# Introduction to Indexable Tooling for the Metal Lathe



## 7milesup (Mar 17, 2021)

So, I hope I can do this here and it doesn't come across as an advertisement.   As many of you know, one of our members, David P Best, has been toiling over a book that he intends to publish.  It is titled  "*Introduction to Indexable Tooling for the Metal Lathe: A User Guide Paperback" .  *He has completed it and it is available to order from Amazon.  I know that David does very fine work, and I would anticipate that this book will be no less of an example of his capability.
I ordered mine last night.  Should be here next week.  Really looking forward to it.

*





						Amazon.com: Introduction to Indexable Tooling for the Metal Lathe: A User Guide: 9798753874993: Best, David P.
					

Amazon.com: Introduction to Indexable Tooling for the Metal Lathe: A User Guide: 9798753874993: Best, David P.



					www.amazon.com
				



*
Reason for Edit:  Updated the Amazon link.


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## Dabbler (Mar 17, 2021)

@7milesup    Perhaps you might do a review of it once you've read it?


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## Aukai (Mar 17, 2021)

Got it too


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## Boxster9 (Mar 18, 2021)

Thanks, just ordered a copy on Amazon.


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## 7milesup (Mar 19, 2021)

Just got my copy in the mail today.  That was quick!
First very initial impression is that this book is nicely done.


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## DavidR8 (Apr 19, 2021)

7milesup said:


> Just got my copy in the mail today.  That was quick!
> First very initial impression is that this book is nicely done.


I looked at it on Amazon and wondered if the content would apply to my lathe.


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## erikmannie (Apr 20, 2021)

I’m going to buy it on Friday!


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## 7milesup (Apr 20, 2021)

I ordered David's book a number of weeks ago by now, right when it first came out.

I had pretty much zero knowledge of insert tooling with the letters and numbers appearing as a jumbled mess.  David walks through different inserts and how to decipher the coding for the inserts and for the tool holders themselves.  Part numbers are listed for particular brands of inserts and holders and eBay search keywords.  David does not mince words when it comes to his view of cheap Chinese tooling, which is fine.  Buy once cry once.
The book is laid out very nicely with references embedded from one chapter to another, a tedious task for sure when writing a book, or lengthy paper for that matter.
A particular highlight of the book is the illustrations.  They are superbly done; some of the best I have seen.  Also included are reference charts categorized according to AXA, BXA etc sizing.  
I have not read all the way through the book because of some time constraints at the moment, but I suspect that I will be utilizing this as reference material down the road.


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## 7milesup (Apr 20, 2021)

DavidR8 said:


> I looked at it on Amazon and wondered if the content would apply to my lathe.


Yes, absolutely as long as you can utilize square and round shank insert holders ( I don't know what type of tool post you have).


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## Cadillac STS (Apr 20, 2021)

Just ordered one.

looks like a nice book with good information I would put to use. Probably will make better buying choices which will save me money. Hopefully I can resurrect the use of a couple tool holders that are now not used because I used up the inserts and not sure what to buy to replace them. May improve my own tooling if the inserts I use could be better for my purpose. All saves lots of money and gives me better skills.

Always a nice feeling to support a fellow forum member and encourage others to make things we all could use.


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## Rifleman1384 (Apr 20, 2021)

Mine has already arrived, There is much valuable information contained within. I think the experience shared will help folks when getting started by purchasing the correct type and quality tooling will more than pay for the book. Sometimes spend good money for quality on the front end will save lots on the back end. The charts and calculation formulas are very helpful since they are in one place instead of all over the internet or in one of the manufactures catalogs.  Who knows since mine is a First Edition the grandson may just look at it one and go wow this is cool. OK, Dave now I want it autographed. Thanks Dave!!

Steve


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## 7milesup (Apr 20, 2021)

Rifleman1384 said:


> OK, Dave now I want it autographed. Thanks Dave!!


That is what I was thinking too!  I would bet that I have one of the first ones sold, if not THE first one.  Least he could do is autograph it...


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## Aukai (Apr 20, 2021)

Mine is at least out of the first box


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## DavidR8 (Apr 20, 2021)

Based on the previews David provided I decided to spend the cash for the book. $75 CDN, free shipping.


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## Shotgun (Apr 20, 2021)

Is the book available anywhere other than Amazon?


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## davidpbest (Apr 20, 2021)

Shotgun said:


> Is the book available anywhere other than Amazon?


Amazon is the publisher and printer, so it's only available through them but it is available in all Amazon markets including outside North America.


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## davidpbest (Apr 20, 2021)

Rifleman1384 said:


> Mine has already arrived, There is much valuable information contained within. I think the experience shared will help folks when getting started by purchasing the correct type and quality tooling will more than pay for the book. Sometimes spend good money for quality on the front end will save lots on the back end. The charts and calculation formulas are very helpful since they are in one place instead of all over the internet or in one of the manufactures catalogs.  Who knows since mine is a First Edition the grandson may just look at it one and go wow this is cool. OK, Dave now I want it autographed. Thanks Dave!!
> 
> Steve


Steve, I'd be happy to autograph it for you.  DM me if you are serious - I'd even return it with a carbide insert used during evaluation for inclusion in the book.


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## myfinishingtouch (May 1, 2021)

My son and I are completely new to metalworking and the whole topic of indexable tooling for the lathe is indecipherable without a proper decoder ring.  David went to great lengths to help us deice upon which mill and lathe to buy and his book provides the necessary foundation to understanding the tooling needed for our lathe.  It explains things that in a way that make sense to someone with no prior knowledge of the topic.  Hours and hours of googling would have been completely unnecessary if David had only published his book a few months earlir.

Thanks, David "Simply the" Best

Dave Davies


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## mksj (May 1, 2021)

David put in countless hours in distilling down the basics for lathe tool holders/indexing inserts, and then put it in a step wise fashion for different levels of use. In the long run buying a book like this saves you from making lots of mistakes and then not knowing why your are not getting good cutting performance. Worthwhile investment for anyone getting into lathes and/or trying to figuring indexable tooling.
Mark


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## Jake P (May 10, 2021)

Just ordered my copy! 

David was nice enough to send me some information on tooling and he provided an excerpt from the book which was enough to convince me of the value.


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## DavidR8 (May 10, 2021)

As a result of reading the book I have a nice Micro 100 CCMT holder and matching inserts winging their way to me.


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## Janderso (May 10, 2021)

I'm not surprised if the work is outstanding. David is an extremely talented individual. If you haven't seen the beautiful job he did rebuilding his brand new PM lathe and mill, you should check it out.
I think I'll wait for the Audible version....... Oh come on, that was funny!


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## davidpbest (May 10, 2021)

Janderso said:


> I'm not surprised if the work is outstanding. David is an extremely talented individual. If you haven't seen the beautiful job he did rebuilding his brand new PM lathe and mill, you should check it out.
> I think I'll wait for the Audible version....... Oh come on, that was funny!


Ron Howard called last night and wanting to negotiate the movie rights.  I told him I was open to the idea if Brad Pitt played me, otherwise he could take a hike.


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## Aukai (May 10, 2021)

I think you should play yourself, and start a new career.


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## Janderso (May 10, 2021)

davidpbest said:


> I told him I was open to the idea if Brad Pitt played me,


Ha Ha Ha Ha Ha Ha Ha Ha Ha...... Oh man that was funny.


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## Beckerkumm (May 10, 2021)

Brad Pitt playing David Best isn't as far off as Tom cruise playing Jack Reacher.  David is the Lee Child of the metal set.  Dave


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## rabler (May 19, 2021)

David's book arrived today.  Now I'm already thinking of a few new tools I want to buy.  This could turn out to be a very expensive book 

Well done, thanks David!


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## .LMS. (May 19, 2021)

davidpbest said:


> Ron Howard called last night and wanting to negotiate the movie rights.  I told him I was open to the idea if Brad Pitt played me, otherwise he could take a hike.



Smart move making sure the guy playing you is less attractive to the ladies than you.


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## davidpbest (May 19, 2021)

rabler said:


> David's book arrived today.  Now I'm already thinking of a few new tools I want to buy.  This could turn out to be a very expensive book
> 
> Well done, thanks David!


The intent was to actually save you money by avoiding the purchase of tools and inserts that don’t perform or are incorrectly specified.


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## Aukai (May 19, 2021)

I have been looking and understanding a little at a time, and have a question on a nose radius. I have a project that uses a knurl in 316 SS, and for aesthetic purposes I like to cut a band in the knurl. Without burning up inserts I am wondering if cutting the knurl would do better with the bigger radius of a K bit than a smaller radius of M, or MS bit 16 vs 04? These are just what I have on hand, I'm not sure what to look for in a dedicated bit for this operation.


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## davidpbest (May 19, 2021)

Aukai said:


> I have been looking and understanding a little at a time, and have a question on a nose radius. I have a project that uses a knurl in 316 SS, and for aesthetic purposes I like to cut a band in the knurl. Without burning up inserts I am wondering if cutting the knurl would do better with the bigger radius of a K bit than a smaller radius of M, or MS bit 16 vs 04? These are just what I have on hand, I'm not sure what to look for in a dedicated bit for this operation.


I'm not understanding your question.  Please elaborate.  I assume you're machining the knurl with a knurling tool, right?  Then you want to put decorative bands into it.  I don't know what you mean by "bigger radius of a K bit than a smaller radius of M, or MS bit 16 vs 04?"  Are you talking about a drill bit, an ISO grade on the carbide insert - what is a "K bit" and "M, or MS bit 16 vs 04"?


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## rabler (May 19, 2021)

davidpbest said:


> The intent was to actually save you money by avoiding the purchase of tools and inserts that don’t perform or are incorrectly specified.


David
I’m sure it will help me a lot, some very good info.  But to be honest, I’m long past saving.  lol

Honestly, it is the wasted time in trail and error saved that I’ll value most.


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## Aukai (May 19, 2021)

Sorry David, the nose radius difference in the inserts like position seven, 16, and 04. I knurl a 2' length, and where I am going to drill through holes I clean out a band .500 wide through the knurl. I'm assuming the knurling process does a lot of things to the SS in this process. Hardening, interrupted surface and such. Looking at the inserts the cast iron insert has a bigger radius, vs the SS insert being sharper. I'm confusing myself now too....


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## davidpbest (May 19, 2021)

Aukai said:


> Sorry David, the nose radius difference in the inserts like position seven, 16, and 04. I knurl a 2' length, and where I am going to drill through holes I clean out a band .500 wide through the knurl. I'm assuming the knurling process does a lot of things to the SS in this process. Hardening, interrupted surface and such. Looking at the inserts the cast iron insert has a bigger radius, vs the SS insert being sharper. I'm confusing myself now too....


I will DM you on this rather than sidetrack this thread.  But if I were doing this, I would be using an indexable grooving or parting tool to remove the knurl in certain sections.


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## jpackard56 (May 20, 2021)

Just got David's book and could tell in the first few pages this clearly explains the things I'd been beating my head against the wall on !!!! 
Thank you David for putting the time, research, experience, and dedication to helping others save ourselves from ourselves.
Absolutely well done.
In case of fire this is one of the books to grab as you leave the building !!
Thanks again,
Jim


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## mksj (May 20, 2021)

I also have a copy of David's "Introduction to Indexable Tooling for the Metal Lathe" and just got through reading it. I was very impressed, wish a book like this had been available when I started to use indexable carbide tooling. It is clearly and concisely written, and well cross referenced between sections with great recommendations on tooling/inserts.  It is a fantastic starting point for those getting into indexable carbide or never understood the differences and just stick with the same old thing. One thing that David has pointed out is each lathe will be different as to what works best and the importance of understanding the speeds, feeds and DOC for different materials for a specific carbide insert. This was proabably one of my biggest first mistakes is I was too conservative with my speeds and feeds, and the surface finish suffered in some materials. There are also some excellent videos which show how the tooling type, insert used and cutting parameters effect the cutting performance, two very nice videos (of many) discussing cutting performance and chip breaking are below.

Also want to thank David for all his contributions to the HM forum and helping others, as well as his hard work and long hours in putting this book together.


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## Aukai (May 20, 2021)

Big time yes


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## riversidedan (May 21, 2021)

$59 for a paper back???!!!!!!!  holyrabafrabitz!!!!!!  dont about anyone here  but you could prolly learn more by actually playing with tool bits like " on the job training.


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## Jake P (May 21, 2021)

riversidedan said:


> $59 for a paper back???!!!!!!!  holyrabafrabitz!!!!!!


That was my first thought too, $59!!!!!!!!

However, everything we purchase falls into the "economy of scale" equation.

I don't know how many of these books David will be able to sell, it's not a big market.  And I don't know what his share is on each copy sold.

But I can say that I would be surprised if the effort that it took to create this resource can be fully paid back on the volume that will likely be sold.
I sincerely hope he makes some nice coin for the effort!
Just my take.

I can tell you that I've had mine for about a week.  Haven't even received my lathe yet!  But I've already learned enough (and I'm not even halfway through it yet) that I'm sure I will save, at the very least, the cost of the book by not making poorly informed purchases.



riversidedan said:


> but you could prolly learn more by actually playing with tool bits like " on the job training.



OJT can be expensive when you are your own employer


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## mikey (May 21, 2021)

riversidedan said:


> $59 for a paper back???!!!!!!!  holyrabafrabitz!!!!!!  dont about anyone here  but you could prolly learn more by actually playing with tool bits like " on the job training.



I have not seen David's book yet but I have some idea of the work it takes to assemble a fund of knowledge that book represents and his price is more than fair. Personally, I suspect he did it as a service to the hobby more than anything else. It is also my opinion that you can learn this stuff on your own ... maybe ... but it will take you a lot longer to do it. If I was a new guy starting out in this hobby, I would buy David's book and be way, way ahead of the game.


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## vtcnc (May 21, 2021)

riversidedan said:


> $59 for a paper back???!!!!!!!  holyrabafrabitz!!!!!!  dont about anyone here  but you could prolly learn more by actually playing with tool bits like " on the job training.


Several years ago I co-authored a self-published workbook on a training methodology utilized during WWII (think: what was behind the war production effort) and how that program is still in use today with a couple of well known companies. Toyota is the prominent one, but the program was exported to Japan by a couple of the wartime officers and no less by General MacArthur's occupation office in Japan to revitalize Japanese industry.

You will likely learn more by doing, but _acquiring knowledge_ is the best first step. When you learn by doing without any prior knowledge, you are likely going to make some expensive mistakes, likely going to develop some bad habits that you are completely unaware of and your success will largely be based on average skill and quite a bit of luck (read: industry knowledge that you are unaware of - yet works in your favor) that is built into the products by the industry.


mikey said:


> I have not seen David's book yet but I have some idea of the work it takes to assemble a fund of knowledge that book represents and his price is more than fair. Personally, I suspect he did it as a service to the hobby more than anything else. It is also my opinion that you can learn this stuff on your own ... maybe ... but it will take you a lot longer to do it. If I was a new guy starting out in this hobby, I would buy David's book and be way, way ahead of the game.


Self-publishing is not a get rich quick scheme. I spent a week at the National Archives in Maryland, another week at the Case Western Reserve Library in Cleveland and countless hours researching a topic that became a labor of love. I'm better for it, but I lost money.


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## mikey (May 21, 2021)

vtcnc said:


> You will likely learn more by doing, but _acquiring knowledge_ is the best first step. When you learn by doing without any prior knowledge, you are likely going to make some expensive mistakes, likely going to develop some bad habits that you are completely unaware of and your success will largely be based on average skill and quite a bit of luck (read: industry knowledge that you are unaware of) that is built into the products by the industry.



Very well said, Bryan. Having been through this exact process with boring bars, I know how obscenely expensive it can get while researching how carbide tooling works. I also know that it isn't that easy to figure out how to use those tools and bring the cutting process under control - not by luck - I mean control. If a book can enable you to leapfrog the very slow, painful and expensive process of learning to use carbide tooling, it will make you a better machinist while saving you money. 

I look forward to reading this book soon.


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## Janderso (May 21, 2021)

Beckerkumm said:


> Brad Pitt playing David Best isn't as far off as Tom cruise playing Jack Reacher.  David is the Lee Child of the metal set.  Dave


Oh well done!
I got into Lee Child and Jack Reacher about ten years ago. Read them all.
Now I’m back to dry history.


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## Rifleman1384 (May 21, 2021)

I have found the book to be very helpful, it's over 100 pages with plenty of photos. The explanations provided are useful when deciding what you want verses what you need when starting unless you have already made up your mind to get everything on the front end. I think David sharing what did and what did not work has and will save much more that the cost. I do prefer to purchase better quality tooling if I can instead of buying something to get by and upgrading later. While learning if you have good tooling I think it's easier "read the chips" in order to have things work correctly or at least understand why you are getting the results you are. JMHO.

Thanks again David for all the work put into this.

Steve


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## Janderso (May 21, 2021)

I just watched the videos on 6’s and C’s.
Then I walked out to my chip pan. All the aluminum is in a birds nest design.
Some of the steel is in long beautiful braids. Some are looking good. Must have got lucky.
The NY CNC video is good except I couldn’t get past that spinning four jaw chuck and long sleeves.
I kind of lost focus on chip development, and went for finish.
Time to learn more about carbide tooling and speeds and feeds.
I’ve also noticed my parts are getting too hot.
I fly by the seat of my pants. 
So much to learn,
Say, maybe I’ll buy David’s book.


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## wachuko (Nov 12, 2021)

I can use all the help that I can get... let me order the book...


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## Cloudancer (Nov 12, 2021)

wachuko said:


> I can use all the help that I can get... let me order the book...


One more purchase here.  A small donation to his next tool fund .


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## Karl A (Jan 16, 2022)

I received the book yeaterday.

I am not among the target readership, being that I have a small lathe -- a Sherline. The recommended tools in the book are generally too large for my lathe, but reading the book helped me to better understand the tool holders and inserts that Sherline sells -- why they sell what they sell on how to use them.

There appears to be a good correspondence between the book's recommendation and the smaller (3/8-inch shank) toolholders that Sherline sells.

Reading about neutral hand toolholders raised a question in my mind: Compared to the right hand and left hand toolholders, do the neutral hand toolholders produce a better finish -- being that they have a positive side cutting edge angle?

Karl A


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## davidpbest (Jan 16, 2022)

Karl A said:


> I received the book yeaterday.
> 
> I am not among the target readership, being that I have a small lathe -- a Sherline. The recommended tools in the book are generally too large for my lathe, but reading the book helped me to better understand the tool holders and inserts that Sherline sells -- why they sell what they sell on how to use them.
> 
> ...


You are correct that the specific tool recommendations in the book are for medium sized (10-14") lathes.  There are indeed smaller 3/8" and maybe even some 1/4" shank tools that are equivalent to those recommended in the book.  

I just looked at the Sherline indexable tool offerings, and the specs are all for positive inserts C_*P*_MT, D*P*MT, etc. which have an 11° relief angle and a 0.250" I.C. and appear to be industry standard. Their turning/facing toolholders are not sufficiently specified to know precisely if they are neutral or positive rake, and the lack of industry standard nomenclature suggests to me that the Sherline toolholders are proprietary. 

For the Rhombus (80°) CPMT21.5 type inserts Sherline sells, the industry standard turning/facing toolholders would be designated SCLP such as the 3/8" square shank Kennametal _*1095594*_ (right hand) and *1095686 *(left hand), both of which mount the insert at a positive 5° rake angle. So it's likely the Sherline toolholders mount the CPMT inserts at a positive rake also. Below is the drawing for the Kennametal equivalent toolholder - you can clearly see the positive rake mounting. The positive rake puts less demand on the required HP of the machine and should be freer cutting than a neutral rake holder which is probably why Sherline chose this geometry and positive rake insert type.



That said, quality of finish will have a lot to do with the specific insert, nose radius, etc.  The Sherline inserts are CPMT21.51 with a 0.016" nose radius which is why* they spec* a minimum depth of cut of 0.004".  Sherline says this about their inserts:  
"Carbide cutters give good finishes on hard-to-machine materials such as cold-rolled steel. They will also work on aluminum, brass, or leaded steels, and will last practically forever. However, the best finishes on those materials are still achieved with a good, *sharp* high-speed steel tool."​For the sharpest insert cutting edge you'd want a CP*G*T insert rather than a CP*M*T which Sherline doesn't offer, hence their admonition about using HSS on softer materials. The difference between the two types is covered on page 23 in the book and relates to the tolerance. The "G" tolerance is the most constrained and the inserts are typically ground to meet that tolerance spec, and thus will have a sharp (rather than blunt) cutting edge. The _*Iscar 5510088*_ would be an excellent CPGT21.50 (0.004" nose radius) insert for semi- and fine-finishing turning with a wide variety of materials including aluminum. And because of the smaller nose radius, minimum depth of cut would also be less - perhaps as low as 0.0015".

Hope this helps.

David Best


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## akjeff (Jan 16, 2022)

I've not read David's book yet, but intend to order a copy. If the book does nothing more than save the reader from ordering just one wrong 10-pack of inserts, it's basically paid for itself. Plus, I love reading technical type stuff, and don't believe one can ever learn too much.


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## Karl A (Jan 16, 2022)

davidpbest said:


> You are correct that the specific tool recommendations in the book are for medium sized (10-14") lathes.  There are indeed smaller 3/8" and maybe even some 1/4" shank tools that are equivalent to those recommended in the book.
> 
> I just looked at the Sherline indexable tool offerings, and the specs are all for positive inserts C_*P*_MT, D*P*MT, etc. which have an 11° relief angle and a 0.250" I.C. and appear to be industry standard. Their turning/facing toolholders are not sufficiently specified to know precisely if they are neutral or positive rake, and the lack of industry standard nomenclature suggests to me that the Sherline toolholders are proprietary.
> 
> ...


Yes, it helps.

I have the Sherline 55° diamond-style right-hand and left-hand toolholders. I have not read any statement by Sherline that the inserts mount with a positive rake. From using squares to look for an angle, I concluded that the inserts do NOT mount with a positive rake angle.

I looked at the cutting edges of the of my DPMT 21.51 inserts from Sherline, using a 7x loupe. The edges appeared surprisingly rough.

Thank you for the 80° rhombus-style toolholders and insert recommendations for Sherline lathes.


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## mikey (Jan 16, 2022)

Sherline seems to favor the 55 degree inserts over the 80 degree rhombus for most of their tools to enhance access to shoulders. I'm not sure this is a valid choice because clearance is clearance and both 55 and 80 degree inserts give you that clearance, not to mention the increased strength of the 80 degree insert. 

I think Sherline is relying on the positive rake geometry of the inserts they sell instead of machining in a rake in the insert holder pocket. They used to sell Valenite inserts but I'm not sure what they're using now. Ever since Joe Martin died, I have  been less impressed with Sherline.

I own 3/8" SCLCR tool holders from Iscar and Seco and have used them on the Sherline lathe. They work but require you to use finishing inserts and smaller nose radii so pay attention to the inserts you buy. Finishing inserts have a much smaller gap between the cutting edge and the contour of the chip breaker; they are more fragile than roughing inserts but require less horsepower to cut. The insert I use most on the Sherline have the AK chipbreaker for aluminum; these work well on aluminum but also work on steel and stainless, although the edge doesn't hold up as well. 

Personally, I think inserts on a Sherline don't make a lot of sense. If your only lathe is a Sherline and you have to cut higher carbon steels or have a work-hardened piece of 304 SS then okay, you gotta do what you gotta do, but for the vast majority of the work a Sherline lathe is called upon to do HSS is a far better choice. You have to remember that the Sherline motor only has *0.08 HP* so it cannot take heavy cuts with an insert; it just doesn't have the power or rigidity an insert requires. Do inserts work on this lathe? Yes, they do, but your choice of inserts is critical. In particular, pay attention to the nose radius as David points out. Sherline's inserts have a 0.0015" nose radius which is fine on a larger lathe; for the Sherline, a 0.004" NR is a better choice for accuracy.

*Just keep in mind that a sharp, well-ground HSS tool with a thoughtfully designed tip geometry will vastly outperform a carbide tool on this lathe*. It will rough far deeper, size more accurately, finish finer and will cut what you dial in. Of this, I am absolutely sure. HSS tools are also much cheaper. A good tool will last for over a decade without requiring a re-grind and will remain accurate over that time. If you cannot yet grind a good tool then I suggest that you learn to do it. It is, by far, the best investment you can make for your lathe.


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## davidpbest (Jan 16, 2022)

Karl A said:


> Yes, it helps.
> 
> I have the Sherline 55° diamond-style right-hand and left-hand toolholders. I have not read any statement by Sherline that the inserts mount with a positive rake. From using squares to look for an angle, I concluded that the inserts do NOT mount with a positive rake angle.
> 
> ...


The inserts Sherline lists for your setup are for positive rake toolholders.   D*P*MT. Of course it is entirely possible that their toolholders (being proprietary to Sherline) have some bastardized rake configuration - Sherline does not publish the rake spec for their turning/facing toolholders. DPMT type (positive) inserts are typically used in boring bars rather than turning/facing tools because they provide substantially more relief angle (see page 76 in the book). Most turning/facing toolholders for the 55° inserts are for DCMT inserts which have a 7° relief angle and are intended to be used with a neutral rake toolholders. So it could be that Sherline decided to "standardize" on the DPMT insert primarily for boring bar reasons, but their turning/facing toolholders for that insert are neutral rake.




The "M" designation in the insert specification is a loose tolerance and I'm certain this insert is right out of the mold and has not been ground to a sharp cutting edge.  So I'm not at all surprised by your comment about the rough cutting edge.  If you want an insert for your Sherline toolholders with a ground cutting edge that is sharp, you'd be looking for a DPGT21.5 type.  Several manufacturers make them.  With and 11° relief angle, even if the insert is mounted in a neutral toolholder, it should perform well - assuming your Sherline toolholder pockets are indeed compatible with industry standard DPMT21.5 inserts. 

Here are some alternative DPGT21.5 inserts to consider with 0.004" nose radius:



			https://www.mscdirect.com/browse/tnpla/01046127?affiliate_id=141648&click_id=3842462382&cid=af_q218&clickId=3842462382
		


This version is specifically graded for softer materials like aluminum:



			https://www.mscdirect.com/product/details/15592983
		


Here is one example on eBay, although these have a larger (0.016") nose radius - they look genuine Kennametal to me, but who knows?:  









						8 pcs.  DPGT21.51HP K313 KENNAMETAL INSERT (loc I16)  | eBay
					

Find many great new & used options and get the best deals for 8 pcs.  DPGT21.51HP K313 KENNAMETAL INSERT (loc I16) at the best online prices at eBay! Free shipping for many products!



					www.ebay.com
				




Alternatively, you could try a DCGT insert on the assumption that your Sherline toolholders are indeed neutral rake.   This would be an inexpensive way to find out:  









						DCGT 21.5VFR-J10 J740 | Tungaloy | Insert | Sold Individually | DCGT070200FR  | eBay
					

Find many great new & used options and get the best deals for DCGT 21.5VFR-J10 J740 | Tungaloy | Insert | Sold Individually | DCGT070200FR at the best online prices at eBay! Free shipping for many products!



					www.ebay.com
				




You could of course outfit yourself with the 80° style toolholders referenced in my prior post here, or use HSS.

David


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## davidpbest (Jan 16, 2022)

Keep in mind that I have zero experience with the Sherline.  @mikey will have more "field tested" thoughts about what works best with that machine.


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## Karl A (Jan 17, 2022)

I appreciate the detailed replies and recommendations.

I purchased the Sherline 55°-rhombus-style carbide-insert toolholders two months after I bought the lathe. Two months after that, I wrote down two statements that Mikey made in 2015 in a thread here on Hobby Machinist:
"... buy a QCTP and use 3/8" HSS tooling instead of 1/4". You will rough more deeply, size more accurately, finish finer, chatter less, and save money with HSS. The Sherline lathe responds very well to tool geometry intended to reduce cutting forces."
"If you insist on carbide, I would go with SCLCR/L toolholders that take CCMT/CCGT inserts. ..."
These statements are mirrored above.

I appreciate the agreement between Mikey and David on recommending 0.004-inch nose radius on carbide inserts for Sherline lathes.

I am nearly ready to begin grinding steel keystock, before grinding HSS blanks.

Having the right-hand carbide-insert toolholder has helped me get to this point.

To some degree, carbide inserts have been a distraction. I would be further along on grinding HSS tools if I had spent less time learning about carbide inserts. Knowing about them will probably be good in the long run.

I ordered one DCGT 21.5VFR-J10 J740 insert. I am curious to see how well it fits and works on a Sherline toolholder.

I took photos of the left-hand Sherline 55° toolholder and its insert -- to show that the insert appears to not be mounted with a positive rake angle, and to show the roughness and dullness of the cutting edge of the insert.





Karl


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## davidpbest (Jan 17, 2022)

That tool holder is clearly neutral rake.  A DCGT or DCMT insert should work if the pocket is industry standard.  IMO the insert in your photo is inappropriate for a lathe like a Sherline - it’s straight out of the mold, and the nose radius is excessive.  But what do I know - I’ve never used a Sherline.   What I can say is that I wouldn’t attempt to use that insert on my 1340 with aluminum - it would tear rather than cut.  It’s probably swell on cast iron.  

The DCGT 21.5VFR-J10 J740 you ordered should work with your left handed tool holder, but not the right handed version since there are only two cutting edges.  But at least you’ll know if it fits and whether a 4-edged version of a DCGT will work with your right handed tool holder.  Keep us posted.


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## mikey (Jan 17, 2022)

Karl A said:


> I am nearly ready to begin grinding steel keystock, before grinding HSS blanks. Having the right-hand carbide-insert toolholder has helped me get to this point. To some degree, carbide inserts have been a distraction. I would be further along on grinding HSS tools if I had spent less time learning about carbide inserts. Knowing about them will probably be good in the long run.



A lot of us start out with carbide just so we can learn to use the lathe. Nothing wrong with that, and the knowledge you gain from your experience with inserts is always valuable. One day, you may step up to a larger lathe and everything you learn on a Sherline lathe will transfer, including your knowledge about carbide insert geometry. I honestly believe that a hobby guy should know how to use all kinds of tooling so he can use the right tool for the job at hand. Elitism in tools is foolish; competence is not. 

With that said, if you approach HSS tool grinding and appreciation for tool geometry in the same way you did for inserts then you will realize the potential of your lathe very quickly because the key to unlocking this lathe is tool geometry.

My apologies to David for derailing his thread. I do not wish to detract from the comments on his book and will be writing my own review of it soon.


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## bigolbeast (Jan 21, 2022)

Just ordered mine


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## Karl A (Jan 21, 2022)

davidpbest said:


> That tool holder is clearly neutral rake.  A DCGT or DCMT insert should work if the pocket is industry standard.  IMO the insert in your photo is inappropriate for a lathe like a Sherline - it’s straight out of the mold, and the nose radius is excessive.  But what do I know - I’ve never used a Sherline.   What I can say is that I wouldn’t attempt to use that insert on my 1340 with aluminum - it would tear rather than cut.  It’s probably swell on cast iron.
> 
> The DCGT 21.5VFR-J10 J740 you ordered should work with your left handed tool holder, but not the right handed version since there are only two cutting edges.  But at least you’ll know if it fits and whether a 4-edged version of a DCGT will work with your right handed tool holder.  Keep us posted.


The DCGT 21.5VFR-J10 J740 insert arrived. I installed it on the right handed tool holder, and used it to turn down 1144 steel and a bronze-aluminum bushing.  Here are photos that compare the DCGT insert on the right-handed tool holder and the Sherline DPMT insert on the left-handed tool holder. In the photos, the left-handed tool holder is on the left.
	

		
			
		

		
	








Note: I damaged the tip on the trial insert. The nose radius was 0.001 inch. The finish was poor during the finishing pass (2500 rpm spindle, 0.0003 inch / spindle revolution, 0.0005 depth of cut.) on two 1 1/8-inch diameter bronze-aluminum bushings.


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## Karl A (Jan 21, 2022)

Here is another photo. This shows the holders and inserts from the underside. The experimental insert is on the right side.


The experimental insert DCGT overhangs the tool holder more than the Sherline insert DPMT.  I think that the extra overhang is due to experimental insert having a smaller clearance angle: 7° versus 11°. The inserts are the same size (0.25-inch inscribed circle) on top and have the same thickness (3/32-inch). The smaller clearance angle gives the experimental insert a larger underside. I conclude that the experimental insert does not fit the tool holder well.


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## davidpbest (Jan 22, 2022)

Perhaps we should take this off thread to a DM?


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## davidpbest (Jan 22, 2022)

Karl A said:


> Here is another photo. This shows the holders and inserts from the underside. The experimental insert is on the right side.
> View attachment 393234
> 
> The experimental insert DCGT overhangs the tool holder more than the Sherline insert DPMT.  I think that the extra overhang is due to experimental insert having a smaller clearance angle: 7° versus 11°. The inserts are the same size (0.25-inch inscribed circle) on top and have the same thickness (3/32-inch). The smaller clearance angle gives the experimental insert a larger underside. I conclude that the experimental insert does not fit the tool holder well.


As I suspected, the Sherline indexable tooolholder is proprietary and doesn’t conform to industry specs. Good thing the test insert was $8.00.  Now you know. Lets take this to another thread please.


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## Aukai (Jan 22, 2022)

Possibly you could start this thread in the Sherline section, so it's not lost to everyone?


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## Karl A (Jan 22, 2022)

I don't think that the result of the experiment means that the Sherline toolholder does not conform to industry specs. l I think that the result suggests that an insert with a smaller clearance angle will be large on a toolholder that is designed for an insert with a larger clearance angle. If that is correct, then the result is applicable generally.

If the DCGT insert had fit well on the Sherline holder intended for a DPMT insert, then I think that would have been good news to share on Sherline forums.


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## akjeff (Jan 26, 2022)

Just received my copy today, and you can color me impressed; very informative book. Outstanding work, David!


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