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New Lathe Bits DCMT21.51 Amazon Gamble

whydontu

whydontu

I Tried, It Broke
Premium Member
First try with new 1/2” DCMT21.51 holders & bits from Amazon, just wanted to see if they would be as good or bad as various reports describe.

Test piece of 316 stainless pipe.

Quite pleased with results, very nice finish, and able to run my BB B2227L lathe at the Machinery Handbook 200 SFM for carbide. Finish pass at 0.010” DOC, feed of 0.005”/rev.

Only problem was no chip breaker, so swarf is miles long.

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Although I can't really zoom in on your last photo, the insert does "look like" it probably does have a chip breaker. To work properly, the insert has to be used at the feeds and speeds that the insert manufacturer specifies. That may not be what your handbook recommends. Have a close look at the insert packaging or at the info on the website you purchased them from.

Chip breaking is one attribute that is not usually well executed on the cheaper inserts we all like to buy.

Sometimes those long springs cannot be avoided. I hate them too. Especially when they start whipping around on the floor..... Yikes!
 
Exactly what @Susquatch says. You are very likely outside the range where chip breaking occurs. If a CNC used your DOC/feed it might may well yield the same results. It which case they might have already switched to a completely different finishing tool, or they have the rigidity & stability the final swarf would be a whisker & therefore less problematic. And chip breaker styles also vary & seem to have even less documentation.

I posted this elsewhere but was very pleasantly surprised these ones (Ali) did an amazing job on some nasty 304-like SS material that basically sits there because I hate using it. Finish & small DOC was excellent, but yup, strings we do have. I haven't found a good solution. I don't like monkeying around in there with pliers. Best thing I found is just intermittent the power feed so the strings are not crazy long, that's here it can be very dangerous if they decide to transmute into a steel version of a ball of knitting yarn spinning at 500 rpm in front of your face
 

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whydontu said:
Inserts:
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Well, the online info shows that the inserts do have a chip breaker. But nothing there tells us anything about the technical info.

Can you take photos of the insert box? Front, Rear, as well as both ends. There is seldom anything on the sides.

My fingers are crossed for you
 
Susquatch said:
Well, the online info shows that the inserts do have a chip breaker. But nothing there tells us anything about the technical info.

Can you take photos of the insert box? Front, Rear, as well as both ends. There is seldom anything on the sides.

My fingers are crossed for you
Click to expand...
Can you imagine being so proud of the products you manufacture that there isn’t even a name on the box?

I’m picturing a sweatshop in China, with a row of 55-gallon drums of loose inserts, and a row of young women grabbing handfuls of inserts to fill the little plastic boxes. (Although, to be fair, I’ve been in a factory in Chicago that had a worker who spent 25 years at a desk counting out ten 1/4” nuts, ten washers, and ten bolts and putting them into a ziplock bag. 8 hours a day for 25 years.)

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whydontu said:
Can you imagine being so proud of the products you manufacture that there isn’t even a name on the box?
Click to expand...

Holy cow! That's a first for me. Not even a name! I don't have a clue what to suggest next.

whydontu said:
I’m picturing a sweatshop in China, with a row of 55-gallon drums of loose inserts, and a row of young women grabbing handfuls of inserts to fill the little plastic boxes.
Click to expand...

Prolly no row of young women. Young women are quite rare in China. The single child policy of the past was very very hard on girls.
 
Side note related to these DCMT tool holders I'll mention a detail that arose with a recent Alixpress order. I bought model C & glossed over 90-deg really does mean 90-deg. My other (branded) toolholders look like C, are named 90-deg, but their pocket is milled so the insert has some clearance in an orientation more like model E, but without the extended boss. Its not a huge deal because I can cock C at a slight angle in the tool block, but many times I do reference the shank coincident to cross bed axis. So if one or the other is more important to you, realize that distinction beforehand. Now I'm out a whopping $14.

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PeterT said:
Now I'm out a whopping $14.
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You are not really out the money. You just didn't get one of the things you wanted from them.

I don't have that shape in carbide. But I do have it in a HSS insert and holder from ARWarner. Even they are a bitch to use as is and needed some relief grinding to meet my needs. The problem is that working in small corners is the typical application, and the damn tool holders are too tall let alone the tip of the insert itself. It's one reason why I wanted (and still want) a little spindle motor spinning a tiny burr or small grinding stone.


Anyways, it's only 15 bucks Peter. Try grinding one to get what you want.
 
@PeterT and @whydontu - Lets see if we can find something out there with the same chip breaker pattern.

Or set them aside to abuse as needed and buy another cheap but labelled box of inserts to use when really needed.
 
Susquatch said:
You are not really out the money. You just didn't get one of the things you wanted from them.
Click to expand...
Exactly, my bad humor. I will survive the financial crisis LOL. Just mentioning as FYI. Some sellers don't have the little schematic of insert orientation which clearly shows all the angles I should have paid closer attention to. They might just say '90' and not necessarily offer the other style to highlight a distinction. Like this

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PeterT said:
Exactly, my bad humor. I will survive the financial crisis LOL.
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I figured as much but decided to just go with it as written. Now I'm laughing out loud!

Still, I'd like to see if we can help @whydontu.

You know what? I'm learning to like using carbide inserts, but all-in-all, they are still a royal PIA..... LMFAO!
 
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