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mickri

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#1
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

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#2
Witch Craftsman lathe do you have?
 

mickri

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#3
I have a craftsman 12x36. I can get the model number if that would help
 

kd4gij

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#4
Set up a dial indicator and check your movement. A picture of your dials will help determine if they are stock.
 

Rooster

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#5
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

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#6
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

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#7
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

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#8
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

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#9
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

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#10
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.
 

mickri

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#11
When boring the hole I did not move the compound and I was not using the compound to bore the hole. Only the cross feed.
This morning I set up a dial indicator and measured the movement of the cross slide. I did it in both directions and I did two complete revolutions in each direction. I took out the backlash before taking readings. One complete revolution of the cross feed dial moved the cross feed 0.100. I had the same amount of movement in both directions.

Based on Robert's post and my measurements this morning I should have only had to move the cross feed a total of .0625" to enlarge a 1/2" hole to 5/8." I am at a loss as to why I had to move the cross feed almost double this distance to enlarge the hole to 5/8." While I was boring the hole and it became apparent that I was moving the cross feed way more than I thought I should have to move it, I checked my set up over and over and could not find any thing amiss. I was not taking heavy cuts. The biggest cut I took was 0.005."

I have a mystery that I can't solve at this point. Maybe something will come to light when I enlarge the bore in the base plate from 1/2" to 5/8." I will use the exact same setup.
 

Bob Korves

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#12
Depending on the boring bar and how sharp it is, the cuts you actually achieve can be much less than the amount dialed in. Use the most rigid setup and tooling possible, make sure that the cutter is sharp and the geometry and mounting is correct, look for possible rubbing below the cutting edge, and watch out when you get close, because spring in the tool can easily cause spring cuts to go too deep and ruin the job.
 

wa5cab

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#13
Another possible source of error is that the carriage gib is set too loose.
 

mickri

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#14
Here is a picture of my set up. Even though the compound and the cross feed are almost in alignment I only used the cross feed and never touched the compound.

IMG_3607.JPG
 

Rooster

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#15
mickri, it's often the simplest things that cause the most frustration. Is it possible the tool holder is loose, i see in your set-up pic what appears to be a shim under the hold down bolt.
 

mickri

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#16
I had already taken the setup apart and had to put it back together for the picture. I just set everything in place. The position of the shim in the picture is not where it was when I bored the hole. Sorry about that. I used two shims. One on each side of the hold down nut and I made sure that the shims fit between the nut and the 4 way without any gaps. I had to use the shims because the arm on the nut was hitting into the steady rest in its normal position. I had this problem one other time and have added another project to the list to make a washer of the right size and thickness to prevent this from happening in the future.
 

wa5cab

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#17
Disregard all of this - because the boring bar wasn't the normal black oxide finish, I thought that it was part of the work piece.

Mickri,

If aside from the shims, that is how your setup looked during your test, I see the or at least a problem. You would perhaps be surprised at how much a work piece of that small a diameter will flex and bend away from the cutter if the cutter is more than about 3 to 5 diameters away from whatever is holding it centered. You could improve the situation somewhat by center-drilling the right end and supporting the right end with a live center in the tailstock. But even with that, given that long a rod of that small a diameter, if you were trying to take a .005" cut, I wouldn't be at all surprised to find that it was only cutting something like .002 midway between the center and the steady rest. If you make enough spring passes, you might eventually get the diameter 0.010" less than it was when you started. But the only way that you are going to get consistent results with a rod that long and that slender is with a follow rest plus the tailstock and live center. And the steady rest needs to be as close to the end of the larger diameter part as it is possible to get.

And another general rule to follow is that if you are in doubt as to whether you need to use the tailstock and center, use them.
 
Last edited:

mickri

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#18
Robert
You lost me on your suggestions. I was enlarging a 1/2" hole to 5/8" to a depth of around 2 1/2" The 3/8 boring bar is the largest boring bar that would fit in the hole. I had the steady rest as close to the end of the work piece as possible. Any closer and the carriage would hit the base of the steady rest. The work piece is 1 1/4" in diameter. The finished wall thickness is 5/16." Were you thinking that the boring bar in the picture was part of the work piece?
 

wa5cab

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#19
Oops, my bad. I completely forgot that you were trying to bore out a hole. I guess that I'm too used to boring bars being black oxide finish and when I looked at the photo, I "saw" a workpiece that was over an inch in diameter where the part of it sticking out past the compound had been turned down. Sorry.

I would recommend swinging the compound around to 30 or 45 degrees so you can choke up on the boring bar and not have so much hanging out. And tighten one of the gib screws to lock the compound. On my 3996, I have replaced one of the gib screws on both the compound and the cross slide with a T-handle screw so that the gibs can be locked down conveniently. The one on the cross slide was actually made for the slide on the milling attachment. I bought it from Clausing. The one in the compound I had to make.

Anyway, shortening up on the boring bar will stiffen it. And locking the gibs will stiffen the cross slide and compound.

I hate running a boring bar into a blind hole when the bar almost fills the hole. Unless there was some reason not to, I would have used a 5/8" 4-flute end mill mounted in the tailstock chuck. Much quicker and easier.
 

mickri

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#20
I thought about using a 5/8 end mill. I have one. I measured the 5/8 bolt that goes in the hole and it was a thousand or so smaller than 5/8 and I was concerned that the 5/8 end mill would bore a hole slightly larger that 5/8 leaving me with a sloppy fit.
I first tried having the compound at a 30 degree angle. Due to the small size of my tool holder the corner of the compound stuck out further than the tool holder. By aligning the compound with the cross slide I was able decrease the distance that the boring bar stuck out from the tool holder.
When I was doing the boring I was concerned about movement in the compound and never thought to lock the compound in place by tightening a gib screw. I will do that in the future. There are 3 gib screws on my compound. Which one would you recommend to replace?
I have a bunch of different boring bars and most of them are black in color. The one I was using is part of a set made by Clark. The set includes 1/8, 1/4, 3/8 and 1/2 boring bars. And they are bight and shiny. Almost look like stainless steel. That's just a guess on my part.
Thanks for your suggestions.
 

wa5cab

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#21
On the Compound slide, replace the middle one. It will have the least effect if you loosen it to move the slide and forget to adjust it. On the cross slide, the 2nd or 3rd, probably the 3rd. Note that if you use the milling attachment lock screw, if it is turned so that the cross bar is vertical, the bar will hit the saddle wings. So watch that and when loose, be sure that the bar is horizontal
 

wa5cab

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#22
On the end mill issue, bolt and screw diameters are supposed to be slightly under nominal so that they are guaranteed to be a slip fit in a hole that is dead on nominal. That doesn't guarantee that two screws will be a slip fit in two holes whose centers are merely within tolerance of where they are supposed to be, but that's another issue not germain here. However, if the tailstock is not centered and/or is high or low, it will in fact cut a hole larger than its diameter. That isn't usually an issue but if it's critical that the hole not be over 0.6250", then you are safer using the boring bar.
 

mickri

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#23
I am more than a little embarrassed here.

Today I enlarged the hole in the base from 1/2" to fit the 5/8 bolt. I was really careful doing this. First my cheap 1/2" HF drill measured about .495 and since I am horrible at measuring the diameter of a hole I didn't even attempt that. Next I put a dial indicator on the boring bar. The DI was a little over an inch from the tip of the cutter. I couldn't get it any closer. The deflection was .002. I am sure that a boring bar when it deflects is a parabolic curve and my best guesstimate is that the boring bar was deflecting over .010 at the tip of the cutter.

Here is what is truly embarrassing. My technique sucked big time. I realized today that when I was backing off the boring bar I wasn't going back past my zero. I was only going back enough so the cutter would clear when I backed it out of the hole. Every time I did this the amount of the backlash increased the movement of the dial and I believe this is the main reason why my total dial movement was .1115 when it should have been around .0625 when I was boring the post.

Today my total dial movement after allowing for deflection was .070. Live and learn.
 

Rooster

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#24
Again, it's the simplest things that cause the most frustration. Glad you got it all figured out.
Unless you can afford a really expensive bore gauge you should practice with a snap gauge and micrometer.
 

mickri

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#25
Rooster
I have starrett snap gauges and have practiced how to use a snap gauge based on the suggestions that I received in another thread on the forum. I consistently measure a hole smaller than it actually is. If my measurements were consistently smaller by the same amount then I could allow for my error. But so far there is no consistency to my measurements. I'll keep practicing.
 

Rooster

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#26
mickri, i use a inside spring caliper and micrometer, seems to work well. I find it easier to get the right feel. I have been thinking of making some go/nogo gages, say 2" long with one half a thou over and other half a thou under. It's the smaller holes that are the hardest to measure.
 

Bob Korves

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#27
Here is an excellent guide which will save me a lot of typing:
Pay VERY close attention to the recap of the most important issues at the end of the video, and remember them.
Do everything you possibly can to help the gage self center in the work accurately and repeatably.
Do not tighten the gage down more than is necessary to sweep the bore and read it with the mic. Over tightening a snap gage will ruin it, and give poor results.
Measure so the gage just bumps the mic spindle in only one location as it swings through.
Practice until you have confidence in your technique and attain consistent results. Having an accurate ring gage or better yet several several sizes when learning grades you as you practice.
Do not look at the mic numbers when measuring the gage. When the technique is correct, the final achieved numbers on the mic are golden. You should not need to pick the best average or guess over several tries.

Measuring bores consistently to within a tenth or two is not difficult after learning correctly.
 
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