12x36 Lathe: CCMT21.51 or 32.51?

This boring treatise Mikey did is stellar work. It taught me a lot, as did Mikey as he graciously answered my questions I had after reading it. Thank you Mikey and everyone who contributes for all the info and assistance you provide.
 
Thanks, Joe and Splat. I really appreciate the kind words.

stioc said:
Haha, ok, I'll get some standard turning bars, I didn't know if all SCLRs are the same or if this one was different.
As for boring bars, do you have any recommendations? I hate the brazed carbide tipped bars, they're terrible and just rub. These ones seem to work a little better but if there's a better option I'm all ears.
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The SCLCR geometry is the same on turning and boring tools. The hold an insert that is made to provide 5 degrees of front and side clearance. However, when a flat is ground on top of a boring tool it's purpose is to present the tool with a negative rake. Negative rake is generally used to provide added relief under the cutting edge for clearance but at the same time, it greatly increases tangential and radial cutting forces. This is not a good design for a boring bar, at least in my opinion, and certainly does not promote accuracy in a precision bore. If the flat were not there and you could use the bar with the insert horizontal, now that would be more useful.

Brazed carbide tipped boring bars are actually really good. Even the cheap Chinese ones work well if you sharpen the carbide and maybe add a very tiny nose radius to it. They don't finish as well but they can be quite accurate.

For use on the lathe, the best option is an indexable bar, in my opinion. Have a look at the Primer. It should answer most of your questions but if not, ask and we'll all chip in.
 
Thanks guys, just read through it quickly, lots of great info in there and I'll be reading it again taking my time.

The SCLR boring bars I have do have a radial 5deg negative rake but no axial negative rake. I thought I'd read in one of the lathe books that negative radial rake is better for boring operations but I could be wrong. It's been a while.

If the negative radial rake is undesirable are there any decent/recommended indexable boring bars (preferably that use CCMT21.51) that don't cost more than $50+ each? I'm just a home gamer...

I'd think these indexable boring bars can also be used for internal threading too?

Edit: link to the bars I have https://www.amazon.com/gp/product/B01LNEF81W
 
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stioc said:
... are there any decent/recommended indexable boring bars (preferably that use CCMT21.51) that don't cost more than $50+ each? I'm just a home gamer...

I'd think these indexable boring bars can also be used for internal threading too?

Edit: link to the bars I have https://www.amazon.com/gp/product/B01LNEF81W
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There are many, many SCLCR bars out there. The best of these have carbide shanks. What you're looking for is an SCLCR bar with no flat on top.

I am not aware of any SCLCR bar that accepts threading inserts but some boring bars do. Most folks use a bar specifically made for internal threading and separate bars for boring.
 
You don't have to position it at a negative rake angle. Just make sure you have the clearance.
 
ddickey said:
You don't have to position it at a negative rake angle. Just make sure you have the clearance.
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... and a tool holder that surrounds the bar so it can be locked off angle. Tool holders that use screws to lock down the bar will not allow you to turn the tool - it will rotate the bar as you tighten them.
 
darkzero said:
I have a 12x36 & I use 32.5x the most. Don't have to worry about your lathe not being able to handle them. Heck I use CNMG 43x also. I do use 21.5x for my boring bars though. My second to largest boring bar uses 32.5x & my largest boring bar uses CNMG 43x. I keep the worn out 32.5x inserts cause I have a face mill that uses the unused 100° degree corners so I really get my money's worth out of them. I don't think I'll ever need to buy another 32.51/2 insert again, I'm pretty sure I have a lifetime supply of them now.
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Any branding on that face mill? I'm in the market right now for that exact situation and coming up zeros on eBay.
 
Mikeskid07 said:
Any branding on that face mill? I'm in the market right now for that exact situation and coming up zeros on eBay.
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It's a Dorian Recycle Cutter. It came in different shank configurations as well for CNMG inserts. Travers also sold it under their T&O house brand. Unfortunately a member here informed me that it's been discontinued but maybe the info above might help to possibly find a used one.

But you can get lathe turning tools to use the 100° corners of CCMT inserts.
 
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