colchester threadcutting

[whensparksfly]

i have a colchester student 1800 i want to learn how to do threadcutting
i have tried it before the problem is it will cut a thread but it wont be the right one for example how would i cut a 8mm 1.25 thread i must be reading the chart wrong any help with this would be great

 

[Wedg1e]

I have a Student Mk2 so the gearbox is probably different: can you directly select that pitch on the 'box? If so and it cuts it wrong it probably has an incorrect gear in the drive 'chain'. For example, my Boxford has 20 and 50 tooth stud gears, some threads are only correct if the 20T is fitted and some with the 50T.
On the Student Mk 2 it's so many with the 42T stud gear and the rest with the 21T gear.

 

[whensparksfly]

i looked at the chart on the machine and checked it looked to be right for the thread i was cutting but im not sure

 

[Flathead_Dave]

What pitch is it cutting instead of 1,25?

 

[madkayaker]

On the master and the student I trained on there was a chart on the head stock telling you what the setting were and the start number. Then you set it all up and start on that number even if it's before the stock to be cut, cut away till the end on the feed (different handle from normal) and when at the end you have to stop the feed and pull the tool out at the same time

 

[whensparksfly]

there is a top and bottom handle on the carage i never figred how the top handle works ?http://www.mikehow.com/images/Colchester_Student_1800_-_1_575.jpg

 

[ronan]

there is a top and bottom handle on the carage i never figred how the top handle works ?

top handle on the apron is the power feed lever, there should be a knob you push or pull in or out , for x-axis feed the knob should be in , or for cross feed the knob should be out.
the bottom lever is the threadcutting lever, the chart on the head stock should tell you all you need to set the gears up correctly. can you post a picture of the charts ?

ps. just seen your picture , are you putting the lever on the left to "c" or the lever on the right to "v" depending on the pitch you want ? also are the gears connecting the screwcutting gearbox in high or low according to the little drawing on the top left of the chart ?

 

[awemawson]

There are iirc three additional change gear combinations within the left hand belt cover. They are illustrated on the chart but rather obscurely - you need to find out which combination is installed as it totally changes the threads cut. Usually the alternative sets are not still with the lathe as they've been lost over the years.

 

[snowcat]

Older Colchesters have a metric Imperial change handle, and then 2 graduated slides and a change gear in the back IIRC, the more modern machines have a twisting set of handles with letters on them, On the chart along with the settings it will also have which change gear needs to be in, again IIRC theres one thats only used to cut really course threads..

 

[Engineer1964]

Just found this on You Tube

http://www.youtube.com/watch?v=d1ZBTJUFheE

 

[whensparksfly]

i was using the bottom lever which is for machine.
it is the top lever that is for thread cutting.
my problem is that when Engaged the power feed the leadscrew is turning coming out of the machine but it dose not turn the leadscrew shaft

 

[wyn]

I don't have that particular lathe but on the one i have the screw cutting shaft has a sort of clutch on it. This is on the end nearest the gearbox...it needs to be pushed towards the gearbox to engage it.

 

[whensparksfly]

i found out what wrong the leadscrew has a pin that joints it to the gearbox drive the pin was broken.thanks for everyones help

 

[awemawson]

Shear pin it's called - saves breaking more expensive parts if you crash.

That video shown above is very bad practise - the bar is overhanging from the chuck much too far without support - it should either be supported by a centre in the tailstock or use a travelling steady on the saddle. If you watch closely you can actually see the bar deflect in a few places on the video!

 

[Wedg1e]

Jesus, why oh why do people have to put music (usually cr&p music) on every bloody Youtube video?