interrupted cut in boring

[joe d]

Hi all

The cross-head guide for my vertical single requires slots in the sides parallel to the axis of the bore (as well as letting you see the cross-head go up and down, these would allow removing the pin that secures the connecting rod to the cross head). The only tool I have that is the right size is a piloted counter-bore, so I'm thinking that I could drill pilot holes, counter-bore the beginning and end of the slot, and clean up with a smaller end mill. In order for this to work, I would have to leave boring the the guide till after this operation in order to have some meat there for my pilot holes. This will leave me with an interrupted cut when I bore: is this likely to be a problem? (The part is brass).

Thanks

Joe

 

[cfellows]

My gut reaction is probably, using a single point cutting tool in an interrupted bore could cause some uneveness in the bore. This can likely be minimized by:

1. Use as large a boring bar as you can to minimize springiness.
2. Make sure your cutter is as sharp as possible.
3. Take shallow cuts, particularly as you near the finish diameter.
4. Feed the boring tool slowly, again, particularly as you near the finish diameter.

These are just my thoughts.

Chuck

 

[Swede]

Chucks thoughts are good ones. It never hurts to use caution. I have done more interrupted boring cuts than I can remember, including cuts where the arc cut is less than 90%, with 270 degrees in air. This of course cuts a channel. I don't think a single one of them presented any serious challenge, and I don't think you'll have any problems whatsoever, especially if your bar is heavy and sharp. If your feed down is heavy, and the RPM quite slow, there is a tendency for the tool tip to "jump" downward when the tool is in the air portion, resulting in a heavier bite once it again encounters metal. Setup and equipment permitting, keep the RPM up and the feed a bit lighter than you normally might.

It may also make an annoying noise, but unless it's extreme, there's nothing to worry about. Good luck!

 

[georgeseal]

While we are on the subject of interupted cuts

If I have to do one I will take a piece of oak about two feet long ( on my lathe, yours may be different) and wedge it so that it drags on the chuck. This puts enough drag to stop the interupted cut. You don't want it tight just a little drag. sometimes I oil the wood at times not.

I have used this technique on both external & internal cuts.

George from Conyers Ga.

 

[rake60]

Joe
For an interrupted cut in a bore Chuck pretty much has it covered.
Sharp tools, but with a small nose radius. That's a balancing act!
Too sharp a radius will chip even in brass. Too much of a nose radius will push off as it feeds.

Another issue with an interupted cut is the tool bouncing in or out of the cut.
The possibility of that can be reduced by snugging up the gibs a little tighter than normal,
then setting your cut and backing the screw pressure away from the compound.

Rick

 

[joe d]

The consensus seems to be a consensus! I'll let you all know how it works out. (First I have to build a steady, the only one I have is too small).

Thanks, Joe