Cross feed rate of travel

[mickri]

Was finally able to get back to working on the post for the norman style qctp that I am making. The piece of mystery steel that I am making the post out had an approximate 1/2" hole in it which I needed to enlarge to 5/8". That's .125" and because each pass will take 2 times the amount of the cut I figure that I will be moving the cross feed a total distance of .0625." I thought that I had read somewhere that on craftsman 12 lathes the cross feed dial gives the actual distance that the cross feed moves whereas on some lathes the dial gives the amount that the workpiece is reduced in diameter or in my case how much the diameter of a hole is increased.

I am merrily working away and as I get close to a total movement of .0625 on the dial I am not anywhere near 5/8" diameter for the hole. By the time my 5/8" bolt will fit in the hole the cross feed dial has moved a total of .115. A little over one complete revolution of the dial. I have always had trouble accurately turning a workpiece or boring a hole to a certain diameter on my lathe.

So is the cross feed dial on my craftsman 12 lathe supposed to read the distance that the cross feed actually moves or as I found out today the amount that the workpiece changes in diameter?

 

[kd4gij]

Witch Craftsman lathe do you have?

 

[mickri]

I have a craftsman 12x36. I can get the model number if that would help

 

[kd4gij]

Set up a dial indicator and check your movement. A picture of your dials will help determine if they are stock.

 

[Rooster]

If you start with an approximate size hole, first take a skim cut with your boring tool and then zero your cross-slide dial. Then you need an accurate measurement of the hole, subtract that number from the .625 and you will take half of that.

 

[mickri]

First I ran a 1/2" drill into the existing hole. It seemed to be a close fit. Maybe a little off center. Then I did like Rooster said. I took a light pass with my boring bar. I put the tip of the cutter against the side of the hole and did a pass for the depth that I wanted. I did not at this point try to measure the inside of the hole but I did set the dial to zero. I had to use a 1/4" boring bar to start with because my 3/8" boring bar wouldn't fit. I did a couple of light passes and then was able to get the 3/8" boring bar to fit inside the hole. I re zeroed the dial. It was from this point that the dial showed a total movement of .1115."
Tomorrow morning before it gets hot I will put a dial indicator on the cross slide and measure the movement of the cross slide. Temp is supposed to over 100 here tomorrow and not fun to be in my non air conditioned garage when it gets that hot.
As far as I know the dials are stock dials. They look just like the dials that I have seen in photos of a craftsman 12x36 lathe. I am the 3rd owner. The first owner was a local citrus farmer who used the lathe in his hobby to rebuild some type of small pump engines. The second owner bought the lathe from the estate of the first owner with the intend to learn how to use it. He told me that he never used the lathe himself and it was only used a couple of times by a friend. It just sat in his garage collecting dust for a couple of years. He didn't change the dials and I have not changed the dials.

 

[Rooster]

Mickri, you have to take a measurement of the hole when you set the dial to zero. Only then do you know how much you still need to cut to reach your target of .625,

 

[mickri]

I agree with you about the need to measure the hole. I have just had horrible luck trying to get an accurate measurement of the inside of a hole. My measurements tend to indicate that the hole that I am measuring is smaller than it actually is. I have been through this with lots of suggestions in a previous thread here on the forum. In this case I have the bolt that goes inside the hole and as I got close I kept doing test fits until the bolt fit in the hole with a very, very tight fit.
The hole is just over 2" deep. When I got close to size I stopped doing full depth passes and only went in about 3/8." I did this in case I made the hole oversize. A small oversize portion of the hole would not ruin the part and it would still be usable. Once I got the exact hole size I wanted I bored the rest of the hole to that size.
Thanks for your suggestions. I need and appreciate all the help that I can get as I learn more about machining. I will never be a machinist. I just hope to someday graduate from being an absolute hack.

 

[wa5cab]

The original dials on all Atlas lathes made between 1932 and 1981 indicate the amount of movement of the cross feed slide and the compound slide. WRT the compound, if it is sitting at 0 degrees, it also would read directly the movement of the cutter point relative to the spindle axis. If the compound is sitting at 30 degrees, the movement of the cutter relative to the spindle axis will be .866 of the movement of the dial (COS 30 or COSINE 30). At 60 degrees. it would move relative to the spindle axis, 1/2 of the dial movement. Which would mean that the dial movement would track the diameter decrease or increase. This of course assumes that you took the back lash out in the proper direction before commencing the movement.

If yours doesn't do this, either the dial or the screw and nut aren't original.

 

[Asm109]

The very first time I step up to an unfamiliar lathe, I take a skim cut on a chunk of material, measure the part, zero the dials, and dial the cutter in 0.010.
Take another cut and remeasure.
New diameter 0.010 inches smaller , I am working on a diameter lathe.
New diameter 0.020 inches smaller, I am working on a radius lathe.
Burn that piece of info into the brain cells and work from there.
If that piece of info is unknown you are not machining you are guessing.