Newbie - Buying first metal lathe

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BigDumbDinosaur
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Re: Newbie - Buying first metal lathe

Post by BigDumbDinosaur » Sun Jun 16, 2019 2:43 am

Harold_V wrote:
Sun Jun 16, 2019 1:57 am
pat1027 wrote:
Sat Jun 15, 2019 6:19 pm
I did fall into the trap of carbide inserts but managed to wiggle free.
That's an interesting comment, one that needs to be read and understood.

Those who have the intestinal fortitude to read my ravings are all too familiar with my admonition to avoid that trap. Not doing so robs an individual from learning one of the most valuable lessons that is to be learned in the shop--the one of grinding cutting tools. That skill, above most others, will permit a guy to take cuts that most likely would not have been successful with insert tooling. It's hard to understand, and many will argue the point, but the harsh reality is the use of HSS tool bits on light duty machines is far better than the use of carbide (there are exceptions).

Thanks for your contribution.

H
I'll second what Harold says about inserts. Years ago, I needed to slightly reduce the diameter of the wheel-mount flange on a set of Strange Engineering drag racing axles. These axles were for use in a Dana-Spicer 60 series rear end, and were made from E4340 steel, arguably the toughest steel available for high-stress applications. After receiving the forged blanks, Strange would spline the inner ends and turn the bearing surfaces and wheel flanges close to finished size. The axles were then heat-treated, bringing them up to about Rockwell 55C-58C. Final dimensions of the bearing surfaces and wheel flanges were achieved by grinding, which gives you some idea how tough these things are.

Anyhow, due to a miscommunication on my part, Strange finished the wheel flange OD to the wrong size, about 3/16 inches larger in diameter than needed. Despite having an assortment of large hammers at my disposal, the disc brake rotors wouldn't fit, the weekend was only a day away and I was trying to get the car on the track. As I was working for a large railroad industry supplier at the time, one with a very well-equipped tool room, I decided to take the axles to work and cut down the flanges after hours, since at the time, the tool room worked on two shifts. I knew, of course, the axles were very tough but also knew I could cut them with carbide, as long as work and tool were flooded with coolant and the lathe was sufficiently substantial.

It helped that the tool room had a Lodge & Shipley lathe big enough to sink a small ship—it had a 96 inch bed and if memory correctly serves me, a swing of 24 inches over the ways. The machine was massive, so I knew nothing was going to deflect when I started taking bites out of the axles. So I mounted an axle between centers, put an insert-type carbide cutter into the tool post and went to work. Much to my chagrin, I could not come up with any combination of feed and speed that would keep the damned cutter from chattering and making a mess. I had the tip as close into the tool post as possible, everything was cranked down tightly, etc. What was I doing wrong?

Finally, I swallowed by pride and went to the tool room foreman's office for help. The first thing he said was "Don't use those (expletive deleted) replaceable inserts. They're no damned good!" Taking his advice, I went to the tool crib and got a large cutter with the carbide silver-soldered in place. A little grinding got the cutting edges where I wanted them, along with a nice radius on the tip, and I was off to the races, so to speak. I got the accuracy I needed and a nice finish to go with it.

I must say, though, the chips were coming off almost red hot, even though I had plenty of coolant flowing. Heat-treated E4340 is sure tough!
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John Hasler
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Re: Newbie - Buying first metal lathe

Post by John Hasler » Sun Jun 16, 2019 8:16 am

BigDumbDinosaur writes:
I'll second what Harold says about inserts. Years ago...

Carbide has changed quite a bit. Sharp micrograin inserts are readily available with chip breakers, positive rake, and included angles down to 30 degrees. I'm looking forward to experimenting with some as soon as I find time to build a holder.

I saw a Lodge & Shipley much like the one you used (but 156") sell for $850 the other day. I didn't bid. Most of the brazed carbide cutters for it turned out to be in one of the "Take as many as you want for $10" boxes I bought. I gave it all to the amishman who bought the lathe.

Harold_V
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Re: Newbie - Buying first metal lathe

Post by Harold_V » Sun Jun 16, 2019 3:32 pm

I'm of the opinion that modern carbide is drastically improved, of that there is no doubt. When it was in its infancy, it was almost unusable because of it being so fragile.

That said, the problem with carbide still remains when it is applied to low powered and light duty machines. Sure, it's a little more forgiving (modern carbide, that is), but without the power and rigidity to benefit from its real advantages, the cost of tooling up isn't worth what little gain one might get. You're still far better off resorting to HSS. And, if you find it's not performing as well as you might hope, you still have the option of turning to Stellite when greater heat and abrasion resistance may be required. Again, there are exceptions. None of this is carved in stone.

H
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Re: Newbie - Buying first metal lathe

Post by LIALLEGHENY » Sun Jun 16, 2019 10:41 pm

At this point I only use insert style tooling on my lathes. The problem is there are so many different types of inserts depending on the material to be cut, how hard it is, etc. Mind you I do this for a living and factor the costs of inserts into the job. For the hobbyist it can get rather expensive very quickly, and would agree that in most cases grinding HSS would be the way to go. My go to inserts are the CNMG style, and I have a large drawer full of different inserts to choose from, most of which I have picked up from auction, but now and then something comes along and I have to order a box.
I just finished a job making a couple of pins for an excavator, 4140 material, 100mm dia. , 31" long, case hardened to Rc58. The heat treat shop told me that I should leave the material oversize as the case hardening would distort the bars, which it did about .020" . Being that my customer needed the pins ASAP I didn't have the time to send them out to be ground to size so onto the lathe they went. I had nothing but problems with chatter, no matter what I did with speeds/feeds and inserts, until I remembered I had purchased some insert for cutting Inconel, sharp ground cutting edge with .005 radius tip, so I tried them. They cut like butter.
4140 HT (Rc32-35)is a material I frequently turn on the lathe. I am making the axles for my Berkshire from this material. With inserts I can rip through the material .012 feed at about 600 RPM, no coolant, couldn't even think about doing this with HSS.

Nyle

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Re: Newbie - Buying first metal lathe

Post by mihit » Sun Jun 16, 2019 11:46 pm

LIALLEGHENY wrote:
Sun Jun 16, 2019 10:41 pm
At this point I only use insert style tooling on my lathes. The problem is there are so many different types of inserts depending on the material to be cut, how hard it is, etc. Mind you I do this for a living and factor the costs of inserts into the job. For the hobbyist it can get rather expensive very quickly, and would agree that in most cases grinding HSS would be the way to go. My go to inserts are the CNMG style, and I have a large drawer full of different inserts to choose from, most of which I have picked up from auction, but now and then something comes along and I have to order a box.
I just finished a job making a couple of pins for an excavator, 4140 material, 100mm dia. , 31" long, case hardened to Rc58. The heat treat shop told me that I should leave the material oversize as the case hardening would distort the bars, which it did about .020" . Being that my customer needed the pins ASAP I didn't have the time to send them out to be ground to size so onto the lathe they went. I had nothing but problems with chatter, no matter what I did with speeds/feeds and inserts, until I remembered I had purchased some insert for cutting Inconel, sharp ground cutting edge with .005 radius tip, so I tried them. They cut like butter.
4140 HT (Rc32-35)is a material I frequently turn on the lathe. I am making the axles for my Berkshire from this material. With inserts I can rip through the material .012 feed at about 600 RPM, no coolant, couldn't even think about doing this with HSS.

Nyle
I have been peeling lots of pre-hard 4140. 0.3mm DOC. (0.011") Which is as much force as the machine it's on, and the inserts (no idea what), will give. 550RPM. Nice blue swarf.
That must just be the speed and feed it likes.

I didn't get chatter just tearing or rubbish surface finishes. Still had to swipe these with 320 emery after turning. Fussy stuff the 41xx.
Normally my go-to for fixing finish is to slow down and feed hard, most materials come up good.

Harold_V
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Re: Newbie - Buying first metal lathe

Post by Harold_V » Mon Jun 17, 2019 2:01 am

I fully endorse the use of carbide as mentioned in the last two posts, as indications are that they are used as they should be. I hope readers understand that my comments are directed towards folks with light duty machines, machines that rarely have the necessary power and rigidity to benefit from the use of carbide of any nature (brazed or insert).

Frankly, I don't know what I'd do if I didn't have negative rake carbide for roughing. You can move a lot of material with HSS, but the overall production rate is not the same, assuming one has a machine capable of benefitting from carbide use. The D4 spindle on my lathe, coupled with the fact that it is equipped with a three horse motor makes it possible for me.

I am no longer engaged in running my machines for gain, but even when I was, a typical tool setup almost always included at least one tool ground from HSS. It's still a very decent way to machine, especially if you're not in a hurry, and have limited funds. As has been stated, tooling up with insert holders and a complement of inserts can be cost prohibitive when purchased for use with hobby work.

H
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SteveHGraham
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Re: Newbie - Buying first metal lathe

Post by SteveHGraham » Mon Jun 17, 2019 10:31 am

Whether inserts cost a lot kind of depends on where you get them and how picky you are. Ebay generates a lot of bargains.

I don't use HSS much. If carbide was letting me down, I would.
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pat1027
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Re: Newbie - Buying first metal lathe

Post by pat1027 » Mon Jun 17, 2019 1:55 pm

I'll preface this with the machine I'm using. It's a South Bend 9A with a flat belt drive that originally shipped with a 1/4HP motor. Today it has a 1/3HP today. It's a nice machine but it has its limits.

I got by grinding HSS but it wasn't my favorite thing to do. Mostly because I didn't have the practice to be good at it. I saw a insert tool set that fit my tool holder and said this was the ticket. No more grinding, just swap inserts. They weren't cheap but no more grinding. For the most part it worked. I did my drivers, crank pins and axles with insert tools. Over time I had couple re-occurring frustrations. Surface finish at times was poor with an ever so slight squeal or chatter that was easy to get going. Fine cuts were difficult to make repeatedly. The tool might not cut anything or cut a few more thousandths than I intended. I went searching for what people with machine like mine did, not the heavy whoppers but light machines. I found a video of Elmer Verburg working with a 9" South Bend. Nice cuts, nice finish using HSS.

The solution, for me at least, is to give up free hand grindings, put a better rest on my grinder and use a couple fixtures to position the tool. Fairly simple once you sit down and think about.

On the subject of tools and light machines, what are thoughts on tangential tool holders?

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Re: Newbie - Buying first metal lathe

Post by mihit » Mon Jun 17, 2019 3:35 pm

I'm not at all knocking HSS. I run it almost exclusively on four of my lathes.
Learning to sharpen it properly is a foundation skill as far as I'm concerned. I can free hand it, though I was taught by a very old, very grumpy and very frugal scostman. If you need a guide or rest, no drama at all, the skill is understanding angles and forces.

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SteveM
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Re: Newbie - Buying first metal lathe

Post by SteveM » Mon Jun 17, 2019 3:36 pm

pat1027 wrote:
Mon Jun 17, 2019 1:55 pm
On the subject of tools and light machines, what are thoughts on tangential tool holders?
I don't think you'll find a better discussion than here:
https://www.gadgetbuilder.com/ToolHolders.html#Tangent

Steve

Harold_V
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Re: Newbie - Buying first metal lathe

Post by Harold_V » Mon Jun 17, 2019 4:00 pm

In regards to "free hand" grinding, I use no rest at all. My tool grinder has nothing more than the shroud around the wheel. Otherwise you're too limited.
Grinding the way I do takes a little practice, and a true running wheel, which becomes the guide. You must have the ability to see the tool in your mind, and to understand why it is shaped the way it is.

A tool rest tends to get in the way of grinding chip breakers.

The entire point of learning to grind tools is the education one receives in the process. Once you understand why the tool cuts, you can then make determinations as to why one isn't working as hoped. Until you understand tool geometry, that most likely won't be the case, and one of the best possible reasons I can offer for NOT using insert tooling when learning. Avoiding learning basics is a recipe for constant struggle.

Is the finish you're getting in keeping with your desire? If not, do you understand why? Do you know what to do to correct the problem? All of those questions are easily answered if you understand tool geometry.

H
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Re: Newbie - Buying first metal lathe

Post by Harold_V » Mon Jun 17, 2019 4:11 pm

SteveHGraham wrote:
Mon Jun 17, 2019 10:31 am
I don't use HSS much. If carbide was letting me down, I would.
How do you know?
Without a little experience with how both cut, you may find you're "settling" for the results you achieve, when there may be better conditions.

One of the comments I found interesting (not by you) was the hit or miss when taking a cut, which is often accompanied by tearing. I can't help but wonder how many use negative rake carbide for finishing. That's precisely what it does, especially when operated with less than a minimum depth of cut, and under the "sweet spot", where it yields a nice finish.

Before you, or anyone without a little experience, can judge that they are achieving good results, they must have something with which to compare. Sticking with any given type of tool does NOT provide that experience. You may be struggling, but accept that as normal. Are you? :wink:

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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