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Colchester Master 2500

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Alan .20417/11/2018 15:32:53
304 forum posts
14 photos

Ive changed my lath now I’ve a Colchester Master 2500, it’s seams ok apart from one thing, when threading somthings not quit right, it’s a metric machine so when I set up to cut any metric thread I should be able to use the thread dial but for some reason the machine is not dropping back on the thread in the same spot each time, something else is if you put a bit of pressure on the handle when engaging the lead screw it will stop the lead screw and the drive bar from turning, I was wondering if there is some sort of adjustment needed, I’ve tried different pitches and tried using the same number but it still does it, if I leave the lead screw closed and revers the lathe it stays as it should, any suggestion chaps.

Regards Alan.

Ian Parkin17/11/2018 16:51:20
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626 forum posts
169 photos

Sounds like your safety pin has broken

Alan .20417/11/2018 16:58:49
304 forum posts
14 photos

Thanks Ian, would that be the shear pin on the end of the lead screw ?

Alan.

Ian Parkin17/11/2018 17:16:04
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626 forum posts
169 photos

well on my Colchester lathe (earlier than yours) its on the first gear drive next to the spindle

Ian Parkin17/11/2018 17:17:28
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626 forum posts
169 photos

Just take the end cover off and use the lathe ....trying to stop the lead screw turning as you described ....you should see where its broken

Edited By Ian Parkin on 17/11/2018 17:18:01

Chris Evans 617/11/2018 17:38:27
1442 forum posts

The shear pin is a regular fail point. I used to use a Triumph 2000 which is similar, even with the Ainjest rapid threading attachment I could not rely on "dropping in" on the thread dial, I just left things engaged and reversed the lathe.

Alan .20417/11/2018 18:03:16
304 forum posts
14 photos

On this machine the pin is at the start of the lead screw, but the pin is in one piece, what I don’t get is if you put pressure on the threading handle the lead screw and the drive bar stop moving, I’ll check the gear train tomorrow to make sure it’s correct, what it does is when you reengauge the lead screw it is starting in again forward of the last cut, not by much but you can see it creeping forward on each pass, the lathe does not stop quick enough for me to want to keep the lead screw locked and then reverse, need to find the problem.

Alan

John MC17/11/2018 18:20:52
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168 forum posts
24 photos

Are you sure various levers (that select the thread/feed) are properly engaged?

There really is no need to use the thread dial on these lathes, as CE6 says, use the clutch and the foot operated brake, that to me is a major positive feature of the lathe.

John

Alan .20417/11/2018 18:43:53
304 forum posts
14 photos

Yes John the levers are in the correct position as what ever metric pitch I chose it’s correct when I check it with a pitch gauge, I have to politely disagree with you on the not using the the thread dial as that’s what it’s for, I’ve cut hundreds of threads on my bantam lathe using the thread dial so that’s how I prefer to thread, there’s something wrong somewhere so ignoring it doesn’t fix it, I do leave the lead screw engaged on the bantam when cutting metric as it’s an imperial lathe, but on this metric lathe I shouldn’t have to ?

Cheers Alan.

SillyOldDuffer17/11/2018 19:05:32
4527 forum posts
971 photos
Posted by Alan .204 on 17/11/2018 18:03:16:

... but the pin is in one piece, what I don’t get is if you put pressure on the threading handle the lead screw and the drive bar stop moving...

Alan

When my shear pin broke it left the two ends in place and everything looking fine. And there was still enough friction from the broken ends bearing against the sleeve to turn the leadscrew,. All seemed normal except it slipped under load, which sounds like your symptoms.

More of a drama than a crisis but it was a bit of a pig to fix on my lathe. I hoped to get the broken pin out and replace it without any dismantling. Nope - I had to release the other end of the leadscrew and pull the whole thing out of the sleeve with the pin stuck inside. Only then was the broken pin knocked out easily, leaving me to put the lathe back together and re-align the leadscrew...

Dave

Alan .20417/11/2018 19:16:39
304 forum posts
14 photos

I pulled the pin out Dave it’s about 12 mm long I think it seemed ok but I’ll have another look tomorrow, I still don’t get why the drive and the lead screw stop turning if I put a bit of pressure on the lead screw lever ?

Alan.

Andrew Johnston17/11/2018 21:05:58
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4710 forum posts
532 photos

I hesitate to say, but on a metric lathe the metric thread dial indicator has a stack of gears, unlike an imperial lathe which only has one. So as well as using the TDI in the normal way you need the correct gear selected for any given pitch.

Andrew

Alan .20417/11/2018 21:22:35
304 forum posts
14 photos

The levers on the head stock are in the correct position, do you mean the threading dial itself, also have you any idea why when the lathe is running if you press the thread lever right down it stops the lead screw and the carriage drive, could you explain a bit more in-depth please Andrew.

Alan.

Alan Waddington 217/11/2018 21:59:18
436 forum posts
86 photos

Alan, have you removed the lathe end panel and checked that all is well with the change gears etc.

The whole gearbox and in turn both lead screw and carriage drive are fed from there.

Have had both shafts out of my student 1800 in the past, but for the life of me i can’t remember how they actually picked up the drive from the gearbox

On my old Harrison you had the option of stopping the shafts driving by turning a knurled sleeve where the shafts entered the gearbox, but fairly sure they are not present on the Student.

Unfortunately i cant get to my lathe at the minute to inspect.

May not help but here is a cutaway of the gearbox

**LINK**

Andrew Johnston17/11/2018 22:59:28
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4710 forum posts
532 photos
Posted by Alan .204 on 17/11/2018 21:22:35:

The levers on the head stock are in the correct position, do you mean the threading dial itself, also have you any idea why when the lathe is running if you press the thread lever right down it stops the lead screw and the carriage drive,

I mean on the DTI itself. The problem with metric threads is that the pitches are not simply related to each other over a fixed length, unlike imperial. Rather than have awkward size gears in the screwcutting gearbox it is easier to have a range of gears on the DTI. They're usually on a spindle under the DTI and you pick the one you need and fit it to engage with the leadscrew. I believe that 6 gears are needed to cut the entire metric range of pitches. The manual for my lathe (Harrison M300) indicates that the metric version DTI has only 5 gears available, so in general will only cut limited range of pitches less than 1mm.

Here's a link that explains it better than me, quite a way down the page under "Metric Threads":

**LINK**

I have an Ainjest high speed threading unit fitted to my imperial lathe. It's simple to use; one setting for all integer TPI values. Interestingly the manual shows that the metric version is also rather more complex, having a 5, 6 or 7 position selector gearbox in addition.

I'm not sure about the problem of the drives stopping. I'll have a think before we talk tomorrow. It's a bit risky to try but can you stop the leadscrew or feed shaft by hand without using the threading lever? To be safe try pressing on them with a lump of wood.

Andrew

Ian Parkin18/11/2018 09:57:05
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626 forum posts
169 photos

As i said earlier

if you take the end cover off and defeat the safety microswitch if there is one

run the machine and use the half nut lever to engage and as you say stop the lead screw and drive shaft.

it will be obvious where the problem lies

if the whole gear chain stops the problem is at the headstock

if it stops but the shaft that the first gear runs off still spins its a shear pin there ( like earlier cols)

if the gears run but the input shaft to the gearbox stops its a shear pin there

if everthing runs its a problem within the QCGB

Alan .20418/11/2018 19:30:24
304 forum posts
14 photos

Getting there, I wrongly assumed that with the lathe being metric I could use the thread dial the same as I would on my imperial bantam, however as Andrew kindly pointed out that it minght not be quit that simple, I read the link He posted and it made sense, so this morning I looked at the thread dial on the lath and sure enough there are five more gears to alter to the give pitch you require, so I took it of the lathe and stripped it, washed the parts with some break cleaner, ( I don’t think it’s ever been used from new ) fitted it back on the lath, I should have said there’s and data plate I didn’t see that’s showed how to set it up, I cut a 1.75 m12 thread with no problem, happy days thanks Andrew, now for Ian, your advice was also spot on Ian, the shear pin on the lead screw is ok, so I did what you suggested and took the end cover of the gear train, when I press the lead screw handle with a bit of pressure it stopped the lead screw and the drive bar, the bottom gear which turns the lead screw keeps turning on the shaft, I haven’t been into it yet but it could be a brocken key way ? Hopefully tomorrow I’ll find out.

Thanks again chaps, don’t know what I would do with out you.

Regards Alan.

Alan .20403/12/2018 21:35:12
304 forum posts
14 photos

Thanks for the advice Ian I finally found time to pull the bottom part of the gear train of and sure enough there it was another shear pin, but this one was in to half’s so I made a new one quick sharp 3mm x 11mm I think it was, now everything’s working as it should, just have to get used to working in metric but so far so good.

Thanks again chaps, Regards Alan.

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