Need boring head recommendations

[ARC-170]

If my knee mill has an R8 spindle (Bridgeport clone) is there any reason I would want to get a straight shank instead of a RB shank boring head? It seems like an R8 shank would be one less piece in the puzzle (no collet) and less likely to flex?

R8 ones are not as widely available as straight-shank ones at the moment. I've seen about 2 on sale now, but I've seen about 10 straight-shank ones. The shanks do screw off, so one could buy the head and the shank separately. I was just trying to find everything in one package.

I asked the question about using a straight-shank in an R8 collet in in earlier post in this thread, but haven't got an answer yet. I'm sure someone will chime in.

 

[ARC-170]

I am wondering how a Criterion head is superior to the boxed up kits all over eBay for way less?

I wondered the same thing until I tried one. It cuts just fine, but the adjustment is not consistent at all. One turn of the adjuster knob would result in different distances each time, rather than being exactly the same. I'm not sure if there's too much slop in the adjuster screw or something else. I even accounted for backlash by screwing it one direction only and not backing it out.

I was thinking of getting a Precision Matthews or LMS boring head (they are about $100), as they have better quality control, but everyone has recommended Criterion.

 

[Winegrower]

Regarding Criterion vs. Imports, thank you gentlemen for these comments and others:

Insofar as size, the DBL-303 is BIG and heavy.

It cuts just fine, but the adjustment is not consistent at all.

The unbalanced mass on the Bridgeport is something I have not noticed, but can appreciate. I run the boring head at lower speeds, avoiding this. The adjustment factor is important…neither my 2” or 3” identify whether the index marks are radius or diameter, so I had to test to determine. If it’s critical, I set up with a dial indicator for the final pass.

 

[mikey]

The unbalanced mass on the Bridgeport is something I have not noticed, but can appreciate. I run the boring head at lower speeds, avoiding this. The adjustment factor is important…neither my 2” or 3” identify whether the index marks are radius or diameter, so I had to test to determine. If it’s critical, I set up with a dial indicator for the final pass.

The leadscrews on Criterion heads are class 3 threads. I'm not sure what they are on import heads but I suspect they are not a class 3 fit. Moreover, Criterion heads are direct reading, meaning that if you need the hole ID to be 0.003" bigger then you dial in 0.003" of advance on the screw and the head will cut that diameter 0.003" bigger.

Insofar as balance is concerned, running slow works but sometimes you need to use carbide and carbide needs speed. Given that centripetal forces skyrocket with velocity, speed is a major deal. I can tell you that when a 2" Criterion head goes above 3" ID, speed is a factor in how much vibration the head generates.

 

[ARC-170]

I was watching several Criterion heads and got a good offer on this one, so I accepted it. Tip: if you are selling something, make sure the pictures are not blurry!






It appears to be missing a set screw, but every one I looked at was missing at least one.

Can someone recommend some good boring bars?

Thank you everyone for your help and comments. It was very helpful.

BTW, I talked to my colleague at the adult school machine shop and he told me a straight shank one is just fine. It allows you to use the boring bar on any machine.

 

[rwm]

I'm glad you found one! Please report back how you like the straight shank. I am also in the market and have been pondering the same question.

 

[ttabbal]

I have a straight shank on my DBL-202 and it works great. If you hate it, R8 shanks are easy to get.

For bars, I love the Borite cobalt bars. The set is pricey, but they work great. I've used some insert bars as well, but I get better finish with the cobalt. Could be that I don't like running the boring head really fast.

 

[mikey]

I was watching several Criterion heads and got a good offer on this one, so I accepted it. Tip: if you are selling something, make sure the pictures are not blurry!
It appears to be missing a set screw, but every one I looked at was missing at least one.

I saw that head. Looks pretty good except its missing one of the bar holding screws. The replacement is a 5/16-24 Z 3/8" long fine thread socket set screw with a knurled cup point. You can get them on Amazon.

Can someone recommend some good boring bars?

I agree with @ttabbal. Borite cobalt bars are one of the best bars but they are no longer in business and finding a full set is going to be difficult and expensive. An alternative I would jump on is this one from KBC. Might seem pricey but they are 8% cobalt and will last your lifetime if cared for. They will also work really well at the speeds you are likely to use.

Straight shanks are fine. They allow you to use an R8 collet to hold the head or any other tool with a straight shank. I use the TTS system that uses a modified R8 collet to hold tools with their 3/4" shanks. It is very fast to switch tools because you only need to loosen the drawbar to change tools, and the accuracy is more than acceptable. You might want to look into the TTS system.

 

[great white]

??? Its a single point tool, even if it did "pull something off center", its a single point adjustable tool. It would not matter in the least bit.

Not as if a boring head tool is "on center" ever anyways. And that is the point and why its accurate. The spindle itself generates the cyclinder and does not rely on the accuracy of the tool itself like drills, end mills, and to a certain extent reamers are.

Perhaps I didn't explain myself adequately or made a poor choice of words.

Metal moves when you weld it. Nearly impossible to not have it pull one way or another as when the weld cools, the metal shrinks.

It's not "on center" that would be the concern in my mind, it would be "tilt". So while the shank may run "true" to the quill, the head may not be running true to the shank.

So if you're using it like a fly cutter, it may cut on the forward sweep and not on the rear sweep. For boring, you may be able to compensate for the "less than true" cut, but I believe you'd have to measure the bore because graduations on the tool may (or may not) be accurate.

At any rate, I'd be skeptical buying a tool like that with a weld where it is. Maybe the manufacturer has a process to compensate for the welding, maybe they don't.

Personally, I'd much prefer a tool that has a grub screw, lock pin or some other locking mechanism rather than to weld the threaded shank to the head.......YMMV.

 

[great white]

I wondered the same thing until I tried one. It cuts just fine, but the adjustment is not consistent at all. One turn of the adjuster knob would result in different distances each time, rather than being exactly the same. I'm not sure if there's too much slop in the adjuster screw or something else. I even accounted for backlash by screwing it one direction only and not backing it out.

I was thinking of getting a Precision Matthews or LMS boring head (they are about $100), as they have better quality control, but everyone has recommended Criterion.

That's probably the varying production tolerance you get with "no name" tooling. My ebay special cuts fine and the adjustments on the tool itself are also accurate. At least accurate enough for the work I do. I can easily work my impost boring head to .001. But as I said, it's probably more luck than anything else that my unbranded one works as good as it does.