Boring Bar

[Cross Slide]

I have a project that is going to require the use of a Boring Bar. I have not used boring bars before this project. When I bought my lathe I was talked into getting a set of small boring bars at the same time. They are a cheap set. The style where a piece of carbide brazed on the end. 
I can’t get them to cut at all. I’m using the shortest possible length required to do the depth. 
I don’t know if it’s the way I have it set up (directly on center line) or if the boring bars are just that bad. 
I was wondering if anyone has a design for a homemade boring bar holder, and the angles to grind HSS to fit and work as a boring bar. 

Trevor

[EdK]

What material will you be boring?

Ed

[Cross Slide]

I’m not exactly sure what the material is. It was given to me. So it’s a mystery metal.
I’m thinking it’s 1018

[Highpower]

What type of tool post are you using? Square 4-position or QCTP?
What type of boring bars? Like these?



I find the brazed carbide tools work much better after being ground to a sharp edge and a decent clearance angle. Center height is the correct way to go.

[Dr Stan]

What is the finished diameter and the length of the hole?

How much undersize was it drilled?

[rleete]

I bet he has the typical Chinese set that HF and LMS sell. Decent carbide, but not sharpened worth a fart in a windstorm. My set actually had a round edge on some of them.

Buy a set of diamond hones (https://www.harborfreight.com/3-piece-2-...36799.html) or similar, and carefully sharpen the cutting edge and top surface to get an edge on them. Once you get them sharp, they will serve quite well.

[Cross Slide]

(12-21-2019, 12:41 PM)Highpower Wrote: What type of tool post are you using? Square 4-position or QCTP?
What type of boring bars? Like these?



I find the brazed carbide tools work much better after being ground to a sharp edge and a decent clearance angle. Center height is the correct way to go.

I have a Piston Type QCTP
I have a set of Accusize Boring Bars that look just like the ones you attached the picture of.
I didn’t try sharpening them. 
How much clearance angle should I be looking for?

[Cross Slide]

(12-21-2019, 01:09 PM)Dr Stan Wrote: What is the finished diameter and the length of the hole?

How much undersize was it drilled?

I have to take out 1/2” at a depth of 1” with no shoulder at the bottom. 
And 5/8” at a depth of 1/2” up to a shoulder at the bottom

[Highpower]

(12-22-2019, 06:37 PM)Cross Slide Wrote: I have a Piston Type QCTP
I have a set of Accusize Boring Bars that look just like the ones you attached the picture of.
I didn’t try sharpening them. 
How much clearance angle should I be looking for?

Here is a page that shows a couple of different options for holding a boring bar in your QCTP. http://www.micro-machine-shop.com/boring_bars.htm

Toward the bottom of the page they show a set of simple bars that you can make yourself if you want than can be used to hold round or square bits. Grind your own in HSS tools and clamp them into one of the through holes in the bar.

The import brazed carbide boring bars generally have a rounded relief below the carbide and I just grind it away as needed if it is rubbing the bore. They typically have a 0° end angle as well, so I grind about a 5° positive angle on mine to keep it from rubbing on the bottom of a bore.The idea is to have just enough clearance but not too much. The side 'angle' needed will change with the size of the bore.

rleete said: "Decent carbide, but not sharpened worth a fart in a windstorm. My set actually had a round edge on some of them."

I have a couple of sets that came the same way. The cutting edges were indeed rounded and wouldn't even cut Delrin (plastic) they were so bad. It would just rub on the side of the carbine and burnish the material. After putting a good sharp edge on them with the grinder they cut like buttah...

[TomG]

If you are boring a 1/2" hole with those boring bars, they are likely rubbing below the cutting edge. Sharpen them up and add a secondary clearance angle so the area under the cutting edge doesn't rub on the bore. For most jobs you would be better off with high speed steel bars instead of carbide. They are easier to sharpen and much more forgiving.

Another option I've used in a pinch is to substitute an end mill as a boring bar. You just have to orient it so a cutting edge is horizontal and on the center of the part.

Tom