Boring holes with nice finishes

[benmychree]

One of the biggest problems that I see is the way excessive amount of stickout of the boring bar. besides that it would be much faster to do the boring job on the lathe rather than in the mill. For most all boring on the lathe or mill, I use HSS Bokum boring tools, they are the BEST!

 

[jmarkwolf]

Well, how can you bore a 2in deep hole without 2in stickout?

 

[benmychree]

Well, how can you bore a 2in deep hole without 2in stickout?

In the picture, it looks like considerably more than 2" of stickout.

 

[mattthemuppet2]

I would have done all of it on the lathe, it's allot easier to bore a hole to size on a lathe than it is on a mill. Do you have any boring bars for your lathe? A set of sclcr insert bars can be had for not much money, plus a set of ccgt inserts and you'll look like a pro in no time

 

[pacifica]

On the mill relief angle will make a big difference. I switched from a tp insert (11 degree relief) to a td(15degree relief) and all of the sudden a poor quality finish went to a nice finish.

 

[NC Rick]

To me the tool looks small in diameter for the size of the bore.

 

[jmarkwolf]

In the picture, it looks like considerably more than 2" of stickout.

Update from OP here:

Right you are benmychree. The boring bar stick out in the pic is indeed longer than two inches. I double checked by re-installing it in my boring head and measuring. It sticks out 2-1/2 inches. The taper makes it appear even longer. I couldn't choke it up any further because it "bottomed out" in the boring head.

So that's my bad.

What I didn't relate in my story is that this was my 2nd attempt at boring the 2in deep hole in a different piece. This was also my last "new" boring bar which happened to be longer. The previous attempt was done entirely in the lathe with a shorter bar, with only enough stick out to reach the bottom of the 2in hole. The bar was situated in the tool holder such that the bar indeed had 2in stick out, and the tool holder nearly contacted the end of the work, so no further stick out was even possible, and I still experienced the same issues (severe striations, screeching, etc.). At this point, I believed the issue to be unrelated to stick out.

And in fact, I think we have identified my issue to be brazed carbide tools that are dull (I admit, that possibility had not occurred to me) despite being new, and possibly insufficient attention to contact angle, and other issues, for which I thank the respondents to this thread.

I think I will invest in new indexible boring bars for the next boring project. Assuming here the inserts are sharp right out of the box?

 

[Badabinski]

Update from OP here:

Right you are benmychree. The boring bar stick out in the pic is indeed longer than two inches. I double checked by re-installing it in my boring head and measuring. It sticks out 2-1/2 inches. Couldn't choke it up any further because it "bottomed out" in the boring head.

So that's my bad.

What I didn't relate in my story is that this was my 2nd attempt at boring the 2in deep hole in a different piece. This was also my last "new" boring bar. The previous attempt was done entirely in the lathe with a shorter bar, with only enough stick out to reach the bottom of the hole. The bar was situated in the tool holder such that the bar had indeed 2in stick out, and the tool holder nearly contacted the end of the work, so no further stick out was even possible, and I still experienced the same issues (severe striations, screeching, etc.). At this point, I believed the issue unrelated to stick out.

And in fact, I think we have identified my issue to be brazed carbide tools that are dull (I admit, that possibility had not occurred to me) despite being new, and possibly insufficient attention to contact angle, and other issues, for which I thank the respondents to this thread.

I think I will invest in new indexible boring bars for the next boring project. Assuming here the inserts are sharp right out of the box?

They should be, although I've purchased some very cheap import inserts that were definitely not the sharpest.

In addition to HSS inserts, I've had great luck boring with some SECO CCMT 21.50.5-F2 inserts I got off of eBay. They have no coating and basically no nose radius so they're scary sharp and can take very light cuts. Surface finish is also surprisingly decent. I tend to wear them out fairly quickly, however. That's likely due to my own incompetence, but these things are cheap like borscht so it doesn't bother me too much.

Edit: I just checked, and they're not as cheap as I remembered still not too pricey though.

 

[epanzella]

My boring head uses the 3/4 inch brazed bars and I've had pretty good results from it as long as I set the cutting edge angle right. I find the if I set the bar to what looks like the correct angle to my eye it invariably rubs and produces a hatchet finish. To present the cutting edge to the work at correct angle the top surface has to on the center line of the head or it rubs. This takes me a bit of doing to get right with my old eyes.