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Just getting started
« on: November 16, 2007, 08:22:45 AM »
Hello to all and THANKS for the welcome.
I've been a manual machinist for many years. Very little CNC exposure, no hands on.
I saw a HAAS lathe  at a trade show that I would like to copy.
It was small with a row of gang tooling on the cross slide plate.
I have numerous THK and IKO rails and trucks for the slides and several stepper/driver combinations from various mfg.
I did build one machine with steppers that was controlled by a microcontroller but it was a pain to program and it would not interpolate.
But.....it did what it was intended to do perfectly.
This new machine will be mainly to do delicate threading as well as profiling.
What I would like to know before I get started is:
   With readily available components, what would the MAX spindle RPM be to cut a 3/8-48 thread in Brass ? Looks like Mach3 would have no problem but are high end components needed to run around 750 rpm for this thread ? What is a realistic rpm that I can expect ?
   The spindle will be fixed speed with an encoder. Will any encoder work as long as it has an index signal ?
I can give more details of the motors and drivers that I have if needed.
Speedy threading is my main concern. Hopefully I can cut this thread well over 500 rpm.
Thanks already, I can see that you guys know what you're doing and I came to the right place.
Overloaded

Offline Hood

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Re: Just getting started
« Reply #1 on: November 16, 2007, 01:41:10 PM »
For threading I dont think you will be able to use the Index pulse from an encoder, if you are using the parallel port, as the pulse length wont be long enough. However an optical switch and a slotted disc will provide an adequate pulse and is easy to fabricate and very cheap.
Hood
Re: Just getting started
« Reply #2 on: November 16, 2007, 02:00:47 PM »
Thanks Hood,
 So...any encoder, say 200 ppr would work for the spindle to interpolate with Z and another sensor for the index ?
I have many inductive proximity sensors. Would one of these be OK ?
Can you link me to common setups ?

Mainly, does 500 to 700 rpm sound reasonable for 3/8-48 threads in brass ?
I know the surface speed is OK for the tooling, but what about the software and electronics ?
Thx

Offline Hood

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Re: Just getting started
« Reply #3 on: November 16, 2007, 05:58:58 PM »
All you need is the optical switch/slotted disc for Mach to read the spindle speed and sync with the Z  for threading.
 Not actually done any threading myself on my lathe as its not quite finished but I think threading at the speeds you mention should be no problem.
 Lots of guys use prox switches for limits but not sure if they are used for spindle sensors. You will see a pic of the setup I have on my mill, my lathe is exactly the same. http://mysite.wanadoo-members.co.uk/hoodsmachiningpages/BOSScomplete/SpeedSensor.jpg

Hood
Re: Just getting started
« Reply #4 on: November 16, 2007, 07:45:07 PM »
Holy Smokes !
  I had it all wrong.
I assumed that the spindle had an encoder on it so the z axis would follow it proportionally regardless of the actual rpm.
Even if you turned the spindle by hand and it's rpm fluctuated greatly the thread pitch would still be right.

But..all that mach needs is 1 ppr to determine spindle speed and Z  feed rate..... COOL !
I've got small Banner through beam sensors that should work nicely.

Do the higher end production machines work this way or do they have an encoder with an index output ?

Thanks for clearing that up for me.

Offline Chaoticone

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Re: Just getting started
« Reply #5 on: November 16, 2007, 09:40:20 PM »
The large machines I work on have an encoder on the motor as well as one that is driven directly by the spindle via a timing belt. The fanuc controller monitors both, looking for differences. If they differ past a set amount, it will throw an alarm. All of this isn't necessary for threading, just redundant.

Brett
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!
Re: Just getting started
« Reply #6 on: November 17, 2007, 09:52:43 AM »
Brett,
It is more clear now.
I suppose the machines that have a spindle axis with a brake and live tooling on the cross slide or turret need to have the encoders to position the part for the live tooling.  Correct ?

Thanks for the info.
Any and all input is welcome.
I'm a GLUTTON for information !

Offline Chaoticone

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Re: Just getting started
« Reply #7 on: November 17, 2007, 10:01:55 PM »
The machines I'm speaking of are vertical lathes. The reason for the redundant encoders on these are to check belt slippage. They use 30KW ac servos and drive the spindle with 2, 7 groove v-belts.

Brett
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!
Re: Just getting started
« Reply #8 on: November 17, 2007, 10:17:58 PM »
YES.. I can see where that would be necessary. HEAVY DUTY !
AMAZING machines.
I've fallen WAY behind the technology.
Stuck out here in the sticks doing repair work and "one of's".
Thanks for taking the time.