By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

Micro Mill

Fails again,

All Topics | Latest Posts

Search for:  in Thread Title in  
Paul Kemp08/12/2019 22:05:03
548 forum posts
18 photos

Well it's happened again! My long suffering micro mill has stopped going round! Last time I used it I had a problem but poking around in the controller seemed to set it off again. Today, no chance. Plug in, all good, switch to fwd, green light comes on as it should, turn the pot on to make it revolve, orange light comes on (as it would if the overload had tripped), no motion! Same in reverse. Quick prod about inside with a meter reveals no volts to the motor under any condition. Yes the fuse is good.


Given the limited space in my workshop at home it's a handy little machine but on the limit of things I do! Generally though it puts up with it although I have had my share of broken gear selectors and split gears and on a marathon session with no regard to the temperature of the motor burnt it out. A new motor was £100!

i have checked the motor and the resistance seems good, brushes are good so this time I think it's something on the control board, there is nothing obviously fried though.

i have a spare inverter (well 2 actually) and looking around I can get a 3ph 240v motor rated at 0.12kw at 2700 50hz but continuously rated between 5 and 75hz 200 to 4050 rpm for £35! Original set up is 240v AC in, 230v DC out to a 4000rpm 150w motor. Anyone think I will notice the difference?


Emgee08/12/2019 22:18:37
1652 forum posts
224 photos

Hi Paul, if you have had many problems with the motor perhaps you are expecting too much from the power available, going smaller will make the situation worse, if replacing the motor and can use a larger physical size go for a .37kW but you then have to consider the strength of the drive system from motor to spindle.


Paul Kemp08/12/2019 22:50:15
548 forum posts
18 photos


i can't find a higher power 3ph motor with a 50mm spigot. The drive train is a weakness anyway. Yes I definitely ask too much of it but my big mill is in my mates shed about 20mins drive away so having the small one at home is handy. The DC motor is 150w in and the 3ph is 120w out so power at the spindle won't be a lot different. I have never stalled a cutter on the old motor the rest of the machine is not up to heavy enough cuts for that! As the new 3ph motor is only just over £30 and a new DC is £100 and a new board I think was around £50 economically it's a better bet, inverter is free cos I have it already.


Emgee09/12/2019 00:01:10
1652 forum posts
224 photos

Hi Paul, like you say could be a very low cost solution at £30 will certainly get you away from the DC controller problems.


not done it yet09/12/2019 07:37:23
4893 forum posts
20 photos

Current motor may well have a second hand value if it is still operational (clearly needs checking out with a DC supply) so conversion may cost nothing in the long run, if it is successful. Board my also have a value if it is either working or is repairable.

If you are correct, with the power used by each motor system, the 3 phase may well be as good as the old one (let’s face it, most electric drills are more powerful!). The motor power rating will not be the same at those extremes of rotational speeds, so may well need checking out/comparing, before you dive in to any conversion.

Personally, I would find a different motor and convert to a belt drive, if possible.

Extending the workshop might be a better option?smiley

Ron Laden09/12/2019 08:06:08
1987 forum posts
393 photos

Hi Paul, with the Dc and 3ph motors having similar power figures it sounds to be worth a try at £35.

In your searching have you seen a 3ph motor with a bit more power, say 250/300 watts but with the wrong size spigot..? If the spigot was smaller you could turn up a spacing collar and if it too large remove the motor end plate and turn down the collar to 50mm. You maybe dont want to mess around that way but it was just a thought providing there is a motor with a little more power and at the right price of course.


Michael Cox 109/12/2019 10:11:39
533 forum posts
27 photos

I have a Micromill similar to yours. I found there were two annoying problems with it. One was the noise from the gear selector fork that vibrated badly . The second problem was that even a slight overload would cause the default light to come on and sometimes it would blow the fuse. Fortunately the motor control board was never damaged by these slight overloads.

I converted my Micromill to belt drive, see:


The absence of the gear selector eliminate the noise but the main benefit was that since doing the conversion I have had no problems with slight overloads triggering the default light and blowing fuses. I think the stretch of the belts and or belt slippage in overload conditions eliminates shock loading of the motor.


Ian P09/12/2019 10:58:52
2412 forum posts
101 photos

This is my belt drive conversion.

The PolyVee is really only one of the modifications that have transformed this mill. The weight of the motor is no longer dulling the feel of the quill as I elongated the keyway in the spindle and mounted the pulley on ballraces so its more like a conventional quill. I also moved the Z axis leadscrew so it is much closer to the dovetail slide so is no longer on whet felt like a flexible mount.

This picture was take a while ago and the motor has been changes since. It currently fitted is a 4000rpm 1Kw servo motor (because I had it) which has massive torque from zero rpm up to 8000, not that I run at that speed for long.

Ian P


Paul Kemp09/12/2019 22:05:28
548 forum posts
18 photos

Thanks gents,

Replies in turn;

Ron, I had a mate who knows a lot more about these things than I do some calculations and he reckons the three phase due to the difference input / output ratings will give me slightly more power than the original. Unfortunately the next motor up has a 60mm spigot and as the end plate is recessed inside there isn't enough meat to turn it down to 50mm. I could open up the hole in the existing plate but there will be little room left for the motor holding bolts so given the info above I am going to give it a go, little to lose!

Michael, I have not had the gear selector rattle but I have broken it twice! Second time I realised what was happening with the poor fitting short radiused end of the key which was effectively jacking the gears apart first time I bought a new one but second time I welded it back together and since sorting the key issue have had no more problems. The motor gear gets loose on the shaft, I assume that is a combination of heat through the spindle and load. With the new motor the spindle is 1mm larger so I can bore out the gear to a good fit and cut a new keyway, the 3ph should run cooler as it has a fan so that may improve too.

Ian, Wow, some radical surgery there! Interesting, not sure I want to go that far but food for thought in the future if am looking for a project. Having the bigger industrial grade mill I do only tend to do smaller jobs on this one now, it's handy for quick jobs that I don't want to travel to the big machine (would love a larger shed at home in response to the other suggestion re extending but we are completely out of space! Need to move!). Good to see / hear what others have done though, where there is a will.....

Will update when I get the motor and get it running again.


Paul Kemp14/12/2019 21:08:34
548 forum posts
18 photos

I decided to go for it, motor came from Inverter drive supermarket or something like that, bit miffed when I ordered it that their quoted prices don't include VAT so it was £9 carriage plus £9 VAT so final price was closer to £50 than £35, hey ho, it came in 24hrs, well packed and allegedly made in Portugal. First mechanical job was to transfer and drill new holes for the mounting bolts, motor was a universal mount so used 2 of the cap screws that held one of the feet on as I didn't need the feet! The other two bolts had to be turned down hex heads to get the clearance on the mating gear. Then had to set up the nylon drive gear which was as slack as a yak on the old 8mm motor spindle to open it out to 9mm. Easy enough then had to open out the keyway deeper. Then needed a couple of spacers with keyways to clear the key and get the gear in the right position relative to the input gear on the two speed shaft, had a bar end of free cutting stainless on the bench the right OD so used that for the spacers and a new clamp washer. Reassembled and connected the VFD (currently laying on bench) programmed it up for. 4 pole motor max 75hz so I can if I want match the old top speed (never really used that much though), switched on expecting the lights to go out and she burst into life! All works as it should, about as noisy as it was before and the advantage the VFD allows an instant reverse of direction which will be handy for power tapping. Despite following the terminals faithfully I had to swap 2 phases to get it to run forward when the VFD indication said fwd! Not cut any metal yet as the battery drill was flat and I have to screw the box on the wall, tomorrow for that, so far so good!




6 wall plugs and a couple of cable clips and we are away! One improvement is the old DC drive knocked out Planet Rock on the dab workshop radio as soon as it was switched on, no problem now! Sorry about the last two sideways pictures!


Ron Laden15/12/2019 05:07:49
1987 forum posts
393 photos

Well done Paul looks good I wouldn't be surprised if the failure did you a favour. I bet you also have a bit more power now as the figures quoted on the old DC motor was probably input not output.

I have been meaning to ask, how is the engine build going I know you were quite well on with it, finished next year..?


Paul Kemp15/12/2019 13:07:50
548 forum posts
18 photos


Well the moment of truth approaches! I have just mounted the box on the wall and about to try it on the webs for the valve rod support bracket for the engine! Not particularly challenging for it, just milling down the edge of some 1/4" steel plate but will give me an idea how it compares. Original was input power and calculations done by my mate suggest the new one will give more at the spindle.

As to the engine itself, I was moving it forward quite well at the beginning of the year and the plan was to be in steam for August just gone! Then foolishly I agreed to help out a company based in London, part time working mainly from home for a fixed 3 month term - that has ended up pretty well full time recently so progress has suffered badly! However hopefully in the new year a balance will be struck and progress will improve. I have machined all the large castings now, cylinder is finished with the liner in, trunk guide I am just finishing now so lots of studs to make in the new year to start joining everything together so need to get my Coventry die box up and running!

Seasons greetings!


All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
Eccentric July 5 2018
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

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.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest