Suggest index toolholder set please

[G-ManBart]

@G-ManBart, I’d like to indulge your patience and explore a nuanced selection of cutting tools that I don’t understand well. This is drawing on your comment: “For that machine I would start out with something positive rake first.”

Quick recap, the lathe is an Enco 13x40 with Phase II BXA quick change. Additional info is that it is 1.5 HP, single phase and weighs in at a claimed ~1100 pounds w/o stand.

I am imagining a continuum of lathe properties where some range of these machines can be binned as “start with positive rake” and others as “use zero or negative rake”. In that continuum, which properties are of key importance? Is it HP and weight? And, of course, where does my machine sit in that space?

Next, and again in the context of my machine. Up to this time I have been using hand ground HSS. I have not found rake specified for inserts in the manner it is defined for ground HSS . Rake must be built into the chip breaker in some fashion? Can you educate me here? I see clearance or relief angle on the insert and that you suggest “C” which is a 7deg relief. The inserts I bought are “N”, or 0deg relief. I have never used 0deg relief before, is this an error with my machine?

Here are links I have used in this note:

Insert Shape Selection

Carbide Insert Shape Selection

www.carbidedepot.com

Insert Designation Chart - provides ANSI and ISO designation code definitions for carbide insert shapes, relief angles, tolerances, chipbreaker codes, hole types, size values, thickness values, radius values, wiper lead angle, wiper clearance angle,

Carbide Insert Designation Chart

www.carbidedepot.com

Toolholder ANSI Designation Chart - provides ANSI and ISO designation code definitions for lathe toolholders for the insert holding type, insert shape, toolholder style, insert relief angle, direction, shank size, insert inscribed circle (IC), and

Toolholder ANSI Designation Chart

www.carbidedepot.com

The short version is that negative rake tools are stronger, but take more HP and rigidity to run well. Some, like the WMNG can be flipped because they have parallel sides, so you get twice the life out of them, which is a nice bonus, but probably shouldn't be a primary consideration for most people.

Your lathe is sort of in the middle for size/power, so it should be okay with negative rake inserts in some situations, but maybe not others. As an example, take the WMNG inserts you mentioned. A common size would be 432 or 332 inserts (same profile, different sizes) and those have a tip radius of 1/32, so .03125". The normal rule is that you want a DOC to be equal to the tip radius (1/2 is about the minimum). The negative rake increases tool pressure (work is coming down on it) and you're starting out at a pretty deep cut for most hobby machines....that can lead to chatter. Backing off on the DOC can lead to poor surface finishes because the tool is bouncing or smearing and isn't stabilized in the cut. The first thing I would try there would be a 431/331 insert with a 1/64 radius to see if it helps (and having both tip radius is probably smart anyway).

I use negative rake tools (CNMG) on my 13" lathe for roughing, and it's fine, but if I want to get a really nice finish I switch to something positive rake like the CCMT. I went with CNMG for that because they've very strong, extremely common and you can usually find deals on them even really good brand name inserts if you keep an eye on the folks selling inserts on eBay from business closeouts. I can often get a pretty decent finish by playing around with speeds and feeds, but it's definitely just okay, never great.

To add visuals, I took a picture of an MCLN tool that uses CNMG inserts (negative rake) and added a line showing how the top is angled down towards the front...there's your negative rake. I did the same with an SCLC tool that uses CCMT inserts with a positive rake. The positive rake means the CCMT insert has to be tapered from top to bottom for clearance, so they can't be flipped.

As far as tool and holder size, the standard BXA 250-201 and 202 will hold 5/8" tools. The 250-201-XL and 250-202-XL will hold 3/4" tools. The difference between 201 and 202 is that 202 has a grove in the bottom for using round tools like boring bars.

 

[pontiac428]

I'm curious about where negative rake's usefulness starts. I could only run neutral rake on my Atlas, and the big Nardini is pushing 1" tools that are exclusively negative rake. That's two extremes. So for the OP, with a 13" lathe and 1.5 hp, I don't know how to answer the question. The reference material tends to say that at a certain point, negative rake rules, but what point is that? The OP has a hobby lathe on the larger side, and I consider commercial capital equipment starting at 14", but many hobbyists have 10-12 lathes at or below 2 hp. Where in that range should people give up trying to run negative rake tools? Sure, we can manipulate DOC, feeds, and speeds, but in general when is it better to choose zero rake?

 

[davidpbest]

I'm curious about where negative rake's usefulness starts. I could only run neutral rake on my Atlas, and the big Nardini is pushing 1" tools that are exclusively negative rake. That's two extremes. So for the OP, with a 13" lathe and 1.5 hp, I don't know how to answer the question. The reference material tends to say that at a certain point, negative rake rules, but what point is that? The OP has a hobby lathe on the larger side, and I consider commercial capital equipment starting at 14", but many hobbyists have 10-12 lathes at or below 2 hp. Where in that range should people give up trying to run negative rake tools? Sure, we can manipulate DOC, feeds, and speeds, but in general when is it better to choose zero rake?

I own a PM-1340GT lathe that has been modified with a 3-phase vector rated 2 HP Baldor motor and VFD controls (build log is here). So the HP and specifically the torque is substantially better than the stock motor. With this configuration, I can run negative rake tooling just fine, but hitting tolerances better than ±0.002" is very challenging because of the sponginess of the compound. Even retracting the QCTP back directly over the center of the compound, there was still enough deflection to preclude hitting tighter tolerances with negative toolinng as well as successfully parting off difficult materials. To gain more rigidity, I replaced the compound with a solid tool post (discussed here), and since then have had no problems parting, and can hit tolerances of ±0.001 with negative rake tooling (and better with neutral rake tooling). Generally, I run negative rake tooling only for deep rough cutting operations exclusively and have inserts on hand that are properly graded for the material being machined.

The specific insert grade, chipbreaker geometry, and tolerance spec also impact things. A negative insert type graded for cast iron has a blunt cutting edge, whereas one graded for aluminum will have ground edges and is more free cutting producing less tool pressure. And nose radius also impacts the minimum depth of cut without the tool intermittently cycling between cutting-scraping-cutting.

Rigidity is king when it comes to this topic. I have friends with 1.5HP 12" swing lathes that can run Trigon (negative rake) tooling just fine, but with sloppy tolerances. Obviously, negative rake tooling increases tool pressure substantially, and depending on the diameter and material, the part being machined can deflect when a follow-rest isn't employed.

So there are a number of factors here to consider including the HP and torque, but also the tool mounting setup, the rigidity of the compound arrangement, as well as part deflection.

 

[AllenV]

@G-ManBart and @davidpbest , Thank you for such detailed, thoughtful, and educational responses. And @pontiac428 , thank you for restating my question re: lathe size and tooling in much more succinct fashion.

Bottom line is that all this will raise my game significantly. I know I am not getting all that I can out of my lathe. My hope is that shifting over to ceramic inserts will provide the quantifiable and repeatable cutting tool geometry that is lacking in my hand grinding. I am already seeing evidence of that in your posts covering insert selection as a function of the job to be done and the lathe available.

As a kid I used my Dad's Clausing-Colchester but did not go deeply into optimal tool shapes for the job. I just ground tooling per his instruction. In retrospect that was a missed opportunity as he had great depth of knowledge in these areas. The Hobby-Machinist forum has proven a hugely valuable resource and I thank you all.

So, reporting back on choices made. This discussion, combined with a few other posts, has made clear that for my lathe the CCMT and DCMT insert shapes are a great stating point. My false start with the WNMG may prove useful or may become something of a hanger-queen. Also, I have seen several positive reports of using Shars index tool holders. Now, I know sets are frowned upon as leading to purchase of too many items. However I did find and purchase a Shars set that focuses on CCMT and DCMT and tosses in a threading and a cut-off tool. I went ahead and picked that up.

5/8" Indexable Carbide Turning Tool Set

Shars Tool

www.shars.com

Finally, here is a link to my Dad's Clausing. Ultimately I decided that I did not want a new hobby of classic lathe restoration and ownership. I'll stay with the Enco and we are in-process of rehoming the Clausing.

Clausing Colchester Info Request

Greetings, I have inherited my Father's wonderful Clausing-Colchester 13x36 lathe. See the attached image. This has been in his workshop in the San Diego area since the late '60s. Before that I understand it was in the tool and die shop at the aerospace company where he worked. My request is...

www.hobby-machinist.com

 

[G-ManBart]

That set will be a really good start...I think I have four of those same holders and maybe five. I use a different parting tool, but the included style should work nicely.

Nice Clausing...it'll make someone very happy!

 

[GeneT45]

I would encourage you to actually use your "false start" with WNMG before condemning them. Nothing wrong with CCMT either, though I would definitely reserve DCMT for those times when you actually need that acute angle. Again, I'd discourage you from buying sets...

GsT

 

[AllenV]

I very much plan to use it. All three insert shapes will be explored with the intent of understanding what works well on my machine.

 

[AllenV]

Time now for a session of learning from my mistake.

The first holder I went shopping for was SWLC to fit a Trigon shape at -5 deg for RH facing. It was desired to have a 1/2" shank. What I bought was the Mitsubishi SWLCR082. Below is the data sheet on that holder.

I then rushed off and bought inserts, WNMG332GX

 

[AllenV]

Continuing from above...Do you see the error?

Yep, I bought the wrong inserts. The WNMG332 is a 3/8" inscribed circle.

The data sheet on the holder clearly says the -082 holder needs size 21.5 or a 1/4" inscribed circle.

It also seems to say that WCGT or WCMT inserts are needed. Both of these have 7deg relief angle. So no "N" or 0 deg allowed.

So I went to e-bay and bought some WCMT 21.5

I looked around a bit for 0 deg "N" in the 21.5 size, but did not find any.

Here is a question, Is the data sheet listing of just WCGT and WCMT inclusive? If I find WNMT would it be okay to use? I kind of think the 1/2 shank may rule out "N".

I suppose I might find 0 deg to fit the Shars SCLC with the 5/8 shank and 32.5 insert size. I would like to try the 0 deg

 

[Ischgl99]

You can only use the WNxx inserts in a negative insert holder. What you have is for positive inserts, which is probably better for your size lathe, so I would start with that and then get the negative tool holder after you have some more experience. Most of us have probably made these mistakes, I know I did and why I have a bunch of negative inserts I am using for roughing lol

Don’t worry about it, but don’t make impulsive purchases. The negative holders for smaller inserts are not as common, so it might be hard to find something, so it would probably be best to take it slow and try the positive inserts first and only move to negative later.