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Question of finish on manual lathe

I am trying to teach myself how to use a lathe after learning some basics from an old timer. Please see my pictures. I expected a much better finish both turning and facing. So I have a couple questions:
Is the angle of the tool to the work piece correct?
I am at 140 rpm which would be about right for a HSS tool and this diameter. But should I use a different speed for this insert?
I am taking off 0.010 each pass.
Maybe I am missing some other factor? Chuck rigidity?

Thanks for any help.

Get a material like 12L14 so you can eliminate issues trying to machine some shitty material that might not give you a good finish no matter how hard you try
 
I was given a short length of 12L18 with the words, you will like this. I did.
The same gentleman was making tools for Harley Davidson motorcycles.
Later in the year he had to settle for something else because his supplier was out of the 12L18.
I was over his place and watching with the different metal. He said he was paying for it with a poor finish.
 
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Precisely! The longer crank arm means your hand has to travel a longer distance for a given amount of feed. And that means that any slight variations show up on a much smaller scale on the part. So overall, the variations are reduced and the finish is a lot better.

And I mean a LOT better. You can talk about speeds and feeds and inserts and alloys and tool geometry and angles and machine rigidity or weight and whatever, but in my experience and I do not claim to be an expert, but in my experience using a more CONSTANT feed rate is the one factor that stands out high above the crowd for producing a better surface finish.

So use power feed or use a longer crank arm or use CNC. And then experiment with all the other factors. My first choice would be the cutting fluid, but that's just me.



In a strict digital world the movement of a hand is in small increments like a digital value. In some cases with the shakes the values vary more.
Your lever arm reduces the average amplitude of those values in the same distance. :scratchchin:
 
I am sure a higher RPM, even just a moderate increase, would provide a much greater increase in the temperature at the point where the separation occurs than any reasonable heating in an oven or with a torch before machining. After all it is easy to have blue chips come off.



Maybe you should try it. Myself, I'll just turn up the RPM.
 
I am sure a higher RPM, even just a moderate increase, would provide a much greater increase in the temperature at the point where the separation occurs than any reasonable heating in an oven or with a torch before machining. After all it is easy to have blue chips come off.

Yeah, my response was also tongue-in-cheek...
 
The OD turn, Facing and the threaded hole are all poor.

The spindle should be tested(simple lift test with a wood 2x2), the part file checked, the set up revised, the tool sharpness, feed rate and RPM considered, rake and clearance considered.

I would expect an apprentice to do better
QT OP (after learning some basics from an old timer.)
Where is your old timer?

RE: the very first thing you do with unknown material , It strike it with a file to check if it is hard, tough or or soft
 
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Pretty much as soon as an insert edge is honed, it's negative rake on a light cut. And I am not onboard with the 90% either. 99% of the problem is that the cutting speed is too low and the cut is too light, IMO. This problem occurs with positive inserts on 1018 and it's ilk as well, I have had it happen countless times on machines that couldn't run enough RPM. There are several things that can be done to improve this. More speed will help. Deeper cut will help. Sharper edge will help. Cutting fluid will help.

I'd like to see the finish after he kicked the speed up. He said it was much better simply from that change. How about it OP?
 
A 5x5 or 7x7 negative rake holder with a 12 degree positive chip breaker is a positive rake cutting tool.
Built up edge occurs at some bad combination of geometry, feed rate, lead angle, depth of cut, tool coat, edge type and surface footage.
This cycles as the top edge loads and unloads and you will know it happening by some good finish, some bad finish, rinse and repeat.
Generally people go faster. You can also go slower sometimes to get out of "no man's land". Seems counterintuitive but it can work.
Cermets and ceramics almost always have a T-land (20 degrees the standard) . For sure this is negative cutting in any holder but they generally give a great surface finish.
There is also the side of the tool. "M" inserts and "G" inserts are different on the sides for friction and if positive molded for sure the shape at that critical side edge.

Agree that speed is good, sort of. Super sharp edge is good in some materials, bad in others. Decent chip load is a good thing.
Coolant. That helps but I have gone to dry cutting on most steel stuff. Have enough coolant problems on the grinders.
Deeper cut and now we get into chip thinning based on tool radius size. This why many like tenny tiny radii on their inserts.
Also the chipbreaker on the tip of most inserts can not work with super light cuts.

Unfortunately this is why there are a zillion different insert styles.:nutter:

Outside this In post #15 Buck mentions the fingernail test.
So I am looking at tools from Valentine that are outrunning me.
Do the scratch test for edge prep. The toolroom guys says to me : "It is amazing that you cutting tool guys have any fingernails left, you all do this"
 
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I'm surprised that you think nobody saw that... I saw it right away, but having had this exact same thing happen about a million times, I am pretty sure his feed rate is probably fine. The irregular tearing and chunking that inevitably happens with 1018 when it's cut at too slow a speed often makes it look like a higher feed rate was used, even when it wasn't. I would be interested in hearing what his feed rate was, though. And generally in my experience, running too low a feed rate with too low a cutting speed and too light a DOC in 1018 only magnifies this problem, because it gets even less heat into the cutting zone. And that lathe doesn't look all that small to me. It appears to be holding a tool with a 1" shank, so I'd guess it's at the very least 14" swing.
You are spot on. I was feeding by hand - so I really don't know the feed rate but trying to go slow and at an even pace. It is a bigger machine - maxturn 21x80. You are right - once I turned up the rpm and more depth of cut - I saw heat in the chips and it really improved the surface finish.
 
Pretty much as soon as an insert edge is honed, it's negative rake on a light cut. And I am not onboard with the 90% either. 99% of the problem is that the cutting speed is too low and the cut is too light, IMO. This problem occurs with positive inserts on 1018 and it's ilk as well, I have had it happen countless times on machines that couldn't run enough RPM. There are several things that can be done to improve this. More speed will help. Deeper cut will help. Sharper edge will help. Cutting fluid will help.

I'd like to see the finish after he kicked the speed up. He said it was much better simply from that change. How about it OP?
Here it is with higher rpm and more depth of cut. Left side could have been about 800 and right side was a bit over 1000 if I remember correctly. Getting better. Thanks for the help.

This brings up another question. As I turn up the rpm, I can feel some vibration in the wheel as I feed in the cutter during turning. Is this due to slop in the carriage ways? Worn out machine in general? I think this machine was sent to my location because it was the worst machine at it's previous shop.20231110_151610.jpg
 
Here it is with higher rpm and more depth of cut. Left side could have been about 800 and right side was a bit over 1000 if I remember correctly. Getting better. Thanks for the help.

This brings up another question. As I turn up the rpm, I can feel some vibration in the wheel as I feed in the cutter during turning. Is this due to slop in the carriage ways? Worn out machine in general? I think this machine was sent to my location because it was the worst machine at it's previous shop.View attachment 415554

Looking better. Probably don't want to go too awful much faster unless you can switch to a smaller chuck. If you're out of speed you can increase the depth of cut further. I've finished in 1018 with .100" per side in some cases just to try to get a decent finish. If that still doesn't get you there, try some of the other recommendations.

In my experience, vibrations are usually indicative of a rigidity problem in either the bearings or the workholding. You may need to check the headstock bearings and adjust them. And use the power feed, you wuss! :D
 
Huh. Rigidity problems plus negative rake tooling - what vould go wrong. Having walked a lot of novices through lathe work all I can say is don't walk, RUN away from negative rake tooling, as wall as avoid random-acessed insert tooling, as well as those inexpensive brazed carbide on steel shank items. Most newcomers will wind up wiping out a cabide tool in one way pr another. Negative rake stuff on a light lathe - avoid.

That leaves a HSS blank, ground by the new lathe owner themselves. Easily re-sharpened on a grinder. Most novices *don't have a diamond wheel.
 
HSS and brazed shank carbide tools are plenty good enough for 95% of home shop work. Inserts are a luxury most people don’t need. Learn how to hand grind a tool, it’s really not that difficult.

Regards Tyrone
 
A bit of emery cloth makes a world of difference.
Wrap some around a peg of wood, clamp it in the toolpost and run it across the part.
 
I think that if you're concerned with making parts, more so than beauty.........1018 is a good mainstay. So are the other mild steels in the structural category.

I seldom exceed 400rpm. It's a thing with me. I spent too much time rebuilding the headstock to run it, what I consider, hard. It's a small "unmentionable" 13x40 machine. Good for what it is, and good for what it's used for.

Besides..........I lack the rigidity to run too hard. I get mondo chatter if I do.

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A-36, or an equivalent grade of structural. It smears, but it's an acceptable finish for what it's intended for. The dimensions are the critical thing.

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HRS. Not beautiful, but it's what gets the job done. These are 6" diameter, and were never turned any faster than 190rpm.

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ERW A-500 pipe. 6 5/8 pipe, turned same speed.

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You want beauty at low rpm's....................12L14. It makes you look like you actually know what you're doing.

Realistically........if you look at the results I'm getting at a lower speed on the mild steel, they're stacking up with the results you're getting at upwards of 1000rpm.

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The CCMT insert will do an adequate job at lower speeds.

I'm not arguing with the wisdom of running faster, if you can. But if you can't, there's ways around it that will give you parts that you can work with.

I've done the custom grind shear style tool, NOT AS PICTURED EARLIER IN THE THREAD. The "vertical shear tool" is impractical. I went a different route. This too was impractical. I like an indexing tool that doesn't lose my place when I need to replace an insert. And, they last longer than HSS. Less hassle for someone who's only interested in making useable parts.

I may seem argumentative at times, but I'm looking things from a different perspective. Because of my business, I need one-off parts. Most job shops aren't interested, or charge an astronomical price for these parts. And..........I'm not quite sure that they would be as innovative in sourcing materials, or coming up with workable designs. It's not their bag, and I wouldn't expect it to be. I need someone who's familiar with the end product, and what it's used for.........and I guess it's mostly me. It's a unique situation that a lot of ag people face.

So, anyways, If I were you, I wouldn't be discouraged by a less than ideal surface finish. It's mostly about the steel you're dealing with.
 
A bit of emery cloth makes a world of difference.
Wrap some around a peg of wood, clamp it in the toolpost and run it across the part.
I liked to live dangerously, I wrapped the emery around the job and held it in my hand/hands. Don’t hold on too tight unless you want to lose a thumbnail. I’ve seen that happen right in front of me.
l did have a home made big pair of wooden “ nutcrackers “ that I could grip the emery cloth with around the job. They had several sized holes drilled in them for different diameters. They worked pretty good.

Regards Tyrone
 
Thanks for all of the replies! I tried a faster speed - now 840. Much better finish. Also tried varying depth of cut. Now I can see the chips getting hot.

I do not know if this insert is carbide or ceramic. I am using what is currently available at work. The material is unknown. It is an old fixture out of the scrap bin. But if I had to guess, I would say it is probably 1018.

How do you determine the best speed for this insert? Do the manufacturers have a table of speeds/feeds? Or a formula?
,
obvious insert manufacturers have recommendations, some inserts give a mirror
finish for 20 minutes, then finish deteriorates. vibration will give a rough finish whether
from machine, tool holder, dull insert, part vibration, etc
BUE is built up edge, going so slow metal sticks to insert, you get rough tares cause
usually not hot enough. many iron and steel got to be 700 - 1100 sfpm to get mirror finish.
but I have seen stubborn alloys or parts that best can do is a even dull finish with
waviness under .0004"TIR
.
manual lathe making a few parts most use a file and or sandpaper, cratex or rubber
abrasive like a abrasive pencil eraser works where you stick into shallow bores, etc.
there are abrasive stone holders so no need to get too close, obviously big part on lathe
going 2000+ rpm seen many a machine start shaking. a lot of lathe chucks not balanced
enough or recommended to go too high a rpm like over 1000 rpm
 

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