# PM-1640TL problems getting reasonable surface finish



## jeremysf (Oct 5, 2021)

I’m having a problem getting good surface finish with my PM-1640TL. I don’t have enough experience to figure out what I’m doing wrong and am looking for ideas or to have my expectations reset. I am assuming based on seeing other PM-1640TL user videos on YouTube that it really should not be very hard to get great results over a wide range of speeds and feeds using carbide inserts and mild steel.







So, in detail, I’m trying to turn 1/2” mild steel with carbide inserts, and I always get some variation of the above picture, where there is inconsistent depth of cut. The chips vary somewhat with the speeds and feeds, but generally speaking are are super tight, regular and curly and bright. I am not really ever able to get them to break and be individual chips, which seems to be the issue maybe?







Things I have tried:

- Depth of cut from 0.001” to 0.040”
- 80 rpm to 1200 rpm
- Fine feed (0.004) through to coarse feed (0.22)
- Different carbide inserts and tool holders (right hand tool, and universal tool)
- High speed steel tool (pre-ground from the retailer and my own grind from blanks, sharp nose radius and large nose radius)
- 3 jaw vs collet chuck
- Tail support vs no tail support
- Two different sources of material
- Coolant vs no coolant
- Adjusting tool height from below center, to on center, to above center
- Tightening the v-belt tension
- Cross slide at 0, 45 and 90 degrees
- Making sure tool holder is square to chuck
- Making sure the tool post is tightened
- Making sure the chuck is tight
- Fixing the VFD frequency to 60hz (disabling the potentiometer speed control in the Hitachi VFD)

The depth of cut variation is like a thou or so. It’s more than just showing spiral tool marks, and it varies wildly. 

The setup appears quite rigid and overkill to my (inexperienced) naked eye.

If I use emory paper to smooth down the result to debug it, it takes like 15 min with 340 grit and I am able to see during that process that some of the “banding” are quite deep grooves (and take forever to remove).

Ideas on what I’m doing wrong?


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## jwmelvin (Oct 5, 2021)

Using something other than 1018/A36 would probably help considerably. Have you tried other materials?


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## jwmelvin (Oct 5, 2021)

Also, what inserts have you tried? Specific inserts make a difference and you may try some intended for aluminum, as they have a much sharper edge. Without seeing a good picture of your HSS tool it’s hard to say much about it.


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## jeremysf (Oct 5, 2021)

Not yet, but ordered a range of different materials from onlinemetals.com to try out.


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## woodchucker (Oct 5, 2021)

So I had a problem last week. I bought some metal from someone here years ago. I tried HSS, with and without a chip breaker, different geometries, then went to cnmg, then wnmg... trying all different speeds and feeds. I had similar but bigger curls. I could not get it to break a chip. I hate curly long strands... dangerous in multiple ways. Especially when they wrap.  I was unsuccessful, I finally decided to use the WNMG and just keep using the crossslide to knock out most of my roughing. then move over and rough.. it worked. But I decided I could not do that for more than one.. So I ordered the DCMT holder that I showed in what did you buy and stated it's problem..   with the HSS, CNMG , WNMG I was taking off small, then bigger, and bigger chips... 

First time with the new DCMT, chips... short small chips. Now to play with how far I can go. I did try to go as fast as it would spin, with a fast rate, and it stopped breaking them, went to curly stringy again.  

Sometimes you just have to keep trying, and not every insert or even HSS geometry will work.
It's hard, to impossible to troubleshoot from our arm chairs the situation without watching it. speeds and feeds are usually close, but sometimes you really have to try different things.

I like blue or straw colored chips. It removes the heat from the metal as much as possible. It also means you are doing well, being efficient.
Pushing a tool is usually good, it doesn't build heat as much. Rubbing builds heat.

Harder metals break chips easier.  Some metals are just plain bendable, so the chip won't break.

BTW the ultimate cheat is to auto feed, and stop the feed every once in a while to break the chip.

As far as your bar showing different looks, to me it looks like the curly is getting in the way, or you are running out of oil.

With coated carbides you can run dry.. give it a try.
Give it a try with constantly wicking more oil.

just keep trying. You'll be learning.. and if all else fails... keep something soft around to punch... not the wife or kids.


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## jeremysf (Oct 5, 2021)

Thank you! Love this community!


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## maspann (Oct 5, 2021)

If that is cold rolled rod, it is difficult to get a consistent surface finish. Try getting some free machining steel bar (12L14) and see what result you get. There are several vendors on Ebay that have small quantities you can buy that won't break the bank.


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## Larry$ (Oct 5, 2021)

12L14 turns beautifully. I've had some mystery metal that was terrible turning. The chip breaker design on carbide inserts will determine what your ideal DOC should be. Ideal cutting tables exist for all sorts of metals, mostly based on surface feet per minute. I have no experience with name brand inserts and only rarely use the Chinese ones I have. Since I don't do production turning HSS works fine for me. 
You might try grinding a shear cutting tool and see if that helps.


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## woodchucker (Oct 5, 2021)

maspann said:


> If that is cold rolled rod, it is difficult to get a consistent surface finish. Try getting some free machining steel bar (12L14) and see what result you get. There are several vendors on Ebay that have small quantities you can buy that won't break the bank.


12L14 is cheating, it's impossible not to get a good look, thats why its free machining.
you will learn to do things with it... but you won't learn about breaking chips in hard to use materials with it.

So if you just desire to make things... 12L14 will get you there, any of the free machining will. They will make you think you are the greatest..
But dealing with an unknown metal, or tough to machine metal will test your patience.. Just remember it's a hobby.
And remember like everything in life, the tough things make you appreciate where you came from and where you are at.


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## Aukai (Oct 5, 2021)

Wait till a friend sends you a Thompson bearing rod to turn, and not tell you what it is


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## Janderso (Oct 5, 2021)

Larry$ said:


> 12L14 turns beautifully


This.
Or 360 Brass


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## Ulma Doctor (Oct 5, 2021)

1045,1144sp ,303 stainless, 416 stainless all seem to machine well, even on smaller machines with HSS


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## rabler (Oct 5, 2021)

Are you using the inserts that came with the Accusize tool set?  If so I suggest getting some quality, name brand inserts, Korloy, Iscar, Kennametal, Tungaloy.  @davidpbest on this site has written a book on lathe insert tooling, well worth the cost of the book.   While mild steel doesn't turn the best, you should be able to get better results.


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## Batmanacw (Oct 5, 2021)

1018 / A36 tears horribly as you cut it right up until you get some decent back pressure. Take it up to 1500 rpm taking 0.05" off the diameter at 0.005" and tell us what happens.


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## Firstram (Oct 5, 2021)

Batmanacw said:


> 1018 / A36 tears horribly as you cut it right up until you get some decent back pressure. Take it up to 1500 rpm taking 0.05" off the diameter at 0.005" and tell us what happens.


Exactly. Don't forget to take pictures of the random burn spots on your hands, wrists and occasionally on the back of your neck!


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## rabler (Oct 5, 2021)

Also, carbide likes at least 200 SFM at a minimum, so ( 200 sfm x 12 in/ft) / (pi x diameter in inches).  For 1/2inch stock, that comes out to roughly 1600 rpm.  400 SFM isn’t unreasonable although your lathe probably won’t spin at 3200 rpm.


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## mmcmdl (Oct 6, 2021)

Aukai said:


> Wait till a friend sends you a Thompson bearing rod to turn, and not tell you what it is


Huh ?  Who would do such a thing as that !


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## matthewsx (Oct 6, 2021)

There's a reason they make special files just for lathes. We do what it takes to get the finish we want, it's not cheating to sneak up on the dimension you're shooting for with emery paper.

John


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## ddickey (Oct 6, 2021)

Bigger depth of cut and higher feedrate.


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## addertooth (Oct 6, 2021)

That is a mighty small diameter you are cutting.  You will have more control over chip production with a hand-ground braised carbide tool.  The tool pressure which most carbide inserts need to cut (due to their edge geometry), can encourage more of a smearing (versus cutting) action on small diameters. Tools for cutting small diameters gain a benefit from a smaller radius Chip Breaker groove cut into them.  A stone honed edge helps as well.  They guys who work with "mini-lathes" are constantly dealing with small diameter parts.  It may be counter intuitive, but read some of the tool-grinding postings by the folks who have the 7 X 12/14/16 and Sherline lathes.  They swim in these waters daily.  They get great finishes, even with less horsepower and rigidity.


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## bakrch (Oct 6, 2021)

Cermet inserts +all of the RPM's you have on the finish pass works pretty well, but it is okay to just accept the horrible finish and polish the crap out of it .. we all get the same results other than the rare cut in which it doesn't tear (using conventional tooling).


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## xr650rRider (Oct 6, 2021)

Try some CCGT inserts.  Says they are for aluminum but they'll give you the best finish on steel too.  Better finish that I've been able to achieve with HSS.  My Precision Matthews turning set came with some and after having your same isssue, I gave them a try.  They are the cheap variety you can find on Amazon, Ebay or AliExpress.


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## MtnBiker (Oct 6, 2021)

jeremysf said:


> I’m having a problem getting good surface finish with my PM-1640TL. I don’t have enough experience to figure out what I’m doing wrong and am looking for ideas or to have my expectations reset. I am assuming based on seeing other PM-1640TL user videos on YouTube that it really should not be very hard to get great results over a wide range of speeds and feeds using carbide inserts and mild steel.
> 
> 
> 
> ...


Same issue here. Glad you asked...glad you got all those helpful tips. I was getting awesome surface finish on Delrin (which was both good and frustrating given the mess I was making with some practice 1018). Love the collet chuck. How do you like it? Where did you get it?


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## markba633csi (Oct 6, 2021)

Mild steel always tears like that in my experience, but carbide tooling can compound the problem.  
Chrome-moly steels cut better, and steels with lead like 12L14
-M


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## macardoso (Oct 6, 2021)

Haven't read all the replies, but here are my thoughts to the original question:

1018 or most low carbon mild steels are hard to get a good surface finish. They tend to be gummy and tear out a bit. If you're not against leaded or sulphurized steels (better machinability), try 12L14 or 41L40. They cut like butter and give a much better surface finish. Harder alloy steels also give better finish, so try 4140. Bit more expensive but makes strong parts.

The general purpose inserts that ship with the import kits are poorly suited for fine machining. Either try so HSS, or better, experiment with different insert grades, edge preps, chipbreakers, and coatings to find ones best suited for your application. When finishing steels, I tend to use a CCGT32.50 (CCGT09T0304-AK) which is a razor sharp insert for non ferrous materials, but also gives outstanding finishes in steels, albeit with a reduced tool life. Here is an EXAMPLE. The general purpose inserts are pretty tough and are great for roughing, especially when your stock has a scale to it.

Even on a massive lathe, your thin workpiece is approaching or exceeding the 3:1 (length to diameter) extension rule for an unsupported workpiece. This suggests using a live center on a tailstock for added support when, say, you need to hold a 1/2" bar out more than 1.5". You'll find improved finishes and dimensional accuracy when supporting the work with a tailstock, even on seemingly short workpieces.

Inserts will NOT break chips unless you engage them enough (high enough depth of cut and feed per rev). The chip needs to be heavy enough to run into the chip breaking geometry on an insert. This also means you might be using different inserts for roughing vs finishing. Most quality inserts have a recommended SFM, depth of cut, and feed per rev which will get the insert working "properly". You can definity cut slower or lighter than these recommendations but it may not break chips. Also inserts made for brittle materials (cast iron) won't break chips on ductile materials (mild steel) due to the difference in chipbreakers. If you cut with a depth of cut less than ~75% of the nose radius of the insert, your radial cutting forces go up dramatically causing dimensional issues and poor finish. For example the CCMT32.50 insert has a 0.005" nose radius (fine finishing) so you should try to always keep your depth of cut greater than 0.004" (0.008" on diameter) or you could rub. The sharper inserts (CCGT) suffer from this less thanks to the sharp edge.

Here is an example working range for a CCMT09T0304-mm 2025 insert from Sandvik (high end). The shaded yellow region in the graph shows the recommended depth of cut (Ap) and feed per rev (Fn) in mm. In this case, you'd want the stay above approximately 0.8mm (0.031") depth of cut and 0.1mm (0.004") feed per rev. This is just an example and other insert manufacturers should have similar data available for each tool they make. Roughing inserts will have a higher minimum/maximum depth of cut, but will be stronger, and the opposite is true for finishing inserts.






In general, try to not sneak up on your final dimension. You'll find that taking a moderately deep finish pass will give you better finish and dimensional accuracy than skimming the last thousandth off the diameter. You'll have to characterize the deflection of the cut by taking similarly deep semi-finish passes and measuring in between.

Inserts are amazing when properly applied, so don't be discouraged that the freebie ones that came in the kit are giving you less than desirable results.

EDIT: Found a great picture from Sandvik showing the difference in DOC and feed for inserts made for roughing "PR", medium "PM", and finishing "PF". This was for some random insert family, but the nose radius, top rake, and land varied for each insert.





-Mike


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## ArmyDoc (Oct 6, 2021)

Can you give us an update on this?


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## macardoso (Oct 6, 2021)

Some of the deeper banding/grooves are likely built-up edge (BUE). This is where some of the workpiece material pressure welds itself to the cutting tool. This built up edge then does much of the cutting, effectively increasing the size of the tip of the cutting tool. Eventually it breaks off the tool and rolls under the edge allowing the carbide to start cutting again, until another BUE forms. This looks like rough grooves, ending in a "pill" or bump of material before the finish looks good again.


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## Christianstark (Oct 6, 2021)

macardoso said:


> Some of the deeper banding/grooves are likely built-up edge (BUE). This is where some of the workpiece material pressure welds itself to the cutting tool. This built up edge then does much of the cutting, effectively increasing the size of the tip of the cutting tool. Eventually it breaks off the tool and rolls under the edge allowing the carbide to start cutting again, until another BUE forms. This looks like rough grooves, endinging in a "pill" or bump of material before the finish looks good again.


Thats an incredible representation. Thanks for posting that!


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## macardoso (Oct 6, 2021)

Christianstark said:


> Thats an incredible representation. Thanks for posting that!


For sure! There a ton of older machining videos that are very informative. Also a whole series of these electron microscopy videos of single point cutting. Pretty awesome.


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## sdelivery (Oct 6, 2021)

TNR Tool Nose Radius.  Select a tool with a larger TNR it will be easier to get a better finish. 
Also little passes are for finishing.
If you have .100 to remove to achieve your finished dimension then take two passes.
The pressure of a larger cut forces the "slack" out of the machine slides and makes the machine more rigid.


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## mattthemuppet2 (Oct 6, 2021)

heavier depth of cut, higher feed, higher speed. I only ever used CCMT inserts on nasty steel (rust etc) on my Atlas as the cut looked like a beaver had chewed on it. Tried them again on my South Bend heavy 9 and got a beautiful shiny almost polished finish and chips pinging off the chip shield like gunfire. CCGT cut much better at a shallower depth of cut, but gave a more matte finish even though it was very smooth. It was quite a revelation.


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## jeremysf (Oct 6, 2021)

This is the most encouraging and helpful set of responses!


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## jeremysf (Oct 6, 2021)

MtnBiker said:


> Same issue here. Glad you asked...glad you got all those helpful tips. I was getting awesome surface finish on Delrin (which was both good and frustrating given the mess I was making with some practice 1018). Love the collet chuck. How do you like it? Where did you get it?



Here’s the collet chuck I got. Super cheap, but pretty happy with it for the price:









						5C Collet Chuck Set, Collet Adapter 6000 RPM, D1-6 Cam Lock Mount Lathe Use  | eBay
					

Find many great new & used options and get the best deals for 5C Collet Chuck Set, Collet Adapter 6000 RPM, D1-6 Cam Lock Mount Lathe Use at the best online prices at eBay! Free shipping for many products!



					www.ebay.com


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## jeremysf (Oct 6, 2021)

ArmyDoc said:


> Can you give us an update on this?



Still digesting, watching videos and reading. I ordered a copy of [mention]davidpbest [/mention] ‘s book on insert tooling and am waiting for delivery of some easier materials than the 1018 I have been trying to cut.

Despite that, with more speed (1200 rpm) and a heavier cut (0.020”) and flipping the inserts to a fresh edge (hard to say if this mattered), I was able to get a MUCH better finish.

I think one of my many takeaways from this thread is that I had inadvertently picked one of the more challenging material combinations as a starting point (small diameter, high aspect ratio 1018) and inappropriate speed (too low) and depth of cut (waaaay too shallow) with cheap carbide inserts.

Another takeaway (but not news) is how great this forum is in terms of quality of responses, speed of responses, and encouragement.


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## Batmanacw (Oct 6, 2021)

jeremysf said:


> Still digesting, watching videos and reading. I ordered a copy of [mention]davidpbest [/mention] ‘s book on insert tooling and am waiting for delivery of some easier materials than the 1018 I have been trying to cut.
> 
> Despite that, with more speed (1200 rpm) and a heavier cut (0.020”) and flipping the inserts to a fresh edge (hard to say if this mattered), I was able to get a MUCH better finish.
> 
> ...


Sweeeeeeeet!


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## Logan Novice (Oct 6, 2021)




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## keeena (Oct 6, 2021)

I saved this link when i started learning about lathe work; was a great overview for me: link

I think it might be worth pointing out to not confuse DoC with diameter of cut. My lathe's dials read diameter which is double the DoC. I know its a very basic thing but might help those who are learning.



sdelivery said:


> TNR Tool Nose Radius.  Select a tool with a larger TNR it will be easier to get a better finish.
> Also little passes are for finishing.


Could you please elaborate? I learned the opposite - small radius when taking light cuts to get a better finish for the reason that macardoso illustrated (minimize the ratio of radial to axial forces....did I say that correctly?). But maybe I'm misunderstanding what you wrote. If you meant that a larger nose radius for a better finish when taking large DoC (vs. small DoC): then I get it.

I agree that sneaking up doesn't seem work well with carbide inserts. I do like you say: understand total diameter and then try to divide into appropriate, equal DoC passes. Its a good learning experience when a lot of material has to be removed because you can dial in your DoC, make a pass and measure result as well as the finish. You can then tweak remaining DoCs so you know that you will accurately hit your #'s and finish on the final pass.


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## macardoso (Oct 7, 2021)

keeena said:


> Could you please elaborate? I learned the opposite - small radius when taking light cuts to get a better finish for the reason that macardoso illustrated (minimize the ratio of radial to axial forces....did I say that correctly?). But maybe I'm misunderstanding what you wrote. If you meant that a larger nose radius for a better finish when taking large DoC (vs. small DoC): then I get it.



Most manufacturers will measure surface roughness in terms of Ra and Rz, essentially a statistically averaged surface height deviation. In the home shop, we most often shoot for "jewelry" finishes. Here's how they differ.

A CNC lathe will be programmed to make a part in as little time as possible. Running a 10 minute finish pass on a machine means wasted money so the programmer will opt for methods to meet their Ra/Rz requirements (measured on a profilometer). For a given feed rate, a tool with a larger nose radius will produce scallops in the part with a lower height (hence better finish) than a small radius tool. See the highly exaggerated image below, and play with this calculator: https://www.custompartnet.com/calculator/turning-surface-roughness






Now the same holds true in the home shop with a few notable exceptions:

Time is not usually nearly as important to us as we don't run production
We do not spend lots of money on fancy ($$$) inserts to give optimal results on each material
Our machines (even your 16") are WAY less rigid than a production CNC. Your 16" is much better than my 12" in this category, and mine much better than the guys running 7" lathes, but the CNC lathes outclass us all.
So why does this matter. Well, the logic above drives you to select a tool with a very large nose radius for finishing. But in doing so, you accept very high cutting forces. You end up needing to take a finish pass at 75% or more of the nose radius (that can be a very meaty cut) or if you do less, your radial cutting forces will be very high, deflecting the tool, deflecting the workpiece, ruining your accuracy, and potentially allowing the tool to rub and mar the pretty finish.

If you can get used to taking a 0.050" or more finish pass, then the larger nose radius tools will allow your to finish at a higher feed rate. But if you are after a precision fit and you need to sneak up on the final size, a sharp, small nose radius insert will allow you to take very small depth of cut finish passes, get a very accurate final size, and get a great surface finish, BUT, your finish feed rate will need to be comparatively slow.

Using xxGT style inserts, I've taken 0.0005" depth of cut passes that have come off as one continuous chip. I've also used these inserts to turn bearing diameters within 0.0002" on diameters without needing any sanding or polishing to get the fit right.

So in summary, the large nose radius suggestion is correct, but needs to be applied with an appropriately large depth of cut on the finish pass. Small nose radius tools generate less cutting forces and can take smaller depths of cut, which allows delicate finish passes. Both can give great finishes, but the large nose radius will do it faster.

EDIT: Great pic from Sandvik


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## macardoso (Oct 7, 2021)

I'll throw one more tooling complication into here  

Besides the nose radius, the insert's* included angle *or shape plays a big part in the amount of cutting forces generated.












Compare the 3 inserts above: CCMT, DCMT, VCMT (left to right).

EDIT: Great pic from Sandvik






Each of these inserts could have the exact same nose radius, but the tools on the right will have significantly lower cutting forces. They also allow access into restricting undercuts and grooves much better too. The downside is they are weaker, so probably not for roughing.

For my most precision work, I always use a VCGT insert, narrow, sharp, ground edges. For general turning I use almost exclusively the CCMT insert.

In fact, most production tools will rough with something like a CNMG (negative rake version of the CCMT) and finish with a VNMG, especially on boring bars. This helps those CNC lathes squeeze out more accuracy.


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## jeremysf (Oct 8, 2021)

This thread is the gift that keeps on giving!


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## Lo-Fi (Oct 8, 2021)

I use TCMT with my Myford. 20 thou DOC, highest RPM I can set it to and a feed rate that gives decent chips leaves a great finish:





That's a bit of hot rolled plate I machined this afternoon. Baby it with shallow cuts and it ends up with the same awful finish you were struggling with. 

Sorry I can't give numbers for speed and feed, it's belt drive, who knows what pulleys it's got, and no QCGB means I rarely change the feed rate or know what it actually is. Blue curly chips that break is what you're aiming for with carbide, though it's not always comfortable to be around.

If you want to hit accurate diameters and get a nice finish (no sneaking up with tiny cuts), all you need to know is right here:






I literally can't tell you how grateful I am to Stefan for that video. Was a lightbulb moment for me and I've never looked back. 

Happy machining


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## jeremysf (Oct 9, 2021)

Awesome, thanks!


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## erikmannie (Oct 9, 2021)

Referring to your first picture (Post #1 in this thread), I would use tail support.

I have a PM-1660TL. Files, emery paper and Scotch-Brite are very often used.

You can rough finish with carbide, and then switch to HSS for the last .005” or so. You can do the last .001” with emery paper and smooth files. Of course, you have to make sure to move the emery paper and files evenly across the work surface.

I am always finishing things off with a green Scotch-Brite.


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## BladesIIB (Oct 9, 2021)

Little late to the party here but as a TL owner, figured I should jump in.  Skimming through, you have been given some great advice.  The mild steel I think is your main issue.  If I was turning that dial of mild steel I would max the RPM about 2000 for me.  I would take .075 to .100" roughing cuts and feed at a minimum of .011.  If the tolerance allowed, I may even bump that feed up a little more.  Finishing, I would use a brazed carbide and run it the same speed and maybe down to about .008" feed.


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## jeremysf (Oct 9, 2021)

erikmannie said:


> Referring to your first picture (Post #1 in this thread), I would use tail support.
> 
> I have a PM-1660TL. Files, emery paper and Scotch-Brite are very often used.
> 
> ...



Great advice! Not evident from the photos but I have been using tail support on everything (except for a few tests without just to confirm I wasn’t messing up my tail support).

That does bring up another issue which is with a CXA quick change tool post and larger tool holders, I find it challenging to sneak the tools in on such small diameter parts with the live and dead centers that came with the lathe.


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## jeremysf (Oct 9, 2021)

It’s mentioned above, but for anyone coming to this thread in the future, [mention]davidpbest [/mention] ‘s book is awesome.

I have been collecting and reading lots of classic machining materials, and I feel like his book is the “missing manual” filling in some major gaps for me.


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## BladesIIB (Oct 9, 2021)

jeremysf said:


> Great advice! Not evident from the photos but I have been using tail support on everything (except for a few tests without just to confirm I wasn’t messing up my tail support).
> 
> That does bring up another issue which is with a CXA quick change tool post and larger tool holders, I find it challenging to sneak the tools in on such small diameter parts with the live and dead centers that came with the lathe.


A long nose center is a great addition to your work holding. I have this one from Shars for my TL and use it all the time on small parts. 





__





						4 MT Morse Taper Long Nose High Performance Heavy Duty CNC Live Center - Live Centers - Workholding - Products
					

Shars Tool




					www.shars.com


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## erikmannie (Oct 9, 2021)

jeremysf said:


> …That does bring up another issue which is with a CXA quick change tool post and larger tool holders, I find it challenging to sneak the tools in on such small diameter parts with the live and dead centers that came with the lathe.



You can use a HSS tool bit with a custom (as in “You grind it”) “long reach” grind.  

This is AXA (and it is in need of sharpening), but it provided me extra reach in to a tight area.






David Best’s book is AMAZING. It is truly a must have.


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## macmccaskie (Oct 10, 2021)

For you HSS gurus: Is there any differences between grades/brands and quality of cut?  I’ve been trying a brand of old stock T-15 and got BUE (now that I know what that is).  Would backing down to M2 or something finish better at .002” DOC?


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## erikmannie (Oct 10, 2021)

macmccaskie said:


> For you HSS gurus: Is there any differences between grades/brands and quality of cut?  I’ve been trying a brand of old stock T-15 and got BUE (now that I know what that is).  Would backing down to M2 or something finish better at .002” DOC?



At home (as opposed to school), I have only ever used cheap import HSS tool bits. It does the job for a while, & then requires resharpening sooner than I would like.

At the one school I went to, they used the good stuff. It was rare to see a tool bit require a trip to the grinder.

I should change to quality HSS tool bits. If the tool bit is getting smaller (i.e. “dulling”) during a single pass, then you would get a slight taper.

Is anybody else doing the roughing with carbide & then switching to HSS for the last .005” or so?


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## macmccaskie (Oct 10, 2021)

erikmannie said:


> At home (as opposed to school), I have only ever used cheap import HSS tool bits. It does the job for a while, & then requires resharpening sooner than I would like.
> 
> At the one school I went to, they used the good stuff. I never saw a tool bit require a trip to the grinder.
> 
> I should change to quality HSS tool bits.


Agreed, I pitched all my Chineseium. The T-15 is Vasco Supreme - VERY hard to grind but I have found a very good routine: 36 grit ceramic belts, then CBN wheels.  Plus my shop made tool rest for the grinder helps big time.


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## Lo-Fi (Oct 10, 2021)

erikmannie said:


> Is anybody else doing the roughing with carbide & then switching to HSS for the last .005” or so?


Not unless I've managed to stuff up my balanced cuts with the carbide and haven't landed on my target dimension. I use HSS if I have a not so rigid setup that requires very positive cutting action and low cutting force or where a form tool or odd shaped tool is needed. If you haven't watched Stefan's video I posted above, I'd heartily recommend it as he's talking about exactly this topic. For me, it turned frustrating fussing with finishing cuts into lovely finishes right on dimension straight off the carbide. For tough materials it's absolutely essential.


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## erikmannie (Oct 10, 2021)

Lo-Fi said:


> Not unless I've managed to stuff up my balanced cuts with the carbide and haven't landed on my target dimension. I use HSS if I have a not so rigid setup that requires very positive cutting action and low cutting force or where a form tool or odd shaped tool is needed. If you haven't watched Stefan's video I posted above, I'd heartily recommend it as he's talking about exactly this topic. For me, it turned frustrating fussing with finishing cuts into lovely finishes right on dimension straight off the carbide. For tough materials it's absolutely essential.



I will check out the video.

I have yet to be successful in any balanced (“managed”) carbide cut. 

I have always been so scared to overshoot it (and thus scrap the part) that I purposely undershoot it with the plan of doing the last few thou with HSS (and files and emery paper). And then a green Scotch-Brite makes it pretty! Yes, I know that this is not the optimal strategy.

One day I will have more time to practice on *scrap* in order to learn how to be successful with a balanced cut.

Most of my lathe work is making pipe welding coupons so the finish is unimportant.


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## jwmelvin (Oct 10, 2021)

erikmannie said:


> Most of my lathe work is making pipe welding coupons so the finish is unimportant.



Then so is hitting a precise dimension; seems like a good opportunity for practice with balanced cuts.


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## ddickey (Oct 10, 2021)

Ray C has a nice write up about hitting a dimension.
Starts on post #43








						Bull Nose Live Center
					

Ray  I one of your many posts you mentioned the inset that you use to achieve the fine finishes. I know that I saved it somewhere , but can't find it in my smarter than me filing system Tks for your patience ed




					www.hobby-machinist.com


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## Lo-Fi (Oct 10, 2021)

Don't forget that you can balanced cut your entire way through any hogging operation, checking as you go. By the time you get to the final cut you will have built confidence that dialing up, say, 15 thou is going to remove exactly 15 thou because it has the last seven times. Applies to carbide or HSS just the same. I really like it as a methodology, it just makes so much sense to me.


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## mattthemuppet2 (Oct 11, 2021)

just for fun, here's the result of a 50 thou roughing cut with a name brand (Mitsubishi I think) CCMT insert in mysterium steel. OD is ~1"





Not a super shiny finish, but good enough for what I needed. I'd probably reduce the DOC to 20 thou or so and up the speed a bit for a finishing cut.


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## davidpbest (Oct 11, 2021)

I use a balanced cut method all the time, somewhat similar to what Ray C is trying to convey but without all the math.  It's fully described in much simpler terms_* in this video*_, and I use the DRO instead of the dials. Using this technique on my PM1340, I can routinely hit target dimensions to within 2/10ths, and there is no way this is possible creeping up on the final OD with shallow finishing passes. Granted, I have a solid tool post which helps, but even with the compound, this method works. Watch Stefan's video to the end, and realize that the technique is even more accurate using a DRO. He is also demonstrating the technique on 4140 with a similar sized lathe, using the style of insert (CPMT) that I would pick for your material and machining condition.


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## ddickey (Oct 11, 2021)

mattthemuppet2 said:


> just for fun, here's the result of a 50 thou roughing cut with a name brand (Mitsubishi I think) CCMT insert in mysterium steel. OD is ~1"
> 
> Not a super shiny finish, but good enough for what I needed. I'd probably reduce the DOC to 20 thou or so and up the speed a bit for a finishing cut.


What was you feed rate?


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## mattthemuppet2 (Oct 11, 2021)

about as fast as I could go without the motor belt slipping  You can see one of the chips out of focus on top of the toolholder at the bottom of the pic.


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## ddickey (Oct 11, 2021)

Is that .050" DOC or off of the diameter?


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## mattthemuppet2 (Oct 11, 2021)

50 thou depth of cut


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## jeremysf (Oct 11, 2021)

BladesIIB said:


> A long nose center is a great addition to your work holding. I have this one from Shars for my TL and use it all the time on small parts.
> 
> 
> 
> ...



Mine just arrived! Made by Rohm. I have been waiting for a few weeks for it to arrive, and was wondering if I was crazy buying one. Glad to have confirmation from you that I might be crazy, but in good company.


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## Watchwatch (Oct 11, 2021)

jeremysf said:


> Mine just arrived! Made by Rohm. I have been waiting for a few weeks for it to arrive, and was wondering if I was crazy buying one. Glad to have confirmation from you that I might be crazy, but in good company.



I have the exact same center. Got it for a really good price off Amazon. I never regret spending money on quality stuff. I have some Far East stuff that angers me just looking at it.


Sent from my iPhone using Tapatalk


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## Janderso (Oct 11, 2021)

jeremysf said:


> Mine just arrived! Made by Rohm. I have been waiting for a few weeks for it to arrive, and was wondering if I was crazy buying one. Glad to have confirmation from you that I might be crazy, but in good company.


The tapered tip is great for tool access


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## ddickey (Oct 11, 2021)

The Rohm is about $50 more than the Shars.


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## Beckerkumm (Oct 11, 2021)

I made the mistake of buying a normal one and now it sits in the drawer.  The long nose works much better with my 5/8" tooling.  Dave


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## ddickey (Oct 11, 2021)

Someone's gotta bite on this.




__





						Live Center 60 Degree Morse Taper MT3 Röhm 1243505, Small Body Diameter and Profiled Center Point, Size 04, 15mm Point Diameter: Live Centers: Amazon.com: Industrial & Scientific
					

Live Center 60 Degree Morse Taper MT3 Röhm 1243505, Small Body Diameter and Profiled Center Point, Size 04, 15mm Point Diameter: Live Centers: Amazon.com: Industrial & Scientific



					www.amazon.com


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## mksj (Oct 11, 2021)

I already bit on that one, now out of stock, say more on the way HA! I had the older bigger diameter Shar's CNC and it is very bulky and always was a bit gritty and stiff in the bearing after several years of use. Rohm makes great tools and you will be very happy with an extended point, I use it most of the time except for heavy loads. All a learning curve for all of us, when you think you know it all, then you are really fooling yourself.

On the surface finish issues, it is a combination of both speed and feed with the particular insert geometry. Hugh difference between the same style of inserts. Also for the nose diameter there is a particular feed that will give the best surface finish for different materials. Example below is HR 4140 initially had a feed of around 0.004"/r and then doubled it to 0.008"/r using and Iscar CCMT 32.51 IC907 coating. I find it to be a very good all around turning insert, and switch to a CCGT when I need to do very fine light DOC cutting.  I did some recent turning with CR 1018 and got a very good finish, despite hating to turn that metal. I also think your insert does not have a sharp enough cutting edge or positive rake to cut the metal you show, and often you need a different insert for different materials. Get yourself something like a 10X magnifier so you can inspect the cutter tip/edge, you will be surprised how often that when you have a poor finish the tip is damaged or loaded up an not longer cutting. Light cutting fluid also helps. I made my own FogBuster unit for my mill, big difference, and I may add one to my lathe at some point. 

Also understanding the chips coming off both type and color is important to know how you are cutting. You definitely can't fault the lathe in this case.


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