my first part & insert-boring-tool question

[jwmelvin]

I'm pretty new here. I recently bought a used Grizzly 0602 10x22 lathe and yesterday used it to make my first real part. It's an adapter sleeve to mate the tapered shaft of my lower ball joints to an aluminum control arm:


I started with a chunk of hydraulic piston shaft, turned down the body diameter, then parted it off and flipped it around to drill and bore the hole. For the taper, I used the compound and slowly crept up on the right angle by testing the fit. It seems pretty good for what I want (and much better than the ill-fitting, nontapered, dual sleeves that came with the control arm).

I have some tooling that came with my lathe, but didn't have a small boring bar that would fit, and I don't yet have a way of grinding my own tools, so I bought an inexpensive insert boring bar on Amazon. It seems to have worked well, but I'd like to understand it a bit better. For one thing, the insert sits at an angle that appears to create a negative rake:


Should I be putting the cutting edge on the horizontal diameter like usual?

Is this tool wildly inappropriate for what I was doing?

Also, can you help me understand appropriate feeds/speeds?

When boring, I was taking pretty light passes (~0.010" until the finish/spring passes) and, I realize now, pretty slow cutting speed of ~80 sfm (560 rpm).

When turning the body, I was using one of those generic tools with the triangle inserts, going at about the same cutting speed (300 rpm on the 0.75-1.12" diameter) and taking about 0.020" DOC. I believe my feed rate was low, like 0.0025"/rev. I think at some point I also tried taking 0.010" DOC with 0.005"/rev feed. At all times the lathe seemed perfectly happy.* Since I was turning up to a shoulder, I didn't really want to go much faster, but that wasn't too much of an issue. I was using cutting fluid and it smoked plenty but certainly no blue chips.

From my reading today, it seems like I should be running about triple the cutting speed for inserts in steel. My surface finish certainly was't all that good.

I have another one of these to make, so it would be nice to learn something in the process.

* During parting, things were less happy. I was using a HSS tool that seemed kind of sharp but nothing spectacular, and it had more angle on the front edge than I would expect. Initial unhappiness was overcome by lowing the parting tool to be on center. The 0XA tool holder seems way too wimpy to me so will have to be replaced at some point. Things worked out but I'd like better parting operation for sure. This was also running at about 80 sfm to start, and I probably should have sped up the spindle at the end. A variable-speed lathe seems like a better-and-better idea.

Thanks for any advice.
-jason

 

[T Bredehoft]

This may be your first part, but you are certainly not inexperienced with a lathe. good job.

Yeah, the tool has to be cocked so that the "chin" of the insert doesn't drag on the work. Also, there are better inserts for your job, The problem with inserts, you need a whole stockroom full of them to utilize the tooling well.

With high speed tools you can go too fast, but you can't go too slowly. Carbide, on the other hand doesn't work well at slow speeds.
Sometimes we have to make do. A two flute endmill, held in a tool holder will bore a nice hole, but not too deeply.

 

[jwmelvin]

This may be your first part, but you are certainly not inexperienced with a lathe. good job.

Thanks. I learned to machine 15-25 years ago in college and grad school (mechanical engineering) and I had some wonderful instructors. I have fondly remembered them over the years, but truly miss them now. Having started building a home shop, I now realize how amazing our resources were.

Yeah, the tool has to be cocked so that the "chin" of the insert doesn't drag on the work. Also, there are better inserts for your job, The problem with inserts, you need a whole stockroom full of them to utilize the tooling well.

To make sure I understand the terminology, the insert sits at that angle to make the side relief angle? And I guess the top surface of the insert has a feature to effect the rake angles?

What inserts would be more appropriate for what I'm doing?

 

[T Bredehoft]

You are correct in your assumption re: tool position. Your insert looks to be flat top, uncoated, ie., for cast iron.

What inserts would be more appropriate for what I'm doing?

I retired 18 years ago, haven't used carbide since, but many inserts have a top profile that will result in the proper approach angle, I just can't remember the codes. (I no longer have access to the tool crib)

Were I doing that I'd use a HSS tool. Take a 1/2" piece of drill rod, drill a 3/16 hole through it at the end at a 45º angle, put a broken No. 2 center drill in, (either put a set screw in to hold it, or silver solder it in) and grind a cutting edge on it.

 

[jwmelvin]

You are correct in your assumption re: tool position. Your insert looks to be flat top, uncoated, ie., for cast iron.

Here's a better picture of the insert:

I can see that the cutting edges are kind of crude, but that there is some rake built in.

I hear you on HSS. One of my priorities is getting my capabilities for grinding set up. I have a bench-grinder arbor and a motor to run it; just need to work out the mounting. And I plan to build a 2x72 belt grinder.

 

[ttabbal]

2x72 is amazing for HSS tools. You should definitely build one. And read the HSS grinding thread. I think the models are still circulating, so if you want to hold one while you grind, it's a great way to go.

Oh, and make sure to blame @mikey for the grinder.

The part looks pretty good to me, particularly with you being new to that machine. For parting, try one of the carbide tools too. They can be a bit more rigid. With HSS blades, keep them as short as possible. Particularly with smaller setups like ours. Those 1/2" blades just don't have a lot of rigidity. I have better luck when I start with the blade too short and reset it about half way through the cut. It's annoying, but the finish is better.

 

[benmychree]

For carbide insert boring tools, I prefer triangular positive rake tools, especially for finishing, if TPG inserts are used, it gives quite a sharp edge, unlike the negative rake insert pictured. For HSS boring tools, I have used Bokum tools for many years, they come in 3 styles, lead angle boring, flat bottom boring and threading, in both integral shank style and threaded on end style with a separate shank. they are form relieved and are sharpened only on the top. I find them on e bay. Another brand, a "knock off" is Comet.

 

[markba633csi]

JW: Your boring bar was probably intended for larger holes than what you used it for, but at least you got the job done.
I like T Bredehoft's idea about using an endmill. I've also used an old drill bit with a bit of creative grinding as a boring bar
Mark

 

[jwmelvin]

JW: Your boring bar was probably intended for larger holes than what you used it for, but at least you got the job done.

There is a smaller bar in the kit, but since the 10mm diameter bar seemed to fit I figured it was better to use. The taper goes from 16mm (0.630") down to ~13mm (started with 0.5" hole and cut the taper until the angle and large end fit the mating part). Since there was no interference with the boring bar, isn't a larger bar better (they all use the same inserts).

 

[G MORSCH]

Jason:
Looks like you have a great start on your new Hobby Career! My first knowledge of carbide inserts was back in 1970. At first glance, I said to myself, "that can't work!" I changed my mind 5 minutes later after the turret lathe operator took me to school! I haven't looked back since. I use HSS tools only when and where I cannot use a standard tool. I spent 35 years Beta testing new cutting tools, geometries, coatings, and edge preps for Kennametal all over the US. There are so many misunderstandings about carbide that it drives me crazy.... Carbide can't be used for this or that. Most of those conclusions are just plain wrong! Carbide is made in many different varieties from very high hardness used for long tool life and finishing applications to high toughness where speed capabilities are substantially reduced but are very robust and difficult to fracture. Pick up any carbide manufacturers literature and you will typically see the ANSI/ISO designations for each grade of carbide offered. In a range of 1 to 50, carbide hardness will be defined as 05-10 for an example of a hard, wear resistant grade. And 30-45 or higher for a tough, impact resistant grade. I manually thread just about everything from aluminum, 4140, 303, 304, 316, PH stainless to titanium with KC5010 at 75 RPM. At 75 RPM, a 1/4-20 thread is moving at 4.9 SFM. Medium toughness, general purpose inserts are typically rated as 15-25. Toughness is generally obtained by adding greater amounts of Cobalt to the tungsten carbide recipe. A hard grade will typically contain from 5% to 6% Cobalt and a tough, impact resistant grade will contain 9% to 12.5% Cobalt. However, hardness and toughness are also affected by particle size. Sub-micron and 1 or 2 micron particle size mixes are more prone to chipping than larger particle mixes. Being a mechanical engineer, or just mechanically inclined, you can probably understand that the free mean path for crack propagation is much shorter on a fine grain material than a courser grain material. Basically, fine grain materials are harder and more wear resistant and course grain materials resist fracture, again, Cobalt content is the basic indicator of bulk toughness.
The Insert that you show us has a hone on it, which is common and is generally indicated by an "M" in the 3rd position of the insert nomenclature. Simply think of it as "Molded to size" (depending on size of insert, +/-.002 or more) indicating that it will probably not have a sharp edge, just a hone. Honing is common on "M" tolerance inserts and the hone is typically .001 to .002. A hone of this size will not function well at less than .002 IPR feed rate. The tendency will be to rub, burnish, or work harden your parts. The same is true for depth of cut. At a minimum, increase DOC and IPR to exceed the hone levels. When I do finesse work, I try to do it with "G" tolerance inserts. "G" tolerance inserts, 3rd position, indicates Ground tolerance (+/-.001 Typ.) Often, G tolerance inserts will be sharp edged with some exceptions. If the insert is a milling insert, it may not be sharp particularly if it has a CVD coating, but accuracy is required to minimize radial run-out. If the insert is designated as a turning insert and has a PVD coating and a "G" or "C" tolerance, it will more likely have a dead sharp edge. These sharp edged inserts will allow you to adjust size and when adjusted accurately can remove less than .001. To avoid built up edge for fine cuts, continue to use a cutting fluid. I typically use Tap-Magic Protap for everything but aluminum and just apply a small amount with a toothbrush.
There is a lot of tooling out there for cutting off parts. The best performers have a positive topography and a dimple in the middle. The dimple is designed to collapse the chip and make it smaller than the groove width and aid in chip control. The angular style can deflect the blade and affect flatness so stick with a cutoff insert with 5 degrees or less on long/deep cuts.

Best Regards, Gary