Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: uberlinuxgeek on July 16, 2015, 04:08:16 AM

Title: NFS turn metric values for x axis
Post by: uberlinuxgeek on July 16, 2015, 04:08:16 AM
Ok, call me an idiot but I am having issues setting up values for metric threading in nfs turn wizard, my big problem is understanding what to use in the x start and x end fields, because if I follow the machinest handbook on what I thought to use I end up with something less than usable for an external thread. I am trying to make a 8mm 1.25 pitch thread using the wizard, starting with an 8mm rod and I convert all my values to inch and tpi of which is 20.32 and I get the proper pitch measured by thread gauge just not the right diameter for test fit. I am either too large or too small by just enough to not be usable, in the ballpark. I am using diameter mode.
Any help would be great
Title: Re: NFS turn metric values for x axis
Post by: RICH on July 16, 2015, 07:20:54 AM
If memory serves me correctly, the input values for the wizard should be metric if that is your default units and you need not convert.

As far as being under or over, your setup must be accurately done, you need to account for any tip radius, the basic diameter should be correct,
else the basic pitch diameter will not be right. Cut pitch can be correct when visually compared to a thread gauge but the basic pitch must also be correct
else you just end up with "the nut goes on" kind of thread. 

Title: Re: NFS turn metric values for x axis
Post by: uberlinuxgeek on July 16, 2015, 11:45:58 AM
My unit is configured for inch, so in order to cut metric I am converting all values to place in nfs turn to inch and tpi. As was mentioned to me when I asked a question here some time back. I have the axis positions all calibrated. When I say too big or small, it is because when I take the values out of the machinist handbook, I am not sure which to use when plugging in the wizard, because what I thought should work is not,, not a matter of machine accuracy just what values do I use as standard threads using your provided thread table work fine with a minor tweak if needed and with the handbook metric values I convert all the table values to inch and adjust for turning mode. It is a matter of I have never cut metric and was looking to see what plugs in the wizard.
Thank you
Title: Re: NFS turn metric values for x axis
Post by: uberlinuxgeek on July 16, 2015, 01:33:48 PM
If there is a flaw in the basic diameter I would love to hear what should use, I am very new to threading on Cnc and even more so to metric. Once I cut the thread, I measure with a thread and standard micrometer and both the major and minor are coming out different than I want and either the nut threads and is loose or it will not start at all. I keep tweaking the x end and start to try to hit what is needed. If you could point me to an online resource that would be great as I have tried so many and have yet to have one break it down simple enough to get what I need. I have cut standard threads on a manual lathe but never metric so I am missing something basic. One resource said to use major diameter and pitch diameter but that will not allow to thread, another use major and minor like standard thread but then that is too loose, too much material is being removed from major diameter.
Thanks for the help
Title: Re: NFS turn metric values for x axis
Post by: uberlinuxgeek on July 16, 2015, 04:22:18 PM
Hello Rich,
I went back and did some standard thread and you were right the tread profile is wrong in both inch and thread now. I am doing something wrong with my machine. But the manufacturer can not help right now. So there seems to be an issue where the machine is clipping the thread, as in I think I might be loosing sync between the spindle and cnc drive. But the issue is I am not sure where to look in the mach3 setup to resolve it. I have turned on the turn diagnostic plug in and it is not reporting a lost index but not sure where else to look for settings that may fix this. Could use some help with mach3 config and threading. I am using only the nfs turn wizard right now.
Title: Re: NFS turn metric values for x axis
Post by: RICH on July 16, 2015, 10:59:25 PM
First let me say that there is a write up on threading in Members Doc's called Threading on the lathe -Mach3 turn. I covers most aspects of threading but
I didn't cover metric threads so to speak. Have a read of it. It provides for some testing of your lathe!

You need to be using Mach version at least 033 ( see the write up ) or above since  threading was  not working correctly before that. Do not use the threading  diagnostic as that is no longer applicable ( Turn it off) and was done just for testing .

Ezilathe is available for download and has a thread calculator in it which will adjust cut depth based on a sharp v 60 deg tool or one with radius.
In my screen set I have a calc page that does similar but only for Unified threads / Imperial ( I convert if doing metric M profile).
I won't even touch on the different standards used!

The major diameter for a thread has a min and max diameter and depends on tolerance class. Same goes for pitch diameter. To measure pitch diameter you need a threading micrometer, or go no go thread gages,  or use the wire method. Major diameter can be off some but pitch diameter should be within spec ( well I would need to clarifiy that statement but simply said  it is correct - for reasons not worth discussing and is beyond the average user ie; fit verses meeting a design intent ).  

If you have a 60 deg sharp tool accurately set up with no  radius ( no such thing as a zero radius threading tool! ) and start the thread on the Max diameter you will have a different depth of cut than if you had the same tool with a radius, that said...........
I always work / set up  with the max major diameter adjusting cut depth for tip radius so pitch diameter comes out correct.

So have a very close look in the machinist handbook about External Metric threads and also Unified  

Threading on your lathe will only be as good as your "LATHE SYSTEM".
Try doing a 0-80 or smaller ( almost no room for error ) or doing multi start threads or cutting an acme using a sharp v and alternate flank cutting....
you will quickly find out how good Your lathe system is.
If you have a wimpy lathe than choose a different type of machining to do the threading. Wimpy lathes are limited's a HP and rigidity kind of thing.