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First crash

Chawbeef

Chawbeef

Active Member
Back to the drawing board. I am (was) making a new brass bushing for my cross slide feed gear. I was pleased with the ID and the OD but when I tried to part it off BANG. What I get for not using a proper parting tool. Gotta get one.........................Chawbeef
 

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Echoing what @DPittman says.

Parting is basically another whole subject. I used a hack saw for years after I was already very proficient at other lathe tasks. If you think better tools are gunna do the trick, you need to change your medication.

Also, solid bars are way easier to part than tubes. That's because tubes deform more easily, and also because any eccentricity in the part mounting/chuck/part is just hiding there waiting to chew your head off. I've been known to put a temporary plug inside to help part tubes. (sshhhh - don't tell anybody.....)

My advice is to use a hack saw for now. Parting is in the advanced lessons section.

Just my 2 cents for what it's worth.
 
Parting off tubing on a lathe is a major PITA. It’s using a not very effective but very expensive tool instead of a $50 pipe cutter. Or a hacksaw. Either one is faster and easier than using a lathe.

I confess that I often use my lathe to cut tubing, but: I use a rotating chuck in the tail stock to support the tubing. I use a parting tool to score the workpiece to get my cut line just deep enough to be a guide line, and then remove the workpiece from the lathe and cut along the guide line on a bandsaw.
 
It might be well worth your time, and a lot less damage to your wallet if you could spend a couple of hours with another machinist to see how some operations are done safely and accurately. Parting is one of those 'trial by fire' lessons at first.

There are some well used and trusted books on the subject as well:

IMG_6212.JPG
 
I tried a few different parting tools in my lathe. I went from little to zero success with the first few tools that I tried. Then I bought a quality parting tool and my success rate went up to 100%. I mostly part tool steel and aluminum and use LPS gold as a lubricant. By the way I think the gold part of LPS gold refers to the price.
 
StevSmar said:
What about an inverted parting tool?

Like:
Eccentric Engineering Inverted Parting Tool
Click to expand...

Don't need a special tool like that. Just an ordinary blade mounted upside down works fine. It is just slow but works great. I don't think it would work on a brass bushing though.....

Parting upside down is what I did for years when a hacksaw didn't work until this forum taught me how to do it properly.
 
DPittman said:
Well parting tools certainly can make a difference but make sure you've got all the basics covered first...angles, rigidity, speed, feed, lube, etc. The smaller the lathe the more important all those items are.
Click to expand...

I’ll second the above. All the advice I can give is derived from advice I have seen from the experienced plus hard earned experience (learning what not to do by doing it, LOL!). The reference books are good too.

To expand, I think the largest fundamental is rigidity. Your tool must not deflect while in contact with the work piece. No chatter either!

You need to keep stick out to a minimum to give the work piece the least opportunity to pull the cutting edge into the work piece. Less leverage. I see you have a lantern tool post, I have very little experience with those but it looks like it’s effectively giving you a fair bit of stick out so there’s a gain you can make if you switch to a newer style QCTP.

You need to have as much play removed from the mechanisms (slides etc.) so that there’s no play to give the tool the opportunity to pull into the work piece. Lock down the carriage and compound if you can and make sure the cross is tight enough. Gibs etc.

The cutting edge must be on centre and the edge must be ground with proper clearances/angles to fit the material (brass/steel etc.) I keep talking about pulling the tool in, cutting angles & clearances are a big part of that too. Less back rake for brass etc.

One more thing I have found that makes a big difference is honing the cutting edge with a diamond hone (easy lap). You get a very sharp and even cutting edge without the “grain” witness from the grinding wheel. Like a finely honed knife.

Speed wise, start with the slowest speed & feed you can, bull low if you can and use powered cross for consistency. You may be able to up the speed as you have success but slowest is a good fundamental starting point. You can cut tubing without drama.

Lubrication is necessary, don’t be stingy but I haven’t found any miracle juice. You’ll hear it if you’re not giving it enough.

My cutting tools are HSS parting blades, hand ground and honed, no pre-made inserts and you can tailor the edge to the material.

On my Standard Modern I built a massive quick change tool post/holder that works really well compared to the Dicksons on my Myford. The Myford is smaller/lighter and more sensitive compared to the SM. My SM tool post is in post 49 of This thread.

Well, there you have the bulk of my experience. Go ahead and experiment until you see progress, soak up the experience and find out what works for you. There are several very experienced voices around here, I’m sure they’ll speak up and fill in what I missed, LOL!

D :cool:
 
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Susquatch said:
Don't need a special tool like that. Just an ordinary blade mounted upside down works fine. It is just slow but works great. I don't think it would work on a brass bushing though.....

Parting upside down is what I did for years when a hacksaw didn't work
Click to expand...

I’m sticking my neck out here but I don’t think you need to go upside down if you have a good rigid tool post but it probably helps mitigate for less rigid setups.

Susquatch said:
until this forum taught me how to do it properly.
Click to expand...

I think this says a great deal!

Getting all the factors working for you will make parting a lot less stressful. Note I said less stressful! I’m still learning how not to do things when parting but I don’t look for work around first. I might feel different if I had a band$aw….:p

D :cool:
 
Tecnico said:
I’m sticking my neck out here but I don’t think you need to go upside down if you have a good rigid tool post but it probably helps mitigate for less rigid setups.
Click to expand...

No, you are correct. You do NOT need to go upside down. It's just an almost guaranteed method (other than for tubes and bushings).

Since the forum edumacated me, I've been using an insert parting tool right-side up with relatively good success. It's a GTN-3 insert in an Accusize Tool.
 
It might be well worth your time, and a lot less damage to your wallet if you could spend a couple of hours with another machinist to see how some operations are done safely and accurately.
Click to expand...

Also, everything @Tecnico said.

I use a hand ground tool (no insert) and it has been years since I had parting off issues. (Knock wood!) Like so much else, it is a matter of understanding the theory then putting in the necessary hours of practice and "making your first 1000 mistakes". It may require more hours of practice and more mistakes than some other operations, but the same principle applies.
 
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