carbide inserts and lathe holders for same

Helo, all,
I have a set of the 3/8" square lathe toolholders for triangular carbide
inserts with the 1/4" inscribed circle. I used them on a 10" Atlas, and
later on a 12" Craftsman, for over 15 years. I broke a few inserts, and
wore out or chipped quite a few, over the years. This past weekend, I
was doing some heavy turning on my 15" Sheldon lathe, and broke
the nose off one of the holders. It cracked across the front, splitting
at the threaded hole, so the front point of the holder dropped off.
Amazingly, the screw and the insert didn't break, just the holder!
It had a very nodular-looking fracture, like cast Iron, not like some
ductile steel. What are these things supposed to be made of?
I got this set at the same time I got my original QC toolpost from
Enco. The toolpost was a Phase-II, I don't remember if the holders
were also from Phase-II or not.
Any comments? (I'm going to try to get a better set on eBay, and
in the 1/2" holder size, with 3/8" IC inserts. I assume the larger
holder has to be a little stronger, just because of the vertical
dimension, if nothing else.)
Anyone have any comments on the strength and reliability of the
5-pc holder sets that everybody sells? Also, does anyone have
any recommendations for a general-purpose insert, chipbreakers,
positive or negative rake, etc? I have been using a couple of different
inserts that I managed to get at a good price, all positive rake with
molded-in chipbreaker. Now that I have a lathe with the power and
rigidity to use negative rake tooling, does anyone have any recommendations
for those? (I'm a bit leery of buying a bunch of inserts at $9.50 ea
with toolholders running $50 - 100 at the usual machinist supply
outfits like J&L and MSC without some word on others' experiences
with them.)
I do a LOT of aluminum, but I do some tools and fixtures, etc. in
mild and tool steels.
Oh, one other thing. I got a little plastic gadget some time ago that
had a Vee, a flat and a bubble level that was used to make the cutting
tool even with the center of the workpiece on the lathe. It seems to have
gone with my last lathe. I'm trying to find a replacement, but can't
seem to find them in the catalogs. What do they even call these
things? I think mine was listed as something like a "lathe tool height
setting gauge". I couldn't find any on eBay, either, under any name
I could think to search for.
Thanks much in advance!
Jon
Reply to
Jon Elson
Loading thread data ...
You might look at Plastools
formatting link
Quite reasonable pricing on lathe tool holders. I have their holders that use the TNMG 322 and am quite satisfied using it with a variety of materials. Here at school cost is a major factor and I don't try to match inserts to any specific material. Whatever insert I can get cheapest is the right one.
Speaking of cheap inserts try Carbide Depot
formatting link
They have a wide variety of inserts and good pricing. I regularly get the TNMG 322's that we use for a buck apiece. As I say though we are strictly price driven.
Speaking of bucks What's the difference between beer nuts and deer nuts?
Beer nuts $1.49 a bag. Deer nuts are always under a buck!
Errol Groff Instructor, Machine Tool Department H.H. Ellis Tech 613 Upper Maple Street Danielson, CT 06239
860 774 8511 x1811
formatting link
formatting link

Reply to
Errol Groff
Make your own. I did.
formatting link
My machine is comparatively light so I use TNMPs but TNMG's work well in the same holders if you have the power and rigiditiy for negative rake.
I do NOT like the price! It took me a couple hours to make two sets of my design. I keep one set loaded with inserts for ferrous and one with inserts for non-ferous. I've broken a few inserts when I've really screwed up but have yet to break or bend a holder.
Do read my article. Ted
Reply to
Ted Edwards
I bought some of the "USA" holders from MSC around 8 years ago, the style that use the TCMM32x inserts. This is a slightly different insert (different screw hole) from the "Borite" MSC sells for slightly more. The holders are fine, they get used on a 15" lathe, really should be using 3/4" shank tools but these are what I already had. These get used for the quick & dirty work, they generally don't give me a great surface finish.
Two years ago I decided to complete the set with the "Import" set from Enco/MSC that uses the same inserts.
I cant' comment on the grade of steel, but the finish of the insert seats looked like they had literally been cut by hand with a belt sander. The inserts didn't even sit tight against the back of the seat. Went right back, Enco's satisfaction guarantee is that I got to pay shipping both ways.
My lathe, and surely your Sheldon, should do just great with negative rake tooling. I haven't done enough turning lately to explore further into it.
Bob
Reply to
Bob Powell
Thanks. I think I will make a couple of holders that hold the triange insert "backwards", with the flat side almost parallel to the spindle axis. One just a little left, one just a little right. With these, I could cut both left and right faces, turn the diameter, and make steps to one side of the cutter. (I had a project that needed this done on 50+ parts, and doing it with one tool instead of two would have been a great improvement.) The holder needs to be a little narrower than the face of the insert.
Jon
Reply to
Jon Elson
The advantage to negative tooling is you can turn the insert over thus you double the usable edges. The problem with negative holders is you have to have a very rigid setup. They don't work well on long skinny work or thin stuff. Trying to decide on what geometry tooling you use by deciding what type of work you do mostly.Than pick the tooling that is optimal for what your doing and you'll be set up. Ebay is a great place for bargain tool holders and inserts. I had some trangle shaped insertable tooling on some 1/2 inch tool holders for my lathe. I don't like them it seems the edge strength is bad on the insert. My favorite is dnmg 431,432,or 433. I also like vnmg 331,332,or 333 for working up close to profiles
Charlie
Reply to
Charlie
The Borite turning tools are hardened tool steel and are very tough. MSC sells them in all the standard shank sizes. The inserts that come with them are good general purpose types. Watch
formatting link
for good deals on inserts. I found a large supply of cermet inserts that fit my Borite shanks for a very low price.
Randy
recommendations
Reply to
Randal O'Brian
Did you read the whole article and check out the pix?
shows a set of three. I have never missed having any different angles but I have a square tool post can swing at any angle to the compound slide. This lets me set up for both turning and facing without moving or changing the tool.
Indeed! A sharp point 3/8" IC insert is 0.650" on the face. A TNMP321 is a little less due to the rounded point but still wider than 1/2".
Ted
Reply to
Ted Edwards
That is why I am using what are called negative-positive inserts, TNMP-321s. What _looks_ like a chip breaker groove isn't. The grove goes right to the edge giving the insert a ten degree positive rake. My holders
have a five degree "droop" on the nose. This results in five degrees clearance and five degrees positive rake. And six points for ~Cdn$5!
Ted
Reply to
Ted Edwards
Ive been using negative rake tooling quite a bit recently. While its not for every material..if used properly on a solid rigid machine..it cuts damned well and with a very smooth finish.
Gunner
"A vote for Kerry is a de facto vote for bin Laden." Strider
Reply to
Gunner
You can harden your "tool steel" tools to Rockwell bazillion and it doesn't matter a tinkers Dam except on the cutting edge which you say comes from an insert. Rigidity is determined by shape and eleastic modulus and the elastic modulus of all steels is about the same. A mild steel holder is just as rigid as an expensive "Hardened Tool Steel Holder".
The hardened steels generally have a higher yield strength. How many tool holders have you broken or put a permanent bend in?
Make your own holders for pennies a piece out of mild steel and, as the commercial says, "Save your money!"
Ted
Reply to
Ted Edwards
The reason hardened tool holders are desirable is that under hard use the insert pockets don't wear and the shanks aren't deformed by the QC holder set screws. Also, in case you screw up, the insert breaks with less chance of damaging the tool holder nose or the retaining screw hole(ask me how I know). Tool holder failure was one of the complaints the original poster had about his Enco set. And yes, Ted, I am well aware that all steels have nearly the same modulus of elasticity. And no, Ted, not everybody is as "thrifty" as you are.
Randy
Reply to
Randal O'Brian
I started this thread when I *DID* break a toolholder! But, it clearly was *NOT* steel at all, but some kind of cast iron material, from the look of the break.
Jon
Reply to
Jon Elson
Cast iron, if indeed it was cast iron, is extremely weak in tension. A toolholder works as a cantilever beam, tension on top, compression on the bottom. There are grades of cast iron that aren't too bad but I wouldn't expect to see them in a cheap toolholder. Also, IIRC, you said 3/8". For the same loading, 3/8" will stress the material almost 2 1/2 times as much as 1/2".
Ted
Reply to
Ted Edwards
I have yet to see the first and fail to see why the second matters. Appearance?
Again, while I have broken a few inserts in my time, I haven't damaged my mild steel holders.
I'm happy for you that you have miney to burn. Not all of us are so fortunate. :-) Ted
Reply to
Ted Edwards
Right. I've got a 1/2" set coming. As for the Enco holder, I don't know the actual material. But, the break is characteristic of something with high carbon and quite brittle. A very granular surface, and no sign of any flow or deformation, just a very rough, cracked surface. Amazingly, it didn't break the insert or screw!
Jon
Reply to
Jon Elson
I've always wondered how so.. I seem to remember seeing gray iron as at least 30KSI, equal to mild steel.
Tim
-- Just remember, Man was made in God's image. Woman was created out of a rib, which, quite honestly, is a cheaper cut of meat." - toon Website:
formatting link

Reply to
Tim Williams
Even worse, while looking up some stuff, I noticed that cast iron was a lower modulus of elasticity than steel. Depending on the grade, it can vary from 12E6psi to 20E6psi compared to steel at 30E6psi. References: MH and Blodgett.
Ted
Reply to
Ted Edwards

Site Timeline

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.