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Author Topic: Huge Threading Problem Help  (Read 15836 times)

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Offline Hood

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Re: Huge Threading Problem Help
« Reply #10 on: October 23, 2010, 05:50:46 PM »
For stainless the secret is to cut aggressively to avoid work hardening, for 16tpi you would be looking to do a thread in 6 to 10 passes. Most of my lathe work is 316 stainless and I would tend to run nearer the six passes for that thread. Problem is you also have to work within the constraints of your machine, mine is fairly large so I dont have an issue but if you are low on HP and rigidity then you may have to aim for the higher end of the passes.

If I can find one of the threading catalogues I will scan and attach the numbers they give for pitch and passes, if you want.

Are you using carbide inserted tooling? If yes are you using full profile or partial profile tips?

Hood
Re: Huge Threading Problem Help
« Reply #11 on: October 23, 2010, 05:57:28 PM »
Thanks Hood.

I use carbide insert tooling and have both full profile and partial profile bits, but when doing 16 or 32 I tend to use the full profile.

WOW that's very few passes, I'll go try it and see what I come up with.

Offline Hood

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Re: Huge Threading Problem Help
« Reply #12 on: October 23, 2010, 06:04:49 PM »
As said it will depend on the power and rigidity of your lathe but being aggressive with stainless is the secret if you can get away with it.
Heres a couple of scans out of one of the tooling catalogues, its for Korloy inserts but most will be around about the same.
Hood

Offline Hood

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Re: Huge Threading Problem Help
« Reply #13 on: October 23, 2010, 06:07:22 PM »
Afraid the surface speed is in m/min but should be easy enough for you to convert, will look see if I have some catalogues with the old fashioned units you Americans use ;D

Hood

Offline RICH

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Re: Huge Threading Problem Help
« Reply #14 on: October 23, 2010, 06:21:34 PM »
Cartierisum,
Thanks for the info in reply #6. I'll comment a little more later. One to two years have passed since threading was addressed and i wanted to review some of my notes rather than relying on memory. I only have 500 pages of notes....... ;)

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Using Version 3.042.020
Upgrade to at least version 3.042.32 ( there are numerous problems that were fixed from .020 on and you are experiencing some of them )

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Using CV
Use exact stop as CV will affect how the pullout from the thread is accomplished.
See the note at the top of page 34 in Threading on The Lathe write-up.

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Can't really tell about how much RPM loss but looks like about 30 RPM
If you watched the rpm DRO you would have a better feel for the drop, 30/1000=.03 or 3%,
So threading compensation shouldn't be a problem. 10 to 25% could be
Even 3% will affect the thread pitch though.

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Using VFD
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I don't use a VFD and if memory is correct you should manualy set it to a fixed rpm. If the VFD is changing the RPM, Mach is planning the next pass,
they  could be fighting each other, thus  screwing up the compensation ( based on rpn reading) which will affect feedrate, which affect the thread.

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Single Index
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Good ........timing not longer works and should not be enabled.
 
more when i return in a little bit,

RICH


 

Offline Hood

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Re: Huge Threading Problem Help
« Reply #15 on: October 23, 2010, 06:33:09 PM »
Cartesium,
If you  download this programme it may be of use, I used the metric version a while back and found it handy. You can go through all the stages and at the end if you click manual it will give you a depth per pass etc. Again its all dependant on machinery available but it gives you a good starting point.

http://www.secotools.com/CorpWeb/Service_Support/cutting_data_calculators/Threadturningwizard_inch.exe
Hood
Re: Huge Threading Problem Help
« Reply #16 on: October 23, 2010, 06:53:32 PM »
Thanks a lot for the help!!!

I'll look at the program and pages you scanned now.

@Hood, I went ahead and threaded at 200 RPM 16 TPI with 8 passes and it came out fine, thanks. The only thing is the last 2 or 3 passes vibrated the machine a ton. I guess it could be one of two things, either my bit is not exactly on center or that's when it's topping the thread. I persisted and reran the program and it did fine. Still a tiny bit of vibration at the end of the run, mind you I do 6 spring passes to clean it up so it's probably just rubbing.

Two important questions, will upgrading to the newer Mach mess up any settings, macros or VB buttons I run? Also what will exact stop do for regular lathe work when not threading, do I keep exact stop on all the time? Thanks again.

Offline RICH

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Re: Huge Threading Problem Help
« Reply #17 on: October 23, 2010, 06:54:53 PM »
SPINDLE SPEED AVERAGING
Mach3 can keep a running average of the last  8 revolutions. At the start of any pass it either uses the
 average OR the last measured time.  Every thread starts with an unloaded spindle, the 8 rev average is
 typically unloaded average. ( unless your turning very slowly on the spindle and very unlikely it's less
than 8 turns in the air prior to a thread pass)
 
 So the correction code  is all that controls speed during the cut to take  into account the spindle slowdown
 caused by hitting a hard spot or an average  slowdown due to harder material.

The averaging is discounted for correction, it cares only about the real  last index to index time,
 and it compares that to the locked in average or  locked in last rev just prior to the  thread pass starting.

Rule of thumb is  3 to 5 diameters times total thread depth for unloaded spindle travel of the Z axis.  

I use and would recommend you use spindle speed averaging.  It helps if there is a "out of rage / fluke / high" rpm
included in the averaging.  You then get a more refined feedrate. One  "fluke"  may not  influence as much as you
would think.

Some of my words but mostly Art's, ;)

RICH
Re: Huge Threading Problem Help
« Reply #18 on: October 23, 2010, 06:56:40 PM »
Where do I enable spindle speed averaging?

Offline Hood

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Re: Huge Threading Problem Help
« Reply #19 on: October 23, 2010, 07:06:08 PM »
Where do I enable spindle speed averaging?

Ports and Pins, Spindle Setup.

Hood