cutting tool help, please

**Alistair Hosie** · 07-07-2012, 02:27 PM

Work on the lathe is so designed to allow rough turning to near finish dimensions then fine turning to critical dimensions some here will tell you more about speeds etc.I would also adise you to check your tool height sharpening etc as this can affect finish also. Alistair

**lynnl** · 07-07-2012, 02:44 PM

Originally posted by madbear

when i cut around 10,000 DOC i get a pretty good finish but when i only cut about 1,000-2,000 the finish is very ruff.

Unsure what you mean. If by "10,000," you're meaning 10 thousandths of an inch, that's usually expressed in the machining world as ".010"

But terminology aside, what you're experiencing is pretty normal. Finish does tend to suffer when trying to shave off tiny amounts. I'm sure the real machinists get around that problem easily, but that's what I've experienced.

You don't say what you're cutting or what equipment you're using, but if it's beefy enough I'd suggest shooting for at least .005 to .010" left for the final finishing cut.

**madbear** · 07-07-2012, 03:18 PM

Yes i mean ".010" sorry
i have a small grizzly lathe, (9"x21") lathe/mill combo, not very rigid or powerfull. i am cutting 1.5" 316 stainless bar stock. i have some new carbide inserts coming. i'm sure part of the problem is the sharpness of the inserts, i have been trying to sharpen them with a diamond stone & probably got the angle off. there is a big learning curve to this but i am having fun & getting a lot of practice.
madbear

**Peter.** · 07-07-2012, 03:35 PM

In this situation I tend to do my roughing with inserts and finishing with a HSS tool.

**becksmachine** · 07-07-2012, 03:45 PM

Not meant to be an insult, but you are a glutton for punishment trying to learn by using 316, or stainless of any kind really.

I imagine you had a specific project in mind that needed stainless?

Working with mild steel (1018-1020) or 12L14 or even stressproof is much more forgiving.

Dave

**Mcgyver** · 07-07-2012, 03:50 PM

Originally posted by becksmachine

Not meant to be an insult, but you are a glutton for punishment trying to learn by using 316, or stainless of any kind really.

agreed, if it has to be stainless, get some 303 or 416 - they're the free machining stainless steels. The others work hardnen in a flash and generally miserable

**Forrest Addy** · 07-07-2012, 05:43 PM

You noobs: don't feel bad about screw-ups, misconceptions etc especially when you are working/learning alone. You have to learn and making mistakes and problems for your selves is part of the deal. You WILL screw up. We all have and the coming generations always will. Find a good local mentor, one who has worked in the trade for some time. Give him a cup of coffee and a plate of sugar cookies, chips, Buffalo wings etc, sit him on a stool and listen to his yarns and shop talk and folloe hi suggestions. A couple of Saturday afternoons with someone to keep your feet on the path will jump start your early experiences.

Practice first - then go for Carnegie Hall. All to often a noob (by "noob" i mean "neophyte" - one who learns from the very beginning. But I can't spell neophyte) gets a lathe or a mill then launches into an ambitious project without first working through a few exercises. Learn the words; the vocabulary. Probably the very most neglected part of any trade or prosession is teaching its specialized language and culture. Basic machne operation. Everyday practical safety. Measureing. The hand tools. The first practice pieces to learn the basic machine operations: turning, facing, and boring to size and finish. Explorating of feeds and speeds and how to calculate them. HSS tools and how to grind them, carbide tools where and when to use them and what speeds and feeds work best with them. External and internal screw threads. Use of the attachments. Effects of heat, distortion, and deflection. Branching into different materials: steel, brass, aluminum, alloy steel, stainless etc. Coolants and cutting oils. Maintenence, cleaning, and lubrication of your machne tools.

All of these are learned by doing and making mistakes both major and minor. Many of these lessons have to be learned simultaneously. All should be practiced a few times before you move on to actally making precision parts for a project. The whole idea of starting with practice pieces is to screw up cheap stuff. My first job as an apprentice on the lathe was a clevis pin, a straight pin 2" dia x 5" long, with an end champher and a head about 1/2 larger than the pin diameter. Couldn't be simpler but I screwed on up. BobArnold my boss told me deadpan when he gave me a card to get a new piece of material. "We only got a 20 ft bar of this stuff. Should we order more?"

The lathe behind me was run by one the the section's best hands. He was re-seating a double seated main feed regulating valve, a very difficult and demanding job working deep inside a valve body difficult to chuck into accurate alighment where maybe $11,000 cost of replacement hung in the balance. There couldn't be a greater contrast: a big burly ignorant-a$$ apprentice and a scrawny old turkery necked master of his trade.

I did learn and towards the end of my second rotation through the lathes in my third year I was allowed to work a double seat main feed reg valve under the turilage of Hal Cline the aforementioned turkey neck etc. What a nail-biter!

Expect to spend a month or two of evenings in the shop to work through your basic exercises. Expect to turn maybe $10 of perfectly good material into chips in these iinitial learning phases. That will be the best $10 you ever spent because it will prepare you for the actual work you intend to do.

Buy a lathe and start making a complex part from a material known to be difficult is a recipe for early frustration.

**Bob Fisher** · 07-07-2012, 06:04 PM

Try HSS tools, that 9 X 21 is not a good machine for carbide, for which you need higher speeds. A very sharp HSS cutter is an amazing tool. My thoughts on the subject. Bob.

**rohart** · 07-07-2012, 06:27 PM

Carbide inserts are not usually sharpened to as fine an edge as are HSS tools. This is because, at least in the early days of carbide, the inserts could not take the stress.

What carbide is very good at is not getting blunt when it gets hot. So you can take a not very sharp cutter, force it into the work to overcome the lack of sharpness, give it speed and DOC, and it will do the work and not blunt, even though it's glowing hot.

Some think this means high speed is needed for carbide. In my opinion it is not, but it does mean that the average insert is not the best tool for a fine finish.

So, as Peter said, rough with carbide and finish with HSS.

Having said all that, I do have one set of inserts that produce a nice finish, on FCMS at least, but I haven't investigated why this should be, as yet. If and when you do find an insert that does this, keep it for finishing, and it should last a long time, because its carbide of course.

On top of all this, inserts ordered commercially have lots of subtle differences. For example, you can get cut off inserts that cut evenly, that leave a burr on the left, or that leave a burr on the right. You can specify several radii on many types of insert. You can probably specify different degrees of sharpness. If you pick up a job lot of inserts at a sale, you have to factor this into what you expect a perticular insert to do, or to do well.

**madbear** · 07-07-2012, 07:04 PM

Man that sucks!
i just typed out a really long response, poof! it's gone. must have hit the wrong thing!

i have been learning on AL., made some shop fixtures, tools & chips. mostly chips. i guess i jumped in head first seeing how i'm 62 years old, a cancer surviver & trying to cram a bucket list into a coffee cup. LOL but hey i gota go for it. i'm making a suppressor for an AR 15 & yes i have the stamp.
pretty ambitious project i know but it's something i always wanted to do. seems like life just got in the way.
all the info i have received said to use 316 stainless so here we go.
thanks for the help;
madbear

**loose nut** · 07-07-2012, 08:16 PM

As stated, different materials have different "needs" in regards to DOC and feeds and speeds. Machinery handbook may be intimidating but it is still your best bet in this regard.

Many "noobs" give up, complaining that the machine is no good because they can't get it to turn or mill things the way they want (bad finish etc.), me included. I have found that about 98% of the time it is the operator that is the problem and not the machine. The only cure for this is experience and the only way to get that is to persevere. Keep trying you will get there in time.

**Dr Stan** · 07-07-2012, 08:27 PM

Some other sources of very good info are "How to Run a Lathe" originally published by the South Bend Lathe Works. I know its available from several sites, but here's one: http://littlemachineshop.com/product...ProductID=1596

Another is YouTube. Just look for machining videos.

Finally my favorite (its the one I learned from) is the US Navy's Machinery Repairman Manual. Free download http://www.instructables.com/files/o...K7EP282OTX.pdf

**Willy** · 07-07-2012, 08:41 PM

Originally posted by Mcgyver

agreed, if it has to be stainless, get some 303 or 416 - they're the free machining stainless steels. The others work harden in a flash and generally miserable

I'll second the comment made by Mcgyver.
Although I have obtained some wonderful results turning 316 SS with both carbide and HSS, one has to know that it isn't the easiest material to work with.
As long as you're not dwelling in the cut and accidentally work harden the material, it machines nicely. Once work hardened it's a bear to work with.

all the info i have received said to use 316 stainless so here we go

Not sure if you are aware of this but 416 SS is the stainless steel of choice used by many gun and barrel manufactures.
Not only is it a lower cost option compared to 316 SS, but it is also very easy to machine, (the highest rating of all stainless steels I believe).
Plus if the need arises, unlike 316SS, it is also possesses the ability to be hardened by heat treatment.

**Boucher** · 07-08-2012, 11:29 AM

Madbear you don’t show where you are from but you should. If you are located where there is crop irrigation using line shaft turbine pumps you probably can pick up 1 ¼” 416 stainless for free or for scrap prices. The top ten ft. of the shaft is discarded after it wears at the bearing points.

Someone said if you like carbide you will love ceramic. These Ceramic inserts from Carbide Depot work great on the small import tool holders.

the chipbreaker design of the insert determines somewhat the optimum amount of cut. These work well for light cuts.

cutting tool help, please

cutting tool help, please

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