Boring bar material of choice?

886DG · Jul 1, 2021

Greetings,
I'm needing to make a boring bar for a lathe project that goes beyond what is "normal" for what I have for tooling.
In the past I've used 1144 or hardened chrome shafting. Before I get a "stick" of that, is there a better alloy for making boring bars out of without getting too exotic?

The bar is 2" diameter, and will finish off at around 48" long. I'm going 20" deep, starting off at 3.25" (my biggest drill bit) and finishing around 5.2". Of course the hole is blind, so that always makes it "fun".

Vibration with the three jaw dampener is not too bad, but I could be doing better.

lucky7 · Jul 1, 2021

I’ve done better in the past by getting rid of compound and bolting adaptor directly to cross slide. Will also allow for bigger diameter boring bars.

Not sure any different type of steel is better for the bar. Carbide bars tho are definitely better! And lighten your wallet…

With dubious boring bar length to diameter ratios suggest a keenly honed HSS tool, not carbide.

L7

CarbideBob · Jul 1, 2021

There are four steps.
Steel, heavy metal, carbide, and tuned.
One can out a pocket in heavy metal, carbide a brazed on head.
Bob

Joe Gwinn · Jul 1, 2021

lucky7 said:
Not sure any different type of steel is better for the bar. Carbide bars tho are definitely better! And lighten your wallet…

With dubious boring bar length to diameter ratios suggest a keenly honed HSS tool, not carbide.

All steels have the same stiffness.

Some kind of tuned-damper mass design can help.

https://www.google.com/url?sa=t&rct...4/4/2/53/pdf&usg=AOvVaw3PS5NaI4VTaucRPNLm4_pf

Ignore the thicket of math, look at Figure 9.

Note: Also look at Stubby Tools (Posting 16):

What Boring Bar Diameter

886DG · Jul 1, 2021

I think a 2"x48" carbide bar might just give me a stroke!
I'll stick with 1144 and machine the end to hold the insert I'm using now.
Thanks all,
886DG

Cole2534 · Jul 3, 2021

Joe Gwinn said:
All steels have the same stiffness.

This is often overlooked. If the bar has sufficient cross section even 1010hr could be used.

With this in mind, I'm surprised I've never seen a weld-on insert head for sale. Buy the head for a CNMG, or whatever, then weld it on to whatever you want. Let them cut the tight geometry in a good material and then the new owner cant burn it onto some 4140 scrap.

Phil in Montana · Jul 3, 2021

A little too moch reach? Try cast iron...Phil

Larry Dickman · Jul 3, 2021

we often make boring bars from pure tungsten. It's extremely dense and vibration resistant

implmex · Jul 3, 2021

Hi 886DG:
No comment on the material choice, but have you considered having your bar gun drilled so you can plumb it for coolant or air?
If this is a blind bore, chip packing is going to be one of your enemies.
Compressed air down the bar can be a Godsend to keep the bar from graunching as it plows into all the chips you'd otherwise pack at the bottom of the hole, and it's nice to be able to get coolant or Rapidtap down the hole for the finish cut too.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

ratbldr427 · Jul 3, 2021

I have never thought of clamping a chuck on the bar.I wonder if padding the jaws with soft metal,lead or copper would further dampen the bar?
I have never had the time to experiment but it would seem that the shape of the bar would effect its resonance, would a square bar be better or just resonate at a different frequency. I assume that since most bars are round, that is what works best. I'm also aware of hollow bars filled with shot to dampen them,never used one.

Cincinnati had an over arm on some of their older mills that had a tension bar in it to dampen it.

Seems like the only answer is denser material? Surely after all these years someone has done research on different geometries for bars? Any references?

otrlt · Jul 3, 2021

I have made many large boring bars, but their performance hinges mainly on how they are attached.

For a basic boring bar material I would start out with 4140 annealed stock, and machine it hexagon, but leave your arced corners. Drill, tap, and mill your slots.

Send it to heat treat 42-48 HRC.

gbent · Jul 3, 2021

If you are going to drill it to 3 1/4, why are you going to use a 2" boring bar? The only reason I'd use a 2" is to open it up enough to get a 4" bar in the hole.

I agree with removing the compound completely and bolting an adapter in place of the compound to hold the boring bar directly.

Let us know how it comes out. You are asking a lot of that little Regal.

pavt · Jul 3, 2021

Most steels have the same modulus of elasticity so IMHO it doesn't really matter what you use. 1045 would be OK. My rule of thumb is to use the fattest bar you can get in the hole, and still have room to clear the chips. That was good advice about directly mounting it without the top slide. More solid things are, the better.

partsproduction · Jul 3, 2021

I don't know if this is a repeat job, that would offset the initial cost of Trepanning. Evidently Kennemetal sells heads for different inserts and you have to build the hollow tool yourself to bolt the insert holder heads into, pretty fascinating stuff.
Mr. Wilks always uses general engine lathes converted to guide
and push the tool, but it's one pass and your done.
For Tank barrels I think they ream them for the last tolerances.

The way he's doing it a 6" hole leaves a 4" solid when done, that's a complete 4" solid bar's time that isn't wasted turning it into chips, there is no way three or four consecutive passes from solid can be faster.
Nothing in my shop needs it but it's poetry, because for me trepanning was always for short wide holes

I think I've watched most of his videos. Here's one; TREPANNING. Why through coolant is important and what can go wrong - YouTube

Joe Gwinn · Jul 4, 2021

implmex said:
Hi 886DG:
No comment on the material choice, but have you considered having your bar gun drilled so you can plumb it for coolant or air?
If this is a blind bore, chip packing is going to be one of your enemies.
Compressed air down the bar can be a Godsend to keep the bar from graunching as it plows into all the chips you'd otherwise pack at the bottom of the hole, and it's nice to be able to get coolant or Rapidtap down the hole for the finish cut too.

Through coolant and high pressure are very good ideas.

Most of the stiffness comes from the outer annulus, so one can perhaps start with a heavy-walled DOM steel tube.

Drawn Over Mandrel Tubing - DOM Round Steel Tubing | Industrial Tube and Steel Corporation

CarbideBob · Jul 4, 2021

I you are going to make your own insert choice and layout geometry may make a difference.

implmex · Jul 4, 2021

Hi partsproduction:
You wrote:
"I don't know if this is a repeat job, that would offset the initial cost of Trepanning"

Sadly this won't work in the OP's case...he's making a blind bore 20" deep.
So he's going to have to drill and bore it from the solid.

However, if it were a through hole your idea would be a workable choice.
I'm not sure it would be faster though, especially if you have to make a trepanning tool holder, and I bet those trepanning heads are pretty pricey too.

I've never trepanned anything bigger than about 6 mm diameter...how does it compare to a big spade drill and a boring bar in the 6" diameter range?

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

DDoug · Jul 4, 2021

Cole2534 said:
This is often overlooked. If the bar has sufficient cross section even 1010hr could be used.

With this in mind, I'm surprised I've never seen a weld-on insert head for sale. Buy the head for a CNMG, or whatever, then weld it on to whatever you want. Let them cut the tight geometry in a good material and then the new owner cant burn it onto some 4140 scrap.

Seen several cobbled up from lathe stick tools.

partsproduction · Jul 4, 2021

"Sadly this won't work in the OP's case...he's making a blind bore 20" deep."

You're right, I forgot that blind hole aspect.

The Germans during WW1 did it though, when they got the trepanning tool to the right depth they drove tapers
between the core and the tube's ID on one side, then the next back and forth until the core broke out at the deep end, these were for large mortars.
After a final boring pass they would rifle the bore (Rifling a blind hole, another rare technology). Probably if they had the welding technology we have now they wouldn't have done it that way, and one has to wonder what quantity of 6" mortars it took to justify doing it that route instead of drilling and boring them.

4GSR · Jul 5, 2021

Back in 1997, I worked with a older gentleman who worked for Chicago Pneumatic in Ft Worth, Texas back in the 1960's. They were doing trepanning way back then drilling holes in landing gear housings. They designed a retractable cutoff tool that went in to the bottom of the bore and literally parted the core off. I don't remember the hole size other than it was upward toward 8" diameter and around 100" deep.

On a different note, where can a person buy "heavy metal" bar stock for making you own boring bars?

Ken

Edit: Just answered my own question

McMaster-Carr

Wow! Almost better off buying a ready made boring bar, for the price they get for the material!!!!!

Boring bar material of choice?

Plastic

Titanium

Diamond

Stainless

Plastic

Diamond

Stainless

Titanium

Diamond

Titanium

otrlt

Guest

Diamond

Stainless

Titanium

Stainless

Diamond

Diamond

Diamond

Titanium

Diamond

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