I am confused

[Bamban]

Last night I had time to make some noise with 12x36 lathe. I chucked in a 7 inch piece and made 2 passing cuts from left to right for about 4 inches just to check the machine operation. to check the work I used an AXA tool holder mounted indicator, first I checked the run out close to the chuck, was under .001. Did not want to drag the indicator across the piece so I pulled back on the indicator and moved it to the end of the cut. The run out at this locations is the same as the previous reading.

The problem is at the tail stock end diameter, the indicator measured 0.007 fatter. I grabbed the micrometer, sure enough end to end on a 4 inch cut there is a 0.014 difference in diameter. I went ahead and put the indicator back and indicated on the turned piece and ran the carriage down the length of the turned piece. Sure enough I could watch the indicator slowly moved all the way from the tail stock to the chuck end. There is definitely a taper.

What did I do wrong?

What is wrong with the machine?

Is it material flex? The piece is an 0.829 AR shot out bull barrel donated by a friend for me tp learn from

 

[Tony Wells]

You did not say whether you were using the tailstock or not, but if not:

Depending on how much you had sticking out of the chuck, this could be normal pushoff from material flex. I try to keep the ratio 3:1 on the dia v length of stickout if I can. Depends on a few variables.

Also, usually turning is done Right to Left. But then, the tool must be ground for whichever way you are turning.


If you were using the tailstock, you need to set it. It is too far behind centerline by 0.0070. There are a few threads addressing
lathe alignment that you may need to review.

 

[Bamban]

You did not say whether you were using the tailstock or not, but if not:

Depending on how much you had sticking out of the chuck, this could be normal pushoff from material flex. I try to keep the ratio 3:1 on the dia v length of stickout if I can. Depends on a few variables.

Also, usually turning is done Right to Left. But then, the tool must be ground for whichever way you are turning.


If you were using the tailstock, you need to set it. It is too far behind centerline by 0.0070. There are a few threads addressing
lathe alignment that you may need to review.

Thank you, did not use the tailstock, I thought with .005 cut both times, the piece will take the cuts without flexing, will search the alignment

 

[Bamban]

You did not say whether you were using the tailstock or not, but if not:

Depending on how much you had sticking out of the chuck, this could be normal pushoff from material flex. I try to keep the ratio 3:1 on the dia v length of stickout if I can. Depends on a few variables.

Also, usually turning is done Right to Left. But then, the tool must be ground for whichever way you are turning.


If you were using the tailstock, you need to set it. It is too far behind centerline by 0.0070. There are a few threads addressing
lathe alignment that you may need to review.

Tony,


You are absolutely right.

On turning from Left to Right. I am learning how to use the controls on these machines that just got wired last week. I figure it is safer for me to turn this way to avoid the possibility of jamming the cutter into the chuck in case I screw up and turn levers the wrong way or grab the wrong lever as the cutter approaches the end.
In the mail came my new tool bit holder, a bunch of cutters so I just have to stop doing the laundry and play. Maybe I jumped multiple variables all at once, in the short period I have I had to.

Used the new tooling
Center drilled both ends of the material
Used a live center and cut the material, .005 again and another ,005.

Measurements, not that good, material registered smaller at the tailstock end. Researched adjusting the tail stock to the head, I made the adjustment with those 2 opposing set screws. Next 2 cuts of .005 yielded better, may not be perfect, but I am happy for now. At least I can make the outcome wiggle.

Maybe I was dealing with multiple things last night; 1. Dull bit, 2. Flexing material.

Did I do this right? Do I need to get the 0.0005 indicator to fine tune the taper? Or should it be good for now, I will just be turning straight cuts on AR barrels in the future and the measurement are not critical.

Here are the pictures.

 

[Tony Wells]

In reality, it's kind of subjective. Some people are not content until their lathe (particularly new ones) cut straight with a very few tenths. Others are satisfied as long as they can meet the needs of their parts. Be aware that when you adjust a tailstock, it may change it's -X- centerline relationship with the chuck if it is used in a different position on the ways. That's where bed twist and the rest of the worm can usually come come in. Bottom line, if it does what you need, there is no real reason to get fussy about it unless you want to, and it can be frustrating to chase it to the tenth.

 

[Round in circles]

Ensuring that the lathe is bolted down onto a solid concrete base and levelled with a proper engineers spirit level to remove twist and bed bend also helps tremendously when setting up for a better more accurate cut .

I've been advised to always check it once every few months as well for things do change . This can help damp out any unwanted vibrations ( frequencies ) that arise , which could amplify or harmonise up in the lathe bed & affect the quality of your work .

 

[Bamban]

Ensuring that the lathe is bolted down onto a solid concrete base and levelled with a proper engineers spirit level to remove twist and bed bend also helps tremendously when setting up for a better more accurate cut .

I've been advised to always check it once every few months as well for things do change . This can help damp out any unwanted vibrations ( frequencies ) that arise , which could amplify or harmonise up in the lathe bed & affect the quality of your work .

I do not have it bolted down, just leveled with these.

http://www.avproductsinc.com/machine-leveling/anti-vibration-feet.html

 

[chuckorlando]

Are you checking run out, taper, or Dia?

 

[Bamban]

Are you checking run out, taper, or Dia?

At first I was just testing machine operation, tried my hand into turning, and was surprised to see that the turned piece had a taper in it, so I posted for solution, so end up adjusting the tail stock.

 

[chuckorlando]

I must have mussed that part. I was wondering what your tail stock had to do with chuck run out ahahahahah

On the up side, you learned how to turn a taper using the tail stock)