Messages

31

General Mach Discussion / Re: Problems threading on the lathe

« on: February 26, 2009, 02:04:44 PM »

I forgot to mention that I did try the experiment with the 80 some very shallow cuts on a inked shaft with perfect results all three times that I tried it.  Thanks.

Also my apologies for taking over this thread with my questions, though I think that my problem is pretty much the same as the original one that started this thread.

Thanks

32

General Mach Discussion / Re: Problems threading on the lathe

« on: February 26, 2009, 02:02:15 PM »

Rich, Thanks for the reply, Here is a little more about my setup.

1HP dc variable motor-0-1700 spindle rpm, most threading done at 3-500 rpm
Linear rails, and rolled pre-loaded ballscrews, with a couple thou backlash, but no compensation currently enabled in Mach
my velocity is limited to about 70 ipm, so I have set the motor tuning to allow for 50ipm max where there is plenty of power aviliable
The threading tool is a commercial carbide indexable insert with a very sharp point, no radius.  It is set as close to exactly on centerline as I can get.

I agree that  a smaller lathe will take many passes to achieve a good thread, and that not too much can be expected from a 1hp 200lb machine, but what really confuses me is what exactlly is going on when mach does the strange tapered cut that several of us have experienced.  Unfortunately it doesn't allow much room for error since once you "overload" the spindle and the software has to correct beyond a certian ammount(some say 5-6%, I say 10-12%) Then the operation is pretty much doomed since the next cut is going to be cut at a taper, leaving the next pass cutting at basically twice the programmed depth.    As I have stated before the interesting thing is that the pitch of the thread always seems to be perfect for me, with a incorrect depth caused by the taper being my concern.

I will continue to play around as time allows, and for now I will err on the side of lots of shallow cuts.

Thanks again for the input.

33

General Mach Discussion / Re: Problems threading on the lathe

« on: February 26, 2009, 10:40:05 AM »

I am having the same or a similar problem.  I have posted In a another thread, but it seems to be a bit slower than this one.  Here is what I wrote:


Has a solution to this problem ever been found?  I am using .020, and it is giving me very similar problems.  If during a cut the spindle slows down very much at all the z speed compensates just fine, but the next pass is cut very unusually.  The next pass will be cut at what appears to be a constant taper with the z axis very slowly moving from a depth that is outside of the thread to the final depth that the pass should have been cut at.  This movement can be seen both physically, and on the DRO.  I have also had a problem where the next pass after a slowed down pass will be completely outside of the thread in the air.  I am not losing steps, and the pitch is always spot on, but the depth is very messed up.  I have run a test piece of code posted elsewhere in this forum that is a g-32 code that has a very shallow thread cut in 80 some passes.  I have run it three times, and the results are perfect, and repeatable. 

I am very confused as to what is going on here.  I don't have a very good understanding of what the g76 is commanding while it cuts at all the different depths to achieve a thread, but something seems to be amiss.  I am pleased to hear that you can change the output from the threading wizard to a g32, or what I would understand to be a longhand version of the code, I will try that as soon as possible to see what happens.  Thanks



I did do some more playing around yesterday, and I found that I was finally able to cut a 1/4-20 thread in brass and have it come out perfectly, but I had to do it in 40 passes.

I found that if when using the turn diag. screen I can watch the spindle speed deviation and watch the problem when it happens.  It seems that when the speed differs by about 10-12% the following pass will be messed up.  The pitch, or Z movement always stays correct, however the depth of the thread is cut at a taper, starting outside of the thread, and then tapering in so that by the end of the thread it is at the correct depth.  This then has a snowball effect, because as it tries to cut the next pass it is effectively cutting too deep since the material that should have been removed on the previous pass is still there, thus the spindle slows down, and the cycle starts over again. 

I only have a 1hp motor, and I realize of course that it is a limiting factor, but the cutting on a taper is very strange to watch.  Let me know if there are any other suggestions, and I will put them to the test.

Thanks.

34

General Mach Discussion / Re: thread problem

« on: February 25, 2009, 11:59:58 AM »

Has a solution to this problem ever been found?  I am using .020, and it is giving me very similar problems.  If during a cut the spindle slows down very much at all the z speed compensates just fine, but the next pass is cut very unusually.  The next pass will be cut at what appears to be a constant taper with the z axis very slowly moving from a depth that is outside of the thread to the final depth that the pass should have been cut at.  This movement can be seen both physically, and on the DRO.  I have also had a problem where the next pass after a slowed down pass will be completely outside of the thread in the air.  I am not losing steps, and the pitch is always spot on, but the depth is very messed up.  I have run a test piece of code posted elsewhere in this forum that is a g-32 code that has a very shallow thread cut in 80 some passes.  I have run it three times, and the results are perfect, and repeatable. 

I am very confused as to what is going on here.  I don't have a very good understanding of what the g76 is commanding while it cuts at all the diffirent depths to achieve a thread, but something seems to be amiss.  I am pleased to hear that you can change the output from the threading wizzard to a g32, or what I would understand to be a longhand version of the code, I will try that as soon as possible to see what happens.  Thanks

35

General Mach Discussion / Re: M3 Turn toolpath display screen

« on: February 23, 2009, 12:44:43 PM »

Hood, thanks for the responce.  it is good to know that the problem is aknowledged, and will be looked at, that is what has always made this software so great.  Thanks for the time, and I will be patient for updates.  Thanks again

36

General Mach Discussion / Re: M3 Turn toolpath display screen

« on: February 23, 2009, 09:39:34 AM »

Dave, thanks for the quick responce, and I appreciate the input.  What you say makes sense, however I am only dealing with toolpath and rapid lengths of a few inches.  I have programmed several paths within the wizzards, for example a outside fillet where the toolbit was allready set to z-0, x-diameter-say 1 inch.  the bit was physically parked less than a quarter inch from the orgin, and yet the programmed path is just too small to clearly see.  I have used both methods to zoom on two diffirent computers with both kinds of mice, and there is no diffirence in how far I can zoom-not far enough.  Other toolpths such as the wizzard for taper display perfectly which makes it all the more frustrating.  Thanks again for the suggestions.

37

General Mach Discussion / M3 Turn toolpath display screen

« on: February 22, 2009, 07:40:47 PM »

Hello, I am very new to Mach 3 turn, and I am having what seems to be a common previously discussed problem.  The toolpaths shown in the display window are often very small, and unusable.  Other times they will be just right, and be easially zoomed to the desired level.  Sometimes the entire toolpath is so small that it only appears as a single line thru the middle of the display box.  I have this problem about 70% of the time and it seems to happen with both imported, or loaded code, as well as code created with the wizzards.  I have the newest lockdown release (.020).  After doing some reading here and on yahoo it seems that the problem wasn't present in older versions.  I would like to try an older version, but the only other one aviliable for download is 1.90, and while looking over the revision log it seems that alot has changed between the two versions.  I am looking for suggestions as to how I could fix the problem-(if possible), or someone that has a slightly older version without the problem that they would be willing to email to me.  I would really like to be able to see what is going to happen toolpath wise before I hit that cycle start button !  Thanks for the help!