Struggling with boring

I have a set of those cheep boring bars and I can see them flex as they start to cut. My go to boring bars are 3/8 and 5/8 round bars that hold 1/8 round and 1/4 square HSS tool bits respectively. They have worked from day one when I started this hobby.

Set your bar up as per Mikey's suggestions. Then put some dichem on your boring bars. If they are rubbing the dichem will be gone where they are rubbing. Keep grinding until you don't have anymore rub spots.
 
Oops, got my decimal wrong (typo). Point being know your feed rate on the cross slide.
 
raferguson said:
I have a 7 x 12 mini-lathe. I am trying to bore a hole to match a shaft, which measures slightly over 0.750." I have an 11/16" drill, so after a pilot hole, and an 11/16" drill, I started to bore. It seems like I am not making much progress. 11/16" is .6875. 0.750 - 0.6875 = 0.0625. Looking at the dial on the cross slide, one revolution should be 0.040". I believe that the cross slide motion should produce a change in dimeter of twice the motion of the cross slide. (Am I wrong?). So a single revolution of the dial should change the diameter of the bore 0.080". However, I have turned the dial several revolutions, and the diameter is still less than 0.750".

I am using a boring bar that sticks 2" past the end of the holder. I can see the lack of rigidity in my lathe, of course. I can see some chips, so it is not like it is not cutting at all.

Am I just kidding to think that I can bore a hole with my mini-lathe? I could post a video if that would help. It looks like the site supports videos...... Do I need to tune up my mini-lathe.

Richard
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What kind of boring bar are you using? Are you using the kind that comes with boring heads, you know those brazed carbide boring bars? These bars are NOT ready to use out of the box! They will not cut basically unless you first grind the proper relief into them.
 
I think the replies are right on, brazed carbide on a mini is difficult, not enough rigidity or power. cutting angle and clearance are big learning points when starting single point boring. My recommendation is to switch to HSS for your boring bar, as big as will fit into the hole. Make sure your rake angle and bottom clearance is set. Slow surface speed with oil. Experiment with some scrap. You will get it to work. Here’s a great resource at Vintage Machinery and a link to the South Bend book.

 
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