Boring Bar issues...

[The_Apprentice]

So, I decided to try and play with boring bars.

I took a look at what was avail for the asian mini-lathes, and it is mostly 3/8" and 1/2" shanks.

I was on LittleMachineShop and could only see a holder for a standard 4WTP that supported 1/2" shanks. Since the compatibility list showed a lot of clones of my King, and I figured rigidity of 1/2" is better over 3/8" any day, I went with 1/2.

First problem, I noticed that it is an extreme tight fit to get this block into the 4WTP. There is around a 20mm gap only to fit into, and seems just a little too short to fit the boring holder. I can only get PART of it to fit in.

My thoughts were to wait until I get a milling machine, then mill part of this rectangle off so it fits. Then no, that sounds stupid when it may be easier to just use my grinder and manually try that... or better yet, I can probably get away with just using 2k or 3K sand-paper and see how that goes? It's a close fit, but not quite.

But now I am worrying about if I made a mistake about something else. A 3/8" shank in a similar rectangle square holder, is going to be sitting a little lower in a holder than a 1/2" shank, due to the change in radius. I have a theory that my tool may end up off-center. A smaller bar you can shim up always if it's sitting too low...

Or maybe I am just over-paranoid so far and over-thinking this stuff.

I tried to check with a dead-center but without being able to fit and tighten things down, there is too much play to get an accurate reading right now.

In any case, thought I'd share this before I end up doing something silly, ahah!

I will try to sandpaper the top of this rectangle holder tomorrow until I can get it to slide in easily enough into the 4WTP... does this make sense for now?

 

[cathead]

A grinder or disc sander would work. I would think the tool holder would have up-down adjustment but
maybe not. Also a lot of times the boring bar won't fit comfortably in a small hole so once again the grinder
or disc sander would be the go to tool. I have resorted to making my own boring bars to fit the application
at hand. Usually the off the shelf boring bars are too fat, too short, wrong geometry, etc.....

 

[markba633csi]

Sounds like you need to invest in a small collection of metal files- invaluable!
Mark

 

[mikey]

A 3/8" shank in a similar rectangle square holder, is going to be sitting a little lower in a holder than a 1/2" shank, due to the change in radius. I have a theory that my tool may end up off-center. A smaller bar you can shim up always if it's sitting too low...

This. You need to get the tip of the tool about 0.005 - 0.010" above center line and you need room to do it. If the tool holder fills up all the space then the tool will not cut. I suggest you buy or make a smaller adapter.

 

[fitterman1]

I'd set it up in the 4J and turn off a mm/040" off the top of it with another tool. Then try setting up.

 

[kd4gij]

I would ditch the block that the boring bar is in and just clamp the round bar in the four way. When I was using a 4 way, I always clamped round bars in it.