What Boring Bar Diameter

Plz forgive me with the stupid questions I'm asking while I'm learning some of the fundamentals for the craft...
So I was curious the other day and got to thinking about boring bars and the diameter of the bars as to what be better suited for general all around needs, and to what diameter hole/or depth of hole they should/would best suited for...Since bars are expensive and I am just a novice and can't afford multiple bars I was thinking I may just get a couple to cover most of the bases I may come into contact with from time to time...
Is there a General consensus/understanding on Diameter of the bar in relation to the depth of the hole your cutting?
My thoughts were and they are only thoughts but would a 3/8" dia. bar be used for say up to 1" depth
1/2" be used up to 2"-3" depth
3/4" be used up to 3"-4" depth
1" be used up to 4"-5" depth
being all equal with the diameter of the hole and material
I understand a 1" diameter bar would not go into a 3/4" hole
However if that hole was say 4" deep and had to be within a given tolerance then what size of bar should be used?
Thanks
Paul

it will depend on the material your turning. are you talking about steel?

A good mental reference - twice the diameter = at least 4 times the stiffness - or resistance to chatter. This is directly related to depth used at

Nothing quite as useless as "chatter bar"

Sandvik silent bar for the win!!!! Get several different ends for it and enjoy.
Don


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The rule of thumb I always heard was 1:4 ratio for bar diameter to extension length. You can exceed that but you have to start doing things to help prevent and dampen chatter.

I always use the biggest bar I can that still lets chips out.

D Nelson said:

Sandvik silent bar for the win!!!! Get several different ends for it and enjoy.
Don


Sent from my iPhone using Tapatalk Pro

Click to expand...

For a newbie starting out ?

I think not, learn on the normal ones.
Figure out chatter problems, testing what tool radius does, extension from the tool block, lead angle, etc.

And when a tough job comes along that you can't
stop chatter, then bring out the specialized tools.

The biggest one you can fit in the hole. Always.

I have boring bars down to .017" x .625" reach. I'm not going to grab that unless I'm working in an .025" bore though....

The massiveness of the toolpost has a lot to do with bar performance. My CNC lathe has a 20" swing, but a turret that is only 2.5" wide. Looks like a beast, but doesn't bore worth a shit unless the overhang ratio is about 3:1 max. Fancy carbide bars don't fix anything there, besides you cannot really have an indexing turret with 6" of bar sticking out the back. So they have to be cut short, and that is not good. A bar needs to be able to wiggle its ass end to damp, then just a little clamp pressure on it to make it go away.

I can get 6:1 (steel bars only) on a manual lathe with a size C multifix. I use 3/8, 1/2, 5/8, 3/4, 1, 1.5 and 2" bars. T or D shape insert performs better on a bar than C does, because the latter has a heel which wants to ride the vibrations on the surface, so if vibration starts, it'll grow worse. I know that the cute little sets of CCMT bars are out there, but they underperform in unusually deep boring depths.

D Nelson said:

Sandvik silent bar for the win!!!! Get several different ends for it and enjoy.
Don


Sent from my iPhone using Tapatalk Pro

Click to expand...

You paying ?

kenton said:

The rule of thumb I always heard was 1:4 ratio for bar diameter to extension length. You can exceed that but you have to start doing things to help prevent and dampen chatter.

I always use the biggest bar I can that still lets chips out.

Click to expand...

Can you elaborate?
perhaps a formula for a 3" hole used as example...

D Nelson said:

Sandvik silent bar for the win!!!! Get several different ends for it and enjoy.
Don


Sent from my iPhone using Tapatalk Pro

Click to expand...

Don't have that kind of funds...
Thanks
Paul

Texasbowhunter said:

Can you elaborate?
perhaps a formula for a 3" hole used as example...

Click to expand...

The 1:4 or 4:1 ratio is for steel bars. Generally the max you want to hang out is 4x the diameter of the bar.
For a carbide shank bar it's 8:1 ratio.

If you're doing a 3" hole, depending on how deep you're boring it, a 1-1/2" or a 2" bar will suffice.
Usually people only have the capacity to hold a 2" bar as the largest... for most general turning work.
Obviously there are lathes that can handle bars way larger than 2" though.

What lathe do you have?

Oh and the Sandvik Silent bars are unreal... but so is the price.

So I have a couple boring bars at the present...1/2 and 5/8
I have a holder for my BXA mount which allow a 3/4" bar or I can remove the sleeve and have a 1" hole which to my uneducated mind would allow for a 1" bar to be inserted and held securely in place...So the thought was perhaps a 3/4" bar would allow for me to bore a hole say 3"- 4" deep? But if I'm going to buy one I might just look for a 1" that seems would do the job...
Now I think carbide bar might be out of the question due to cost vs how often I would use it...so a steel bar would be the choice...I saw a 3/4" bar 10" long in a reasonable price range...Thoughts? or just hold out for the 1" bar...One thing I would like to find is having the inserts that I presently use to interchange with the boring bar....I haven't looked real hard yet at the 1" bars but hope that the inserts I use would fit providing the consensus is the holder will secure the 1" properly...
Thanks
Paul

Mtndew said:

The 1:4 or 4:1 ratio is for steel bars. Generally the max you want to hang out is 4x the diameter of the bar.
For a carbide shank bar it's 8:1 ratio.

If you're doing a 3" hole, depending on how deep you're boring it, a 1-1/2" or a 2" bar will suffice.
Usually people only have the capacity to hold a 2" bar as the largest... for most general turning work.
Obviously there are lathes that can handle bars way larger than 2" though.

What lathe do you have?

Oh and the Sandvik Silent bars are unreal... but so is the price.

Click to expand...

I own a Clausing 5900 series 12 x 36
So after re reading post you say that a 1" bar would handle up to a @4" deep bore?
A 1/4" bar would handle a 1" deep bore...I'm kind of along the thinking that the diameter of the hole would not be an issue if the bar can go into the hole...But the deeper you go the larger the diameter is required for ridgity...
Thanks
Paul

Texasbowhunter said:

But the deeper you go the larger the diameter is required for ridgity...

Click to expand...

Correct.
Imagine a 1" bar that is hanging out 4 feet, it wouldn't be nearly as rigid as one that is hanging out 4 inches.

I think you might be surprised at how economical a carbide bar can be. See if you can get a quote on these guys. I have a couple in half inch and 3/8" that were stupidly cheap, and they work great.

Stubby(R) Boring Bars – NTM

Texasbowhunter said:

I own a Clausing 5900 series 12 x 36

Click to expand...

What you lack is a rigid platform more than a rigid bar material.

- Scout yerself some used or NOS turret-lathe toolholders. You want an OD around 2" to to 2 1/2" and enough variety to hold several bar sizes.

- Build a monobloc to hold those to take the place of the compound.

- fab your self a collection of bars out of 12" to 24" lengths of ignorant mild steel. Add more as the need arises.

-- Drill & broach for HSS-Cobalt // Stellite, not carbides.

Now.. boring times cometh?

- Leave your "BXA" QCTP in-place on the compound.,, but..REMOVE the compound, entire.

- Mount the monobloc, instead.

Get it right? Same animal also holds drills, taps, a drill chuck, ER-XX, or TG-XX master collet on straight-shank instead of a bar. Now you can power drill and ream as well as bore.

Don't forget that you can bore upside down and/or in reverse if appropriate to provide better chip egress ... and for climbing OUT of a blind hole.

-- Keep the overhang short. Always

-- Damp the arse-end. Always.

Skill at crafting the cutting tool shape & sharpness, plus paying close attention to what you can - and cannot - reasonably do on a featherweight "chatterbox" lathe as to the cut does the rest.

Down & dirty is that with that grade of lathe, you simply do not HAVE a platform that can put a(ny) of the "expensive" bars to useful work.

Drooling over specs, wishing, and dreaming won't change the lathe into something it was never and will never, be.

Don't piss-away the premium cost of exotic bars until you DO have such a lathe. Settle for what you CAN do, instead.

IOW?

JF "Run what you got".

It's lightly and cheap built? Surely.
So just KEEP it "cheap"!

Substitute patience you can find "somewhere" ....

...for machine-tool goodness you cannot find "anywhere"....

... not in a lightweight Clausing or any other lightweight lathe.

Carriage and topslide are what they are. Thankfully, compounds - and shakey-flakey "QCTP" are 100% "aside-able."

Take advantage of that small blessing. Aside those wobbly bits.

You could be overthinking the problem. You probably don't need anything fancy, at this point. If I were starting out right now, with a manual lathe and a tight budget, something like this would be at the top of my list:

Carbide Tipped Boring Bars C-6 5/8 Shank 12 Pc Set 817679016122 | eBay

If you have a bench grinder with green and gray wheels, you can modify them to whatever you need, within reason. That'll get you 90% of the parts you'd want to cut on a lathe with a BXA sized tool post. When the time comes that you need to go bigger or smaller than is realistic with those bars, get what's best for that specific job. By then, you'll have a much better idea of what you need.

For a little more money, something like this is nice, too:

4PCS SCLCR INDEXABLE BORING BAR SET 3/8 1/2 5/8 3/4" + 4 INSERTS $124 OFF S] | eBay

But I'd get this set in addition to the cheaper set, not instead of it. Insert tools are vastly superior to brazed tools, for most jobs. But there's a lot to be said for dirt cheap beater tools, especially when you're still learning. And to me, the ability to regrind them puts the cheap ones over the top.

You are obviously a beginner. Instead of trying to purchase "the" perfect boring bar right off the bat, I would suggest that you purchase an inexpensive set that has different sizes. On the internet you can find braised carbide sets with 3/8" and 1/2" diameter shanks. Buy a set of one or the other size and get or make a tool holder for that diameter. Then play with them to get a feel for boring.

You may also find a diamond stone of value to sharpen them. I find that even a boring bar that is extended well beyond what some rule says can still be of use if it is sharp and light cuts are taken. You are going to have to start with a drill first anyway so the boring bar may only need to take off a small amount.

Then, you will have a better feel for what your machine can do with them. And I would also recommend that you then just buy new, better boring bars as you need them for particular projects.

Lots of good advice here...but the basic answer is to buy a 3/4" bar, and make sure it's not Chinese made.

Later, buy a 3/8" bar for smaller holes.

That's all you need for 99% of what you will do on a 12x36" lathe.