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View Full Version : Coatings on cutting tools? -- TiN for example?



Bill Pace
06-08-2008, 05:05 PM
Recently got a big haul of solid carbide endmills off ebay, probably CNC rejects, and most needed at least minor touch up on flutes and cutting tips, and having a Cuttermaster T&C grinder I figured I could handle that. Most of them had a gold coating, TiN?...

Can someone give some insight on this-- and there are others-- coating -- what are the advantages? I'm sure there are a lot like me and notice that real quickly this "gold paint" rubs/comes off very quickly and have to wonder just what it was accomplishing. Is it worth that -- sometimes hefty -- difference in cost for this coating?

During the dressing/cleaning up of the ebay EM's, the slightest touch of the stone and the gold paint was gone...

Speaking of the stone... I had been doing HSS endmills and had a CBN wheel on the T&C grinder, so, having a senior moment I guess, I just went right ahead with the carbide sharpening and did something like 30-40 of them on the CBN ... did a beautiful job! I didnt even realize the diamond wheel wasnt on there til the next day when I went to do another HSS and noticed the CBN was already mounted.

DICKEYBIRD
06-08-2008, 07:00 PM
WOAH! Cuttermaster, CBN, carbide em's..go ahead, rub it in rich guy.;) I'm dyin' over here. Serious tool envy goin' on.:)

More seriously, could you do one of your nifty photo-documentaries whilst you have all this neat gear all warmed up and the mind and hands are fresh & practised? I'd love to see how it's done with real equipment. Close-ups, before & after....etc.

macona
06-08-2008, 08:10 PM
I think TiN is just supposed to help with wear. Other coatings act like lubricants for dry machining. Some help keep aluminum from building up on the edges and flutes. There are a whole bunch of different ones.

Some places redo the coating after resharp. But that take rather special equipment.

tiptop
06-08-2008, 09:32 PM
Bill, The TIN coating is very thin. When I sharpened my first ones on my Cuttermaster, I was disappointed at loosing it also. They sharpen just fine and work well afterward. Mine did not seem that sharp at the gate compared to when they were resharpened. I really could not notice a difference in them not being TIN coated anymore. Jay

oldtiffie
06-08-2008, 09:49 PM
Thanks all - good topic.

I have wondered about that over time. It seems that it definitely has its uses if applied and used correctly.

Try these links as they may help.

http://en.wikipedia.org/wiki/Titanium_nitride

http://www.google.com.au/search?q=TiN+coating&btnG=Search&hl=en&sa=2

DR
06-08-2008, 09:53 PM
Bill, The TIN coating is very thin. When I sharpened my first ones on my Cuttermaster, I was disappointed at loosing it also. They sharpen just fine and work well afterward. Mine did not seem that sharp at the gate compared to when they were resharpened. I really could not notice a difference in them not being TIN coated anymore. Jay

Some coatings require slight dulling of the cutting edges for the coating to adhere. Some coated cutters will sometimes not feel as sharp as uncoated.

Resharpening of the OD of an EM still leaves the coating in the flutes where the contact occurs. Same with twist drills, end sharpening still leaves coating on the face of the cutting edge.

Bill Pace
06-08-2008, 10:37 PM
These EM's were pretty obviously resharps ... with a high tech type set-up, probably another CNC rig and had the coating re-applied. Had probably reached the resharp limit for use on the machines and sold. They all ran a few thou under the usual sizes which in the ones I got ran from 3/16 to 5/8. I got 80 of them in varying length & flutes for under $2 a piece ... I figured it was worth it to see if they would resharp for home shop use .... I have test tried several and they cut really smoothly (IF i can keep a steady hand & concentration:o) I think there was 6 of them that were just too bad to try and save, and several others had a chip out of one flute end,-- but they still give a pretty decent finish, -- probably 60 or so that cleaned up very nicely ... all in all I'm quite pleased with the end result.

Just have wondered about those finishes before, and then get all these EM's with it on them.....and, well, thought I'd ask ....

Dicky B, I'm afraid I finished all of them up -- thank goodness!! so no pix this time. As for doing them on a "real" sharpener, -- well, thats a good reason to HAVE a "real" sharpener, the machines gotta be a contorsionist to get all those angles set and then have the capability to manipulate the tool across those angles:eek:. Here again, my mentor and friend Lane has come thru in providing much needed guidance in (mostly!) figuring all that out. As for acquiring the Cuttermaster, I prowled ebay for several weeks and lucked up on this one for a little under $500 (I dont remember exactly) and the Diamond & CBN wheels have come down considerably, being offered by CDCO, Shars & others.... and now that I've used them, I'd probably have paid double to get the amazing difference in performance out of them... just NO comparision, AND CLEAN!! no mess.

lazlo
06-08-2008, 11:23 PM
Some coatings require slight dulling of the cutting edges for the coating to adhere. Some coated cutters will sometimes not feel as sharp as uncoated.

On the multi-layer coatings on inserts, the edge to needs to be dulled, or the coating process itself rounds the edge (depending on the type of coating). When you get up-sharp inserts, they're usually uncoated.

But every coated endmill that I have is razor sharp, so I'm guessing the coating is a lot thinner.

I was told by the Sandvik rep that TiN is the only coating that's really useful for home-shop types: like Macona says, it's a hard wear coating. The exotic coatings like TiCN, TiAN, ... supposedly do some kind of phase-change at extremely high temperatures and pressures that protects and lubricates the cutting edges, but I don't think any home shop machine, even a Bridgeport, will get anywhere close to the speeds/feeds you need to make them work.

oldtiffie
06-09-2008, 04:21 AM
Following on from posts by others, I'd guess that TiN coating would be ideal/best used with climb milling on end milling cutters.

That way maximum "bite" is taken at the start of cut on each tooth and the chip will be more inclined to break off ahead of the cutter and rub on the cutter "top rake" face behind the cutting edge - similar to using (at least some) TC tools/edges. That being the case the sharpness of the cutting edge is not such as issue where-as hardness and lubricity ("slipperiness") at the rubbing face/point is very much required.

"Conventional" milling requires a much sharper edge as it is inclined to "rub" before "picking up" and "forming" the cutting edge.

For an up-date/revision on the mechanics of "climb" and "conventional" milling see the bottom of the page on this link:
http://en.wikipedia.org/wiki/Milling_cutter

Forrest Addy
06-09-2008, 04:32 AM
You will need diamond to grind carbide. You can rub it off with a CBN wheel if you accept a high wear rate but diamond is not only far superior but gives a cleaner keener edge on carbide tooling.

Save the CBN for HSS tools. That's where it really shines.

Quite often the carbide substrate under the fancy coating doesn't last if the coating is ground away or it may not be suited as a cutting grade for some materials. Something to think about as you load a honking big tool carousel.

bobw53
06-09-2008, 10:01 AM
The exotic coatings like TiCN, TiAN, ... supposedly do some kind of phase-change at extremely high temperatures and pressures that protects and lubricates the cutting edges, but I don't think any home shop machine, even a Bridgeport, will get anywhere close to the speeds/feeds you need to make them work.

TiCN(light purple) comes into play around 900degrees F, which even on a light cut is not out of the question. It doesn't have to be the whole chip, just where the maximum pressure/heat is, just behind the cutting edge on the inside of the flute.

TiAlN, or AlTiN comes into play around 1700 degrees F. That is why it is so good at dry cutting. I've actually found that cutter life suffers about 30% when run wet compared to uncoated carbide.

As for the dulling of the edge from the coatings, I'm not sure how much is actually the coating, but the cutting edges will sometimes be slightly dulled to provide more edge protection (similar to a honed insert). Still pretty darn sharp though.