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Strange Carbide Insert Internal Threading Tool Geometry

YYCHM

YYCHM

(Craig)
Premium Member
Bought a set of threading bars with carbide inserts from Amazon.....

1.JPG


Does this look right to you?

2A.JPG


The mounting flats on the bar cause the insert thread cutting edge to be canted down significantly. It didn't work very well when I tried it today?
 
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If that set has the 8/10/12 mm bars I recently bought the same set. I've used them over the last couple of days, 5/8- 18, and have worked okay, the carbides break easy but that could be me. I used them for about 90% of the thread and then finished off with the tap.

I thought the angle looked weird as well but it seems to work.

What thread were you cutting and what DOC?
 
YotaBota said:
If that set has the 8/10/12 mm bars I recently bought the same set. I've used them over the last couple of days, 5/8- 18, and have worked okay, the carbides break easy but that could be me. I used them for about 90% of the thread and then finished off with the tap.

I thought the angle looked weird as well but it seems to work.

What thread were you cutting and what DOC?
Click to expand...


1/2-13, 0.005 DOC
 
YotaBota said:
I'll try that next time, this time I was pretty much right on center.
Click to expand...

That's my point..... How can you be on center with the insert tipped down like I depicted in the image.

I used the largest bar that fit. The insert refused to cut a clean chip. Never made it to full depth of thread before giving up.

Running 50 RPM with SS stock (which machines rather nicely otherwise).
 
try them in a sleeve and flatten out the insert. That tipped down geometry looks nothing like any of the internal bars i have. I can't imagine its ever going to work properly
 
I use those same inserts on external holders. They are very positive rake and cut very well. The way they are on you bar is very nuetral if used in a tool holder. In a boring bar holder you should be able to andjust the rake and clearance to get a good cut.
 
Darren said:
I use those same inserts on external holders. They are very positive rake and cut very well. The way they are on you bar is very nuetral if used in a tool holder. In a boring bar holder you should be able to andjust the rake and clearance to get a good cut.
Click to expand...

Are the flats on the bar not meant to position the insert correctly? You cannot rotate the bar and lock it down properly to provide a different presentation.
 
I have similar internal holders and they have the same angle on the insert as yours. I haven't used them yet, but I have used the external threading insert toolholder with good results. It holds the insert at an angle -'canted' down - in a similar way. I follow the advice that @John Conroy gives when cutting internally or boring - set the tool tip a bit above center. then when/if (depending on how rigid your lathe setup is) the tool flexes under load the DOC is reduced, not increased.
 
YYCHM said:
o_O Look at the thread title......
Click to expand...

Sorry! I missed that! My phone doesn't show the title unless I scroll up.

Wondered why you were asking about it! Thought maybe they shipped you a boring bar with a threading insert installed or something.

That, plus I was falling asleep. Shouldn't post anything then.

Never know these days. But ya, if I had seen the title and read your question a bit better I would not have posted that. My bad. Feeling kinda dumb right now........ o_O
 
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The flat of the bar should be level. This aligns the insert to achieve proper geometry in regards to clearance inside the hole. You must then put the tip of insert on center, or a couple thou' higher to compensate for any downward flex of the bar. The amount higher from center will depend on boring bar material, stick out, depth of cut, work material and hardness.
 
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