Any Reason Why Not?

[Joe S.]

I reacently got this little boring bar thinking I could go all the way in with it. I was reminded about how little I know right now Is there any reason not to rig up a little milling deal to cut that flat part back further? I would hate to ruin a $75 tool! I can't really think of a reason, but I have already demonstrated that I still don't quite know what I'm doing! Thanks in advance for any advice.

 

[Curly]

Joe the reason the tool doesn't have a longer reduced diameter is that for most metal work the longer the tip is unsupported the greater chance there is for tool vibration. If all you want to do is cut plastics for pens then you can turn away more of the hexagonal portion of the tool. If you also want to use it on metals, you may find it no longer suitable.

 

[Joe S.]

Thanks, I guess I'll have to reevaluate before I decide.

 

[JF36]

As Pete said, the farther out the tool is from your tool holder the more vibration you will get. It is a little more expensive but you could also get a boring bar, like this one Grizzly.com that has the same diameter over the entire length of the shank, so you can get some extra depth when you need it. The other option you have, that may work depending on what you are tying to do, is to get a set of adjustable reamers if you need an off size hole that you cannot get with a drill bit or conventional reamer.

 

[Joe S.]

A boring bar like that would be great! I've spent a little too much money on this already though, so it will need to wait.

 

[Dick Mahany]

I had the same thinking. Then I found an inexpensive boring bar set from Enco that has graduated lengths. It does mean more tool changes, but it allowed me to get deeper with minimal chatter. I'm using 3/8" dia bits with C2 carbide Asian made bars on a 7x12 lathe. Less than $45 for a 9 pc set.

 

[frank123]

It's pretty easy to make a boring bar out of a piece of drill rod that will bore to any depth you want it to bore.

The deeper the bore the more likely to get a poor finish or even a slight taper with smaller diameter boring bars in harder materials, but it shouldn't present much of a problem in plastic or wood or other soft materials.

FWIW, there's not much difference between making a boring bar and an internal threading tool - turn all the diameters and angles on the lathe then grind the cutting end surface flat to center and the relief under the cutting edge (if desired) for the cutting end of it using a fine wheel on the grinder.

 

[Paul in OKC]

General rule of thumb in the machine shop for boring bars is a 4 to 1 ratio. You can stick the bar out 4 times the diameter on steel bars. 8 times on carbide bars. That's for steel cutting. Some times on this smaller stuff and plastic you can get away with more over hang.