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- Nov 27, 2012
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Ok, your lathe seems to be somewhat similar in size to my import lathe. As I mentioned earlier, there are basically two types of inserts, negative & positive. Negatives are stronger than positives. Generally, carbide doesn't like shallow depths of cuts. Slow feeds is ok but they also don't like slow SFPM, YMMV of course & depending on carbide grades. When I means grades, I'm not talking about the generic C2, C6, etc grades for brazed carbide. All the insert manufactures have thei own specialized grades & coatings which is a whole different world of confusion for starters, I won't get into that.
Smaller lathes generally don't do well with negative inserts because they require more power to do well with them. I found that out the hard way. Although my lathe does ok with negative inserts, I mainly use positive inserts. Positive inserts are great for lathes with less HP & less rigidity. However there are also high positive geometries within negatives & positives, usually these are available specific for aluminum but not always. For instance I use CNMG for heavier turning which is the only negative insert I use. But I also use CNGG which is a positive geometry insert that will fit in the same tool holders that use CNMG. CNGG is still considered a negative insert, but it's ground to have a positive profile. And for positive inserts, there are also the high positive ground inserts for alumn, very sharp & work great on plastics & woods, I also use then for final finishing on Ti. Confusing right? Yup it is & I probably don't even know what I'm talking about.
Ok, I don't want to cause anymore confusion. If you want to get into indexables, I would suggest the following for starters as they are very common, since they've been around for a while, tooling can be had for cheap instead of paying $20 per insert for some new line on the market.
TCMT are 60° triangle positive inserts, you'll get 3 cutting edges per insert. Great for less HP lathes & has fair strength. Great for less HP means reduces chances of chatter. Probably the cheapest turning inserts you can buy & very popular. Boring bars are available that use the same insert. A 5pc set or turning holders are available from many places & are inexpensive. TCGT & TCGX are the equivalent high positive ground inserts.
CCMT are 80° positive inserts, usually 2 cutting edges per insert for turning, but there are other holders & facemills that allow you to use the other two "unused" edges. Requires a bit mor HP than the triangles & they are also stronger. The holders are SCLCR/L (the last letter you would use R or L for RH or LH holders). Boring bars are also available to accept these inserts. CCGT & CCGX are the high positive equivelents. I use these the most. My boring bars also use these inserts which is great cause I can use the same inserts for most of my turning, saves money on having to buy different inserts for your turning tools vs boring bars.
DCMT are 55° positive inserts, similar to the CCMT but are longer, 2 cutting edges per insert. These require less HP than the triangle inserts so they perform well but they are also not as strong as the triangle inserts so they're not good for heavy turning. The holders are SDJC/R/L & SDNCN. I use these for finishing sometimes & mostly for times where space is tight. There are also boring bars available that use these but require a bigger starting hole than the previous style inserts mentioned. DCGT & DCGX are the high positive equivalents.
TNMG are 60° triangle negative inserts. You'll get 6 cutting edges per insert as you can flip the insert upside down to get the additional 3 edges. Stronger insert but requires more HP. If you'll lathe can't handle it, you'll get poor finishes, this is generally the case for most negative inserts. Holders are MTJNR/L. TNGG & TNMP for positive style equivalents.
CNMG are 80° diamond negative inserts. 4 cutting edges per insert, again flip to get the other 2. Like the CCMT, there are holders & face mills that will allow you to use the other 2 "unused" edges. Very popular in shops, common so they are cheap & strong. Holders are MCLNR/L. CNGG & CNMP for the positive equivalents. I use these for heavier turning & roughing. They last me forever as I don't use them to their full potential often.
DNMG are 55° negative inserts. 4 edges per insert, 2 per side. These are negative version of the DCMT. By now you can see the pattern of the common positive & negative insert shapes. So not as strong as the the TNMG or CNMG but has a smaller tip that allows you to reach into tight areas. These might actually work better than the TNMG on lathes that don't quite have enough HP & rigidity for negatives. I don't use them cause they cost more than CNMG. Holders are MDJNR/L. DNGG & DNMP for the positive equivalents.
There's more styles but I'm tired now & the ones above are most popular which should save you money. So to sum it up. Negatives are stronger but require mor HP & rigidty. The narrower the tip on insert shape, the less power requirement but also less strength. Generally you can tell what type of insert a tool holder takes as the positive inserts use a screw for locking, negatives use a post and clamp for locking.
Again I'm no expert & this is just what I've learned so professionals may not agree.
Smaller lathes generally don't do well with negative inserts because they require more power to do well with them. I found that out the hard way. Although my lathe does ok with negative inserts, I mainly use positive inserts. Positive inserts are great for lathes with less HP & less rigidity. However there are also high positive geometries within negatives & positives, usually these are available specific for aluminum but not always. For instance I use CNMG for heavier turning which is the only negative insert I use. But I also use CNGG which is a positive geometry insert that will fit in the same tool holders that use CNMG. CNGG is still considered a negative insert, but it's ground to have a positive profile. And for positive inserts, there are also the high positive ground inserts for alumn, very sharp & work great on plastics & woods, I also use then for final finishing on Ti. Confusing right? Yup it is & I probably don't even know what I'm talking about.
Ok, I don't want to cause anymore confusion. If you want to get into indexables, I would suggest the following for starters as they are very common, since they've been around for a while, tooling can be had for cheap instead of paying $20 per insert for some new line on the market.
TCMT are 60° triangle positive inserts, you'll get 3 cutting edges per insert. Great for less HP lathes & has fair strength. Great for less HP means reduces chances of chatter. Probably the cheapest turning inserts you can buy & very popular. Boring bars are available that use the same insert. A 5pc set or turning holders are available from many places & are inexpensive. TCGT & TCGX are the equivalent high positive ground inserts.
CCMT are 80° positive inserts, usually 2 cutting edges per insert for turning, but there are other holders & facemills that allow you to use the other two "unused" edges. Requires a bit mor HP than the triangles & they are also stronger. The holders are SCLCR/L (the last letter you would use R or L for RH or LH holders). Boring bars are also available to accept these inserts. CCGT & CCGX are the high positive equivelents. I use these the most. My boring bars also use these inserts which is great cause I can use the same inserts for most of my turning, saves money on having to buy different inserts for your turning tools vs boring bars.
DCMT are 55° positive inserts, similar to the CCMT but are longer, 2 cutting edges per insert. These require less HP than the triangle inserts so they perform well but they are also not as strong as the triangle inserts so they're not good for heavy turning. The holders are SDJC/R/L & SDNCN. I use these for finishing sometimes & mostly for times where space is tight. There are also boring bars available that use these but require a bigger starting hole than the previous style inserts mentioned. DCGT & DCGX are the high positive equivalents.
TNMG are 60° triangle negative inserts. You'll get 6 cutting edges per insert as you can flip the insert upside down to get the additional 3 edges. Stronger insert but requires more HP. If you'll lathe can't handle it, you'll get poor finishes, this is generally the case for most negative inserts. Holders are MTJNR/L. TNGG & TNMP for positive style equivalents.
CNMG are 80° diamond negative inserts. 4 cutting edges per insert, again flip to get the other 2. Like the CCMT, there are holders & face mills that will allow you to use the other 2 "unused" edges. Very popular in shops, common so they are cheap & strong. Holders are MCLNR/L. CNGG & CNMP for the positive equivalents. I use these for heavier turning & roughing. They last me forever as I don't use them to their full potential often.
DNMG are 55° negative inserts. 4 edges per insert, 2 per side. These are negative version of the DCMT. By now you can see the pattern of the common positive & negative insert shapes. So not as strong as the the TNMG or CNMG but has a smaller tip that allows you to reach into tight areas. These might actually work better than the TNMG on lathes that don't quite have enough HP & rigidity for negatives. I don't use them cause they cost more than CNMG. Holders are MDJNR/L. DNGG & DNMP for the positive equivalents.
There's more styles but I'm tired now & the ones above are most popular which should save you money. So to sum it up. Negatives are stronger but require mor HP & rigidty. The narrower the tip on insert shape, the less power requirement but also less strength. Generally you can tell what type of insert a tool holder takes as the positive inserts use a screw for locking, negatives use a post and clamp for locking.
Again I'm no expert & this is just what I've learned so professionals may not agree.
