What is the magic of Boring Bar manufacturing?

[Your Old Dog]

I didn't want to hijack a currently running thread.

I don't get it. I have 3= 3/4" boring bars of different lengths that I found at yard sales. BUT, to me they look like 3/4" round stock fixed up on one end to accommodate a cutting bit. if a guy is working at home and not on a production setup, why is it so necessary to have a commercially built boring bar that's been heat treated?

I said I have 3 3/4" boring bars, but I have no 1/2 bars. I've had to make my own and it's not a big deal and they work for those times when I need to bore less then 1" holes.

I'll be damn'd if I'd pay $100.00 for something I can easily make for my home shop for about $5.00. I'd find another place for the money.

If I worked commercially I'd no doubt think differently as maybe I'd want to take deeper cuts to work faster. (btw, flea markets around here frequently have 3/4 and 1" boring bars but I've never seen smaller ones.)

related question: What can you do with a "face mill", in a home shop where time is in abundance, that you can't do with a fly-cutter? I'm asking because I really don't know. Would it be useable to de-bark D2 tool steel before machining? Knife makers chew up belts getting through the bark on D2.

[Dr Stan]

YOD,

I've made & used shop build boring bars. Some worked well, others not so much. The commercially made bars are heat treated to help improve rigidity, consequently improving surface finish and the ability to hold a tighter tolerance.

The key to making boring bars is to use suitable material such as 4130/4140 instead of making do with CRS. One should also use the largest bar possible for the job and reduce overhang to a bare minimum.

Regarding the fly cutter/face mill question yes you can debark with a fly cutter. However the face mill is not only faster but also reduces the impact on the spindle bearings assuming you have at least two inserts in contact with the work.

Hope this helps.

Stan

[J Tiers]

hardening or heat treating does virtually NOTHING for the rigidity.

What it DOES do is ensure that the insert or cutter bit will not thrash its pocket into a rounded crater, and that the shank will not get marked up with so many pits and bumps that the thing becomes wobbly and unusable.

Hardening is basically abuse resistance.

Ordinary CRS works fine, it just gets worn and troublesome a lot faster in a commercial shop full of "Bubbas". For you, it ought to work fine.

[tlfamm]

Dr. Stan writes:

---snip---
Regarding the fly cutter/face mill question yes you can debark with a fly cutter. However the face mill is not only faster but also reduces the impact on the spindle bearings assuming you have at least two inserts in contact with the work.
---

I wonder, is Evan's elegant flycutter-from-a-bolt design evolved or devolved by adding additional teeth:


http://bbs.homeshopmachinist.net/showthread.php?t=42062

[Cheeseking]

hardening or heat treating does virtually NOTHING for the rigidity.

.

Are you sure? Seems to me a hardened bar would be stiffer. I was going through some tooling the otherday and picked up a little 1/2" bar and holy cow was that thing heavy for it's size! I asked one of the guys if it was carbide or something. e said it was a heavy metal bar. What the heck is "heavy metal"? (Easy no jokes)

[Dr Stan]

hardening or heat treating does virtually NOTHING for the rigidity.

Hardening is basically abuse resistance.

While hardening does considerably improve the wear resistance of the pocket, it also increases the amount of force required to deflect the boring bar. Check Machinery's for information on the properties imparted by hardening.

[Dr Stan]

Are you sure? Seems to me a hardened bar would be stiffer. I was going through some tooling the otherday and picked up a little 1/2" bar and holy cow was that thing heavy for it's size! I asked one of the guys if it was carbide or something. e said it was a heavy metal bar. What the heck is "heavy metal"? (Easy no jokes)

Yes a hardened bar is stiffer and the piece you picked up was most likely carbide as it is much denser than steel, that is unless it is lead or uranium.

[Mcgyver]

YOD, i think its two things. The hardened material stands up better to use and and abuse and economics. If one's inclined to stop making widgets to make themselves a boring bar, maybe they should be in the boring bar business instead.....for your own use, for sure make them.....or pick up the nice Williams ones for $5 used

[Mcgyver]

Yes a hardened bar is stiffer and

I don't know where you got that from, hardened/unhardened have next to no difference in Young's modulus which determines how much something will deflect for a given load.....where does it say hardened steel is stiffer in Machinery's handbook?

[Dr Stan]

.or pick up the nice Williams ones for $5 used

Good idea. YOD check with Anderson Tooling http://www.usedtooling.com. I have purchased several items from them and have been completely satisfied.