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Messages - fdos

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241
General Mach Discussion / Re: Those pesky circles
« on: September 01, 2006, 03:31:39 PM »
Not always ;)  I've got some square servo's!     

Steppers will generally have 4, 6 or 8 wires.   Servo's 2 for dc and 3 for brushless + the encoder cables.

Wayne....

242
Show"N"Tell ( Your Machines) / Re: hardinge hnc to retrofit
« on: August 30, 2006, 11:38:41 AM »
I used to run those too, but with Allen Bradley controls.  Looks like a 5C machine?

Can't see your servo motors. but I do recall those little tacho's which can be seen in the last pic.  We seemed to be forever fixing em.

I am doing a similar machine, see the HXL-S thread.    Be glad to help if I can.

Wayne...

243
Show"N"Tell ( Your Machines) / Re: Just got a lathe to retrofit
« on: August 29, 2006, 02:51:43 PM »
Hood

Re Current.

Unless you go for very expensive commercial drives you are not going to exceed the current rating of those motors.

You will be limited by the drives max current rating in the case of the 3 different brands of DC drives available from the usual sources.  ie 20A for Gecko's and whatever the two ozzie brands are rated at.

Lower current will just limit the torque available.

My Hardinge uses just 1nM motors with 2.5:1 reduction at 3300 rpm.  I reckon it will still be more powerful and faster than the original 1.2nM motors at 2000 rpm and 1.85:1 reduction.

It's quite strange that your machine uses servo's at 1:1.   But I guess with that torque available they didn't need any!

I always use steppers at 1:1 but they are a different animal.

Wayne....

244
Show"N"Tell ( Your Machines) / Re: Just got a lathe to retrofit
« on: August 28, 2006, 05:45:48 PM »
Hood

I've seen it (the cpr v's ppr) argued before, and I guess there's no real answer except that I have never seen the count quoted as the actual quadrature output.   In my experience whatever they quote has to be multiplied by 4.

The rating of the Teknix drives is all down to the mosfets.  Same with the Rutex drives I think.

Wayne...


245
Show"N"Tell ( Your Machines) / Re: Just got a lathe to retrofit
« on: August 28, 2006, 04:43:20 PM »
you'd need to check on that.   

The usdigital encoders are not that expensive.   Just make sure they dont send via air courier as they did with me years ago!

Wayne....

246
Show"N"Tell ( Your Machines) / Re: Just got a lathe to retrofit
« on: August 28, 2006, 04:32:54 PM »
2.5 micron resolution would require on a 5mm ballscrew 500 line encoders.   These would be better with a Gecko than 1000 line +.   The gecko's fault at +-128 counts which is a little fine for heavy machines.

The Rutex drives seem to offer more, but it's just my cynical nature causing me concern.  It seems I've never got the answers I wanted whenever I enquired about them.  CNC Teknix on the otherhand have been very forthcoming, and so far can't fault their enthusiasm.

Don't if you can help it goto steppers on that machine.   The difference is like night and day.

I'll gladly help wherever I can, so no fears.

Wayne....

247
Show"N"Tell ( Your Machines) / Re: Just got a lathe to retrofit
« on: August 28, 2006, 03:50:44 PM »
Sorry to confuse you!    I use CPR, Lines per rev as the same thing.  PPR is the quadrature output IMO.

Looking at the pic of that ebay listing, it looks like it says 2000 LPR on the encoder, so thats 8000 PPR.  Manufacturers don't usually rate them at the quadrature rate.

They look very much like Heidenhain, but with a different colour case.

Whatever happens you are going to need some serious drives for those motors!   You can run them at below the max voltage at the expense of some speed.   The current is the killer.   Depends on how heavy a cut you want to take I guess.

Something about the Rutex drives always has worried me.   Hence the reason I'm looking at the Teknix drives, at least the people behind them give me confidence.

2000 lines and Gecko's are not a good marriage either.


Wayne...

248
Show"N"Tell ( Your Machines) / Re: Just got a lathe to retrofit
« on: August 28, 2006, 03:05:48 PM »
2000 lines?   Thats 8000 pulses per rev.

Usually encoders are rated in lines per rev, and you multiply by 4.   2000 pulses would be a 500 line encoder.



Where are the encoders to be mounted?  do you have reduction between the motor and ballscrew?

For 2000 lines

If you had a 5mm pitch ballscrew, 2:1 reduction and the encoder were mounted on the motors, then you steps per mm would be

(5/2) = 2.5mm per rev
8000/2.5 = 3200 steps per mm.

If the encoder were mounted on the ballscrews then it's 8000/5 =  1600 steps/mm.

Or for 500 lines divide the results by 4 which is what your example gave.

Wayne....

249
Show"N"Tell ( Your Machines) / Re: Just got a lathe to retrofit
« on: August 28, 2006, 02:13:37 PM »
The rack mentioned may be part of the square toolposts mechanism.  The one on my machine has a rack, and indexes against an Air Cusioned stop.   I've not been too far into it, other than retiming it severaltimes after getting the sequencing wrong.

I expect your other turret has some form of hydraulic motor.

I'll be watching your thread with some interest too.   Nice to see another lathe being done.  There's far too few of them in the Mach scene!

Wayne...

250
Show"N"Tell ( Your Machines) / Re: Just got a lathe to retrofit
« on: August 28, 2006, 01:36:50 PM »
Yes Budget machinery is where I saw the machine.

My HXL Hardinge also has a square turret, it's quite a convoluted sequence to get it indexed, and if it's done in the wrong order it needs retiming!   I had to learn how it worked the hard way!   Looks like someone has started taking the square turret off your machine ;) 

It also has a air operated tailstock. but it's only for use with a centre.  In fact a dead centre as there's already a bearing in the tailstocks quill to make it a live one.   The tailstock on my machine goes though a separate air circuit with a flow sensor.   This puts the machine into "feed hold" while the quill is moving.  The same circuit is used for a parts catcher.   So that maybe something you should bear in mind.


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