Author Topic: Lathe Screwcutting problem  (Read 7594 times)

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Offline fisherjim

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Lathe Screwcutting problem
« on: November 14, 2008, 03:15:58 PM »
Hi,

I'm using the latest version of Mach 3, V3.042.18 and I have a lathe threading problem.
On the first pass of the tool I get a different feed to the one programmed in the G76 canned cycle, the same when using G32.
For example if I set a pitch of 1.411mm (18tpi) the first pass of the tool shows a feed of 1.8mm,as shown by the DRO, then all the rest of the passes are correct at 1.411.

I know it's me but I can't see what I'm doing wrong.

Jim.

Offline Hood

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Re: Lathe Screwcutting problem
« Reply #1 on: November 14, 2008, 03:23:34 PM »
you say the feed shows 1.8mm, is it actually doing 1.8mm or just showing? I have never paid atention to what the DRO is saying so just wondering.
Hood

Offline fisherjim

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Re: Lathe Screwcutting problem
« Reply #2 on: November 14, 2008, 05:35:48 PM »
Hi Hood,

No it's actually doing 1.8mm on the first cut , then it does the programmed thread of 1.411, which leaves the thread crest torn up. Suppose I could try a cut above the thread dia. on the first pass then do the actual thread in subsequent passes, using G32 it would be possible. Be a pain in the A.. if I have to do it on all threads though.
Are you using V3.o42.18?, are your threads OK?.

Jim

Offline Hood

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Re: Lathe Screwcutting problem
« Reply #3 on: November 14, 2008, 05:39:46 PM »
Nope, not upgraded since 015 as I have  not used the lathe much in the last week as its been all milling and welding this week. Threads were fine in 015 but then again I use the smoothstepper so my testing of the 018 version wouldnt help you out :(

Hood

Offline fisherjim

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Re: Lathe Screwcutting problem
« Reply #4 on: November 14, 2008, 06:03:03 PM »
Ok,  thanks for the reply.

jim.

Offline Hood

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Re: Lathe Screwcutting problem
« Reply #5 on: November 14, 2008, 07:04:37 PM »
Just wish I could test for you but afraid I dont have a parallel port on that computer in the lathe :( Hopefully someone else will do a test and let you know.
Hood

Offline fisherjim

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Re: Lathe Screwcutting problem
« Reply #6 on: November 15, 2008, 10:31:38 AM »
I tell a lie, first pass of the thread runs at 2mm pitch, second pass runs at 0.95 pitch, it's not until the third pass does the thread pitch revert to the programmed pitch of 1.411mm.
Have checked all my settings, spindle index led works on the Diags page so Mach should pick this up, also turned off spindle speed averaging.
Anyhow, I've added two lines of code to my G32 thread, two air cuts then do the thread. This seems to work on G32 but I think G76 will be a no no.
I'm starting to look kindly at SmoothStepper, pity the exchange rate is bad.

jim.

Offline Hood

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Re: Lathe Screwcutting problem
« Reply #7 on: November 15, 2008, 10:46:13 AM »
Have a look at the plugins and enable the one for threading and send your data to Art with a description, he has been doing fixes on threading for the PP and  although most people seem to be sorted with the latest versions he is still trying to track down a few errors that people are seeing.
Hood

Offline Hood

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Re: Lathe Screwcutting problem
« Reply #8 on: November 15, 2008, 10:48:17 AM »
Oh on the SS yes the exchange rate is not in our favour at the moment but there is a place in the UK that has them (not sure where you are) they were more expensive than actually buying direct from Greg but that may have changed now due to the $/£ exchange rate.
Hood

Offline fisherjim

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Re: Lathe Screwcutting problem
« Reply #9 on: November 15, 2008, 01:40:26 PM »
Hi Hood

Well I ran the plugin and lo and behold the first two passes have no Index pulse, after that it finds the Index pulse and runs as normal.
I've emailed support so we shall see if its my setup or Mach.
Do you know where I can get the smoothstepper in the UK? If so it might be a good idea to get one.
I'm in the Isle of Wight by the way otherwise I could drop in for a chat hi.

jim.