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Tool Lathe parting tools

Tool

Chipper5783

Super User
Another thread on lathe parting tools. Over the years I have tried / used a few different parting tools and found the GTN style carbide insert works well for my use (with the clamp in block for a regular tool holder). The generic HSS blade and holder that is commonly included in a qctp set looks good in that it sets the blade in close to the tool post, but for me rarely seemed to work well and was relegated to use on soft materials. The CXA I had already modified by cutting a relief for the T portion of the blade (that didn’t seem to help much).

The Aloris71 appears to combine the blade pulled in close and the ability to use carbide inserts. I don’t have one, expensive. I like to try to use the tools I already have.

On a recent project, I popped the end off a GTN holder blade (darn) - hey, that’s an opportunity to improve the little used parting tool holders! Pictured here is the before and after, two holders: a CXA phaseII and an ”A” size 40 position. The blades were 1” tall, now trimmed to 3/4” - one at GTN2 & GTN3, can fit either holder. A new clamp block was needed on the 40P, and skimming in a 15 degree bevel on the CXA. The CXA incorporates 4 degrees of back rake, perhaps chips will flow off a little easier? The blades are not quite as strong, so paying attention and not pushing it too hard may be important. I’m looking forward to trying them out.
 

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Susquatch

Ultra Member
Administrator
Moderator
Premium Member
Another thread on lathe parting tools. Over the years I have tried / used a few different parting tools and found the GTN style carbide insert works well for my use (with the clamp in block for a regular tool holder).

I'm no parting wizard myself.

But I can part almost anything successfully by parting upside down. Just flip the tool upside down and run the lathe in reverse. It just plain works. The rigidity sucks but it doesn't matter. The tool just skips instead of digging in. @PeterT showed a nice drawing a while back that shows why it works.

I've never tried it with carbide but I suspect it won't work well. For now I just use HSS Blades when parting upside down.

I have some tools in the design stage that I hope will improve regular parting through improved rigidity. But lots of guys on here are also using a plinth to increase rigidity.

That said, you have a CXA size tool holder. That implies a fairly big lathe that ought to be rigid enough to part almost anything. So I feel for you.

Give the upside down parting a try.
 
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The issue with parting is your cutter must be center, touch below and it digs in, touch high it and it doesn't cut correctly and drags causing excessive pressure.

By flipping it and cutting in reverse you basically allow the cutter to release when in the "low" position in a normal cut as the carriage lifts preventing dig in.

It took me a long time to learn this simple concept of centering perfectly for parting and AXA holders made this so much easier as I could dial it in ;).
 

Chipper5783

Super User
The GTN blades in the separate clamp holders have been working out well for me, whether in the CXA on the 15” lathe or 40P “E” holder in the 11” Smart & Brown (quite a sturdy little lathe). Depending on the machining details (material, size, part / setup rigidity) it may still chatter. The intent of my project, and sharing it was to present a use idea for a couple of seldom used tool holders in my kit (not my idea, basically copying an Aloris 71).

I like your suggestion next time I’m parting something, I’ll give it a try (dead easy to flip the blade and lift the holder). Thank you.
 

Susquatch

Ultra Member
Administrator
Moderator
Premium Member
The issue with parting is your cutter must be center, touch below and it digs in, touch high it and it doesn't cut correctly and drags causing excessive pressure.

By flipping it and cutting in reverse you basically allow the cutter to release when in the "low" position in a normal cut as the carriage lifts preventing dig in.

It took me a long time to learn this simple concept of centering perfectly for parting and AXA holders made this so much easier as I could dial it in ;).

No. I learned to center properly 50 years ago. The issue here is a shortage of rigidity.

I've had good success using different profiles on hss blades, and recently with carbide parting tools. But every once in a while it goes south on me. Usually when the part has a big diameter requiring a lot of tool stick out, or when the part has a lot of stick out from the chuck, or when rigidity goes down for whatever reason. When this happens, upside down always works. I'd stop there, if all I wanted to do was part successfully.

But I don't think this thread was intended to be a lesson on how to part. @Chipper5783 has indicated he can part. So can I. Unless I missed it, this thread is about looking at alternative methods to address rigidity, and making improvements. A passion that I share with him.
 
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