Bridgeport Boring Bar Troubles


Last night I helped Luigi setup and bore out an automotive shock absorber upper mount about 50 mills radius of metal so the part could be mounted on the mounting stud of a different model car.

I got out the new boring head/bars kit. Good news is that it seemed easy to install, use and adjust. By the time we finished, one bar had a fractured cutter and another had a heel drag mark.

I set up for taking shallow cuts, no more than 5 mils each pass, used wd40 lube (this was steel).

But in retrospect a few other factors may matter determine cutter longevity and bore quality:

Use the autofeed. Being concerned about the quill having to be unstuck from the autofeed for each pass caused me to elect manual down feed for each pass. It is very possible to get too fast, especially when tired.

Pay attention to the gibs on the diameter setting slide. I believe they were a bit loose at first.

Pay attention to the alignment of the cutter face. It should be parallel the diameter setting slide. If the angle is off, cutter performance will suffer. I don’t recall being very studious of this point during the work. (The heel mark)

Pay attention to the temperature of the piece/cutter. Smoking lube may be OK, but it means that heat is building along with the troubles that come with it.

When working with a piece that has a tapered hole, such as we had, keep in mind that a shallow cut at the big end, ends up being much more cut depth at the small end than one had intended when setting up the cut based on the big end. Best mount the piece with the smaller end up. Don’t think that we did it that way last night.

Remember that if the hole being worked is not true vertical and/or the hole is not centered accurately with respect to the spindle, the bar may end up taking a much deeper cut at one side or one side deeper in the hole than intended.

Remember that the boring bars necks can flex, so use the shortest bar that can do the job.

Reviewing “How to use a boring bar on the Bridgeport Mill” by on Youtube helped me do this review. Don’t let boring bore you into complacency.


Yea, I had a similar with dimensions. I found on this set, you cant take as an aggressive cut as the previous set. I was doing 5-10 thou in cutting with good results.


Sounds like American steel won out against Chinesium once again.
Let me know the length on the boring bar and we’ll replace it.
@BobKarnaugh thank you for helping out a fellow member. cheers!


Good video. Thanks for the suggestion.