Home › Forums › Workshop Tools and Tooling › Carbide inserts on interrupted cuts This topic has 28 replies, 15 voices, and was last updated 8 August 2024 at 14:10 by MikeK. Viewing 25 posts - 1 through 25 (of 29 total) 1 2 → Author Posts 4 August 2024 at 19:46 #745177 MikeKParticipant @mikek40713 I’ve recently starting using carbide insert boring bars.  The attached photo is one such project. Two pieces of 3/16″ bar that had previously heavily chamfered edges.  I tack-welded the pieces together, and then drilled and bored in the lathe. In hindsight, I should have squared-up the edges first.  The chamfered edges created an interrupted cut that chipped my CCMT insert.  And I was only taking 5 or 10 thou DOC. Is there a best practice in this situation?  Use HSS instead?  Don’t do any interrupted cuts with carbide ever? Mike Advert 4 August 2024 at 19:56 #745183 JasonBModerator @jasonb I’ve never found it to be a problem and regularly turn and mill odd shaped steel fabrications, castings or just simple things like square or hex section bar, even facing off the end of a porely sawn round bar can give an interuppted cut. Don’t think we can even blame the welded joint as I’ve used carbide on welds without problem. Did you drill out to the minimum clearance diameter that the bar requites? 4 August 2024 at 20:17 #745189 Andrew CrowParticipant @andrewcrow91475 Hi Mike, for the most part model engineers don’t operate at the speeds and feeds which justify the use of carbide insert tools. So for most steels I generally use HSS, particularly if you have uneven or broken cuts, at least if you damage the tool its quickly re-sharpened. Although TC is very useful for difficult materials like stainless steel, phospher bronze and screwcutting, parting etc. They are as you have found to your cost very easily damaged. There are grades of insert that are more resistant to shock and abrasion like those for machining cast iron. I’m not up to speed on the grades required, you would probably be better to speak to someone like JB cutting tools if you want to continue using TC tips for this type of work. Andy. 4 August 2024 at 20:40 #745192 JasonBModerator @jasonb I don’t use any special inserts, just my usual general purpose ones. Infact i#ll often use the CCGT inserts which have an even more delicate edge. Couple of examples that give interupted cuts but no problems with the inserts Crankshaft from 50 x 25 bar Bit of a fabrication. **GT insert on that and on large diameter work on variable speed machines I advocate running towards the top end of the inserts speed range. Similar shaped iron casting, just over 100m/min or 325ft/min on that one. 4 August 2024 at 20:52 #745196 old martParticipant @oldmart Having bought, over the years mostly on ebay a large quantity of shapes and sizes of inserts, the big brands commonly have their suitability to sustain interrupted cutting on the box. This is important for industrial users and is generally lacking on the cheaper brands. It helps to have a variety so that you can find which are best for any particular job. I have bored soft chuck jaws with inserts intended for aluminium successfully to get a fine finish and got away with it, your metal might be simply too hard for your CCMT’s. If boring a difficult job, it is important to have the absolute minimum of unsupported bar projecting to maximise the stiffness, having a movable stop on the bed allows close work without the danger of a crash. 4 August 2024 at 21:05 #745204 MikeKParticipant @mikek40713 On 4 August 2024 at 20:17 Andrew Crow Said: Hi Mike, for the most part model engineers don’t operate at the speeds and feeds which justify the use of carbide insert tools. So for most steels I generally use HSS, particularly if you have uneven or broken cuts, at least if you damage the tool its quickly re-sharpened. Although TC is very useful for difficult materials like stainless steel, phospher bronze and screwcutting, parting etc. They are as you have found to your cost very easily damaged. There are grades of insert that are more resistant to shock and abrasion like those for machining cast iron. I’m not up to speed on the grades required, you would probably be better to speak to someone like JB cutting tools if you want to continue using TC tips for this type of work. Andy. Thanks, Andy.  I have been a die-hard HSS user, but carbide is hard to pass up.  I wasn’t turning all that fast, just a bit more than with HSS.  And likewise for feed. Mike   4 August 2024 at 21:07 #745205 MikeKParticipant @mikek40713 On 4 August 2024 at 20:40 JasonB Said: Don’t think we can even blame the welded joint as I’ve used carbide on welds without problem. … … I don’t use any special inserts, just my usual general purpose ones. Infact i#ll often use the CCGT inserts which have an even more delicate edge. Actually, I wasn’t even machining the welds.  I put the welds at the outside edges of the bars and then cut them free with an angle grinder cutoff disc after boring the center.  The bar was leftover from another thing and had the edges already chamfered. I should have pointed out as well, that after I chipped both corners of a CCMT insert I switched to CCGT and got a very nice finish and no insert damage (even inspected with a magnifier).  But I wasn’t sure if that was a fluke, since the CCMT got me to nearly full bore. Mike (This editor kind of bites it.  I couldn’t unbold that quote.) 4 August 2024 at 21:55 #745212 HuubParticipant @huub Inserts and HSS tool tips have a hard life when they have to restart cutting at every edge. A steady power feed will ensure an equal depth of cut at every position of the workpiece. In general, but not always, I use insert tools on the mini lathe and on my bigger lathe. For interrupted cuts I use cheap Iscar WNMG080408 IC908 inserts that are meant for use on more rigid lathes. They are thicker, have a large tool nose radius and don’t have a sharp cutting edge so they don’t chip that easily. They have 6 cutting edges per insert and last pretty long. They can (and I do) be run at 300 m/min (990 sfm) and at that speed, the chips get hot and soft so the tool load reduces.   4 August 2024 at 22:00 #745213 MikeKParticipant @mikek40713 Okay, next time I do something like that I’ll try a much higher RPM.  I don’t think I was anywhere near 990 sfm.  Or even half that. Mike   4 August 2024 at 22:13 #745217 FulmenParticipant @fulmen If carbide couldn’t handle interrupted cuts, why would carbide mills exist? Carbide can be somewhat counterintuitive in that they don’t like too slow speeds. Interrupted cuts combined with cooling is another source of problems as the thermal cycling can cause excessive wear on certain qualities. 4 August 2024 at 23:00 #745228 HuubParticipant @huub On 4 August 2024 at 22:13 Fulmen Said: If carbide couldn’t handle interrupted cuts, why would carbide mills exist? Carbide can be somewhat counterintuitive in that they don’t like too slow speeds. Interrupted cuts combined with cooling is another source of problems as the thermal cycling can cause excessive wear on certain qualities. If you can, run carbide at the recommend speed (RPM). Non rigid lathes can handle axial forces better than radial forces. So reduce the depth of cut and if that is not enough, reduce the feed/rev to avoid/reduce chatter. If I run out of options, I also use an insert for aluminum on steel and stainless. Because they are very sharp and mine have a 0.2 mm tool nose radius, the cutting forces are much lower then when using inserts for steel. If that also doesn’t help, i try a HSS tool. On my non rigid lathes, I use inserts intended for finishing most of the time (VP15TF). 4 August 2024 at 23:27 #745232 Neil LickfoldParticipant @neillickfold44316 There are tough grades of carbides, for interrupted cutting like milling or turning where there is a slot etc. Most of the general turning inserts are the tough ones. Then there are grades made for the heavy interrupted cutting as well. Generally these dedicated grades are not sharp, but are coated and the edge is slightly rounded over under a loupe. The very sharp CCGT inserts do cut quite well with the interrupted cutting, as long as the cut is not too deep and not too high a feed rate. A really good tough grade is the Seco TH1000 range of inserts, that have a coating for hard turning, like the Hard bar, that is induction hardened outer and a tough inner. Some of these, have quite a sharp edge making them very useful with the lower powered hobby lathes. They are making more in that range and work very well on interrupted hard cutting and softer materials as well. Generally with interrupted cutting , I keep the feed rate in the 0.05mm to 0.1mm per rev range. Usually any higher than that and the tool life is a lot lower. 4 August 2024 at 23:29 #745234 Nigel Graham 2Participant @nigelgraham2 As a general rule I try to minimise interrupted cuts as much as possible, with any type of tool, and the larger the radius the less I like them. That is not just a matter of what the tool can handle, but also the hammering effect on the lathe. I don’t often use fly-cutting on the mill, for the same reason. If I need machine a chain-drilled surface I always remove the worst of the ridges first, by filing or (less often and certainly not as first choice) grinding. On my manual shaper, I file a chamfer on the approach edge first to take some of the shock out of the action. Regarding speeds and feeds, I must admit I do not sit down with a calculator first! I judge the action by watching and listening; and quite honestly have never found any real problems using carbide tips at modest speeds. . One exception is some mild steel of unknown parentage and even less quality-control, originally the tie-rods for a big cable-drum. It tears dreadfully with carbide but a sharp HSS tool, cutting oil and experimenting with speeds and feeds brings acceptable results for the intended purposes (not fine-finish moving parts, and often painted). The alleged steel stocked by a certain DIY supermarket chain is similar, and sometimes so rough and approximate to diameter it has to be skimmed before die-threading, but again, I use this only for non-critical applications. On a model it would be for parts that on the full-size were likely to have been just brush-painted over hot-rolled or forged surfaces – tie-rods, brackets and the like. 4 August 2024 at 23:36 #745236 MikeKParticipant @mikek40713 On 4 August 2024 at 22:13 Fulmen Said: If carbide couldn’t handle interrupted cuts, why would carbide mills exist? A good point indeed. 4 August 2024 at 23:57 #745241 Dave HalfordParticipant @davehalford22513 If you need an interrupted cutting insert the info is in the grade number along with the metal type. Obviously premium makers only. 5 August 2024 at 07:38 #745272 JasonBModerator @jasonb When I said my “usual general purpose” inserts that is what I generally use not what the maker sells as GP. The CCMT are markled “LF” light finishing and are 060202 so small tip radius and the same with the others either CCGT 060202 or DCGT 070202 5 August 2024 at 07:42 #745275 Nigel Graham 2Participant @nigelgraham2 Fulmen- There is far less impact between the work surface and cutting edge in milling, than in turning with interrupted cuts; and the cutting geometry in milling is quite different from that of turning. There are big multi-point face-milling cutters with inserted carbide tips, but the tips are designed for that duty. 5 August 2024 at 07:46 #745277 JasonBModerator @jasonb Plent of people about who put a lathe tool holder into a fly cutter and get good results with that so can’t be the geometry or number of inserts. I also use insert holders on my boring head that take lathe inserts often start with an irregular shaped hole or use them to cut a concave surface rather than a complete hole. 5 August 2024 at 09:06 #745291 JasonBModerator @jasonb One other thing to watch if you feel the need to go for an insert intended for interupted cuts is they tend to be *N** not *C** so you will need to buy additional tool holders to suit the neutral edge as they don’t fit the common 7deg edge of the “C” type holders. Also likely to only come in the larger sizes so if you are limited for tool height then the associated larger shank holders may not fit. Ditto if wanting to bore a small hole. 5 August 2024 at 09:49 #745304 FulmenParticipant @fulmen @Nigel: No argument there, just pointing out that carbide isn’t inherently ill-suited for interrupted cuts. Climb milling isn’t far from an interrupted turning cut. And while there are qualities more or less suited for these loads most general purpose inserts need to handle the occasional interrupted cut without instantly breaking. 5 August 2024 at 10:04 #745311 SillyOldDufferModerator @sillyoldduffer On 4 August 2024 at 20:17 Andrew Crow Said: Hi Mike, for the most part model engineers don’t operate at the speeds and feeds which justify the use of carbide insert tools. … A bold assertion from Andy! But carbide’s ability to remove metal faster than HSS isn’t the main reason many prefer it to HSS.  It’s because inserts are easier to use and/or more convenient than HSS!  Reasons include: No need to buy a grinder. (Cheap modern ones are no good – a heavy industrial unit with a suitably hefty tool-support is needed.) No need to learn grinding.  Many find acquiring grinding skills difficult, despite the persistent claims of HSS fans that it’s easy! Most common tool-forms are available off-the-shelf, with many inserts supporting up to four cutting edges.  Thread forms are particularly useful. Once the tool-holder is set to height, inserts can be swapped and rotated without readjusting anything.  Not possible with HSS, though similar flexibility can be obtained by buying a Quick Change Tool Post and several tool-holders.  (Whilst HSS is a cheap  material, spending money and wasting time is no object when it comes to using it!) Inserts aren’t perfect.  They’re consumables, not meant to last forever!   Not a problem because, when they wear out, inserts are quickly replaced without disturbing the workflow.  Stopping to resharpen HSS is much more disruptive. Early carbide was brittle compared with HSS; this is much less true today.   Like Jason I don’t have much trouble doing interrupted cuts, certainly not enough to condemn carbide outright. In practice I use both, carbide preferred at least 80% of the time.   Main reason I switch to HSS is that it’s easier to get a good finish on difficult materials – carbide is fussier than HSS about rpm, depth of cut and feed-rate.   The other reason is special form tools; HSS can be custom ground – cutters aren’t limited to standard shapes. Bottom line, though carbide delivers best results when driven harder than HSS,  that’s not essential, or the main reason I prefer it. Dave 5 August 2024 at 11:08 #745324 Roderick JenkinsParticipant @roderickjenkins93242 This Hoglet crank web in mild steel was turned with a CCGT tip at about 600rpm.  No problems at all and a very nice finish. Rod 5 August 2024 at 11:48 #745337 Anonymous This was a fairly brutal interrupted cut: Cleaning up these chain drilled bores in hot rolled steel: I used a CCMT insert at 370rpm, 0.05″ DOC and 8 thou per rev feed. I got through one edge per part. The noise was horrendous, with plenty of chatter, but it got the job done. The inserts didn’t chip but the edges wore away over time. I only chip an insert if I do something daft, like run the insert into the chuck when everything is stationary. Andrew 6 August 2024 at 22:29 #745616 Mick BaileyParticipant @mickbailey28509 I recently used an inserted tool to turn up some punches from hex bar cut from 3/8″ Allen Keys – good quality ones, not the cheap type. I got a bit too ambitious and increased the depth of cut too much, chipping a fresh insert. Afterwards though I took my time and didn’t have any further problem. I’d previously tried HSS but the edge disappeared quickly and ended up rubbing. Coolant was Rocol Ultra cut. 7 August 2024 at 12:53 #745701 PeteParticipant @pete41194 There’s multiple grades of carbide, and those letter designations to identify replaceable carbide tips doesn’t mean there all exactly equal in performance between the multiple brands. Each different manufacturer almost for sure uses various binders and possibly slight differences for the same grade of carbide and it’s letter designation. Even the sintering processes are unlikely to be exactly the same between each manufacturer. So there’s multiple reasons MikeK may have had his CCMT inserts chip and others mention having no issues. Yes rpm and feed rate is important, depth of cut even more so. Double the depth of cut with everything else equal, and the shock impact levels the carbide tip sees will be much much higher. Depending on the steel alloy, the welds might be easily machined, but that heat might well have hardened or created a heat affected zone. With harder metal, the carbide will chip much more easily. Even a small tip radius verses a large one will chip easier. Braised tip carbide will also be more chip resistant than the replaceable simply due to the better support behind the carbide that type of cutting tool has. He didn’t mention it, but infrequent applications of coolant or cutting oil can also cause micro fracturing with carbide that also helps the carbide to chip. I have a fly cutter specifically designed to use the round RNG round carbide tips. Obviously it’s never once seen anything other than an interrupted cut. And like Jasons examples, boring heads excel at producing accurate partial internal radii. But I still reduce my DOC compared to doing a continuous cut when boring. And most of my boring bars are either solid carbide, braised or have replaceable tips. I don’t agree that most amateur’s don’t use the extra rpm carbide is capable of, While I personally chose to never use the maximum, I do try to stay within 85%-90% of it whenever possible. I also read the chip color when machining steel. Turning light to medium blue after the chip has left the work piece is my cutoff point for maximum rpm with carbide, and what the manufacturer says for rpm may or may not be true for what I’m doing. There maximum rpm listings are only handy but suggested starting points anyway. Chips turning dark blue to purple is for commercial work in my opinion where speed and bulk metal removal is more important than the best cutting edge life. Afaik, there’s in general at least 6 grades of carbide hardness. I don’t recall seeing any C1 carbide used for cutting tools, but I believe C2 & C3 are used for wood router bits. C4-C6 is likely the grades of replaceable tips we might be using. But there could easily be more I have no knowledge of. It’s my understanding that the higher the amount of cobalt binder used, the more chip resistant the carbide becomes. But more binder reduces the tools effective cutting edge life span. Pick which one you want because you can’t get both in the same piece of carbide. Author Posts Viewing 25 posts - 1 through 25 (of 29 total) 1 2 → Please log in to reply to this topic. Registering is free and easy using the links on the menu at the top of this page.

Also likely to only come in the larger sizes so if you are limited for tool height then the associated larger shank holders may not fit. Ditto if wanting to bore a small hole.

If you need an interrupted cutting insert the info is in the grade number along with the metal type. Obviously premium makers only.

Two pieces of 3/16″ bar that had previously heavily chamfered edges.  I tack-welded the pieces together, and then drilled and bored in the lathe. In hindsight, I should have squared-up the edges first.  The chamfered edges created an interrupted cut that chipped my CCMT insert.  And I was only taking 5 or 10 thou DOC.

I should have pointed out as well, that after I chipped both corners of a CCMT insert I switched to CCGT and got a very nice finish and no insert damage (even inspected with a magnifier).  But I wasn’t sure if that was a fluke, since the CCMT got me to nearly full bore.

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This Hoglet crank web in mild steel was turned with a CCGT tip at about 600rpm.  No problems at all and a very nice finish.

Early carbide was brittle compared with HSS; this is much less true today.   Like Jason I don’t have much trouble doing interrupted cuts, certainly not enough to condemn carbide outright.

Hi Mike, for the most part model engineers don’t operate at the speeds and feeds which justify the use of carbide insert tools. So for most steels I generally use HSS, particularly if you have uneven or broken cuts, at least if you damage the tool its quickly re-sharpened.

Okay, next time I do something like that I’ll try a much higher RPM.  I don’t think I was anywhere near 990 sfm.  Or even half that.

The CCMT are markled “LF” light finishing and are 060202 so small tip radius and the same with the others either CCGT 060202 or DCGT 070202

I don’t use any special inserts, just my usual general purpose ones. Infact i#ll often use the CCGT inserts which have an even more delicate edge.

But carbide’s ability to remove metal faster than HSS isn’t the main reason many prefer it to HSS.  It’s because inserts are easier to use and/or more convenient than HSS!  Reasons include:

As a general rule I try to minimise interrupted cuts as much as possible, with any type of tool, and the larger the radius the less I like them.

Plent of people about who put a lathe tool holder into a fly cutter and get good results with that so can’t be the geometry or number of inserts.

Inserts and HSS tool tips have a hard life when they have to restart cutting at every edge. A steady power feed will ensure an equal depth of cut at every position of the workpiece.

The alleged steel stocked by a certain DIY supermarket chain is similar, and sometimes so rough and approximate to diameter it has to be skimmed before die-threading, but again, I use this only for non-critical applications.

Image

In general, but not always, I use insert tools on the mini lathe and on my bigger lathe. For interrupted cuts I use cheap Iscar WNMG080408 IC908 inserts that are meant for use on more rigid lathes. They are thicker, have a large tool nose radius and don’t have a sharp cutting edge so they don’t chip that easily. They have 6 cutting edges per insert and last pretty long. They can (and I do) be run at 300 m/min (990 sfm) and at that speed, the chips get hot and soft so the tool load reduces.

Carbide can be somewhat counterintuitive in that they don’t like too slow speeds. Interrupted cuts combined with cooling is another source of problems as the thermal cycling can cause excessive wear on certain qualities.

I don’t agree that most amateur’s don’t use the extra rpm carbide is capable of, While I personally chose to never use the maximum, I do try to stay within 85%-90% of it whenever possible. I also read the chip color when machining steel. Turning light to medium blue after the chip has left the work piece is my cutoff point for maximum rpm with carbide, and what the manufacturer says for rpm may or may not be true for what I’m doing. There maximum rpm listings are only handy but suggested starting points anyway. Chips turning dark blue to purple is for commercial work in my opinion where speed and bulk metal removal is more important than the best cutting edge life. Afaik, there’s in general at least 6 grades of carbide hardness. I don’t recall seeing any C1 carbide used for cutting tools, but I believe C2 & C3 are used for wood router bits. C4-C6 is likely the grades of replaceable tips we might be using. But there could easily be more I have no knowledge of. It’s my understanding that the higher the amount of cobalt binder used, the more chip resistant the carbide becomes. But more binder reduces the tools effective cutting edge life span. Pick which one you want because you can’t get both in the same piece of carbide.

One other thing to watch if you feel the need to go for an insert intended for interupted cuts is they tend to be *N** not *C** so you will need to buy additional tool holders to suit the neutral edge as they don’t fit the common 7deg edge of the “C” type holders.

Climb milling isn’t far from an interrupted turning cut. And while there are qualities more or less suited for these loads most general purpose inserts need to handle the occasional interrupted cut without instantly breaking.

I don’t use any special inserts, just my usual general purpose ones. Infact i#ll often use the CCGT inserts which have an even more delicate edge.

If I need machine a chain-drilled surface I always remove the worst of the ridges first, by filing or (less often and certainly not as first choice) grinding.

I used a CCMT insert at 370rpm, 0.05″ DOC and 8 thou per rev feed. I got through one edge per part. The noise was horrendous, with plenty of chatter, but it got the job done. The inserts didn’t chip but the edges wore away over time.

Bottom line, though carbide delivers best results when driven harder than HSS,  that’s not essential, or the main reason I prefer it.

Inserts aren’t perfect.  They’re consumables, not meant to last forever!   Not a problem because, when they wear out, inserts are quickly replaced without disturbing the workflow.  Stopping to resharpen HSS is much more disruptive.

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Although TC is very useful for difficult materials like stainless steel, phospher bronze and screwcutting, parting etc. They are as you have found to your cost very easily damaged. There are grades of insert that are more resistant to shock and abrasion like those for machining cast iron. I’m not up to speed on the grades required, you would probably be better to speak to someone like JB cutting tools if you want to continue using TC tips for this type of work.

I have a fly cutter specifically designed to use the round RNG round carbide tips. Obviously it’s never once seen anything other than an interrupted cut. And like Jasons examples, boring heads excel at producing accurate partial internal radii. But I still reduce my DOC compared to doing a continuous cut when boring. And most of my boring bars are either solid carbide, braised or have replaceable tips.

I recently used an inserted tool to turn up some punches from hex bar cut from 3/8″ Allen Keys – good quality ones, not the cheap type. I got a bit too ambitious and increased the depth of cut too much, chipping a fresh insert. Afterwards though I took my time and didn’t have any further problem. I’d previously tried HSS but the edge disappeared quickly and ended up rubbing. Coolant was Rocol Ultra cut.

Having bought, over the years mostly on ebay a large quantity of shapes and sizes of inserts, the big brands commonly have their suitability to sustain interrupted cutting on the box. This is important for industrial users and is generally lacking on the cheaper brands. It helps to have a variety so that you can find which are best for any particular job. I have bored soft chuck jaws with inserts intended for aluminium successfully to get a fine finish and got away with it, your metal might be simply too hard for your CCMT’s. If boring a difficult job, it is important to have the absolute minimum of unsupported bar projecting to maximise the stiffness, having a movable stop on the bed allows close work without the danger of a crash.

In practice I use both, carbide preferred at least 80% of the time.   Main reason I switch to HSS is that it’s easier to get a good finish on difficult materials – carbide is fussier than HSS about rpm, depth of cut and feed-rate.   The other reason is special form tools; HSS can be custom ground – cutters aren’t limited to standard shapes.

I’ve never found it to be a problem and regularly turn and mill odd shaped steel fabrications, castings or just simple things like square or hex section bar, even facing off the end of a porely sawn round bar can give an interuppted cut.

Bit of a fabrication. **GT insert on that and on large diameter work on variable speed machines I advocate running towards the top end of the inserts speed range.

Generally with interrupted cutting , I keep the feed rate in the 0.05mm to 0.1mm per rev range. Usually any higher than that and the tool life is a lot lower.

If I run out of options, I also use an insert for aluminum on steel and stainless. Because they are very sharp and mine have a 0.2 mm tool nose radius, the cutting forces are much lower then when using inserts for steel. If that also doesn’t help, i try a HSS tool. On my non rigid lathes, I use inserts intended for finishing most of the time (VP15TF).

There’s multiple grades of carbide, and those letter designations to identify replaceable carbide tips doesn’t mean there all exactly equal in performance between the multiple brands. Each different manufacturer almost for sure uses various binders and possibly slight differences for the same grade of carbide and it’s letter designation. Even the sintering processes are unlikely to be exactly the same between each manufacturer. So there’s multiple reasons MikeK may have had his CCMT inserts chip and others mention having no issues. Yes rpm and feed rate is important, depth of cut even more so. Double the depth of cut with everything else equal, and the shock impact levels the carbide tip sees will be much much higher. Depending on the steel alloy, the welds might be easily machined, but that heat might well have hardened or created a heat affected zone. With harder metal, the carbide will chip much more easily. Even a small tip radius verses a large one will chip easier. Braised tip carbide will also be more chip resistant than the replaceable simply due to the better support behind the carbide that type of cutting tool has.

If you can, run carbide at the recommend speed (RPM). Non rigid lathes can handle axial forces better than radial forces. So reduce the depth of cut and if that is not enough, reduce the feed/rev to avoid/reduce chatter.

What did you do Today 2024 Brandy Milling vice Choice My week this week! My workshop videos “Quality” milling cutters, adn where to buy? Bed for 6040 CNC? Tapered gib problem Arnfield Gravity Escapement Tich Loco. A sad tale. Can anyone help? Mill Tramming Tool (& Use on a Centec With Riser.)

That is not just a matter of what the tool can handle, but also the hammering effect on the lathe. I don’t often use fly-cutting on the mill, for the same reason.

One exception is some mild steel of unknown parentage and even less quality-control, originally the tie-rods for a big cable-drum. It tears dreadfully with carbide but a sharp HSS tool, cutting oil and experimenting with speeds and feeds brings acceptable results for the intended purposes (not fine-finish moving parts, and often painted).

I also use insert holders on my boring head that take lathe inserts often start with an irregular shaped hole or use them to cut a concave surface rather than a complete hole.

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Actually, I wasn’t even machining the welds.  I put the welds at the outside edges of the bars and then cut them free with an angle grinder cutoff disc after boring the center.  The bar was leftover from another thing and had the edges already chamfered.

Regarding speeds and feeds, I must admit I do not sit down with a calculator first! I judge the action by watching and listening; and quite honestly have never found any real problems using carbide tips at modest speeds.

He didn’t mention it, but infrequent applications of coolant or cutting oil can also cause micro fracturing with carbide that also helps the carbide to chip.

Thanks, Andy.  I have been a die-hard HSS user, but carbide is hard to pass up.  I wasn’t turning all that fast, just a bit more than with HSS.  And likewise for feed.

On a model it would be for parts that on the full-size were likely to have been just brush-painted over hot-rolled or forged surfaces – tie-rods, brackets and the like.

Hi Mike, for the most part model engineers don’t operate at the speeds and feeds which justify the use of carbide insert tools. So for most steels I generally use HSS, particularly if you have uneven or broken cuts, at least if you damage the tool its quickly re-sharpened.

There are tough grades of carbides, for interrupted cutting like milling or turning where there is a slot etc. Most of the general turning inserts are the tough ones. Then there are grades made for the heavy interrupted cutting as well. Generally these dedicated grades are not sharp, but are coated and the edge is slightly rounded over under a loupe. The very sharp CCGT inserts do cut quite well with the interrupted cutting, as long as the cut is not too deep and not too high a feed rate. A really good tough grade is the Seco TH1000 range of inserts, that have a coating for hard turning, like the Hard bar, that is induction hardened outer and a tough inner. Some of these, have quite a sharp edge making them very useful with the lower powered hobby lathes. They are making more in that range and work very well on interrupted hard cutting and softer materials as well.

Hi Mike, for the most part model engineers don’t operate at the speeds and feeds which justify the use of carbide insert tools. …

There is far less impact between the work surface and cutting edge in milling, than in turning with interrupted cuts; and the cutting geometry in milling is quite different from that of turning.

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Although TC is very useful for difficult materials like stainless steel, phospher bronze and screwcutting, parting etc. They are as you have found to your cost very easily damaged. There are grades of insert that are more resistant to shock and abrasion like those for machining cast iron. I’m not up to speed on the grades required, you would probably be better to speak to someone like JB cutting tools if you want to continue using TC tips for this type of work.

Carbide can be somewhat counterintuitive in that they don’t like too slow speeds. Interrupted cuts combined with cooling is another source of problems as the thermal cycling can cause excessive wear on certain qualities.