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View Full Version : Carbide inserts brazed to boring bars?



ahidley
09-17-2012, 10:35 PM
I have brazed alot of carbide bits to boring bars to replace a broken/worn out one with new ones purchased off ebay. My question is can I braze on a "gold insert" ? One that is titanium nitride coated? Anybody done it succesfully?

PixMan
09-17-2012, 11:14 PM
It can be done, but why would you? Sooner or later you should consider joining the 20th century and just get or make a boring bar that allows you to just use a screw to change the insert. They can be had for (depending upon size, material and quality) as little as $15.

macona
09-18-2012, 07:11 AM
You really need to remove the coating. Even then it is kind of tough to braze. The black silver solder flux is supposed to help.

Spend $50 and get a solid carbide bar off ebay. I got one with a 3/8" shank and it holds the little diamond inserts. It works great.

ahidley
09-19-2012, 07:24 AM
I have a dozen or so boring bars with replacable inserts and they are great. But I use the brazed ones for one off jobs. Thus I make a custom ground one for things like internal orings, and in this case an internal acme thread. But I ended up making several threaded parts and the insert broke off. While this was "in process" I won a bid for some acme thread inserts on the internet. Thats why I wanted to braze one on due to not having the correct holder.

This brings up question #2. When using carbide cutters I thought that the cutting speed should be increased vs HSS. But how do you do that if your threading?

PixMan
09-19-2012, 08:12 AM
Can you just go back to Ebay and get an internal threading bar to hold the inserts you bought?

There's an overwhelming number of machinists thread at far too-slow of a speed. Why go so slow? Still, the threading inserts are made of chipping-resistant carbide of high cobalt content specifically because threading usually happens at far-reduced speeds. They should hold up fine, but try to thread at higher speeds just the same.

As for internal o-ring grooves, I have a few Micro 100 (brand) solid carbide I.D. grooving bars. Excellent stuff, good bargains on Ebay. For larger diameters, I have both double-ended "dogbone" insert grooving bars and one Top Notch style. The Valenite VTG dogones are also my choice for much cutoff, and they work GREAT.

Mcgyver
09-19-2012, 08:16 AM
I'd guess the titanium nitride isn't going to silver solder.....you could try it or just remove the coating from the bottom of the insert with a diamond lap then easily silver solder or otherwise braze the insert. Carbide is very easy to silver solder once you remove the oxide layer.

That insert tooling has its place does not address the topic and question: how to silver solder these. btw, they are useful tools for boring or in the mill and have the additional advantage of being easily sharpened and shaped to suit. If you don't abuse them these shop made tools can last a very long time.

JCHannum
09-19-2012, 08:48 AM
For one time, limited use, when you can't wait for an order to arrive or an eBay auction to end or if you are just being thrifty, there is no reason not to make up a boring bar or any other form of cutting tool by silver soldering carbide inserts, carbide pieces or HSS cutters to a piece of stock.

It is simply one more technique to be added to your skills inventory that will give you an advantage over those who have not mastered it.

bob308
09-19-2012, 09:17 AM
when i was learning the tool making trade. we had to make our own boring bars by brazing pices of carbide to our own bars we made. after many years i still have all the ones i made. i have also made more.

Ian B
09-19-2012, 12:05 PM
Pixman,

Why thread so slow? In my case, it's because I'm very often threading up to a shoulder, and / or threading short lengths. I suppose it would be possible to run the lathe in reverse, use a threading tool on the back side of the work and thread away from the shoulder, but if using pre-ground tips, they'd need to have a different relief angle.

So - largely to avoid heart failure, I tend to thread slowly...

Ian

Guido
09-19-2012, 12:34 PM
Those one-off, hand made, one-of-a-kind type cutting chingaderas have saved my bacon way too many times. 'Tis the challenge. Helped keep the boss type people 'within budget' and 'on time'.

Still have several for the rare need, when high production, long life cutters are not available.

--G

ahidley
09-19-2012, 12:55 PM
Pixman,


So - largely to avoid heart failure, I tend to thread slowly...

Ian

AWSOME reason........ My point was really that when cutting threads the feed rate mandates a slow RPM. In the case which caused the last breakage it was 8 TPI thus if it were 1000 RPM the quote above would be dead accurate.......

Mcgyver
09-20-2012, 12:55 PM
A it was 8 TPI thus if it were 1000 RPM the quote above would be dead accurate.......

at somepoint its leadscrew whip that does you in :)

I can to do the two handed disengage the half nuts and retract the crossfeed with the best of them.... but past a couple hundred rpm on a coarse pitch it becomes an issue of engaging the half nuts - there's a limit to doing so without abuse with a quickly spinning thread dial