Parting (off) is such sweet sorrow

[smfr]

After spending several hours making a new piston rod for a Stuart Beam, I had something like this (that's the old rod at the top):



Now to turn down the shoulder, and shorten it up:



Gee, thought I, I'll just use my handy parting tool to cut off the top! It's held by a live center, what can go wrong?? As the tool was getting towards the point of no return, I thought "mmm, maybe I should back off and cut the last part with the hacksaw". Of course, just then the tool broke through, something went "thunk", and the top end of my piston rod spun around with an ominous wobble



It's not too obvious from the photo, but the part is junk.

In hindsight, I should have had the square part in the 4-jaw for this operation. Ah well!

 

[Ken I]

Welcome to the club.

I'd try beating that back into line with a blunt instrument and a clock gauge.

Ken

 

[cd600]

It is hanging out of the chuck a long way, to part off especially with a tipped tool, try and straighten it..

 

[smfr]

Is it fair to say that the parting tool should only be used for (duh) parting off, i.e. when the part you care about is away from the chuck, so it just falls off when the cut is complete?

 

[John Rudd]

Is it fair to say that the parting tool should only be used for (duh) parting off, i.e. when the part you care about is away from the chuck, so it just falls off when the cut is complete?

Ummm.. in a word Yes!

Sorry you had to find out the hard way, good luck with the rest if your project.

 

[mu38&Bg#]

You can part anywhere as long as it doesn't result in chatter or so much overhang the part will bend. The likely hood of chatter increases as you get away from the chuck. I often turn put the finished part in the chuck and part off the portion used for chucking if that is deemed better. You have the right instinct though, chucking the square would have been fine.

In this case the length to diameter ratio was not in your favor. Any operation, with that much overhang after the support is removed from the tailstock could have resulted the same.

 

[Ken I]

Using the centre - nothing wrong with the idea - and your were right about stopping earlier - always mandated with a centre in place during part off.

That said I would never part off something I can remount closer to the chuck - in your case and with such a small part I would have 4 jawed it and turned it off - wouldn't have crossed my mind to use the parting tool there.

That said there will be more stuffed up parts in my future - so don't feel bad about it.

Ken

 

[maverick]

Sorry about your part, chalk it up to education and keep on going.

 

[mrehmus]

Parting off something held between a chuck and center is a really bad idea. Don't ask me how I know. Subsequently I found out that my friends who are 'real' machinists sometimes do this but as the cutoff tool and the work heat, the tool tends to jam and bend up the good parts.

I have a few scrap connecting rods with 'small' problems like this.

 

[Ned Ludd]

As a general idea, it is best to always part off as close to the chuck as you can get and not to use support. but there are occasions when support will help.
There is no problem using tail stock for support, but best to relieve pressure as the cut nears completion. If there is too much pressure, at the end of the cut, you will almost certainly cause the parting tool to be pinched. This is a sure way to spoil your day!
Ned

 

[Mosey]

Nice looking part before you bunged it up. Start at that point and make the final as nice. Look at it as if it were a shortcut to perfection.

 

[Blogwitch]

What happens is that people seem to think they have to part everything off, whereas in many cases, it is easier, quicker and safer just to use a hacksaw and bench vice.

Then it is a matter of a quick face off using the lathe, and the job is done.

Parting off is not a direct replacement for jobs that need a bit of elbow grease, as this job clearly shows.

It is like building workers downing tools on the job, because the battery in their power screwdriver has gone dead. They have forgotten how to use manual tools, and think that nothing can be done without power tools.


John

 

[Rayanth]

Thankfully, we really *can't* build commercial airplanes without our power (pneumatic) tools. I know it's possibly to drill a hole with a hand powered drill, but to get the .003" tolerance on it required of all holes at the Lazy B, is asking a bit much. and driving rivets with a hammer might get tiring quickly =)