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Colchester Student Mk1 Won't Start

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Phil Whitley19/01/2020 17:10:30
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1016 forum posts
132 photos

I thought you wouldlike the video, seeing as it has Student roundheads in it! there are several old films about Cochester lathes on YouTube!

Phil

Richard Kirkman 122/01/2020 13:37:11
45 forum posts
47 photos

So, progress has been made

Pc60 just arrived so I've tried it out.

On the 1.5hp switch, after warming the lathe up a bit, it now runs in 400rpm and 600rpm, So definite progress

However, it will still not run in 1000rpm. It just sort of idles at 100rpm and doesn't get enough speed. It takes a few seconds to ramp up to 600rpm, but it does get there consistently now

As far as I know, static converters only give you around 2/3 of the power of the motor.

So, my thought is that the motor is actually only giving around 1hp of juice, which might not be enough to ever get into top speed.

But, when I went to see Phils lathe and had a feel of that, his chuck ran a lot smoother and more easily than mine, and I mean significantly so. But also, Phil mentioned that his bearings are shot and need replacing, but i don't know that that would make it run more easily.

So, my thoughts are that the motor isn't outting enough force in, or that the drive needs too much force for the motor due to some unfound friction issue (whether it be bearings or anything else)

What are peoples opinions on this?

I have found that the belts make a lot of noise and creak quite a bit, unsure how old they are. They seem too small for the lathe as when the motor is fully hinged up they are still tight. Also, one belt is more worn than the other, so travels more when you squeeze one, could this be an issue and should I replace them?

I have spoken to my electronics friend and i am trying to replace the contactor, overloads and lighting transformer, but we just need to find the correct components.

Thanks everyone

Richard Kirkman 122/01/2020 16:57:40
45 forum posts
47 photos

More about the belts, I think they're definitely too small for the machine. Without the belts on the machine, it seems to run much more easily. for example, with the belts on and attached to the motor, I cannot turn the lathe chuck no matter how much effort I put in, On 52 rpm that is. But, when the belts are off, i can turn it with a little effort. Especially on 1000rpm, it's definitely not free spinning, but it

Also, I'm not sure as i don't have any real way to test it, but it feels a bit easier to turn the chuck

It feels like a big enough difference that the belts are causing too much force on the shaft. They have a bit of damage on them too.

Belts are currently 88cm long. So i've just ordered new belts 1m long to allow the hinge some movement so i can actually tension the belt properly ( I hope). And if not, new belts can't do any harm. Ordered from rs components so they should be here asap

mal webber22/01/2020 18:00:30
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122 forum posts
264 photos

Just a thought Richard cant you but one of the gear knobs in between gears like giving you a neutral and spin the chuck by hand so your just checking headstock for free turning.

Mal.

Richard Kirkman 122/01/2020 18:08:33
45 forum posts
47 photos
Posted by mal webber on 22/01/2020 18:00:30:

Just a thought Richard cant you but one of the gear knobs in between gears like giving you a neutral and spin the chuck by hand so your just checking headstock for free turning.

Mal.

Yes Mal, I tried that earlier today. It spins, but I'm not sure how freely it should spin. I will take a video of how it spins in 'neutral' and get back to you

Thanks

Phil Whitley22/01/2020 20:18:16
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1016 forum posts
132 photos

Hi Richard,

Belts are definitely too tight if there is no adjustment available, the weight of the motor is really all you need and there are 4 (5?) of them , vee belts grip the sides of the vee in the pulley and too much tension wears the bearings and the belts! If you could rig some sort of lever/cam system to lift the motor when starting, acting as a clutch, you might get top speed, but no matter really, the top speed is not neccesary , we are not on piece work!

Common way of testing the spindle bearing tension on machines is to wrap some string round the chuck, fix one end in the jaws, and attach the other end to a spring balance, and see how many units of pull it takes to turn the chuck, then ,knowing the radius of the chuck you can work out the torque required, as in this thread, about halfway down the page.

https://www.model-engineer.co.uk/forums/postings.asp?th=106932

I could do a comparison on mine if you like.

the speedchange on the fromt of the headstock has a centre heutral position where just the spindle is turning. Have the belts been fitted too tight and the input polley bearing damaged, turn the pulley when the belts are off and check for any axial play.

I think it is a bit of a tall order to expect your phase convertor to pull top speed, , even in the days when I dare use mine flat out, there is a lot of gearing to overcome, and the motor definitely ramped up the speed, and that is proper 3 phase with a 3hp motor!

Good luck,

Phil.

Richard Kirkman 122/01/2020 20:59:01
45 forum posts
47 photos

So, this is what trying to turn the chuck is like in neutral and in top gear without belts attached

I still think that it's quite stiff and should rotate more than it does, especially compared to how free Phils lathe was, but please tell me what you all think too!

Test video of neutral and top gear

I know full speed may not be necessary, but it would be nice to have full functionality from the lathe

There are only 2 belts, not sure what you're on about with 4 or 5.

It's not just top speed, it takes a long time for it to ramp up to 600rpm even then.

If you guys think the spindle bearings may be an issue, I can still contact the person who is tearing their Colchester to pieces and try to get their spindle bearings if they are better

Phil Whitley23/01/2020 10:10:10
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1016 forum posts
132 photos

Hi Richard. 4 or 5? I was thinking Covmac, try turning the lathe from the input pulley with the with the spindle in neutral , then put it into top speed and try again, and you are feeling the resistance the motor feels when it trys to start in top gear. Some students were supplied from the factory with single phase motors, but they always had a Matrix clutch fitted in order to allow the motor to get up to speed before loading it up.

Phil

Edited By Phil Whitley on 23/01/2020 10:10:49

Ian Parkin23/01/2020 10:21:53
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704 forum posts
181 photos

Richard

I would say that my student is very much like yours with regard to spinning the chuck in neutral

Mine has a 3hp motor driven by VFD also with a matrix clutch

if yours has only a 1.5hp driven by a converter i'm not suprised you cant get top speed and long run ups to even half speed ( 600rpm)

You are welcome to come over and have a look at what a student with vfd can do ( sheffield)

Ian

mal webber23/01/2020 21:32:40
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122 forum posts
264 photos

Hi Richard,

just looked at the video and my MK 1.1/2 is the same except mine is harder to turn in the lower gear ,if anything a bit louder noise from the head stock but not much.

Mal.

Richard Kirkman 123/01/2020 23:43:07
45 forum posts
47 photos

So, new belts arrived today, wrong size, don't ask. Measure twice, order twice. I was sure I had them right!

Anyway, correct belts ordered and should be arriving tomorrow, not that they will make much of a difference. Although I have gone for a SPA belt rather than the original measurement as more surface area should be good, and the belts I ordered that arrived toady were SPA and the shape fit the pulleys better than the ones that were on already.

I checked the lathe spinning in neutral from the pulley and it seemed fine from what I can tell. If Ian and Mal seem to thin theirs are similar then I suspect I'm fine with the headstock bearings and such.

Lathe revolution in neutral from pulley with no belts

When I purchased the lathe unseen, the description did say that the headstock was noisy, but now its been drained and the oil replaced, I didn't think it was very noisy. Definitely not silent, but not bad at all, especially with the part replaced that needed to be.

Ian and Mal, thank you for replying to the thread, It really has helped me to know that my bearings aren't shot(or are just as shot as yours), so I can proceed with other problem areas.

I am still struggling to size the correct contactor, overloads and transformer for the machine. I can worry about top speed later, but the loud humming coming from the electrical panel is concerning. I do not like it. And it is a loud humm, not a small one. It needs replacing before I reattach the coolant pump, since the coolant box is now welded and properly painted.

Then we can look at changing the pc60 into a rotary. What size three phase motor would I need for that, as it is better to start looking for cheap second hand three phase motor asap, as they come up every now and again?

Thanks again

mal webber25/01/2020 10:41:41
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122 forum posts
264 photos

Hi Richard

With my student [3hp] using the pc 60 when all phase switches are on the machine hums but with just the first two on it runs with out any humming and runs good so does the mill [2hp] ,not sure why it hums with all switches on and not really concerned because both machines run well on the first two ,as for power loss the lathe and mill can take bigger cuts than i would ever want to do on a regular basis .

When you mention about the rotary converter and what size motor to decide on and after reading Ian's post why not just exchange your 1.5hp motor for a 3hp one which will run of the pc 60 , Richard I know nothing about 3phase electrics just going off what set up i have.

Watched a you tube vid on a guy doing a rotary conversion with a pc60 and in the end it would not start his machine and ended up plugging straight in the pc not sure what that was all about.

Easy DIY Rotary Phase Converter Build (Off Grid Three Phase Hydroelectric Power)

Mal.

Emgee25/01/2020 11:15:52
1355 forum posts
212 photos

Richard

The hum from the contactors could be because the pole faces have rusted/corroded, this prevents them closing 100% and hence the noise.

Emgee

Howard Lewis25/01/2020 11:30:28
2747 forum posts
2 photos

Trying to turn the chuck, by hand, with low gear engaged will be harder than in high gear, because you are trying rotate everything in the drive train, back to the motor, faster than the chuck.

If you have changed the oil, and the gears are quieter, this is good, but presumably it was the right grade of oil? If the oil is too high a viscosity, the drag will not help your problem.

having, hopefully got belts of the right length and section, have you checked the alignment of the pulleys?

Have you tried running up the motor without the belts, in case that is reluctant to ramp up quickly, (Has it some fault? )

The devil is in the detail.

Howard

Edited By Howard Lewis on 25/01/2020 11:31:46

Richard Kirkman 125/01/2020 22:32:45
45 forum posts
47 photos

Mal, Yes I've looked at replacing it with a 3ph one, would be about £130 so not too bad, but we'll see. Back off to uni tomorrow so don't need to worry about it till April. Phil posted a link to that same video a while ago, It looks alright, but i'm not sure what he's done. The general idea is there I think, but who knows. Actually, just found a man selling a 3hp 4 pole three phase on gumtree for £50 so I'll get that and we can see

I've talked to my dad so much about motors and things and now he's said to me that we could get the electricity company to reconnect the three phase power supply to the house, since we used to have it from storage heaters. He's saying he wants to get three phase now so the house could potentially have a super fast car charger or something, which might make the house seem more appealing if or when ever they move.

So, faffing around completely, however It will be much cheaper. So after all that rubbish, I'll need to return the pc60 which will be a nightmare since it weighs so much.

Howard- I have changed the oil, I made sure to use the stuff specified in the manual, or at least the modern equivalent since shell tellus stuff is no longer available. The motor runs fine without the belts on. I think I bought some new belts the right size, but I think I've bought the wrong size twice. The lathe seemed to run much more easily on the old belts. I will sort it out

Emgee-You could be very right, the contacts are not clean at all, I tried to give them a good clean with some sandpaper, but they're worn convex so I just gave up. The contactor will be replaced soon anyway so I think it'll be fine, but thank you for telling me why it could be buzzing

Tried some threading today, quite enjoyable, but the cheap chinese carbide threading tool I used was not providing good results. Took me a while to figure out the process, but since it was metric, had to leave the half nut engaged, but still just a good bit of fun before uni.

Threading video

img_20200125_183605.jpg

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