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12th June 2014, 12:17 AM #16
Hi Frank,
I had no idea that you were a momber of this forum... doh
Glad to have you contribute!
While industrial surface cutting speed tables are not that helpful for hobby machines as mentioned already, people learn what their machines are capable of and what the 'sweet spots' for their operations onvarious materials are. My view is that maintaining that 'sweet spot' speed for a given tool tip and material is my 'desired' speed to maintain. SInce I don't operate a CNC machine, I will want to adjust that on the fly based on my 'analog feedback' as described by cba_melbourne of sound, feel, visual observation and smell on the fly - i.e. while machining is in progress.
My perception would be that CNC conversion of a hobby lathe would remove all those inputs.
Using a DRO to manage the overall speed amangement I think is genial. I thought of it as a distict function when starting this deliberation. Using the input from a linear scale only ocurred to me whith RayG's comment.
I look forward to your further contributions!
The tricky bit for me to get my head around will be the use of Modbus/RS485/RS232. Our (hobby machinists) general problem is likely to be the deep market penetration of low cost VFDs which often is not universally don't have those inputs (despite their advertised capabilities). This is not restricted to the common Huanyang either, I have a Telemechanique Altivar, 2 Siemens Micromasters, a Eurotherm 650, 2 Hengtais and 3 Huanyangs. None of them have PLC communications interfaces. The Huanyangs at least canbe retrofitted with the 'missing' components, since their PCBs actually are designed, marked and drilled for them and the reverse engineering has been done by others, notably on the Mach3 support forum.
The alternatives are to design an interface that provides a voltage or current output to control these devices (in the same way that their respective voltage dividing potentiometers do. At least all of mine have that in common....Cheers,
Joe
9"thicknesser/planer, 12" bench saw, 2Hp Dusty, 5/8" Drill press, 10" Makita drop saw, 2Hp Makita outer, the usual power tools and carpentry hand tools...
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12th June 2014 12:17 AM # ADSGoogle Adsense Advertisement
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12th June 2014, 10:55 AM #17Cba
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Nearly all VFD's have in their basic configuration analog speed control inputs for both
- a variable voltage 0 to +10V
AND
- a variable current 4-20mA (or sometimes 0-20mA).
Meaning that you can either control the speed by a variable voltage, or by a variable current. The most simple method is surely to derive a variable voltage from a potentiometer (often included on the VFD front panel). Whereas the current loop is often used when an external logic is to control the VFD.
Modbus/RS485/RS232 are optional interfaces that can be purchased to plug into industrial class VFD's. It's best suited when many VFD's ned to be contolled. Like in a building automation system (where some modern large buidings contain several hundreds of single VFD's for their HVAC etc). Personally, I do not see any advantage to use such a field bus in a one off application to control a single machine tool. But if you have to control hundreds of VFD's in a building or processing plant, you absolutely need a standardized system that is easy to expand and fault track.
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13th June 2014, 01:35 AM #18
I'm glad you explained that, cba. I wondered if you needed Modbus or whatever to do this from a processor source. I was obviously aware of the voltagt and current frequency control, but not if that was easily implemented with a processor.I image then that it would require a D/A converter of some sort to be driven by the digital processor output?
Cheers,
Joe
9"thicknesser/planer, 12" bench saw, 2Hp Dusty, 5/8" Drill press, 10" Makita drop saw, 2Hp Makita outer, the usual power tools and carpentry hand tools...
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13th June 2014, 01:59 AM #19
Something else has cropped up in relation to my ELS (see post https://www.woodworkforums.com/showth...#post1781474): the initiator of the ELS project, John Dammeyer, runs a support & development forum on Yahoo for the ELS. https://groups.yahoo.com/neo/groups/E-LeadScrew/info
I posted there to see what that group had considered, and it turns out that some of the code in the ELS is already written to support spindle speed control. At the time, VFDs weren't very common in hobby shops and John never went any further with it. However the group has now taken an interest in this project too. I'll relay any interesting news between there and here.
The ELS by the way 'knows' where the cutting tool is - in terms of steps from the zero set to start turning (steps of the stepper motor driving the cross feed screw). If that turning involves the axis of the job (like a taper or faing) then it also 'knows' the diameter or radius (in stepper motor steps). It also monitors the spindle speed in order to maintain depth of cut. So that is another way of 'skinning this cat'....
Looks promising at least for me - and others who might build an electronic lead screw project....
In my case that was a necessity as there was no leadscrew and no easy way to drive one mechanically. (Btw, my lathe headstok is back on and looking nice again - photos shortly, then I'll mount the ELS and VFD controller and report - in another thread). My 'sandheap CVA' also has no drive for the leadscrew (since it also didn't have one in the first place), so there may well be another iteration of the ELS in the future..... or maybe not...Cheers,
Joe
9"thicknesser/planer, 12" bench saw, 2Hp Dusty, 5/8" Drill press, 10" Makita drop saw, 2Hp Makita outer, the usual power tools and carpentry hand tools...
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13th June 2014, 06:49 AM #20GOLD MEMBER
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shooting the mouth off
interesting thread. does any body here use dc motors for the machinery?
do machine tools use incoders?
aaron
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13th June 2014, 10:59 AM #21GOLD MEMBER
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13th June 2014, 11:03 AM #22GOLD MEMBER
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dro
i agree the the dro seem like the idel sensor
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13th June 2014, 03:57 PM #23Cba
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13th June 2014, 06:09 PM #24Cba
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John's ELS uses a spindle encoder with one single pulse per revolution (PPR). Unfortunately this does not lend itself well for a VFD spindle drive. Because when cutting, the spindle speed of a VFD drops substantially, especially at lower frequencies, and much more than a fixed speed spindle would drop. This includes "sensorless vector" VFD's (and VFD's with a real closed loop speed sensor or tacho generator are too expensive/exotic to consider). The leadscrew will therefore be ahead of the spindle (and out of sync) until the ELS sees the next spindle sync pulse and corrects. The result are random variations (jitter) in pitch of the thread being cut. The limitation to use only one PPR was due to the limited processor capacity, there just was no time to calculate and correct for more PPR's. In this regard, John's ELS is very much like its British predecessor, the FROG, which also only used one PPR to sense spindle speed.
Another problem with John's ELS (that may or may not matter to you), is that it cannot cut very accurate threads like needed to cut leadscrews. This is because of large incremental floating point rounding errors, which on a 500mm long leadscrew quickly add up to one half a revolution of error. This is for any machine tool leadscrew an unacceptably large error. This limitation came about again by the limited power of the processor used. The ELS works very well for making fastener type threads though. John designed the ELS to replace the missing change gears of his lathe. He wrote a detailed article about his ELS in the "Circuit Cellar" magazine, I recall it did span over 2 or 3 issues.
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13th June 2014, 07:42 PM #25
Hi cba,
I do remember reading about the overflow problem of the ELS. John - or the group - has found a way around it and the newere version of the firmware fixed it by using a diffefrent algorithm. THe jitter issue remains of course because of the single pulse per rev. But in practice, people have found that both the FROG and the ELS work fine whenever the load remains relatively constant - as in threading.
I'm about to find out! over the next few days....Cheers,
Joe
9"thicknesser/planer, 12" bench saw, 2Hp Dusty, 5/8" Drill press, 10" Makita drop saw, 2Hp Makita outer, the usual power tools and carpentry hand tools...
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11th October 2014, 07:47 PM #26New Member
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Hi,
I found this in my travels to sort out a heidenhain DRO dipslay.
http://www.yuriystoys.com/p/android-dro.html
I think using a launchpad or arduino to control the motor speed should be doable.
Fitting a 3 phase motor and a VFD then a cheap linear scale on the crossslide for feedback to the arduino, and using a display to input the sfm required.
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14th October 2014, 11:06 PM #27SENIOR MEMBER
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HI ALL,
Although I don't think that I can provide much Input to your project. I have a question? Couldn't you control the Surface speed by means of using a CNC Stepper motor and using only 1 axis of a Pendant Controller like this one http://www.ebay.com.au/itm/2013-CNC-...item4172125790 ???.
Just for interest my Boss came across this Tool Room lathe that Whitelaw Machinery in Queensland sell its a Eximus CTL-618E http://www.whitelawmachinery.com.au/...-lathes-detail here is a Video of
https://www.youtube.com/watch?v=-Hb2-DlAiMY it and if you Search for CTL-618E on YouTube there is more.All The Best steran50 Stewart
The shortest way to do many things is to do only one thing at once.
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15th October 2014, 08:34 AM #28SENIOR MEMBER
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Pfft, it's only a Hardinge HLV clone made in Taiwan. Not the real thing.
Mind you the Taiwanese 'Feeler' was an almost exact copy of the Hardinge and reportedly very good. Wonder if it is the same factory still producing them?
Ken
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