Tc Mt 21-51 Inserts

i have had a turning tool for awhile now that takes tc mt 21-51 inserts , i never really used it much as i am pretty happy with hss
i finally decided to use it a little over the past few days , i cant say i have any real complaints with it , it cuts nice and leaves a pretty decent surface finish .

i have been wondering about the inserts though , the elcheapo non coated inserts that came with the tool
last about 90 minutes or so per edge before needing turned to a new edge ,.. giving about 4 and a half hours of use per insert . and i could probably stretch that out a bit further if i wanted .

the cheap inserts cost about $2.50 each

would there be any real advantage in this case to spending a few bucks more and buying a good quality coated insert such as the mitsubishi inserts at about $ 6-8 per insert .
are they going to last that much longer and improve surface finish enough to justify the extra cost .

I purchase mine in packs of 10 from this guy http://www.ebay.com/usr/carbidenow?_trksid=p2060778.m2749.l2754 he is here in the States. The coatings should give you a bit more life compared to the non-coated ones as they prevent galling. I run them in my boring head all day long, they should give considerable life on a lathe. If you are cutting a larger inside radius then 2-3 inches you might consider going to larger tooling. A 321 would last much longer but is prone to chatter on small radius cuts or at least that is my experience with a boring head.

There's so many variables involved with turning inserts that you could write a book about it.
First thing I ask, what grade carbide are the inserts? C-2? C-5?
What kind of material are you cutting? What is the diameter range of cutting? What RPM are you using to cut? What feed rate are you using?
From this we can give a little more advice on what to do.

hmm where to start .

grade of carbide , i really can not answer this the tool and an extra insert was gave to me ... it is just a regular left hand turning tool .
the material i use most is 01 drill rod with a 1 inch or inch and a quarter dia .

speeds and feeds ... i have played a bit to try to find where things seem to be happy on my lathe .

depth of cut seems to be the happiest so far at between .010 - .025 , my usual plan of attack is to keep the cuts at around .020 and plan on a finish cut at .010
feed seems to be pretty happy @ .006
speed .. 760 rpm for roughing and 1200 rpm for finishing has seemed to be a fairly decent compromise with my limited speed range .

chips usualy come off the tool in a straw color and turn blue just as they break off in little sixes and nines

i do like how the chips are formed ... makes for nice and easy clean up .

Are you able to take deeper cuts than .020"?

Look for a C-5 grade with the gold coating and one of the other coating offered. Not everybody will list the inserts as C-5 Grade. All the major brands will have their own number, and with the newer ISO labeling for insert grades you'll be lost like me!

Sounds like you are in the right direction with your speeds and feeds even though deeper cuts with less number of passes can help tool life.

at .025 depth of cut i still get nice little sixes and nines , but the chip comes off the tool a very bright blue . however surface finish is still good .
at .030 and .035 depth of cut chips start to come off the tool in a long spring but still a decent finish
at .040 and .045 chips lose the spiral and come off in strings and i can feel the crappy motor on my g0602 is starting to get a work out and surface finish isnt that great .
.050 and things are not at all happy ... motor is bogging down , surface finish looks torn and not cut .

i looked at some of the inserts from that seller ... the coated inserts arent a bunch more , i'l have to give them a try .
there are also a few others selling the mitubishi inserts as well , for about double the price and thats what mainly got me to start this thread and ask .

i am not unhappy at all with the cheap non coated inserts ,... i figure if i use them at my currant pace on my die making endeavor i'll go threw an insert maybe once a week at most
and most likely one will last close to two weeks .
that also makes me to feel inclined to consider spending the extra bucks on the mistubishi inserts ... but it is hard to get past being a cheap skate

For myself , I bought the "cheap "inserts to learn with! I found the learning curve to be a costly one with carbide!!! Small things like the whole stopping an insert while in the cut thing. Yea that pretty much destroys them immediately! And speeds and feeds then the general finesse of everyday use. I don't think buying expensive brand name inserts is a bad idea, it just hurts ALOT less when it is a $3.00 insert that the tip gets snapped off of and not a $10.00 one!

My story on coated inserts, I bought a parting tool that used inserts and always got the uncoated ones as I couldn't believe they were worth the extra $$$ (almost double,back in the day) , well I needed a couple new ones and went to my supplier and all they had were to BIG money gold coated ones.......NOT happy me, pitched a fit and told them these high dollar SOB's better last a week! I have to eat my words but they were faster cutting, better finishing and they lasted way more than a week. Coated inserts are the answer for most of my needs now, I do occasionally need to grind a special tool, ie, form tool , acme/buttress threading tool , ect. ,but with all the new coatings out there I am a happy camper. TiN, Al/TiN, and all the other hybred coatings, they are way better than plain carbide. I would go back to only cobalt tool steel before useing bare carbide.

bosephus said:

................at .040 and .045 chips lose the spiral and come off in strings and i can feel the crappy motor on my g0602 is starting to get a work out and surface finish isnt that great .
.050 and things are not at all happy ... motor is bogging down , surface finish looks torn and not cut .

Click to expand...

Long term, invest into a heavier duty motor...But doing that , the gearing on the G0602 lathe may not handle that extra torque...
I do agree with Cactus Farmer on using coated inserts. They will last much longer per edge than uncoated ones!

Edit: If you don't mind spending money on tooling, invest in a different insert configuration like a CCMT, DCMT or the old traditional TPG style. I use a lot of TPG inserts in my shop mainly because I have a lifetime supply of them!

a new motor is on my list ... a good quality three phase to be exact , along with a vfd when funds permit , i have a phase converter set up already so i can go three phase once i find an appropriate
motor to use .
i was not planning on going bigger , a quality true 1 horse motor should be a vast improvement over what i have now .

i went ahead and ordered a 10 pack of the cheaper coated inserts to give them a try ... for about another buck each what the heck .

i have tossed around the idea of buying a few new tools to try ... i do like the idea of just turning or changing a insert when it dulls or breaks if i screw up .
and i most surely like the chip control i get ... that has been my one sore spot with hss , my tool grinding is not the best to say the least .
i can grind tools to cut great , but i have had zero luck with chip control .