Colchester change gears?

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Colchester change gears?

This topic has 9 replies, 6 voices, and was last updated 4 October 2023 at 22:35 by Niall Mccafferty.

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6 April 2016 at 17:43 #8088
Alex Cork
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@alexcork37078
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6 April 2016 at 17:43 #233555
Alex Cork
Participant
@alexcork37078
Hi.

I recently upgraded from a boxford to a student mk1. I tried to cut a 12tpi thread the other night and the thread is nothing like 12tpi. I have checked the gearbox settings again and again and I am positive that they are correct. The only thing I am unsure about is the changewheels in the back of the lathe, it came with some gears still in the original packaging. So my question is; what changewheels do I need in a mk1 student to achieve the imperial threads marked on the gearbox? Thanks Alex.
6 April 2016 at 17:56 #233556
Ian Parkin
Participant
@ianparkin39383
From memory a 21 on the output shaft from the headstock and a 42 on the input shaft to the gearbox
6 April 2016 at 20:39 #233581
Clive Foster
Participant
@clivefoster55965
Sorry Ian, by my reading of the manual that is the wrong set-up which is what Alex probably has.

Standard set up is driver 21 teeth, intermediate 120 teeth, gearbox driver 35 teeth. The 42 teeth gear normally sleeps on the gearbox shaft outside the 35 teeth gear doing nothing. Swopping the 21 teeth driver for the 42 teeth gear gives an extra 9 thread TPI / pitches additional to the standard range of 36. Basically it halves the TPI on any setting.

Usual reason for odd threads is that the 42 tooth gear has been used on the gearbox input shaft instead of the 35 tooth one. That makes the end train gear ratio 0.5 instead of 0.6 which will make any screw-cut thread "really odd" but isn't far enough out to be immediately obvious before you start.

Clive
6 April 2016 at 21:23 #233592
Ian Parkin
Participant
@ianparkin39383
Yes clive i remember now

I have converted my lathe some time ago to belt drive and my ratios are 24 to 40 and place a 48 on the headstock end when i want the fast threads 4,5,6 tpi

sorry for my crap memory
6 April 2016 at 21:32 #233593
Clive Foster
Participant
@clivefoster55965
No worries. 21 going down to 35 always seems odd. Especially if you've not got the manual. Somehow one expects a factor of 2 when driving for TPI. Not having a Colchester I had to cheat by reading the manual!

Clive.
7 April 2016 at 21:03 #233712
Phil Whitley
Participant
@philwhitley94135
Hi Alex, I have a Colchester student manu8al on PDF if you would like one, phil dot hermetic at langtoft dot net.
9 April 2016 at 20:52 #233935
Alex Cork
Participant
@alexcork37078
Hi, Thank you all for the replies. I have been into the workshop and managed to make a real mess!

I have the 42 tooth gear, the 120 tooth gear and a 33 tooth gear. 33 was close enough that I thought I had managed to cut a 12 tpi thread. When I tried to use the thread dial things went badly!

I then read Clive's post and realised my mistake. I will have to try and track down a 21 tooth and 35 tooth gear. I am suprised that they are not with the lathe.

Phil, thank you, I will send you an email.

Thanks Again,

Alex
5 June 2016 at 15:03 #241518
Edwin Bee
Participant
@edwinbee45058
Hi Alex, I actually have a 35Tgear that you can have, and I need a 42T. If you would like to I would be very happy to make a swap. Either way, you can have the 35T.
4 October 2023 at 22:35 #662912
Niall Mccafferty
Participant
@niallmccafferty49121
Hi all , i need 120t and a 35t change gears , i can do without the 42t , but at the moment have done quiet a bit of work to get my auction buy ( hence missing bit) up and running and reliving my trading center youth. i can turn now but would love to have auto feed and sure once i have that i’ll want to thread something as well . apart from missing these gears i have a good machine

any help much appreciated
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