boring bar and brazing

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crayons
Posts: 2
Joined: Sat Oct 22, 2022 5:38 am

boring bar and brazing

Post by crayons »

Hi all

Long time lurker, first time poster.

Background: I've had some success with diy boring bars, by brazing HSS fragments onto a round mild steel shank. So far I've done it by milling a "corner" in one end of the shank, and then brazing HSS into that corner - so its got two contact faces.

Is the corner necessary? Would brazing on a flat face give enough bond strength for relatively light cuts? The bonding numbers I read on silver brazing seems pretty high. I'm contemplating getting a carbide bar for extra stiffness, and hoping I wouldn't have to cut the corner in carbide.

Thanks
Richard_W
Posts: 2031
Joined: Fri Jan 10, 2003 1:00 am
Location: Molalla, Oregon

Re: boring bar and brazing

Post by Richard_W »

If you look at an off the shelf solid carbide boring bar, you will see that there is a silver soldered steel end on it. The pocket is then cut to accept the insert once it's put on. The idea being that if the bond holds up to machining the pocket, then it will hold up to cutting on the machine. Not exactly the answer you are looking for.

Although what you are proposing will work, depending on how good your welds are.

With that being said, it would be easier to use round HSS for boring bars. Anyone who has done any machining has either dulled or broken and end mill or center drill. Don't use drill shanks, because they are soft. The ends/shanks are a good source of HSS that would be thrown away. So if you made your boring bars with round holes in them, this becomes a usable source of HSS for them. Actually, some inexpensive steel boring bars in the smaller sizes do have round holes in them.

Richard W.
K. Browers
Posts: 94
Joined: Wed Mar 21, 2007 11:57 am
Location: Philippines

Re: boring bar and brazing

Post by K. Browers »

Hello friends,
Richards suggestion is a good one. Broken end mills are a good source for cutting tool edges. I repurposed my broken carbide end mills as cutting tips in a boring bar with a round hole for the tool holder. the boring bar is double ended with one hole at right angles to the bar and the other side has the hole at a 45 degree angle to the bar. You can of course make the bars as large a diameter as you need for rigidity The broken end mills work well with a sharpening on the green wheel. I ad a notch on the side of the broken end mill like a Weldon end mill has for secure contact by the setscrew holding it It is just unfortunate I have way too many carbide end tips :( :D
Cheers Karel
crayons
Posts: 2
Joined: Sat Oct 22, 2022 5:38 am

Re: boring bar and brazing

Post by crayons »

Thanks everyone. I understand that Young's modulus (stiffness) is set primarily by the material type, so HSS and mild steel have similar stiffness, whereas carbide has a higher stiffness.

I might just keep an eye on on the no frills carbide rounds and snaffle one up if the price is right. I have the idea of gradually building up a set of low cost homemade carbide bars which gives me more options in the future - relative to the set of steel bars I have now.

Although- if anyone has a source for cheap pre-pocketed carbide bars... :)
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liveaboard
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Re: boring bar and brazing

Post by liveaboard »

I braze carbide chips onto rods that way to make internal grooving tools and internal threading tools.
Technical Ted
Posts: 31
Joined: Fri Dec 25, 2020 10:17 am

Re: boring bar and brazing

Post by Technical Ted »

I've made a few acme threading tools by hard silver soldering hss tool bits to grade 8 bolts and they work fine. I think hard silver solder is the way to go over other types of brazing material. I've never had a bit come loose. At work, we used a flat silver solder that we cut to shape and soldered carbide tool blanks to shanks. Worked well. If you get a good bond they are very strong.

Ted
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