Bad finish on BMS

On a recent posting, one man was remarking on the poor finish he was getting on his turning. Might I suggest that he check out Sparely,s book where he will find this very issue explained ?

OK, I know it,s old hat, everyone uses tips these days [I never use them ], but simple HSS will give a first class finish, using low speed and plenty of lube.

Give it a try, it does "Exactly what it say,s in the book"

Been there, done that !

Carbide inserts for steel usually have a negative rake hone on the edges. It does not perform well at low speed or for light cuts. If one must use inserts buy those intended for aluminum. They have a positive rake and polished surface. It is unfortunate that so many opt for carbide right from the beginning. HSS is more versatile in that the cutting angles can be optimized for the job at hand. Is it a matter of being afraid to mess up grinding a tool? Are they to lazy to learn about tool angles?

I started using HSS on my 10K South Bend then switched to carbide inserts. Now I am using HSS in tangential holders for much of my turning. On the larger lathe with 6 hp. I use mostly carbides.

Unfortunate for whom?

I bought a set of 8mm shank carbide tools for my mini-lathe, took them out of the box, adjusted them in tool holders and used them satisfactorily for years until I replaced the machine with a WM250 that I fitted with the same QCTP and tools. A couple of times a year I'd be hoodwinked into wasting time and HSS by grinding my own tools. After all, it's an essential skill, and is unfortunate not to be able to do it. In all that time I ended up with one that actually did everything it was supposed to. All the others look like they were gnawed off by an angry rat, and some of them sort-of worked.

Too lazy to learn about tool angles? Hell, I even tried scribing lines on each face to 'help.'

Am I afraid to try it? No, but as I have tools that work for no effort, it's not a priority. That's time that would be better spent learning all the leads of Cambridge Minor

I would tend to agree with John. Restricting yourself to insert tools depending on what you are making restricts what you can do, for example trepanning a small recess in a face, turning small radius curves (too small for a radius attachment), machining a groove with a semi circular root, the list goes on. The ability to grind up a tool for a specific purpose on the off hand grinder including form tools will save time, money and frustration in either trying to find a suitable insert, buying it and waiting for it to arrive!

All tooling has its place, HSS, brazed carbide, inserts and holders etc. Reliance on pre shaped and ready sharpened throwaway tooling is undoubtably restrictive.

Dont forget that the advantage of the ability to grind a tool is not limited to the lathe alone! It opens up possibilities for fly cutters on the mill, tools for a shaper and you can even make your own spot facing tools for pennies and not be restricted to proportions available off the shelf.

Paul.

Does nobody use carbon cutting tools any more ?

I do, but nobody wants to hear that lol, they fall in the etc category of my post.

Paul.

Strangely enough, I do use carbon steel tooling on my watchmakers lathe. The reasons? Well I find it difficult to find small cross section HSS and I have a lot of carbon steel, small cross section blanks, that came with the lathe.

The carbon steel tooling lasts a long time between sharpening (presumably as cuts are small), it is easy to get the edge back using a stone, when it does need sharpening. It also produces a better finish than my odd HSS tool.

If someone had told me forty years ago that I would be using carbon steel tooling, I would have laughed in his face!

Andrew.

Yes; all these cutting tools are made from carbon steel:

I don't know why people get so partisan about cutting tools. I use insert tooling, HSS and carbon steel as appropriate to get the job done. But then again I'm an engineer, not a modeller, so I'm happy to buy/grind/make tools as needed without fervour.

Andrew

+1

The right tool for the job is the one that provides the required end result.

As already said, if a tool is needed that is not one of the standards available, you have to make your own, so HSS or CS become essential.

They are invaluable at 8:00 pm on a Saturday night when the last carbide insert chips!, on a VERY urgent job.

Don't know of a 1/8" dia Carbide rod, but a short piece of 1/8" diameter HSS cut a 4 mm pitch semi circular thread when I needed one.

Older machines, being designed before the advent of Carbide, are not really suited to get the best out of carbide (Lack of speed or rigidity, or both )

My favourite for much work is a HSS tool bit in a Tangential Turning Tool. (Have 1/8, 1/4 and 5/16 versions ).

EASY to sharpen using a simple jig.

Carbide inserts get used for roughing, boring or radius work, Especially if the steel is hardened. Lovely to see the blue /brown, or red hot chips coming off!

Horses for courses

Howard

Guys you can get a good finish on mild steel using carbide tips but you have to take a decent depth of cut of around 0.030” . Use a new tip , loads of coolant and a fine feed of around 0.005” per rev . Keep the speed around 200 to 250 revs. If your using HSS tools sharpen your tool and then hone the top and front edges and hone a small radius on the tip ( like you would see on a carbide insert). Use one tool for roughing out and then keep the honed tool for finish cuts.

I disagree.

Some low carbon steels are better with bigger DOC, but by no means all. Speed often has more of an effect, faster is better. I rarely run coolant with inserts. Although I have flood coolant available it gets thrown everywhere at high spindle speeds, and in most cases doesn't help the finish. For 1" diameter low carbon steel I would be running around 800rpm. This post, with quantative results, may be of interest:

Turning Trials

Andrew

I agree with Andrew.

I would use rather more than 30thou DOC too; even a mini-lathe will happily manage double that.

There was a time when the Chinese bucket shops advertised everything as High Carbon Steel because it sounded good. Unfortunately, poor quality control made it synonymous with shattering under load. Now they call everything carbide. Carbide suggests Tungsten Carbide but it could also refer to iron carbide, aka high carbon steel.

Call me Mr Suspicious. Fortunately, this does not keep me awake at night

There are many styles and grades of carbide inserts. The common ones for steel cut best with more agressive use. Then you get close to the size and start to creep up on the size and the finish that was good deteriorates. Inserts for stainless steel can use smaller depths of cut, but the best finishing type are those intended for aluminium, they will cut down to 0.0005", 0.010mm. There are some types of mild steel which rarely seem to machine well, like pure aluminium.