Grade of Steel for Deep Boring Bar

[Dave Bunge]

I've got a Gizmo articulated hollowing rig. Now my largest boring bars are 3/4" diameter which limits how deep I can hollow. I'd like to make a a larger diameter boring bar to use with deeper vessels.

I'm thinking to make one similar to the Jumbo Boring Bar that Lyle Jamieson sells...1.125" diameter bar with a 3/4" diameter tenon on one end to fit into the Gizmo and a hole bored into the other end to accept one of Lyle's bent swivel cutter assemblies. I'd buy one from Lyle, except the tenon on his is too short for the holder on the Gizmo.

My question is what grade of steel to use for the bar. Anyone out there care to give input? This site discusses steel properties: https://www.onlinemetals.com/productguides/steelguide.cfm It seems like Alloy 1018 (cold rolled mild steel) or 1144 (stress proof) are the likely candidates.

So I'd appreciate any input people have on grade of steel to use and any other considerations in making a large boring bar.

Dave

[Adam Petersen]

I've used cold-rolled and it worked fine. Mine wasn't as large as you propose, I think I'm using 1". It works well and I haven't been concerned of any breakage. What's the price difference with the stress proof and 1018? Looking at their chart, the stress proof is nearly double the tensile strength of 1018, so if the price is negligible, and it were me, I'd give the 1144 a try if not anything aside my own curiosity.

[Dwight Rutherford]

As Adam suggested, cold rolled steel will work well.

[JohnC Lucas]

Doesn't have to be anything fancy. Whatever is easy to find in your area will work.

[daryl moses]

I made a 3/4" and a 1" both made out of cold rolled steel. I use the 3/4" for smallish hollowforms and the 1" for larger forms and vases. I've gone over 12" deep with the one incher and i've not had any problems.

[Dave Bunge]

Thanks everyone for the input. I'll see what the local steel providers have available.

Adam, to your question about relative price, I found a supplier on the web offering both. Their prices for 2' section of 1.125" round stock are:


Cold rolled (1018): $15.80
Stress proof (1144): $28.05


So pretty minor difference. If my local sources have both, I'll try the stress proof. If not, cold rolled it is.

Dave

[Larry Frank]

The stress proof is cold drawn with special process and then stress relieved. Personally, as a metalllurgist, I think the Cold drawn 1018 would be more than adequate.

[Dave Bunge]

The stress proof is cold drawn with special process and then stress relieved. Personally, as a metalllurgist, I think the Cold drawn 1018 would be more than adequate.

Larry, thanks for the input. It sounds like there is plenty of experience showing that cold rolled/cold drawn will work fine for a large diameter hollowing bar.

I do, however, wonder if the stress proof would offer any advantages. I.e. for a given diameter rod, would using stress proof steel allow me to hollow deeper before I hit the limit where deflection and vibration got too bad?

[john taliaferro]

A smaller cutter will get you a little more distance but get grabby and slow . The old saying about the weak link comes in here be nice to your gizmo .

[Dennis Ford]

Larry, thanks for the input. It sounds like there is plenty of experience showing that cold rolled/cold drawn will work fine for a large diameter hollowing bar.

I do, however, wonder if the stress proof would offer any advantages. I.e. for a given diameter rod, would using stress proof steel allow me to hollow deeper before I hit the limit where deflection and vibration got too bad?

Deflection will be virtually the same for all types of steel for light loads. Better steel can deflect more without taking a permanent bend or breaking but that will not help for a hollowing bar.

[Dave Bunge]

Deflection will be virtually the same for all types of steel for light loads.

Thanks Dennis, that's the missing piece of info I didn't have.

[JohnC Lucas]

Also when you hollow to all your cutting downhill with the grain. You will get a lot less chatter. I used to hollow by pulling the bar toward me effectively cutting straight across the grain. that's how I learned. Now I cut so the cutter is being pulled toward me and toward the side so I get about a 45 degree cut. This reduces the chatter tremendously.

[John Sincerbeaux]

My two cents:
when it comes to vibration/chatter, there are many factors besides bar thickness that can effect the cutting performance.
Type of cutter, size of cutter, and angle of attack are just a few.

I had my bars made of Stainless. I have a 1” and a 1 1/4” bar. I use my 1” 95% of the time. I prefer SS for all my custom tooling.

I would strongly recommend making a bar like Steve Siner’s bars (Advanced Lathe Tools). A Double bar seems far superior to a “D” style bar.

[Tom Giacomo]

I did something similar in that I made a 5/8" tang or tendon on a one inch bar. I have a small hobby metal lathe so I used the 1018 because it was easier to cut on a small lathe. If you have a large metal lathe then it will not be a concern.