Can coated carbide inserts be brazed?

npinson · Aug 24, 2020

Got a medium short run job for a part with a 7/8 13tooth internal spline. On a similar part, but with a much larger ID, I just ground a top notch threading insert to fit the profile, and clamped it with a standard clamp, just oriented on the face of the toolholder so I could broach it in a C axis lathe.

But on this part, I’m going to use a 1/4” IC T series triangle insert, but the screw for it is very tiny, (M2.2 x 0.45mm). I’m not that familiar tapping that tiny, and I’m also concerned cutting forces may be too much for that screw to handle. I have to make a custom toolholder either way, but I thought about brazing it in. I’m not very experienced in brazing either, from my understanding you want clean, dry, wet able carbide. Because of the PVD coatings on this insert, I’m asking if that can even be brazed in a pocket?

Thanks guys

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Milland · Aug 24, 2020

If you draw up the geometry of the insert and the minor diameter of spline, does the holder have enough beef to the outside that you could add a small cap, held down with its own pair of small screws? If that works, go ahead with mechanical fasteners, not brazing.

Obviously you have to allow for the insert/holder being fully inside the minor diameter of the spline for starting clearance.

As far as the actual tapping, it's no different than larger threads, but I might simply drill the holes and then fixture in a manual mill to do the tapping by hand. Good sharp tap, proper lube, use a spring-loaded tapping guide to help you stay straight.

npinson · Aug 24, 2020

I looked it over again, and I’m going to try a 1/2” IC insert that uses a beefy screw now. The minor is just a tad over 0.75”, but I’ll grind off the 2 other corners of the TCMT insert so it clears with the toolholder in the bore. Only reason for a TCMT insert is that it already has a 60deg form with cutting relief built in. Really just grinding a small flat for the root on top.

Unfortunately, it’s nearly a blind bore, there is a relief groove towards the end of the bore that is allowed, but the cutting edge has to get very close to the hole bottom so adding on mechanical fasteners that protrude yet farther won’t work. I would rather not braze them, I have no clue how hard it is to remove the carbide to replace it. Last run of an 1.75” 20 tooth ID spline bushing with the top notch insert system I made, it lasted 65 parts but was starting to look like it needed a new insert ground again. With the screw, at least I can easily remove it, regardless if I monkey with grinding it for 20 mins.

Thanks for the suggestions.

Npinson

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npinson · Aug 24, 2020

Milland said:
If you draw up the geometry of the insert and the minor diameter of spline, does the holder have enough beef to the outside that you could add a small cap, held down with its own pair of small screws? If that works, go ahead with mechanical fasteners, not brazing.

Obviously you have to allow for the insert/holder being fully inside the minor diameter of the spline for starting clearance.

As far as the actual tapping, it's no different than larger threads, but I might simply drill the holes and then fixture in a manual mill to do the tapping by hand. Good sharp tap, proper lube, use a spring-loaded tapping guide to help you stay straight.

Just for future reference, do you know if carbide has to be un coated to be braze-able?

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winger · Aug 24, 2020

I silver soldered inserts on boring bars. I used old inserts and reground them so the coating was gone anyway.

Dave

mmurray70 · Aug 24, 2020

npinson said:
Just for future reference, do you know if carbide has to be un coated to be braze-able?

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I've tried this before and insert popped off as soon as it hit the part. I ground off some of the coating and tried again and it worked fine.

CarbideBob · Aug 25, 2020

Is your PVD coated insert coated on the bottom?
Often this bottom has little coat and can be cleaned up on some sandpaper and that bottom is enough to hold onto.
Coated carbide does not braze/silver solder well if at all.
You mentioned grinding a top notch so you must have a wheel of some sort to skim the coating off. No care if you kill the backside cutting edge, grind it negative, hack it to heck as it is gonna get brazed.
Brazing clean carbide to steel is so super easy. Best done with shims of the silver braze and some flux. Could send you some scraps and flux in a envelope.
Problem maybe in that braze/silver solder flow or bulge out front that will need to be cleaned off without hurting your inserts cutting edge. Careful hand grind can do that.
You do have a torch? Not a propane guy but a real weld/cutting one as you will need 2000 degrees.
Holding or positioning that small floating tip during the braze process? You want the angle out front dead on after braze as you will not be grinding the tip?
I braze carbide based tips (CBN/PCD) all day long and even when clamped and fixtured +/- 1 degree is a good day across a run.
If out you could twist/shim the shank in use to get the cut angle.

All that and your idea seems good to me.
Bob

Scottl · Aug 25, 2020

could you beef it up with superglue and then de-bond it when the job is done? Most every hardware store now carries gel de-bonder and a tiny bit of alcohol will make it runnier if needed.

CarbideBob · Aug 25, 2020

Superglue??

Hardplates · Aug 25, 2020

Wtf..........

michiganbuck · Aug 25, 2020

We used to use flat braze stock with adding a small snip if flat silver stock, melt/heat until the insert would slide and give it a little slide and then set to desired location. paint flux on and under braze shim. A finger print on the part or on the inset would ruin the brazing.
I would grind off the coating pre brazing.

Gobo · Aug 25, 2020

We used to make all of our internal lathe tools by silver soldering carbide to bars. Yeah, that was 30 years ago, but we made everything we had to.

npinson · Aug 26, 2020

CarbideBob said:
Is your PVD coated insert coated on the bottom?
Often this bottom has little coat and can be cleaned up on some sandpaper and that bottom is enough to hold onto.
Coated carbide does not braze/silver solder well if at all.
You mentioned grinding a top notch so you must have a wheel of some sort to skim the coating off. No care if you kill the backside cutting edge, grind it negative, hack it to heck as it is gonna get brazed.
Brazing clean carbide to steel is so super easy. Best done with shims of the silver braze and some flux. Could send you some scraps and flux in a envelope.
Problem maybe in that braze/silver solder flow or bulge out front that will need to be cleaned off without hurting your inserts cutting edge. Careful hand grind can do that.
You do have a torch? Not a propane guy but a real weld/cutting one as you will need 2000 degrees.
Holding or positioning that small floating tip during the braze process? You want the angle out front dead on after braze as you will not be grinding the tip?
I braze carbide based tips (CBN/PCD) all day long and even when clamped and fixtured +/- 1 degree is a good day across a run.
If out you could twist/shim the shank in use to get the cut angle.

All that and your idea seems good to me.
Bob

This post right here is why I think this forum is great. Thanks Bob. I’ve made the toolholder already, changed my mind again to use a 3/8 IC TCMT. And use a screw. I have the oxy torch assemblies to be able to braze theoretically, I’m gonna do a fair bit of googling if I ever attempt it. Do you by any chance own Carbidedepot.com?

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npinson · Aug 28, 2020

Going to try broaching with this in the morning

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TeachMePlease · Aug 29, 2020

npinson said:
Going to try broaching with this in the morning

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Lieutenant Dan, you ain't got no cutting edge.

Hardplates · Aug 29, 2020

TeachMePlease said:
Lieutenant Dan, you ain't got no cutting edge.

Yes Forest I know

as9100d · Aug 29, 2020

I'm curious to see how that chip breaker cuts lol

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npinson · Aug 30, 2020

It has cutting relief on all faces. Worst case I could grind the face with some more positive rake. The test from today worked, I just had to stop every two teeth to clear chips. Right now it’s waiting to be heat treated in an oven. Learning to use that as well.

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CarbideBob · Aug 30, 2020

TeachMePlease said:
Lieutenant Dan, you ain't got no cutting edge.

In broaching I would expect this to actually last longer than a flat front top edge.
Better yet if that peaked form went all the way to the outside edge.
When used in turn broaching GM had a patent on this in the 80's.
Downside, the flat produced is not quite flat due the rake clear grind. Probably very small size off at this size but a tad of a vee in the center.
This normally splits the chip in the center vs a straight front chip so the OP's problem of clearing chips is curious. I think further into the chipbreaker would have been better.

Tis one of those looks all wrong but works like a charm things.
Bob

npinson · Sep 16, 2020

Problems with chips is because it’s nearly a blind bore. My only option is pushing them into a rear relief groove that was made as short as I could because this machine needs some decel time on rapid feed.

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Can coated carbide inserts be brazed?

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Stainless

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