Evening all,

I've searched for a similar thread on this forum without success so here goes.

I'm looking to convert my ML7-R to variable speed in the not to distant future. I have all the gear ready to go but would like to hear about other peoples' experience's.

I'm concerned about the possible loss of torque at the lower end of the speed range although I realise that the backgears should make up for some loss.

Any comments would be appreciated in particular from those who have already carried out the conversion.

Len. P.

See PM

I have an inverter fitted to my ML7R and can recommend it. It is of the flux vector type so maintains good torque at low frequencies. A tacho is useful to check your speed. I think the belts should still be adjusted to roughly the speed you need and then using the speed adjstment to optimise cutting. I have a foot mounted 1hp motor and this is not a problem as the ramp up to speed is smooth and the motor runs much smoother than a single phase motor. I felt it was worth arranging the drive to have forward and reverse and a slow jog and a rapid speed selection to enable a fast return when screwcutting and the leadscrew sync dial cannot be used.The acceleration ramps if reasonably gentle should not unscrew the chuck if reverse is directly selected but beware of cutting in reverse if using a chuck.

Hi Len,

I agree with all Michael says. I have a standard, i.e.non-vector, inverter on my S7 and it works just fine. When I set up the machine I did use a tcho to verify speeds, but now I just use the full speed figure for the belt configuration multiplied by twice the frequency shown on the inverter. That is, a figure of 50 (Hz) is 100% of full speed, 25 (Hz) is 50% of full speed and so on. Reverse is excellent for metric screwcutting. I still change the belts and have never been worried by lack of torque, although this type of inverter does lose torque at low revs. There has been talk of the motor overheating at low speed due to lack of cooling airflow, but I have never experienced this.

All in all I have found this a very worthwhile mod.

John

Have sent you a reply Kwil.

Len.

I fitted a 3 phase delta connected motor and inverter to my Super 7, the inverter is an early one/type, originally sold by RS Components without all the extra facilities now available.I made up the remote control box to give forward, reverse,jog and speed control.I can recommend the 3 phase motor and inverters.I've never found my motor running hot on slow speeds. Regarding the speed, I made up the digital display unit which was an article in one of the MEW magazines and that is also useful. Regarding possible electro magnetic interference, one can use Sy sceened 4 core cable and a filter unit which can be found at the end of the cable inside a front loader washing machine, the round box to where the lead fits. For the control multi core control wires use a screened computer lead.The control system is low voltage often 24 volts, so low voltage switches can be used. The speed control potentiometer (variable resistor has to be a linear type NOT A VOLUME CONTROL TYPE) are sold by electronic component outlets.don't be afaid of buying second hand, by and large inverters are very forgiving and 3 phase motors are tough and smooth running. Should you need any help fitting things up send me a PM.Ted

Thanks for that info. Ted.

When I converted my Tom Senior (using an Omrom VFD from E-bay, brand new it was as well) I made up a circular scale divided in a linear proportion scaling readout frequency (0-50Hz) against motor speed (1380rpm) in 5Hz bites. That worked out quite well but the digital display sounds interesting, I'll have to research that one Ted.

I also did use the SY cable but didn't find the need for an filter.

Incidentally the VFD to go on the Myford is an Altivar 11, again brand new from E-bay, £41 quid I think I won it for.

I've just got to finish modifying the motor housing which had a reduction gearbox attached to it and sleeve the motor spindle from 12mm to 5/8" and lastly adapt the body to give the same foot mounting arrangement.

Len. P.

Agreed. A good inverter will maintain constant torque while reducing the speed so if for example you reduce the speed to half using the vfd the torque will stay the same but the power available will be halved. Halving the speed with the belts will double the torque and maintain constant power.

Like Len I just made a circular scale for the speed control knob. That is more than adequate.

I found the biggest improvement was in surface finish as a result of the smoother torque vs. angle characteristic of a three phase motor.

Russell.

Hello Len P, John and Russel, regarding your foot mounted motor Len. I had the same arrangment but though the Myford resilient mounting better.So, I obtained 3 piece of 3mm plate and using one piece, copied the original base including the mounting hole. Using the two other pieces of 3mm I copied the verticle cradle end bits,which accomadate the rubber pieces in which the motor sits. I took the motor to the motor factors and they soon found 2 rubber rings, which were a tight fit over the motor bearing housing. Once home I mounted the rings on a piece bar and sanded the inner and outers flat. I next welded the end pieces to the base. Finally made two clamping pieces just like there was on the single phase Myford fitted motor. I left the welded on foot mountings just incase things didn't workout that was 8 or 10 years ago.My workshop is one of continual development.Ted

Been using my Myford ML7 with a variable drive. I purchased a new 180v 1HP treadmill motor off ebay for £50, then purchased a DC-51 motor speed controller DC180v again off ebay for £14. They work perfectly giving me a speed range from 0 rpm to 1500 rpm. I can go upto 2500rpm but respect my old ML7. I use a hand held electronic rev counter, again off ebay £15 (Chinese) bracketed just behind the chuck and just adjust the speed to what I want. Hope this helps. Jim