SB9-first limitation

[JustaDB]

Yesterday I spent an hour or so making a boring bar out of 1/2" drill rod. Drilled a 15/64 hole perpendicular to the length near the end, filed it square & to size for a 1/4" bit, drilled & tapped a hole in the end for a 1/4" set screw. Today I thought I'd try it out.

Have about a 5" length of corroded, pitted 5-3/4" OD thick wall pipe I was thinking of using for a steady rest. Chucked it up into the 4-jaw & squared off the end with the intention of cleaning up the exterior & interior. Get about an inch into the exterior cleanup, I hear something rubbing. Back the carriage off, WTF? The OD is just barely contacting the top of the cross slide housing.

So, although you can chuck up a little more than 9" above the ways, above the cross slide you're limited to a little less than 5-1/2" on mine.

That said, the boring bar worked reasonably well on the interior. It flexed more than I thought but will remove metal w/ a sharp bit. It also revealed a fair amount of flexing in the QCTP/cross slide/compound junction.

 

[trevj]

Ayup. Welcome to the Suck! LOL!

A splash of oil on the deck where the tool post attaches, is worth having, as it will allow you to see if the movement is flexing of that joint, or flexing of the entire top slide assembly. Some between the top slide and the cross slide too. Too much oil never hurt any machine tool that I have heard, and it will show you where the flex is happening. You may need to stone off some raised surfaces under the tool post, or it may be that the gibs could be snugged up a bit. Sorta gotta see what's moving, and work with that info. It's not a big knuckledragger of a lathe anyways, so it may just be that you are finding the limits for the lathe, too.

Yer probably REALLY gonna want a bigger boring bar! Use as big as you can fit in the hole, or as big as you can fit in the holder, and keep it as short as possible too, in the tool holder.
Now, if you want to use the 1/2 bar, you are probably going to have to slow your revs down, WAY down. A slow turn, stops a lot of the harmonics virations from starting up, that will give you chatter, and a headache!

Start somewhere near as big a bar of stock as you can safely clamp in to your tool holder. There are a couple basic tricks to making a square hole across the end, either straight across, or at an angle, so you can reach the bottom of the part. One way is to drill it, and then spend a bunch of time filing, until you can ram a bit blank through the hole (cheap and ugly broaching!), the other is to mill a slot, and weld or silver solder a piece in place, to leave a square hole for the bit. As a hint, you can hold the bar-to-be, in the tool holder, and mill the slot using a right sized end mill, in the 3 j chuck (I can almost hear the old guys rolling in their graves!). Wrap a strip of soda can around the end mill.
I have seen boring bars that were simply a chunk of stock, inlet to allow a lathe tool insert holder to mount in the slot, with a couple set screws, and I have silver soldered my share of HSS bit blanks in to a slot across the end of a big bar. When too used up, heat it up again, and either replace the bit, or slide it forward!

Another path to try, is by playing some jiggery pokery with the arrangement of the top slide on the cross slide. You can extend the top slide so the tool post is almost at the edge of the cross slide. This puts the pressure still on the cross slide, but gets you the most reach in to the work. You want to avoid having the top slide extended or retracted too far, as this leaves one end or the other of the diovetail having to work in tension, a job cast iron, for all it's wonderful properties, kinda sucks at dealing with!

 

[JustaDB]

Thx for the tip re: oil. I'll give it a try. I do have the gibs snug.

As to the boring bar size, I used 1/2" because of a project down the road and I did use poor man's broaching. The file work wasn't that bad, took less than 15 mins. Sans mill at this point, so anything mill related is out.

I had it on the slowest speed short of the back gears, once I got past the corrosion it seemed to work not too bad. Boring bar tool was extended about 2" past the holder, didn't seem to be much chatter.

Appreciate the reply.

 

[140mower]

I have found that this style of boring bar holder seems to work fairly well for me, especially if you turn the compound to run parallel to the axis of the lathe. It's old school, but so are most of us. This one is an Armstrong, I have some other sizes as well.
With some creative work holding, it should be easy enough to make on the lathe alone.