Are lathe tool carbide inserts supposed to be sharp?

[Bentwings]

Different cutting tools as much as anything else have their place, I was taught in a formal apprenticeship how to sharpen HSS and I still do this on custom tools but given the choice I go carbide inserts every time.

My lathe is an EMCO 5, I am the only owner from new and it is nicely setup, recently I had a job where PCD inserts were recommended, so I bought one off insert at £30 (approx $42), this insert has taken the lathe into areas of accuracy and capability that I never thought possible, this insert cuts so well that it has for all intents and purposes removed spring back, I am able to wind on 2 micron cuts and see the tiny amount of material being removed - quite incredible.

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For our small 10” lathe I hone the edges of carbide inserts sharp with a small radius hone on the leadin point this usually gives a pretty good finish however a sharp high speed steel does just about as well . Under microscope carbide is slightly porous or rough. It is a sintered powder so sharp edges break down under heavy cuts . The chip breakers are there to allow heavier cuts with the chip being s chip rather than a string. I also use some tempered steel shims for lack of a word that are ground and positioned as chip breakers as I don’t like stringy stuff flying around. It takes a little monkeying around to get these to work but once it’s working fine cuts are much easier. I save most carbide for the heavier cuts. Our 10” has a 3 phase motor that’s very powerful so even tough steel like 4140 cuts easily. I suppose one day a gear is going to strip or the lead screw will fail . We have given thought to converting to ball screws but I’m more interested in making a reverse for the lead screw. It a grizzly 602 spin off but has a totally different gear train . Leave it to grizzly yo come up with this system. So far I have not seen another lathe or eve one of grizzly lathes that I could use the gear trains from without a lot of work . If some one has a solution I sure would like to know.
Thanks
Byron

 

[DavidBC]

I served my time at an Australian company that manufactured sintered carbide tip tools. All the brazed tip tools were finished with diamond wheels with a positive rake and all the sintered tips were left as they were after the sintering process. Considering that they require a small increase in power all carbide inserts that we used were all negative rake as when required you just turned the insert over and you had virtually a new insert, so we got double the use out off a negative rake insert compared to a positive rake. Even though we had a never ending supply of tipped tools to use we still favored the finishing cut to be done with a well ground and honed HSS tool bit on some machined items.

Regards
DavidBC

 

[Ozwes007]

I served my time at an Australian company that manufactured sintered carbide tip tools. All the brazed tip tools were finished with diamond wheels with a positive rake and all the sintered tips were left as they were after the sintering process. Considering that they require a small increase in power all carbide inserts that we used were all negative rake as when required you just turned the insert over and you had virtually a new insert, so we got double the use out off a negative rake insert compared to a positive rake. Even though we had a never ending supply of tipped tools to use we still favored the finishing cut to be done with a well ground and honed HSS tool bit on some machined items.

Regards
DavidBC

In essence carbide doesn’t lend itself to particularly sharp edges, however with todays coatings and superfine structure they do make “sharps”. They are a honed edge tool designed for aluminium or plastic. I have used them for over 10 years now and they are as good as any other for there purpose. I generally work on 6 to 8 hours cutting time for a tip edge. So most carbides are extremely economical to use.

 

[Richard Hed]

For our small 10” lathe I hone the edges of carbide inserts sharp with a small radius hone on the leadin point this usually gives a pretty good finish however a sharp high speed steel does just about as well . Under microscope carbide is slightly porous or rough. It is a sintered powder so sharp edges break down under heavy cuts . The chip breakers are there to allow heavier cuts with the chip being s chip rather than a string. I also use some tempered steel shims for lack of a word that are ground and positioned as chip breakers as I don’t like stringy stuff flying around. It takes a little monkeying around to get these to work but once it’s working fine cuts are much easier. I save most carbide for the heavier cuts. Our 10” has a 3 phase motor that’s very powerful so even tough steel like 4140 cuts easily. I suppose one day a gear is going to strip or the lead screw will fail . We have given thought to converting to ball screws but I’m more interested in making a reverse for the lead screw. It a grizzly 602 spin off but has a totally different gear train . Leave it to grizzly yo come up with this system. So far I have not seen another lathe or eve one of grizzly lathes that I could use the gear trains from without a lot of work . If some one has a solution I sure would like to know.
Thanks
Byron

just exactly what is the prob with the gear train? What is the center diameter of your gears? What is the size of the teeth? Maybe you could send a photo

 

[Steamchick]

Re #63. I have a few odd bits from a plastic machining job, which were supposed to be cutting angles and sharpness for aluminium. I just use them on everything and touch up edges (diamond hone or stone) if cast iron or something takes off the edge.
K2

 

[clockworkcheval]

The slow turning diameter 250 mm wet grinder of Tormek is very good and outrageously expensive. A couple of years ago I could convince the powers to be that one had to be purchased because it is very good at razor-sharp grinding of kitchen knives. The first few times the enclosed band-aids proved to be not a luxury, because we just were not used to handle this sharp equipment. I used it otherwise mostly for larger drills and for wood-working chisels.
Recently Tormek brought out a set of very nice diamond cutting wheels of 250 mm diameter. I found that their Extra Fine diamond cutting wheel with a little water-dip will sharpen to a fine polish both carbide tips and inserts. And the nice thing is that you can also use the huge flat side of the wheel utilizing the standard Tormek tool positioning equipment. Tormek states that with careful use the diamond wheel will last a lifetime. And all of a sudden I use carbide inserts for all regular work, also very fine finishing work. For all special forms I stick with HSS tools. See enclosed pictures.

 

[Bentwings]

The slow turning diameter 250 mm wet grinder of Tormek is very good and outrageously expensive. A couple of years ago I could convince the powers to be that one had to be purchased because it is very good at razor-sharp grinding of kitchen knives. The first few times the enclosed band-aids proved to be not a luxury, because we just were not used to handle this sharp equipment. I used it otherwise mostly for larger drills and for wood-working chisels.
Recently Tormek brought out a set of very nice diamond cutting wheels of 250 mm diameter. I found that their Extra Fine diamond cutting wheel with a little water-dip will sharpen to a fine polish both carbide tips and inserts. And the nice thing is that you can also use the huge flat side of the wheel utilizing the standard Tormek tool positioning equipment. Tormek states that with careful use the diamond wheel will last a lifetime. And all of a sudden I use carbide inserts for all regular work, also very fine finishing work. For all special forms I stick with HSS tools. See enclosed pictures.

View attachment 138877View attachment 138878

I served my time at an Australian company that manufactured sintered carbide tip tools. All the brazed tip tools were finished with diamond wheels with a positive rake and all the sintered tips were left as they were after the sintering process. Considering that they require a small increase in power all carbide inserts that we used were all negative rake as when required you just turned the insert over and you had virtually a new insert, so we got double the use out off a negative rake insert compared to a positive rake. Even though we had a never ending supply of tipped tools to use we still favored the finishing cut to be done with a well ground and honed HSS tool bit on some machined items.

Regardsinserts usually have some sort of chip breaker built in if you look closely the cutting edge is kinda dull. If you are taking light cuts the tool sorta just pushes a crumpled chip leaving a relatively full surface . The inserts are made to get into the metal . For fine finishes and light cuts I tune the edges and diamond hone to high speed steel sharpness radius the nose a little carbide is a sintered product so by nature not especially sharp grinding and honing does make very sharp edges but you also sacrifice strength of cutting edge so I you suddenly want a heavier cut you need to go back to un tuned insert for edge strength. It may cost you one or more sides of the insert but that’s the trade off . A brazed tool is the same way make it razor sharp but it can micro chip and mess up the finish. So you can see why cutting tools are made for the job . HS steel holds the edge longer I think but you still have to keep it tuned. It’s possible to grind in chip breakers in HS but some times you can just add a blocker bar that curly the smaller chip. I’ve don this a lot over the years but it’s often hit or miss. Grinding in chip breakers can mak the tool a one time use or project specific tool. Either way costs start entering the picture.
When youbhavectobfootvthevtool bill yourself you get more choosey
DavidBC

 

[Steamchick]

Diamonds are forever?
I use a 3in cup diamond "stone"... - replaced a green grit cup stone.tool rest is a few degrees over 90deg. So I naturally grind some relief. Fine for sharpening carbine tips and inserts, for brass n aluminium.
K2

 

[Richard Hed]

Diamonds are forever?
I use a 3in cup diamond "stone"... - replaced a green grit cup stone.tool rest is a few degrees over 90deg. So I naturally grind some relief. Fine for sharpening carbine tips and inserts, for brass n aluminium.
K2

When I first got a green stone wheel, I thot it was going to be the stone to end all, use it exclusively for carbide grinding. However, the stone is so flaky that it grinds away too quickly. Recently got some diamond embedded grinders which are much better in that way, however is very slow grinding. When I workt in industry, we had a different kind of grinder, diamond embedded which you put in a mill or drill. This too was very slow but did excellent work. Those type are quite expensive: 100USD. I have been wanting one for years. Maybe get one this year.

 

[Vietti]

Being cheap I have used diamond discs from China at around $11 ea. The finer grits work best. Glue to a substantial steel disc, and away you go.

Google them

Amazon.com/JOINER-Diamond-Coated-Grinding-Polishing/dp/B01GU3427M/ref=asc_df_B01GU3427M/?tag=hyprod-20&linkCode=df0&hvadid=475864565960&hvpos=&hvnetw=g&hvrand=6923605640146496464&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9029304&hvtargid=pla-1028197055182&th=1

 

[Richard Hed]

Being cheap I have used diamond discs from China at around $11 ea. The finer grits work best. Glue to a substantial steel disc, and away you go.

Google them

Amazon.com/JOINER-Diamond-Coated-Grinding-Polishing/dp/B01GU3427M/ref=asc_df_B01GU3427M/?tag=hyprod-20&linkCode=df0&hvadid=475864565960&hvpos=&hvnetw=g&hvrand=6923605640146496464&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9029304&hvtargid=pla-1028197055182&th=1

Have you tried coarser stuff? I would thimpfk that coarser would rough grind faster. doesn't mean I'm right. What do you grind? I intend to sharpen carbide bits and carbide end mills (that have broken) into cutting shapes.

 

[Steamchick]

I have a 3" version of this:
https://www.ebay.co.uk/itm/23448744...F8/wPmw+sWaPsE6sWO1ZrzOaPQ==|tkp:BFBMkKGbucpgPerfectly adequate..? - Replaced the green grit and doesn't wear away. But very slow to remove any quantity of metal, however, I use it for sharpening existing shaped tools, not creating new shapes.
Or this?
https://www.ebay.co.uk/itm/234519070353?hash=item369a6d0691:g:dTkAAOSwQpZiYRKeK2

 

[clockworkcheval]

The only set-back of diamond grinding wheels compared with CBS is, as I understand, that CBS is very heat-resistant but a bit less hard than diamond whereas diamond is very hard but not really heat-resistant. If diamond gets too hot it will crack and pulverize. So a slowly revolving wheel touching water is a good formula for a long live of your diamond grinding wheel. Just putting a diamond wheel on your high-revs bench grinder may be disappointing, but putting a CBS wheel on it works fine. Basically using diamond for finishing and CBS for shaping seems to be the right choice.

 

[Vietti]

Richard,

I find the coarse discs are too coarse for most work and the diamond density isn't very good so the diamonds tend to get knocked off?

I have one of those Leonard grind/laps, 5". the same machine was sold by other companies with different names. The factory sells diamond discs but last I looked they were over $160, better quality no doubt. I bought a bunch of 5" dia,/1/4" thick drops and glued the discs to them. Need to cut a hole in the center.

I tend to use the diamond discs for all hard materials including carbide. Tried to sharpen carbide tool inserts-not too good! Works really nice on cutoff tools. I never loved the green wheel for a variety of reasons.

John

 

[Richard Hed]

The only set-back of diamond grinding wheels compared with CBS is, as I understand, that CBS is very heat-resistant but a bit less hard than diamond whereas diamond is very hard but not really heat-resistant. If diamond gets too hot it will crack and pulverize. So a slowly revolving wheel touching water is a good formula for a long live of your diamond grinding wheel. Just putting a diamond wheel on your high-revs bench grinder may be disappointing, but putting a CBS wheel on it works fine. Basically using diamond for finishing and CBS for shaping seems to be the right choice.

Can you remind me what CBS means? I thot that was a broadcasting monopoly.

 

[Steamchick]

Cubic boron silicate at a guess? (Whatever that really is!) I must have heard the phrase somewhere....?
K2

 

[Richard Hed]

Cubic boron silicate at a guess? (Whatever that really is!) I must have heard the phrase somewhere....?
K2

there is a CBN--Cubic Boric Nitride which is used as an abrasive second inhardness to diamond. But I haven't found any tool bits made of it yet.

 

[clockworkcheval]

My mistake: it is indeed CBN - Cubic Boron Nitride. Hardness only second to diamond. Rpm for a 200 mm CBN wheel 1400 - 3000. The base of the CBN wheel is a steel disc or drum, so no distortion or explosion, and no dressing.
Diamond wheel 200 - 250 mm rpm 90 - 100. The base of the diamond wheel is also a steel disc or drum, so no distortion or explosion, and no dressing.
Both CBN and diamond wheels are expensive, but a one-time investment. They really last extremely long, if well done at least 20 - 30 years. Both should only be used on hard tool materials, not on regular soft steel.

 

[davesmith729]

Grinding steel on diamond disks can ruin the disks. Yes, diamonds are the hardest thing but when grinding steel the carbon in the hot diamonds can migrate to the steel and cause many problems which why you should only grind carbide on diamond wheels.

 

[ajoeiam]

there is a CBN--Cubic Boric Nitride which is used as an abrasive second inhardness to diamond. But I haven't found any tool bits made of it yet.

Sorry - - - need to look a little further.
Greenleaf Crop is one name that I remember for such tooling.
Used on hardened materials and really tough as used (IIRC for the second).
Didn't use them often but when you drop an insert made of CBN into the lathe and you're turning 4140 - - - - wow - - - feels like race car time!!!!!
(That was the demo in my training.)