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Threading on Colchester triumph 7 1/2

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sean logie10/10/2019 11:04:36
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590 forum posts
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img_20191010_104106.jpgBeen trying to cut threads on this old girl for a while, think I'm missing a gear and I'm hoping someone can help me out. Also I need to know the age of the lathe, is this possible from the serial number.

Thanks

Sean

Ian Parkin10/10/2019 11:08:30
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You should have a 21 tooth to replace the 42 tooth one

as set you can do the bottom row of threads on the chart ( the coarsest ones)

Thor10/10/2019 11:09:57
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Hi Sean,

There are some Colchester serial numbers available here.

Thor

sean logie10/10/2019 11:32:28
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Posted by Ian Parkin on 10/10/2019 11:08:30:

You should have a 21 tooth to replace the 42 tooth one

as set you can do the bottom row of threads on the chart ( the coarsest ones)

The big idler in the middle doesn't appear to move vertically only in a left to right arc.

sean logie10/10/2019 11:33:53
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590 forum posts
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Posted by sean logie on 10/10/2019 11:32:28:
Posted by Ian Parkin on 10/10/2019 11:08:30:

You should have a 21 tooth to replace the 42 tooth one

as set you can do the bottom row of threads on the chart ( the coarsest ones)

The big idler in the middle doesn't appear to move vertically only in a left to right arc.

My apologies sir I missed where it can move up and down

Alan Waddington 210/10/2019 12:57:38
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87 photos

Have a nice Ainjest high speed threading unit to fit that lathe if you are interested ? Makes thread cutting so much easier.

Andrew Johnston10/10/2019 14:06:23
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+1 on an Ainjest unit.

I've got an imperial unit, on an imperial lathe, and it makes cutting imperial threads a doddle, even into blind holes like these 3/8" BSP glands:

screwcutting_bsp_me.jpg

Once I'd got the DOC sorted it was four passes and about a minute per gland at 260rpm with 4 thou clearance at the back.

Andrew

sean logie10/10/2019 15:46:22
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590 forum posts
90 photos
Posted by Andrew Johnston on 10/10/2019 14:06:23:

+1 on an Ainjest unit.

I've got an imperial unit, on an imperial lathe, and it makes cutting imperial threads a doddle, even into blind holes like these 3/8" BSP glands:

screwcutting_bsp_me.jpg

Once I'd got the DOC sorted it was four passes and about a minute per gland at 260rpm with 4 thou clearance at the back.

Andrew

Hi,Andrew,

What change gears do you run for metric. All I have are the 120T,42T and 36T which don't work for unless I've missed something on setup. Leadscrew is a 4Tpi. Serial No of lathe is 4/46477.

Any help would be appreciated.

Regards

Sean

Andrew Johnston11/10/2019 09:45:23
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5555 forum posts
650 photos
Posted by sean logie on 10/10/2019 15:46:22:

What change gears do you run for metric.

I don't; both imperial and metric threads are built into the gearbox, although being an imperial lathe the metric threads are an approximation. As standard the manual recommends keeping the half nuts closed when cutting metric threads.

So in theory I can't use the AInjest unit for metric threads. One can get a unit called a Travadial that essentially tracks distance travelled along the bed allowing one to cut metric threads with the Ainjest unit. However, it is not exact and the errors accumulate with number of passes. Should I ever need to cut any significant number of metric threads I'd add an encoder to the spindle, and a bedstop, so I can reset the saddle to the same place and also reverse the spindle such that the spindle to leadscrew alignment is also reset.

Andrew

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