuitively" suspicious of the text when I saw the 1/2 M (r2 sq + r1 sq) for the annular cylinder so had to go through the whole business to see why it was.  For all those that just want an answer your link will be a great help.  If they are concerned about the how/why it's a good thing to do the math . :-)  I'll take you up on some of the other things in your fabulous collection of items though.
   ...lew...

[mklotz]

BUT it was such fun doing it with the old text from 1955 and even following the integration .  I was "intuitively" suspicious of the text when I saw the 1/2 M (r2 sq + r1 sq) for the annular cylinder so had to go through the whole business to see why it was.  For all those that just want an answer your link will be a great help.  If they are concerned about the how/why it's a good thing to do the math . :-)  I'll take you up on some of the other things in your fabulous collection of items though.

Just do the integrals in your head; no need for paper. :-)

Reminds me of an old math joke (and math jokes are very rare).

At a cocktail party, a smart-ass senior approaches Norbert Wiener (world famous mathematician for the Philistines) and challenges him with this problem...

Two trains, a mile apart are approaching each other on the same track, each traveling at 60 mph.  A fly on the front of train A flys at 5 miles per hour to the front of train B, turns around and flys back to train A.  He continues this shuttle until both trains collide, crushing him into goo.  How far did the fly fly?

Wiener instantly responds, "220 feet".

Student: "Very good. sir.  Most people would try to sum the infinite series"

Wiener: "I did."

[Admiral_dk]

OK / Good joke from a mathematical point - but from physics it is rubbish, as there is no way a fly, flying 5mph can fly back and forth between trains traveling at 60mph .... or are you telling me that I missed the point completely Marv ...?... (not for the first time ....).

[Roger B]

I can raise the stakes with off center turning/drilling with a 4 jaw SC chuck 

For my fuel injection components two 2mm shims move the piece of 10 mm square bar the required 1 mm offset in each direction 

[10KPete]

I can raise the stakes with off center turning/drilling with a 4 jaw SC chuck 

For my fuel injection components two 2mm shims move the piece of 10 mm square bar the required 1 mm offset in each direction 

 

Pete

[mklotz]

OK / Good joke from a mathematical point - but from physics it is rubbish, as there is no way a fly, flying 5mph can fly back and forth between trains traveling at 60mph .... or are you telling me that I missed the point completely Marv ...?... (not for the first time ....).

American flies strong like bull.  Two of them can carry off a horse.  That's why we call them horse flies.

Yeah, you missed the point, the joke and the train.  Ever hear of the humor concept called "voluntary suspension of disbelief"?

Maybe it would have worked better if I had used Neils Bohr instead of Norbert Wiener?

[Tennessee Whiskey]

To be honest Marv, if you could have explained it to me and then I could interpolated into shop floor speak, we could have pulled it off. No emojis were harmed in this post .

Cletus

[mklotz]

To be honest Marv, if you could have explained it to me and then I could interpolated into shop floor speak, we could have pulled it off. No emojis were harmed in this post .

Cletus

I don't think I could have explained it to you.