Paul White 3 | 10/08/2020 12:10:09 |
109 forum posts 23 photos | Hello all, A arecent thread contained reference to the odd vertical head gearing ratios on these machines, the poster had produced an electronic gizmo to drive the normal cheap Rev counter. I have fitted a VFD to the vertical head drive on my Centec and now have great difficulty in estimating cutter speed. Could the forum member concerned please contact me.
Paul.
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Paul White 3 | 10/08/2020 12:16:39 |
109 forum posts 23 photos | Previous post should be headed - Centec mill |
not done it yet | 10/08/2020 15:56:03 |
7517 forum posts 20 photos | It is 0.875 reduction, but I have yet to come across an application that requires a specific speed value of better than plus or minus 15% or more. Any theoretical cutter speeds are simply ‘ball park’ figures to be used as a starting point. |
John Haine | 10/08/2020 16:28:32 |
5563 forum posts 322 photos | Assuming that .875 is between the motor and spindle and your VFD indicates Hz, and you have a 1440 rpm 4 pole motor, this table might help. If you run the VFD faster than 50 Hz (I use up to 100 Hz on my VMB) it's easy to extend this, ditto if your motor is actually 2 pole (2800 rpm). VFD Hz Spindle Edited By John Haine on 10/08/2020 16:28:56 |
Paul White 3 | 10/08/2020 16:32:41 |
109 forum posts 23 photos | NDIY, thanks for your response to my post. The heading was incorrect and the question badly phrased. I will try again- My centec mill has its own vertical head motor, this motor has a VFD . The net of this set up is that cutter speed has no reference . In a thread recently the poster passed an aside that he had made a gizmo to read the cutter speed, this I think was set by comparing the cutter speed as read on a hand held counter then setting the gizmo. . .
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duncan webster | 10/08/2020 16:54:06 |
5307 forum posts 83 photos | I might be the person in question. My box of tricks takes the signal off the horizontal drive shaft, but if you have a separate motor and the top of the spindle is accessible it is a lot easier, a cunningly placed magnet will drive a Chinese tacho direct. Be warned that the update rate on the one I bought was really slow so not a lot of use for adjusting speed. Of course you can make one of mine and not include the reduction factor as explained in the MEW # 294 article. My calibration tacho wasn't a handheld |
john halfpenny | 10/08/2020 17:32:00 |
314 forum posts 28 photos | Or use a cycle computer. I have an £8 one. Set the wheel size as 1667mm, and the km/hr display is an analogue of rpm - ie for 24.4 km/hr read 244 rpm. The pick-up is small enough to put just about anywhere accessible on the spindle. A bit of maths on wheel size will accommodate a reduction gear. Edited By john halfpenny on 10/08/2020 17:33:37 |
not done it yet | 10/08/2020 18:25:23 |
7517 forum posts 20 photos | Is this a Centec head? Mkl, Mkll or Mklll? I suspect the Mkl may well be different to the Mklll, as might the Mkll, also. I might sggest you adjust the pulley sizes, if belt driven, to provide an easy ratio. If direct driven, you only need to count the input turns for a number of output turns (or vice versa) and use a chart like John supplied above. This is all dependent on the level your ‘fussiness’ for speed indications. Motor power was different for original equipment, at least on the 2A and 2B models, so what power are you driving your head with? Edited By not done it yet on 10/08/2020 18:26:07 |
Paul White 3 | 11/08/2020 10:58:56 |
109 forum posts 23 photos | Thank you, to all the respondents to this thread. The original objective was to identify the poster mentioning centec head gearing, this has been achieved by Duncan fessing up. Ndiy- to answer your question, I fitted a1/2 HP ,3phase 1400 motor, I don't know the head model no. , a picture of the set up exists in my album. I had hoped to read the shaft or motor speed, put that output through a very simple electronic item and feed that tto the cheap tachometer units we all know. As this now seems unlikely , a variant on Johns proposal, is the likely outcome.
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duncan webster | 11/08/2020 13:13:43 |
5307 forum posts 83 photos | ...............I had hoped to read the shaft or motor speed, put that output through a very simple electronic item and feed that tto
the cheap tachometer units we all know. As this now seems unlikely , a variant on Johns proposal, is the likely outcome. Your conversion is very neat, saves having the horizontal gearbox thrsashing away al the time. Yet another project for the bucket list, you should write it up for MEW, even just a load of photos, there are lots of Centecs out there Having had my article comprehensively rubbished in recent editions of MEW I hesitate to make any suggestions, but here goes. John Halfpenny's solution is easy and will work you could just put a scale on the vfd speed control knob, you'd need to borrow a tacho, or just work it out from the frequency display and pulley ratios as per John Haine If you make the drive ratio from motor to Centec be 8:7 speed up, put the sensor magnet on the motor pulley. You're not looking for fabulous accuracy Your final suggestion is possible, but would be nearly as much work as making one to my article, you'd still need a micro processor |
not done it yet | 11/08/2020 14:37:10 |
7517 forum posts 20 photos | The separate motor does give the option of altering the throat depth by an amount. |
Paul White 3 | 11/08/2020 16:16:06 |
109 forum posts 23 photos | Posted by not done it yet on 11/08/2020 14:37:10:
The separate motor does give the option of altering the throat depth by an amount. Duncan & Ndiy, thank you both for your comments. It is very interesting to me that the points you make cover my reasons for the drive mods - the std machine when fitted with single phase motor was loud from the cabinet vibrations and gearbox noise. The separate motor has produced a silent operation. The mod allows change in available work envelope both back and forth and up and down. |
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