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Author Topic: Problems threading on the lathe  (Read 330173 times)

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Offline RICH

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Re: Problems threading on the lathe
« Reply #70 on: February 27, 2009, 07:18:26 PM »
TrevorH,
I used your Gcode that you posted to cut  a 1/2-13 thread in 6061 on my Punny little lathe. ( 400 rpm spindle speed)The posted pic is of the G32. Also cut one useing M76. The results were the same. In the pic you can see a difference of 2 thou at the thread beginning and that is due to the actual diameter dfference as i didn't start off with a finished stock diameter.
The spindle did slow down. Never experienced an X runaway.  During the spring cuts there were a few times when more than a hair shaving was taken off. I have about .002" backlash in the X and a little under the same in the Z. So during the spring cut is it's possible for me to get more than just .0001" cut. i can adjust / take out more of the backlash but I leave it as is for now.
The flank cutting ( your code had 15 deg infeed ) worked as it should, just a nice forward curl. Note there are no
steps in the backside of the threads. Your's has them ( that's backlash and i can duplicate it by increasing mine).
I believe your problem is mechanical. Note no waviness in my threads. Software dosen't do that. Mach reacts rather
quickly, but not instantaneously to a slow down, when that accurs the next pass will try and fix it. Yours almost looks like a gouge. On the next cut if it happens again, because of some other / prior pass, then again it tries to fiix, but
then who knows what it's fxing ( just my thought). You may be better off not taking as deep a first pass cut ( .014").
This way you get a v started which can help guide the tool. Just some thoughts for you.

Now i will admit that there MAY be some quirky thing from the software point of view, but not convinced yet.
Or maybe i just haven't stepped in poop lately ( i do have the knack of finding it).
RICH

« Last Edit: February 27, 2009, 07:26:47 PM by RICH »
Re: Problems threading on the lathe
« Reply #71 on: February 27, 2009, 07:26:06 PM »
I just tried to embed the yahoo vidoe here, and it just showed up aith what looked like a very long address, but no picture.  Here is a link to the video.

http://www.youtube.com/watch?v=vb6ozg1Qi1k

I tried to show the cutting, as well as shome shots of the screen.  As you can see and hear The bit is engaging too much and slowing down, then it is cutting air for one or sometimes two passes before it again re-engages the work at what becomes too deep of a depth.  As you can see my toolpost and overall setup leaves alot to be desired, but nothing seems to be moving around too much.  I do have another video showing the machine making some .100 moves in the z direction, and as you can see I do have 2-5 thou of backlash/inaccuracy, and that may very well be causing or contributing to my problem.  I still just don't understand what is causing the machine to cut in the air like it is.  Thanks

Backlash Vid

http://www.youtube.com/watch?v=IhnrRqWhBZs
« Last Edit: February 27, 2009, 07:40:16 PM by TrevorH »

Offline Hood

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Re: Problems threading on the lathe
« Reply #72 on: February 27, 2009, 07:29:22 PM »
Took the liberty of posting it for you.
Hood


<a href="http://www.youtube.com/v/vb6ozg1Qi1k&amp;hl=en&amp;fs=1" target="_blank" class="new_win">http://www.youtube.com/v/vb6ozg1Qi1k&amp;hl=en&amp;fs=1</a>
« Last Edit: February 27, 2009, 07:37:22 PM by Hood »

Offline Hood

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Re: Problems threading on the lathe
« Reply #73 on: February 27, 2009, 07:38:20 PM »
Certainly can see the X moving on a cut, dont have an answer for you I am afraid.
Hood
Re: Problems threading on the lathe
« Reply #74 on: February 27, 2009, 07:41:38 PM »
At least you can see it so that you don't think that I (we) are crazy.  Thanks for putting the video in for me, how did you do that?

Offline Hood

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Re: Problems threading on the lathe
« Reply #75 on: February 27, 2009, 07:42:58 PM »
["flash=640,480]http://http://www.youtube.com/v/vb6ozg1Qi1k&hl=en&fs=1[/flash"]

Without the "
« Last Edit: February 27, 2009, 07:44:52 PM by Hood »

Offline RICH

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Re: Problems threading on the lathe
« Reply #76 on: February 27, 2009, 07:58:30 PM »
Thanks for the video post. Now will listen to it very carefully.
Trevoh, your not crazy in anyway.
But me.......well that's another story!  ;)
RICH
 

Offline RICH

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Re: Problems threading on the lathe
« Reply #77 on: February 27, 2009, 09:12:56 PM »
Trevoh,
Are you using backlash compensation?
What is your stepper rated torque?
RICH
Re: Problems threading on the lathe
« Reply #78 on: February 27, 2009, 09:35:26 PM »
Rich,  No backlash compensation enabled, maybee I should play around with that?  The steppers are 191oz/in increased by the belts pulleys 1.6 to 1, they are driving 5/8 rolled ball screws with a pitch of .200, or 5 Turns per inch.  I am using Linisteppers to drive the steppers in half step mode currently at 12v and 1.5A per phase.


The thread that you cut and posted a pic of looks really nice, I can only hope for those kind of results at this point.
« Last Edit: February 27, 2009, 09:37:40 PM by TrevorH »

Offline Chip

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Re: Problems threading on the lathe
« Reply #79 on: February 28, 2009, 12:48:11 AM »
Hi, Trevoh

My first impression after hearing/viewing your video, Is it's a rigidity/flex issue, Try cutting much closer to the spindle or use a tail stock support.

Also the vertical/center line placement (sweet-spot) of the cutter is very/very critical, Cutter sharpness & type vary with different types of material being cut.

Just some thought's, Chip