Colchester Student 2500 (Harrison M300)

Hi all,

Having recently acquired a modern type Colchester student (1997 vintage) I have noticed I'm missing the thread dial pick gears except the 16 tooth one that's mounted on it.

The other gears are 14T, 18T, 20T, and 22T.

Other than the 600 group (probably a fortune) does anyone have any or know where to get any?

Cheers

Damian

eBay?

Edited By David Standing 1 on 05/06/2018 19:08:52

Presumably the lathe is metric, rather than imperial where you only need one gear? Assuming metric I'd agree with David that Ebay is your best bet, albeit not a very good one. Thread indicators for the M300 seem to come up every now and again, but I've never seen just the gears. Alternatively you could make them. Technically I think they need to be helical gears, but I expect you could get away with straight cuts at the helix angle of the leadscrew.

Andrew

Technically I think they need to be helical gears, but I expect you could get away with straight cuts at the helix angle of the leadscrew.

I don't think they are that sophisticated, from memory of stripping the TDI down to un-sieze it on the Harrison M330 at work - I think they are straight cut from thin plate. I can drop them off tomorrow to measure up / photograph if that would help ?

Nigel B

Doesn't the Student have a motor reversing switch? So no need for thread chaser dial. Just leave halfnuts engaged, withdraw tool and hit the reverse switch until tool is returned to starting point. It's generally quicker and easier than using the chaser dial.

Failing that, you  coiuld make your own gears out of something like 1.5 or 2mm thick brass plate. Tooth profile does not have to be true form involute etc as no power is being transmitted. Each tooth in effect is a place saver just to hold the dial in the right place. Teeth on the gears could be cut with a simple fly cutter ground to about 30 degrees included angle, or slightly rounded to give a small degree of "involuteness".

Edited By Hopper on 06/06/2018 08:35:04

They are helical albeit very slight.

Somewhat blurry picture of the M330TDI - pretty certain these are straight cut. The bottom (engaged) gear shows wear due to the thread helix angle. The M330 is close to the M300 - vari-speed headstock rather than step gears - the apron appears to be the same as the M300 at my last employment. The gears are 3.2mm thick.

Nigel B

Buy Ivan Law's book, and cut them yourself. If you have a shaper, well, even a lot more fun!

Hi Damian,

As several others have suggested, make your own gears, it isn't that difficult. On my 290 lathe I made an extra gear to cover thread pitches not covered by the original Thread Dial gear. I used Delrin and it has worked well for several years, the width of the Delrin gear wheel is the same as the original supplied with the lathe Thread Dial, the diameter is different of course.

Thor

Indicator gears are zero stress and zero precision. You can almost cut them from a piece of plastic food container with pinking shears. Just make a simple flycutter to a suitable shape and cut them from thin brass sheet that way it will never wear the leadscrew so it doesn't matter that it is rough and ready profile.
You will never see them on ebay alone as why would anyone want to strip a whole unit they could get serious money for.
You can also try 3D printing a whole unit. Think there is something the web about doing one for some lathe.

Thanks all for the replies

Great picture Nigel

I have some 4mm brass sheet so will go with making some. At least the dividing head will get some use on the little mill.

The originals will have been lost due to a careless previous user of the lathe. I'm in the process of a strip down and clean so the lathe is in bits.

I did know it would be a long shot finding them on their own. There are some on ebay but they are odd numbered ones.

Damian.

This is the Thread Dial Indicator off mine.
1 off 16 tooth slightly helical.
Works for Metric and imperial i change nothing.

Thats what i have just figured out.

Mines an ex GKN painted horrible green, dont care its a tool. Its an early one 70's lead screw may be imperial never bothered to check since it good for metric and imperial with no faffing about with change wheels, literally dial any pitch in via 4 knobs nothing more to it.
I do have to power out on metric to retain the meshing unlike my old 60's Harrison 140 could disconnect feed and wind back then engage for metric only.

I'll have another check tomorrow got to do a 19TPI my mate cant on a Harrison 11" and asian Colchester copy.