742 forum posts
I have come into some unexpected money I have, for a while, been looking at a new mill, the Warco VMC however what I don't like about it is the they way of changing the speed using the belt drive. My current mill had a gear box and its very easy to change the speed.
So, I am sure I am not the only one. Could I just set it to the max speed and then use a PWM for the speed?
Edit, just though that you probable cant get a 240v PWM. So the other idea is to get a 3 phase model with an inverter?
Edited By petro1head on 28/01/2017 11:52:28
|Mike Poole||28/01/2017 12:26:42|
2845 forum posts
At the Ally Pally show Warco had a VMC with inverter already fitted, it had a 2 speed pulley for high and low range, not the double belt setup on the standard machine. It wasn't on the website when I last looked but a phone call might put you in the picture regarding availability and price.
|Tony Pratt 1||28/01/2017 13:06:16|
|1343 forum posts|
I have a Myford VME so similar to Warco VMC fitted with 3 phase/inverter. I have found that if left with the belts set on max speed it lacks power when say drilling a large diameter hole, obviously changing to a lower speed range solves the problem.
I'm not sure if any inverter / motor combination will produce full power when 'turned down' as you propose? There are people on here who will know.
|Andrew Johnston||28/01/2017 13:23:36|
5828 forum posts
In general no they don't. An inverter/motor combination will normally produce rated power at base speed, usually associated with a frequency of 50Hz in the UK. For a motor connected directly to a three phase supply the internals are designed so that at 50Hz and full supply voltage the phase currents are such that rated power is produced.
As the frequency is reduced a lower voltage is required to maintain the same phase currents. To a first approximation if the phase currents are constant then the torque is constant. The torque produced is determined primarily by the current flowing. But at a lower frequency the rotation speed will be lower. Since power is torque times angular velocity the power will decrease in direct proportion to the frequency reduction.
In a belt, or gear, drive the power out is equal to the power in, less small losses in the drive train. So if the driving motor is running at fixed speed, and hence fixed power, as the speed is reduced in the drive train the torque goes up, to keep the output power constant.
|Clive Foster||28/01/2017 13:30:54|
|2530 forum posts|
Two speed belt and inverter drive works very well on that size of machine. Years back I had a Chester "Lux style" one so fitted. Apparently Chester bought one in to test the market and the demand / capacity / performance / price thing didn't work out for what they needed to sell at to be a viable product so I got a very good deal on the one'n only! That one had a 2 : 1 ratio between high and low speeds 125 to 1400 rpm in low, 250 to 2800 rpm in high. Plenty of overlap and a beefy 2 1/2 HP motor meant that I pretty much never needed to shift the belt mid job. Good thing too 'cos belt shifting was not the easiest of jobs, even with verbal encouragement.
I could be persuaded that a slightly larger ratio between belt pulleys might have been beneficial, perhaps 2 3/4 :1 or even 2 1/2 : 1. Objectively low speed was on the high side for swinging the larger end of face mills or fly-cutters the machine was physically strong enough to handle. But increasing the belt ratio would have meant reduced overlap and more belt changing. Probably never know without trying and even then its likely to depend heavily on what work you do. Ideal is probably 3 speeds and poly Vee belt for easy change although it would sit on middle speed nearly all the time. And someone will still moan "OK I s'pose but..."
Inverter on mine had no speed display and was tucked into the head using up some of the space vacated by the usual gearbox. I fitted a collet knob from RS with 1 to 12 numbering on the skirt to the speed control potentiometer fitted on the front face of the head and stuck a numbers / speed chart on where I could see it. More than good enough for me. Have used inverter driven machines with the usual visible Hz displays since and much prefer the chart and numbered pot. Tony Jeffee's speed disks as printed in MEW way back to sorted out the speeds and first job with one of Mr Lidls laminators was to do a shop and grubby finger proof version of the label.
Bottom line is that if I were buying a VMC "new to keep" and couldn't get an official Warco VFD fitted one I'd consider the extra cost of dumping the standard motor and fitting a 3 phase motor with VFD control money well spent.
|John Rudd||28/01/2017 13:43:46|
|1410 forum posts|
....and that is exactly what I did with mine...
Fitted a 1.1kw 3ph motor TEC brand and an Invertek 1.5kw inverter....the FWD-OFF-REV sw and Speed pot were mounted in a plastic box and located just under the Y axis handwheel....I found that location ergonomically the best for me.....
Edited By John Rudd on 28/01/2017 13:44:08
|Gary Wooding||28/01/2017 14:28:50|
|776 forum posts|
A friend has a VMC mill that he decided, before purchase, to convert to VFD drive. He specified he wanted a 3ph motor fitted which I converted from star to delta wind, and fitted a VFD. He also specified R8 spindle fitting.
In the photo you can see the control pad for speed and direction control, and the 5" raising block we made. With The mill works really well with the VFD.
|David Jupp||28/01/2017 14:49:01|
|759 forum posts|
Remember that Power = Torque x rotational speed
No system can produce full power at low speed, but it may be able to provide rated torque down to very low or even zero speed. Good motor/controller combinations often offer constant torque up to a nominal speed, then constant power (and hence reducing torque) at higher speeds. Many VFDs can even give a short term 'torque boost' for start up.
Reduction gearing or pulleys can give higher torque (power doesn't change, other than for inevitable inefficiencies) - an electrically based variable speed facility can't substitute for the torque multiplication of gearing, unless a higher torque motor is substituted (which might overload other parts).
|Roger Vane||28/01/2017 15:23:50|
|100 forum posts|
When I ordered my VMC from Warco I wanted imperial / R8 / 3 phase which is not a standard. Roger Warren ordered a special for me with a 240V 3 phase motor, saving me the cost of a new motor. Then I bought an inverter and control panel from Newton Tesla which was very easy to wire up (they provide a wiring diagram).
The belts are set to 1180 rpm - I can count on one hand the number of times I've changed the belt ratio in the 7 or so years that I've owned the machine. It allows me a totally variable speed, and not the belt or gear ratios specified by the manufacturer. I find that at this belt setting I can drive a 7/8" drill (at low speed into a piloted hole) or a 2.5" shell mill as long as the feed rates and depth of cut are sensible, whilst with the maximum frequency set to just under 60Hz (1400 rpm) I can drive a small slot drill. A further benefit is that I can tap under power using the jog / reverse functions. Torque levels maintained well down the rev range. Magic!
|Clive Foster||28/01/2017 15:42:47|
|2530 forum posts|
The $64,000 questions are how much power at the spindle is enough power and what is the most appropriate way to get it within HomeShop budget constraints. Large professional machines needing seamless VFD type speed control from near zero to very fast use extremley powerful motors to generate the necessary torque at low speeds. Even modest (by commercial standards) vertical machining centres with work envelopes of Bridgeport or even smaller size generally have upwards of 20 hp on the spindle.
Received wisdom with VFD conversions of step pulley head Bridgeports retaining the standard motor is that the VFD effectively closes the gap between adjacent speeds. So with the belt on one step of the pulley performance is entirely satisfactory over the range from next step down to next step up but beyond that you start running into compromises over cutter size and metal removal rate. Which is generally not of great import for folk like us where the main constraint on metal removal rates with an open machine is mess and chip distribution area. Saving 5 minutes on cutting time and adding 30 to clear up time isn't a good bargain!
If I still had the Chester machine it would be interesting to compare actual operating constraints between that machine with its higher powered motor but only two belt speeds and the VMC conversions described by John and Gary using close to standard power motors which, presumably, retain all the belt drive speeds. I would anticipate that, in practice, the VMC conversions are entirely satisfactory over speed ranges rather greater than one step up and one step down but belt changing still needs to be factored in on jobs needing a wide range of cutter size.
From my experience I'd propose that the best balance would be to go up a bit in motor power, equivalent to running 2 hp on the machine I had rather than 2 1/2, and use three belt speeds with a small overlap between top and bottom and the centre one on the low side of middle. Around 10 to 15 % overlap between top and bottom with the centre range about 15 to 20% offset down from the middle feels about right and should mean that it could be left on centre speed almost all the time. Setting things symmetrical isn't the best use of a VFD as power limitations are primarily on the low speed end where larger cutters will be used. Small cutters running fast don't need that much oomph so you can afford to spin the motor relatively faster at the top end without noticing the extra torque loss.
Roger posted whilst i was typing. His experience certainly confirms that folk like us can cover a decently wide range of speeds and cutter sizes on one belt position.
Edited By Clive Foster on 28/01/2017 15:45:59
|11 forum posts|
I have the same mill, motor and VFD as Roger and have set my belt on the same speed. I agree with him - over the twelve years I have used it I have very rarely changed speed and have never had a problem with torque or over heating.
My lathe has a similar arrangement and has also been problem free for nearly twenty years. When cutting lots of threads the lathe is running very slowly for hours on end and I have given up checking the motor and VFD as they have never warmed up at all.
I have never regretted going VFD but do regret not doing it earlier.
|257 forum posts|
I am just finishing off converting my Chester 626 to VFD.
Motor is now 1.1kw TEC
Pendant control is Ex Ebay seller.
VFD is Teco L510 rated 1.5kw. Thought I would go with another Teco as I like the one on my Harrison.
Ripped out all the electrics and started again. Mains is all RCD protected so went for mains into 3 x MCBs inside the column.
1 to mains transformer down to 24v for LoVo light, 1 to supply DRO and 1 to VFD.
Between the VFD I have put a 4-6.3,amp variable overload protector that i had surplus from my lathe conversion now set at 5 amp.
Pendant is nice piece of kit which through the VFD,s logic controls gives start, stop, jog, NVR E stop, potentiometer for speed control and forward/ reverse switching.
A pleasant surprise is that this particular inverter has the ability to display the actual RPM through its group 12 parameters which can be adjusted by juggling with another parameter. I intend to set the top speed of of the inverter to 75Hz which is max recommended for the motor and then max the belts to give around 2600/2700RPM at 75Hz.
I am currently waiting for a digital tacho coming to then calibrate the the VFD,s RPM display.
I did consider ( and am still considering ) doing away with the idler pulley if possible and setting up with one belt motor to pulley. This may help reduce some belt noise. Have mixed thoughts on this as having the double belt setup as original supply will allow me more chance of lowering belt speed settings per the need for extra low speed torque.
|Mike Bondarczuk||28/01/2017 18:05:50|
|91 forum posts|
Just to add my comments to this topic i also have a pre-owned Chester 626 VMC, which is identical to the Warco model and mine is one of the early ones from Taiwan.
It is fitted with a 2.5HP motor fed via a VFD and stays on the highest speed belt setting and I just vary the speed from very very slow through to about10% above the original speed.
So far, which is now more than three years, I have had absolutely no issues with the performance and also have the benefit of a four axis DRO set-up with the fourth axis being he quill feed.
Would certainly recommend that route for power.
|257 forum posts|
Mine is actually an early re-painted model with 3 axis readout plus vernier on quill. Dont know where made exactly but the original single phase electrics were far better than i thought they would be.
My question is did you retain the centre idler twin belt setup or go for single belt?
742 forum posts
Care to post links to what you bought
One thing I have noticed about the various Warco mills is the at most only go to 1600rpm where the VMC goes to over 2000rpm. How important is having the faster speeds
|257 forum posts|
The Tec motor was used but practically new from Ebay, i only paid £45 for it. New are listed on ebay at about £110. Its a MS90s- 4 pole, 1400 RPM at 50Hz. Delta 230v at 4.57A, Star 414v at 2.54A.
The Teco L510 was listed and boxed as new. It was a private Ebay seller listed at £125 and took offer of £120 which was quite a bargain its the model with the 'A' suffix which denotes the logic controls are 24v to ground.
The pendant is again from an Ebay trader. He has some similar ones listed, see item 222390434689. Mine with the E stop isnt listed at the moment as it was the last while he waits for some new E stop buttons coming.
For speeds it depends what your are going to do. If you wand to do any small diameter milling or drilling then you technically need some high speeds.
Example, 1/8" dia drill or slot drill in low carbon mild steel should be in the region of 180/200 ft/ min. At 200ft/min (2400 ins/min) divided by 0.39" ( cutter circumferance ) it would need 6000 RPM. I am looking to achieve 2700 ish RPM which is still less than half of this which is only about 90ft/min ish. 2000RPM would be even less. If you take things easy however you will be fine.
Until I get my tacho I dont know what the machine will achieve at 75Hz but I reckon it would max out quite a bit over 3000 RPM but thats beyong intended max speed of the machines spindle.
|Gary Wooding||29/01/2017 10:35:23|
|776 forum posts|
I modified my Centec 2B mill and Chester 10x36 gearhead lathe to VFDs some years ago. For nearly all my work I leave both machines in the mid-range gear and vary the speed with the VFDs, the range of which can be varied from 0 to 120Hz. The rpm of a motor is directly proportional to the frequency - double the frequency is double the rpm.
The motor in the mill is 1hp and the lathe is 2hp. Occasionally I've used the mill in the highest gear and cranked the VFD to 120Hz so as to boost the standard top speed from 1400 to 3360rpm.
Power is torque x rpm. As a general rule-of-thumb, at frequencies below 50Hz (standard UK main frequency), motors have constant torque with reduced power, and above 50Hz they have constant power with reduced torque.
|923 forum posts|
Hi Malc - I am making the assumption (always unwise!) that your new set-up does not involve changing pulleys to achieve the total speed range and that the speed range is controlled totally by the VFD. With the highest speed aimed at 2600/2700rpm or even more, what is the lowest speed you can run at?
|Andrew Johnston||29/01/2017 13:51:03|
5828 forum posts
The correct equation for power is:
Power (W) = Torque (Nm) x angular velocity (rad/s)
|257 forum posts|
Hi Chris, Its a bit up in the air at the moment. I have currently set the belts at 1800RPM. As motors were similar speeds on mine, then so should the actual speeds now be the same at 50Hz. This means on this belt setting at 75Hz I should see 2700RPM.
The inverter will slow down to just a literal crawl speed. When i try and grip the plain part of my ER40 chuck with my hand at such a low speed there is no chance of holding it, far too much torque for me to do that.
Like I have said cannot confirm all of this until my tacho comes to me around Feb 1st from Jersey.
I may juggle the 75% max speed or the belts slightly, not sure as depends on what I see as actual speed. If my setting currently remains the same I am pretty sure for me that no belt changes would be necessary.
Please login to post a reply.
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.