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Centec mill cutter speed

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Paul White 310/08/2020 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 White 310/08/2020 12:16:39
109 forum posts
23 photos

Previous post should be headed - Centec mill

not done it yet10/08/2020 15:56:03
6733 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 Haine10/08/2020 16:28:32
4623 forum posts
273 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
50 1260
45 1134
40 1008
35 882
30 756
25 630
20 504
15 378
10 252
5 126

Edited By John Haine on 10/08/2020 16:28:56

Paul White 310/08/2020 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.



duncan webster10/08/2020 16:54:06
3922 forum posts
61 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 halfpenny10/08/2020 17:32:00
232 forum posts
24 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 yet10/08/2020 18:25:23
6733 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 311/08/2020 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


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.

duncan webster11/08/2020 13:13:43
3922 forum posts
61 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 yet11/08/2020 14:37:10
6733 forum posts
20 photos

The separate motor does give the option of altering the throat depth by an amount.

Paul White 311/08/2020 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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