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View Full Version : colchester student: no 3.5mm threads?



Tony
03-28-2012, 05:24 PM
had to cut an M30x3.5 and was stopped in my tracks.. no 3.5!

I could cut a 7 TPI which is about 3.6mm -- think I could get away with
that? Thread length is about 1".

Tony

rohart
03-28-2012, 06:08 PM
My Bantam manual shows that the metric version does it easily, and the imperial will do both 1.75mm and 3.5mm using 49 and 36 tooth change gears. I'm surprised the Student is less versatile than the Mk 1 Bantam.

If this is for a chuck mount, then even though some looseness is OK, because you just register on the clamping face, a 7 tpi thread will register on virtually one point until it wears. I would try to work out some different change gears.

For example, my metric Bantam doesn't list for 13 tpi, 19 tpi or 26 tpi, which to my mind are pretty important threads. I found it fairly straightforward to work out some different change gear pairs to complete the task, even though this meant bringing in 39 and 57 tooth wheels. 3.5mm will need a factor of 7 somewhere compared to 3mm or 4mm.

Tony
03-29-2012, 09:04 AM
Thanks Rich.. was mainly venting. Makes one wonder what kind of world
we live in when you can't just expect your 50 year old English-made imperial
lathe to cut any metric thread you want. :D

Or maybe the previous owner took out the 3.5 when I asked for a better price.

In this case I can switch to a diff pitch as I have to make the nut, too..
but 3.5 is such a popular thread. Maybe it didn't used to be.

Tony

Stuart Br
03-29-2012, 09:22 AM
My imperial Chipmaster, doesn't show 3.5mm using the standard box either...

rohart
03-29-2012, 03:55 PM
I must say that I've never come across a 3.5mm thread before. My Lorch, and the early Emco Maximats, used 39mm x 4mm. That was a b.... to cut on my Lorch.

But you're quite right. If you can't trust post war Britain to produce multi-standard lathes, well, whatever next ? 21st century computers that can't network with legacy printers ? Never !

Anyway, I still haven't got all the change wheels for my Bantam collected. I carry around a list of 'things I need' in my wallet. You never know.

mike os
03-29-2012, 05:11 PM
no 3.5 on my box either...

hareng
03-29-2012, 06:37 PM
Looks like three gear boxes used on these. Dual English/Metric, Dominion English only and a Continental with joystick control.

Joystick model needs 24T driving the 120T in turn driving another 24T for 3.5mm and above.

Should have bought an Harrison:)

John Stevenson
03-29-2012, 06:49 PM
Tony,
What model Student ?
round head, square head UK or UK model and I presume quick change box ?
Makes it hard to guess as you have no location listed.

aboard_epsilon
03-29-2012, 07:02 PM
I'm confused here.

i would have thought if it cuts 1.75 pitch

its just then a matter of setting it for that with the change wheels and setting the Norton box up so that it doubles it.

i think he's in Italy john

all the best.markj

Paul Alciatore
03-30-2012, 03:28 AM
I found some photos of your lathe on the internet and the QC box chart shows 21 and 42 tooth "driver" gears are used for the chart. Do you have any other driver gears and if so what are their tooth counts? Also, please post a photo of your chart as it may differ. I/we can attempt to find a combination of driver gear and setting to cut your thread.

Black Forest
03-30-2012, 04:51 AM
You see Tony you should have bought a German lathe and I could have brought it to you!

My Russian Stanko lathe will cut 3.5mm threads no problem. I just checked to see if it was on the selector lever and it was there.

oldtiffie
03-30-2012, 05:23 AM
Thanks Rich.. was mainly venting. Makes one wonder what kind of world
we live in when you can't just expect your 50 year old English-made imperial
lathe to cut any metric thread you want. :D

Or maybe the previous owner took out the 3.5 when I asked for a better price.

In this case I can switch to a diff pitch as I have to make the nut, too..
but 3.5 is such a popular thread. Maybe it didn't used to be.

Tony

As you have choice of what to use for the screw and the nut - why not use a pitch of 4mm - or for a smaller (lead-screw) lathe a 3mm pitch.

Tony
03-30-2012, 09:07 AM
Its the old roundhead, just like its owner. Mk1.5 .. i think its a
"Colt" -- gap bed with dual gearbox.

Yes, I only have those two changegears.

Here's the chart.. tried to make it easier to read.. hope it works:

http://img.photobucket.com/albums/0903/knucklehead/ColchesterThreadPlate.jpg

Tony

aboard_epsilon
03-30-2012, 01:18 PM
Cant see 1.75 on there ...and 1.75 is very common on 12mm bolts

maybe the chart is, of threads it just happens to be able to cut with the standard change wheels that come with it

as indicated by the statement "when using 42 driver gear"

is the lathe imperial or metric .

you normally need a 127 tooth gear wheel to go from imperial to metric .

maybe there is more info in the manual.

all the best.markj

Tony
03-30-2012, 01:30 PM
The lathe is imperial.
No mention in the book of other change gears / combinations / threads.

This is really only one big drive gear in the back.. and a small driver.. either
21 or 42, both of which I have.

Everything you see in the chart is built into the tumbler / gearbox.

aboard_epsilon
03-30-2012, 01:52 PM
Have you joined

http://groups.yahoo.com/group/ColchesterLathe-User/

that's where the most information will be

all the best...markj

Hood
03-30-2012, 04:01 PM
The lathe is imperial.
No mention in the book of other change gears / combinations / threads.
The manual I got with mine tells you change gears are available for pitches not available with the gearbox and tells you how to work them out.
Whether you can still purchase the gears I dont know, whether you would want to when you got told the price I probably do know :D
Hood

John Stevenson
03-30-2012, 04:10 PM
The lathe is imperial.
No mention in the book of other change gears / combinations / threads.


Everything you see in the chart is built into the tumbler / gearbox.

Got to be different gear setups because left hand column, levers C B it says 60 tpi or 0.5 mm pitch.

Same for levers D A 30 tpi or 1mm pitch.

One position can't do both.

Timleech
03-30-2012, 04:35 PM
Got to be different gear setups because left hand column, levers C B it says 60 tpi or 0.5 mm pitch.

Same for levers D A 30 tpi or 1mm pitch.

One position can't do both.

I used to have a 'square head' MkII Student, not much different mechanically from the round head. I think there was a metric/imperial selector, I do remember that the range of metric pitches was a bit deficient.

Tim

Tony
03-30-2012, 04:36 PM
well look what I found.. just the craziest "formula" ever made. especially
since you can't really "solve" for anything. if you rearrange so you have
X*Y (to at least figure out what the product should be), you end up with
a decimal you can't get by multiplying whole numbers.

Halfway through it reads: "if the values selected give impossible numbers try other values and continue doing so until... you give up and just cut a different thread"



http://img.photobucket.com/albums/0903/knucklehead/ColchesterThreadPlate2.jpg

Tony
03-30-2012, 04:38 PM
John, there's another lever lets me toggle "english / 0 / metric"
"0" stops the lead screw a'spinn'n.. lets me pick between the two
rows you see.

You'll see in the chart to "CA" entries.. thats where I need to switch gears.

Timleech
03-31-2012, 03:30 AM
I think you need a 49 tooth driver gear, on the 1.5mm setting.

3.5/1.5 x 21 = 49.

I've tried some of the other metric settings, they bring up fractional teeth.

Tim