Lathe tool choice...

[Davek0974]

Hi all,
i've been looking for some time for some large tooling to use on my colchester student lathe.

I'm finding it really hard to get a suitable set of tools with tips on ebay, new ones in larger sizes seem to be very ££££

I dont want to get lots of different tools with lots of different pattern tips etc.

As i need to get using it soon, what are the opinions on a set of 1/2" shank brazed carbide tools or a set of 1/2" HSS tools?? Both are available for a good price in ebay shops.

It will mainly be doing the larger work including cast iron and such.

Is brazed better than HSS??

I have got a grinding wheel for carbide as well as ordinary so touching either up should not be a problem.

Thanks in advance
Dave

[Fasttrack]

If its ductile castings that your talking about - go with HSS! Once you figure out how to sharpen the bits, they are the most cost effective way to go for general applications, imo.

They are flexible, in that you can always regrind the bits for different operations or form cutters and if they get dull, you just sharpen them. A 4" chunck of HSS will last you a long time.

If you have to work with hard material, carbide is the way to go. Brazed carbide is handy since its already ground correctly for basic operations and they are cheaper than indexable types.

If you have to do production stuff or have to turn hard material, carbide is the way to go. Remember that carbide HAS to be run FAST! If your lathe can't spin 1000 rpm, HSS better be your main tooling.

Plus, you have to be careful with carbide. Most carbide inserts and brazed tools have a minimum DOC for it to effectively cut. This is true with HSS too, but it is dependant upon tool geometry (along with other factors like feed/speed and rigidity) and is easy to change.

Finally, carbide can be sharpened with CBN wheels or to a much less effective degree silicon carbide. However, there are dangers associated with sharpening carbide since the binding agents are toxic.

ALUMINUM OXIDE won't sharpen carbide worth a darn. Neither will silicon carbide. Once you sharpen with silicon carbide, the edge never lasts as long as one produced with CBN/Diamond. If you look at the edge under a microscope, you see that its not very smooth compared to a new edge.

[Davek0974]

Thanks

I'll go fo good old HSS then.

Looks like i need to dump the AL/OX wheel - more duff advice from a supplier!

Probably fit a wire brush wheel or buffer instead.

Dave

[Evan]

I would go with both. Carbide tooling has a very important place even on a small lathe such as my South Bend. Common wisdom states that my lathe isn't large enough, powerful enough or fast enough to make use of carbide tooling effectively but I beg to differ. I was turning this yesterday. HSS just won't hold up to this.



If all you have is HSS tooling you will be out of luck the first time somebody needs to do some hard turning.

[airsmith282]

i would agree that HSS will not hold up to turnning steels of any kind at hi speed.
but at lower speeds it just just fine. I use mainly HSS cutters now that i grind my self iam in no rush to get something done so the HSS works for anything i turn inlcuding SS.

I do have indexable carbid cutters and brazzed on models as well and they have there place thats for sure. You can turn steel at a higher speed when using carbide but i find they tend to dull fast and snap faster. as for DOC i can take a bigger bite with HSS Cutters then carbid and have no problems.

i also have found that no matter what cutter you use the faster you spin the peice the more heat you get and you wont get proper sizeing in your peice either. i get what i want at lower spin rates then i do at faster with and with out cooling the metal.. slower is better in my opnion..i also take lighter cuts per pass as well. alot of the stuff i have been making lately requires free spin... as there is no room for the live center to be use which also forces lighter cuts.

the other thing i have learned as well is to take my peice down so far the let the metal cool for an hour and then go back to it this gives the chance for the metal to shrink from the expansion it goes threw when heating up.. anyhow just a few things i have found and do and i get the results iam after in the end...

i have seen CNC machines really rip threw alot of stuff fast but for the home machinest with much lower end stuff we have to take things alot slower.

i only have about 2 years in on machineing... but i have learned alot in the last 2 years.. iam not always right either but from my own excperiences these are the things i have learned.

[Evan]

In the above photo nearly all the heat is carried away by the chips. The work doesn't become hot. The tool does and that is where carbide wins over HSS. I grind my own carbide tooling from sticks of solid carbide and I agree that you need diamond and/or CBN wheels to do a proper job. Carbide should be ground with diamond as it tends to glaze CBN wheels. There is no comparison between a diamond wheel and a silicon carbide wheel. I have all types and diamond cuts carbide like aluminum oxide cuts mild steel. Silicon carbide is ok for touching up a tool but for real stock removal when custom grinding carbide a 60 grit diamond wheel is invaluable.

One of the most useful characteristics of solid carbide tooling is that it can be stuck out much further than steel tools. Carbide is three times stiffer than steel so it doesn't flex as much when hanging way out there.

In the above photo I am cutting at about 250 SFM.

[small.planes]

Dave,
try JB cutting clicky, if you give them a ring they have a massive range of tips and tooling at quite reasonable prices.

Dave

[Davek0974]

Thanks all,

excellent website dave, i use carbide tips all the time on my smaller lathe using ccmt060204's and have boring, left and right and a tool that uses the odd two corners of the tips.

I will contact JB and see what they recommend in a larger size.

Dave

[SmoggyTurnip]

I grind my own carbide tooling from sticks of solid carbide.

Where do you get sticks of solid carbide?

[Paul Alciatore]

I go along with all the arguements for using HSS as a first choice in the home shop. But I also have to agree that carbide has it's uses, in that same enviroment. I always grab HHS first unless there is a real reason for going to carbide; usually when machining a hard steel.

I have had bad luck with the brazed carbide tool bits. It seems like they always chip just when you really need them. I have had much better luck with an inexpensive set of indexable carbide tools. They are available from several suppliers. Each insert has three points so they are economical.

http://www.use-enco.com/CGI/INPDFF?P...MITEM=325-7224

All the usual disclaimers.

[Alistair Hosie]

I can see what Evan is saying ! I have both and find that is the best way to go.I don't get such a good finish with carbide as I do with HSS anyway if you can have a selection.Alistair

[Evan]

Where do you get sticks of solid carbide?

My wife sells them.

[Fasttrack]

Yeah, I aggree that carbide has its place, even in the home shop setting. I've been forced to use carbide many times even on my tiny little import guy but as a first choice, general purpose cutting tool, HSS is the best.

It is very forgiving of incorrect speeds or feeds since it is easy to sharpen and it works well with low DOC and low speeds which is what most beginners prefer anyway.

Carbide, on the other hand, MUST be run fast to be effective. Evan's piece was a fairly large diameter, maybe 2"? - so even a lower spindle speed corresponds to a fairly quick SFM.

For turning mild steels, the recommended speed in ft/min is 745, according to the Machinery's Handbook. Now of course, the material that Evan was turning likely required a cutting speed of 250 sfm. Many hard, alloy steels seem to fall in the 150-350 sfm range but most home shop guys do not regularly encounter this material. When they do, then they can purchase the required carbide and build up their collection of carbide more slowly.


DAVE - DON'T toss your A/O wheel just because it won't handle carbide! A/O works fine for grinding HSS, provided its a quality wheel and not super coarse. 60 grit seems to be a good general purpose grit. Plus, A/O is great for off-hand grinding that you occassionally have to do!

And i still stand by what i said, if your lathe can't turn 1000 rpm then make HSS your main tooling. That doesn't mean you shouldn't use any carbide, it just means that for your average bit of 1" or less mild steel you shouldn't use carbide since the lathe won't get you high enough sfm. Thats the biggest mistake i see at the shop here. People run carbide at HSS speeds and wonder why the finish isn't any good and the tool dulls. You don't want heat going into your tool or your work piece. A properly set up carbide turning operation actually stays fairly cool (relatively speaking) since the chip removes all the heat as Evan said. If you look at the carbide inserts from big CNC shops, you'll notice that the edge is in decent condition, the part that is most heavly worn is the area right on top where the chip breaks over. When you run low speed and feed with carbide you generate more heat in the bit and piece of work. It will dull quicker. I've seen guys obliterate brand new inserts on soft 4140 just because they're trying to turn a 1/2" bar at 300 rpm.

[Davek0974]

Thanks guys so far,

just as i thought, its a mine field.

I only use carbide tipped on my Boxford, i tend to run it at about 1500 rpm, and cut anything i need to without a thought, brass, bronze, cast, steel, so on.

I even buy my tips cheap from ebay and half the time dont know what they are! Just bung 'em in and see what happens, obviuosly i'm a HSM

The surface finishes are generally good to very good and i'm happy with it.

BUT, the colchester has a top speed of 1200 and usually runs around 600 and i want to use it to do the bigger jobs and bigger cuts i cant do on the little boxford:- steam engine flywheels, wheels, cylinder bores etc lots of off centre cast iron and great big fat cuts on steel.

The little ccmt tips i use at present dont like big cuts or high feed rates and removing vast amounts of steel at 0.3mm DOC sucks.

I DO like the idea of being able to fling in another tip and maintain the cut i was doing previously without re-setting etc. (no QC holder on the colchester)

What i need is the most flexible tooling with the least amount of types etc.

All my other tip tooling uses one tip-CCMT060204 and i have 3 boring bars, left/right turning and a coarse left for using the other two unused tips.

BUT they suck for getting close to the centre as the tools are quite blunt and fat, so the DCMT looks good for that.

I doubt i will be turning much hard steel so maybe HSS wont be too bad. But then maybe a set of left/right tools for the larger CCMT09 tips would be better along with a DCMT left to get into the centre??

I'm just having a hard time making my mind up before splashing out on a set as i dont have endless funding.

BTW, i'm not sure aboutthe A/O wheel, when i got my grinder, i ordered a set of wheels one for general one for carbide, maybe it was A/Oxide and Silicon carbide?? One is grey one is green.

Dave