Carbide insert tests

[kmanuele]

I had some TCMT and CCMT tools lying around, largely unused till now. I tested them on a piece of 1.5" 1045.

No real questions here. Just newbie observations. Comments welcome, of course.

Using the speed/feed tables, 1045 needs about 800 SFM with carbide. So, at 1.5" - 2100 RPM, which exceeds the max speed of my lathe, so I set RPM to 1800. Feed rate is 0.0025"/rev. Even at that feed rate, things happened really fast. Are there lathes that actually spin near 6000 RPM for a 0.5" piece of stock?

I ran various DOCs, up to 0.1"+. The lathe (PM1130) didn't struggle at all at 0.1", and probably could go deeper.

Images are TCMT at left, CCMT center. DOC was 0.030 here. I was surprised at TCMT finish quality (appearance-wise). That finish was pretty consistent at most DOC, though randomly it would go south - badly. Not sure why. Wondering if a previous cut had work-hardened the surface -- and a deeper DOC was required?

CCMT insert performance was similar but seemed to have a lot of light surface tearing even with a 'good' finish.

Blue chips in most cases but bad chip management -- bird nests, long streamers, etc. I could get good chip breaking only at certain DOCs, with no apparent pattern.

As the diameter got down below 1", the reduction in surface speed (given lathe max RPM) seemed to affect the finish.

Finally, I tried one of my HSS tools at higher speeds/feeds just to see. Tool tip became annealed about half-way in, then quickly wore off.

Might do a similar test on 1215, though will probably start using more carbide -- at least for roughing cuts.

 

[benmychree]

800 SFPM seems very high to me, and the feeds too slow, that is why you got the birds nest chips, and obviously you were running the HSS way too fast, it should not be running more than about 100 FPM, and in my opinion, the carbide should be more like about 400 FPM, and if they are made of Chineseium, likely less than that. Those negative rake carbide tools like more feed to curl and break the chips and are not good for fine finish cuts or shallow depth of cuts. I use mostly triangular positive rake inserts for most work and negative rake tools for rough work and interrupted cuts.

 

[Chewy]

The speeds and feeds are for real industrial machines. They are designed to maximize cutting and usually have a DOC that far exceeds your machine. I use carbide all the time and rarely exceed 800 RPM and usually with shallow DOC and a slow feed rate. You will need to experiment with your machine at different speeds and feeds and angles of cut to see what works best. Don't be surprised if the finish is not great. Some times you will need to switch to HSS for finish cuts. I shoot for around 100 FPM which is what HSS usually wants, then bump up the speed by 25-50% de[pending on material. That is just a starting guide. You can always work slower or faster. Carbide is not for the hobbyist, even though most everybody uses it. I use it all the time. The Chineseum inserts dull quickly, so on the finish pass, turn the insert around.
And surface finish will change as diameter changes. A CNC machine will be set to adjust itself automatically. Also carbide does not like a very shallow DOC. If you need to take .001-2 off to reach dimension, don't be surprised it doesn't cut at all. Then you decide to increase the depth and it over cuts. Blondihacks does a good explanation.

https://www.bing.com/videos/search?...075D07F666902AF48469075D07F666902AF&FORM=VIRE

 

[kmanuele]

The speeds and feeds are for real industrial machines. They are designed to maximize cutting and usually have a DOC that far exceeds your machine. I use carbide all the time and rarely exceed 800 RPM and usually with shallow DOC and a slow feed rate. You will need to experiment with your machine at different speeds and feeds and angles of cut to see what works best. Don't be surprised if the finish is not great. Some times you will need to switch to HSS for finish cuts. I shoot for around 100 FPM which is what HSS usually wants, then bump up the speed by 25-50% de[pending on material. That is just a starting guide. You can always work slower or faster. Carbide is not for the hobbyist, even though most everybody uses it. I use it all the time. The Chineseum inserts dull quickly, so on the finish pass, turn the insert around.
And surface finish will change as diameter changes. A CNC machine will be set to adjust itself automatically. Also carbide does not like a very shallow DOC. If you need to take .001-2 off to reach dimension, don't be surprised it doesn't cut at all. Then you decide to increase the depth and it over cuts. Blondihacks does a good explanation.

https://www.bing.com/videos/search?...075D07F666902AF48469075D07F666902AF&FORM=VIRE

800 SFPM seems very high to me, and the feeds too slow, that is why you got the birds nest chips, and obviously you were running the HSS way too fast, it should not be running more than about 100 FPM, and in my opinion, the carbide should be more like about 400 FPM, and if they are made of Chineseium, likely less than that. Those negative rake carbide tools like more feed to curl and break the chips and are not good for fine finish cuts or shallow depth of cuts. I use mostly triangular positive rake inserts for most work and negative rake tools for rough work and interrupted cuts.

Thanks for the comments, and suggestions.

800 SFPM comes from machinery's handbook for 1045, and understand those values are not practical for my machine -- nor their HSS recommendations either. Was seeing what carbide could do.

Still impressed by how fast and how much material can be removed, and no lube. In some cases, there was actually a small red-hot area at the tip of the tool, and the chips were coming off smoking. Had to remind myself where the fire extinguisher was

It is pretty clear from looking at the insert profiles that they won't cut small DOCs.

Re: HSS, finishing. I often turn the RPM way down, lowest feed rate, and couple thou DOC for a final cleanup pass, with a freshly honed tool. Takes a while, but even works well with 1018 - most of the time.

K

 

[Mitch Alsup]

The speeds and feeds you find in the text books are for industrial scale machines (4,000 pounds and bigger) often with oil or water based lub+coolant flows.

On my 1,000 pound lathe, I typically use 240 and 360 RPMs {Steel, Al, others} with carbide inserts.

For my own personal use I rarely go above 600 RMs, even for drilling with small drill bits (like the tap size for 4-40 at 0.089").