Parting Off :-(

[Garyrmck]

Hi,
I'm having trouble parting off.......... yesterday I broke 2 blades..........

I have a Seig SC$4 lathe fitted with a Seig QCTP. This has a rather strange parting off holder that uses 14mm blades. The only blades I can find for this are simple lengths of HSS. The blades have no side relief so I assume my problem is that the blade is jamming due to expansion as it heats up (I was using water soluble cutting fluid, and the blade was square and on centre). I would like to junk this and get a decent parting off tool.

I anticipate most of my work will be aluminium, mild steel and brass, with only a very odd piece of stainless thrown in.

Last week I bought a pair of Diamond Tool Holders (tangental tool holders) from http://www.eccentricengineering.com.au/ and have found them to produce superb results - I'm getting a mirror finish on aluminium, so I was wondering if anyone has experience of their inverted parting system?    http://www.eccentricengineering.com.au/index.php?option=com_content&view=article&id=31&Itemid=45

Are there other alternatives that can be suggested?

I spent several hours last night reading every thread I could find - including one 15 pager! But it seems that there is no one answer. I've read that the tool should be on centre, above centre, below centre, that inverted is great, inverted sucks, normal sucks, normal is best, rear is best, rear sucks etc etc. All very confusing for someone new...

I'm prepared to buy a good tool, but they are not cheap, so I was wondering what the latest opinions are? Don't want to buy the wrong thing....

cheers
Gary

[sparky961]

This is perhaps an oversimplification, but generally I think parting off on a small hobby machine just plain sucks.  On a bigger (read: rigid) machine, using a nice carbide insert parting tool, it's actually pretty painless most of the time.

My suggestion is that you avoid parting off whenever possible.  Get a decent horizontal band saw, or whatever your budget allows, and saw off the stub you've turned your part on.  Then you can insert it in the lathe backwards and face the rough saw cut.  For the 1's and 2's that most hobbyists work on, a parting tool won't save much time in the long run.

That's not to say you can't find a setup that works for you and your machine.  I'm sure it's possible.  Just saying that it may not be worth the hassle.

[BillTodd]

You might have better 'luck' with a spring type tool (http://www.practicalmachinist.com/vb/antique-machinery-history/more-spring-tools-208588/)  the 'spring' pulls the blade away from the cut as it digs in. A typical lathe set tends to push the blade into the job as the cutting force increases (not too much of a problem on a big rigid lathe but small lathe tend to flex rather more).

Alternatively, you could try parting from the rear with the blade inverted: like the spring tool the flex in the lathe pulls the blade away from the job reducing the tend to snag.

[vtsteam]

This doesn't apply to parting off with a parting tool, but a bandsaw isn't the only alternative for a small lathe, You can hacksaw the part if reasonably small by running a slow speed on the lathe and using a light sawing motion. Don't saw al the way through while running. Turn it off to finish the last bit.

[Garyrmck]

Hi,

well, I managed to borrow a small parting off tool that used a blade with side relief. Set it up exactly as before and what to you know? It parted off a 40mm diameter piece of aluminium 1mm thick perfectly - the end did not need any cleaning up, it was nice and smooth. It seems my problem was the crappy seig holder and flat sided blade. Next time I'll try power feeding the cross slide - I was too cowardly to try this before .......

thanks
Gary

[Arbalist]

I'm using insert parting tools on my little 8 X 14 Lathe at the moment as I often seem to break HSS blades. I've bought some Tee shape HSS blades to try though at some point to see how they work.

[Joules]

Take your flat sided parting tool and hollow grind it if can, even a Dremel would do the job.

[raynerd]

Hi,
I'm having trouble parting off.......... yesterday I broke 2 blades..........

I have a Seig SC$4 lathe fitted with a Seig QCTP. This has a rather strange parting off holder that uses 14mm blades. The only blades I can find for this are simple lengths of HSS. The blades have no side relief so I assume my problem is that the blade is jamming due to expansion as it heats up (I was using water soluble cutting fluid, and the blade was square and on centre). I would like to junk this and get a decent parting off tool.

I anticipate most of my work will be aluminium, mild steel and brass, with only a very odd piece of stainless thrown in.

Last week I bought a pair of Diamond Tool Holders (tangental tool holders) from http://www.eccentricengineering.com.au/ and have found them to produce superb results - I'm getting a mirror finish on aluminium, so I was wondering if anyone has experience of their inverted parting system?    http://www.eccentricengineering.com.au/index.php?option=com_content&view=article&id=31&Itemid=45

Are there other alternatives that can be suggested?

I spent several hours last night reading every thread I could find - including one 15 pager! But it seems that there is no one answer. I've read that the tool should be on centre, above centre, below centre, that inverted is great, inverted sucks, normal sucks, normal is best, rear is best, rear sucks etc etc. All very confusing for someone new...

I'm prepared to buy a good tool, but they are not cheap, so I was wondering what the latest opinions are? Don't want to buy the wrong thing....

cheers
Gary

Speaking as someone who couldn't understand the dark art of parting off for many years, the key to me was a sharp tool and rigidity. I can part on my Boxford and I can part on my tiny Cowells. I spent a fortune on a tipped parting tool and still no luck. It was only until I had my lathe running with little vibration and with the slides locked up that I started to get results and get a feel from it. The tipped tool is in the cupboard and I just use HSS tools now.

[steampunkpete]

I part off quite happily on my mini lathe (C2/C3 clone). As the guys have said it's down to the right tools and rigidity.

Make sure that the gibs on the slides are properly adjusted. Make or buy a carriage lock; one that pulls the carriage down onto the bed, not the Satan cursed other sort.

I don't know what the Sieg SC4 bearing arrangement in the headstock looks like, but if it is like the SC3 it would benefit from the ball-race to taper bearing modification as that improves rigidity.