Love or hate living with a mini lathe

My mini lathe recently started to have a hefty dose of ghostly happenings, mainly when applying mains power it would growl and start up on it's own, the first time it happened I chased Doris the puppy out of the shed, and told here she would have to get used to lathe noises if she wanted to come into my shed, she just growled so went back into shed and the lathe was still doing it's own thing turning a 1/8 to 1/4 of a turn growling then stopping.

As I had replaced the headstock bearings with tapered ones a while back and the lathes been standing for a long while, I whipped of the headstock and smeared everything with a light grease, switched it back on and ran it at 1/2 speed for 5 Mins then flat-out for 10, let it cool down and adjusted the spindle lock nuts smooth now with barely a flicker on the dti at the spindle rim, refitted the chuck and had the same reading on the dti on the chuck, so happy and thinking I’d cured it started some cutting, just my luck the slides were all to cock, so tried to adjust it out but no joy loads of tight and loose spots on the carriage, cross and top slides.

I cleaned everything and reassembled it all, another test turning lathe just growled at me and cut just the same as before, so apart it came again, the worst offender was the saddle as at the rear it seems to jump up and down like a Weston donkey, so out with the blue I last saw it 3 years ago, off up the garden to the other shed 2 hours later I found it under the wheel of my industrial mig welder crushed. upon opening it was as dry as boot leather so I managed to dip a wet finger into the pot and managed to get enough to coat all 3 slide-ways, ran all 3 slides up and down and had a look at the slides, there hardly any contact anywhere, as it was dark and cold I took all 3 slides in house and settled down with a fag and a cup of coffee, so looking at the top slide first I smeared the ways with some solvol autosol chrome polish and soon got into a rhythm of sliding the top slide on the cross-slide using my knee-vice to hold the cross slide(I do not recommend using the knee vice to hold loco frames whilst shaping them with an angle grinder ) when the slides felt smooth I cleaned everything off and ran a tiny bit of spit onto the ways and run em up and down a few times, then removed the top slide(used to grind car valves like this the ring of spit shows where there is no contact and the shiny metal shows where there is contact, I had to do this for about an hour till I got a good balance between contact on the ways and non contact to allow oil to do its job, gave it a good clean then set about the cross slide on the saddle same again.

Only this time more exhausting as the knee vice did not like the weight of the saddle and cross slide, as it was now approaching 1am I decided to give it a rest till the following morning, so in the morning more fags and coffee the a good clean and then I ran some oil on the 2 slides and ran em up and down as soon as the oil got black another clean and re-oil till it stayed clean(just to make sure all the polish had been removed), the top slide had a bearing conversion I did years ago but I was not happy with it, so reassembled the top slide, and now its so much better and I can see why I did the bearing conversion. so with that one set and adjusted I set about removing the, top slide and setting the cross slide again so much better once I was happy I replaced the top-slide and removed the cross slide from the saddle, the saddle was just awful it seemed to rock in every direction so rechecked with blue and there was about 2 strips on the back where it contacted the bed and even less on the front, the front of the saddle was a few thou higher than the rear not good, so I found some wet and dry and some duct tape(another hour lost in the top shed).

I taped some wet or dry paper to the front bed slide and gave it a few strokes 40 odd strokes later saw it about as close as I could get it to being level, so I cleaned it and blued it and the contact area was better but still a long way off. again I taped some fresh wet or dry paper to the bed but this time to the back as well 80 odd strokes later saw a much improved contact area, nowhere near perfect but as close as I can get for now, but the Vee at the front of the saddle will need milling at the top slightly to get a better fit but as I don't have a mill it's something I can live with, so a good cleaning and reassembly and the difference is vast. So decided to do another test and sure enough the lathe ghost was growling at me, but more importantly the cut was so much improved, so I decided to bash out a quick thread as I have never been able to get it to screw cut, that went well so set it up for 8tpi and after about 5 minutes the whole lot seized up and popped the fuse, this time it was the lead-screw and change wheels, so realigned the lead-screw and was able to get it to turn by turning the gear on the lead-screw, so tried again a few seconds in it seized again, it turned out to be one of the change-wheel shafts, it had seized, a good soak in oil and off it went again, by this time I’d had enough and walked away, happy but sad at the niggles, at about 11pm that night the niggles got the better of me so I went out to the shed and bough in the power supply, as I was getting tiered, I decided to put it down, by about 1am the niggles got the better of me again so I searched the web for a schematic which I found on this site(http://www.model-engineer.co.uk/forums/postings.asp?th=38809&p=6), I forgot to mention that as well as the growling noise the power supply had started to smell a bit and seemed to be letting some of the smoke out of the wires, it's was as if the prince of darkness Lucas had designed this board, so went back to bed and unable to sleep because of the niggles I hatched a plan to fix it.



The following day i had a good look at the board and the only component showing any distress was the 0R33 10w resistor, it was shedding its paint where it got hot, so i removed this resistor, the mosfets, the daughter board and the all the electrolytic capacitors, then went over the board with a magnifying glass, the board had a very nice coating of oil and some swarf, so i sent the board on a small holiday it got as far as the ultrasonic cleaner in the kitchen, after a good 20 mins of cleaning (board turned every 5. It appeared to be getting cleaner so a good scrubbing with a toothbrush followed with more cleaning in the ultrasonic, after abut 3 hours worth of cleaning the board looked brand new, a quick rinse under the tap ensued with a good drying, however in the morning there was a residue on the board this turned out to be from the tubing the power resistors have on their legs, so a quick scrub with some acetone soaked cotton buds removed it( if i was to do it again i would remove all the large resistors).


One of those jobs i was going to get around to years ago was to move the controls off the lathe, i bought one years ago and the motor and power supply both blew, and bought another lathe off a friend for £90, one day i will get the other running, so hatched another plan i had a large abs instrument case i bought for a greenhouse controller project that got waylaid, so i set about putting the lathe controls in to that box, the idea being that i can put the controls on a shelf slightly above the headstock, but within easy reach thus keeping swarf out of the controller and at the same time it will allow me to plug it into the other lathe when i get a motor, thereby saving the cost of another power supply.

So onto the case i drilled two holes looking at the case on the far right i have the speed pot, next to it i have the fwd/off/rvs switch, then i have just to the right of the middle an iec chassis plug, this was chosen as i had some laying around gathering dust, above the socket on top the box i have the emergency switch and to the right of that i have the fuse, i put the fuse on the top as its easier to get at should it blow. at the same time i have put the fuse into the live side as per the(mini lathe pcb posts on here).



Inside the case at the far right i have mounted the board with some 6mm stand-offs to allow a bit of air to circulate, the 7 screw terminals on the board are facing the front and connect directly to the switches, mounted to the left of the board is the mains filter and another chassis socket is mounted on the rear for the mains input which is a standard kettle lead, i would have used an ordinary strain relief grommet here but i prefer using a standard set of connectors, i have a spare kettle lead ready for the motor(as im using that type of connector for the motor) , i cant connect that fully yet as the rear motor case is starting to crack(need to find a supplier).



Everything was deliberately placed as far to the right as possible as i have enough room on the front panel to fit either an lcd or 7 segment displays and its associated pcb as i intend to fit a speed display, and if i can get the software sorted an lcd display showing other data like cutting speeds in feet per sec etc. but that's a long way off



Internal wiring is as follows i have soldered flying leads to the emergency switch and these connect as standard to the mains filter and can be unplugged to remove the lid, i have soldered another flying lead to the other neutral on the emergency switch this screws to the control board, then the live goes from the emergency switch to the fuse ,then to the on/off speed control pot this is connected by a chocholate block temporarily ( i've ran out of lucar terminals and will change them at a later date).



Earthing is connected to the input side from the mains filter, the FWD/RVS switch is metal and must be earthed this is connected to the output socket and the input and output sockets are connected together via an earth cable, and the motor via the output cable and also from the lathe to the motor, this must be done as all the earth connect on the lathe but with a remote box has to be done this way, so if you decide to do this mod YOU MUST CONNECT BOTH SOCKETS VIA THEIR EARTH TERMINALS. (please note if you arnt competent to do this find someone who is.



I haven’t refitted the motor to the lathe yet but have tested it on the bench, the motor no longer runs on its own or growls, so if you get some weird behaviour on your lathe motor remove the board and give it a good scrub reassemble and try again, I wonder how many of these boards burn out due to contamination.



My next mod will be putting a needle roller bearing at the far end of the lead screw with a thrust race bearing on the inside of the block, if that works out then the same on the other end, also will fit a thrust race to the rear of the top-slide screw.







Regards

Inee

Needle rollers and a thrust came today, so removed leadscrew and popped the far end block into the 4 jaw and bored to a shade under 18mm. I bored right through the block as i will add an extention later for a handwheel or stepper motor maybe both for an extra fine feed. Then I bored the block a further 4mm for the thrust bearing this unfortunantley removes a large part of the face of the block and leaces the thust bearing exposed. If too much grit gets on during use i can always find an oil seal to cover the thrust bearing.

Whilst the leadscrew was off I set the front block in the 4 jaw and bored for the needle roller i went just a tad deeper than the length of the bearing, at this point a schoolboy error when i say schollboy error what I really mean is complete stupidity. Somehow I had managed to only order one thrust race but even more stupidly measured both ends of the leadscrew and assumed both bearings would be the same size.

The extreeme ends of the leadscrew are the same size but the front bearing surface is bigger, in the end I machined the step out of the leadscrew and made it 3.5mm longer so when i get another thrust race I can remove the block fit the race and pop it back on.

After all that did it work yes the leadscrew spins freely wheras before it was very tight.

The control box works like a charm as well that live to the left of the lathe and does not catch swarf and oil anymore

Dazz,

Well worth reading in detail - might give a few people on here food for thought. Feel sorry for Doris, it weren't her fault. Extra grub to say "sorry" to her ? Still, what you've done will avoid the need for an exorcism ! Perhaps more manufacturers should consider moving controls away from the oil and swarf (fat chance).

Dennis

Found a spare hour yesterday so removed the leadscrew and machinded another 4mm off the front of the leadscrew where it abuts the front bearing block. Then fitted a thrust bearing to the leadscrew , so now both bearing blocks have a needle roller and thrust bearing, reassembled and now i can place a finger on top the chuck and pull it towards me with little effort, whereas before i had to give it a good tug to move it . I can also rotate the chuck by hand with the carrage feed engaged something that no matter how i tried i could not do before.

so with that out of the way i fitted the rocker toolpost i bought, it makes setting the tool a breeze. I then fitted the brass gibs i bought and what a difference they make, smoother with no play in the cross slide or the top slide.

Next on the list is trying to find a replacement motor end cover as mine is breaking up badly and allowing one brush holder to rotate, for now im going to have to try some superglue in the cracks to hold the brush holder in position. Then find a narrow jubilee clip to fit over the end of the cover to hold the bearing as that bits cracked as well.

Was it worh it oh yes the lathe runs smoother,quieter and a cooler. When i can find a bit more time i will take a few pics of the control box.

Stovepipe Dorris is the pup from hell so deserves everytrhing she gets called, i will stick to male dogs in future

Regards

inee

A few photos please forgive the focus as i cant get at my camera so had to snap these with a webcam

View of the top

Front panel with space for an lcd

Internals everything was pushed as far right as possible to allow later fitment of a pcb, although the pics are awful note i reused the connectors for the line filter, also note the warth lead from the mains inlet at rear to the front outlet and also to the forward/reverse switch

Will get some better photos and some photos of the bearings

Regards

Inee

Edited By dazz dazz on 28/10/2012 17:39:40

Hi Daz,

Just tro say lack of comment isn't lack of interest - I'm very interested.

Neil