Author Topic: Question on boring finish (Read 672 times)

Cat Whisperer · « **on:** March 20, 2005, 08:43:42 AM »

Having home-built/modified boring bars I have a question or two.

Here are three of my boring bars - 3/4" and an Erickson (1" shank 3/4 head) and a 1" home-built from a 1" bolt and the 24" long shank from an IBM printer.

Roughing is easy with the 1" shown. .025" cuts are without chatter but the finish is a little rough. Even with the other two (with DeVleig Micro-Bore inserts) roughing isn't bad. Clearing chips is a pain, every inch stopping to clear chips.

So here's the question - finish cut - for accuracy and for smoothness, what do you set the cutter at for angles and what shape(s) of cutters do you use? I'm working for the moment on 1144 and work with 4140 and occasionally with CRS and will soon try cast iron for the first time.

CU_Cannon · « **Reply #1 on:** March 20, 2005, 02:14:40 PM »

I have gotten good results from a slightly round tipped cutter at the slowest feed. I generally take a .01 or less finish cut. The biggest problem I have is boring bar flex. I finely built a 1.125 boring bar. I would have made it bigger but the biggest drill is 1.5. Extended around 8" it doesn't seem to flex at all. For a really smooth finish a small cylinder hone would be your best bet.

Cast iron will take a smooth finish very easily. It machines almost the same as brass. It is my favorite material to machine. You will have a fine coating of black powder on the ways of your lathe and you will blow black snot for a week. A dust mask and a vacuum next to the cutter will help.[/u][/code]

Cat Whisperer · « **Reply #2 on:** March 20, 2005, 02:35:47 PM »

Thanks for the warning about the dust - I've worked in a brake manufacturing plant so I know from experience how it lingers.

Looks like I'll save the final cuts for the 1-1/2" boring bar (for the golf ball calibers) and maybe even see if a steady rest helps.

Third_Rail · « **Reply #3 on:** March 20, 2005, 06:27:14 PM »

I don't see any images... :?

GGaskill · « **Reply #4 on:** March 20, 2005, 09:30:49 PM »

I got a set of carbide insert boring bars at an estate sale. The inserts have a 1/32" radius and give a very nice finish. However, sometimes with a long bar you need a very small radius to get the cutter to cut and finish becomes secondary.