Colchester Bantam Mk2 mech control linkage to fwd/stop/rev motor switch

Hi friends and hello ,

I am a new entry as I have just retired from a marine engineering career. I am in the process of restoring a dilapidated 1978 Colchester Bantam Mk2 2000 lathe that I hope to use for leisure home and hobby use.

I have partially rewired the lathe and now have the Dahlander 2 speed motor running correctly in high and low range and also running fwd and reverse correctly. But only partially safely due to a problem with some missing parts. The cam operated tumbler linkage mechanism that connects the lever operated main control rod linkage has been partially removed with the central “Y” tumbler plate fixed directly onto the small square switch shaft of the rotating fwd/off/rev switch.

This tumbler linkage assembly was used to make and then break the circuit to the main contractor operating coil between contractor terminals A1 and A2 during the lever operation from the Stop to Fwd and vice versa Stop to Reverse. This allowed the motor contactor to operate and close using the 110v coil circuit supplied by the fwd/off/rev switch supply. At the end of the operating lever travel this 110v circuit was then broken by the tumbler action however the contactor then still remained closed due to an additional 110v supply available now from the additional now closed contacts 13 & 14 on the motor contactor. (Latching circuit) This enabled safe operation of the safety interlock switches on the brake pedal, end guard cover, over loads etc, the machine would now stop and trip and could not be reset and safely restarted without returning the operating lever back to the stop position from its either fwd or rev position. My problem is that due to the missing tumbler mechanism the directly connected and fixed “Y”control lever now turns the switch to the fwd or rev position and supplies the 110v to the contactor coil and stays in circuit jointly with the other 110v supply via the contactor additional contacts 13 & 14. As a result the safety interlocks only partially work and depressing the brake will drop the breaker out and stop the motor but upon releasing the brake pedal the breaker immediately re-closes and the machine starts up back up automatically and it is the same scenario with the end guard cover remove cover machine stops and then immediately restarts upon refitting the cover in place.

I am keen to reinstate the tumbler linkage mechanism as original and safe and would like to buy a tumbler mechanism or make a new one from drawings or copy from original components. I am willing to pay for drawing copies or the loan of original spare parts as they seem to be pretty basic parts hopefully within my basic manufacturing skills.

As this is an old machine and the tumbler assembly is a common unit on Mk2 Bantam 800,1600,2000 and is I believe a commonly worn out part, I would like to hear from any other solutions or alternative modifications that fellow members have used to overcome this tumbler mechanism problem on the Mk2 Bantam Range.

I run the machine via an 8Kw rotary phase converter and don’t want to use a Digital Inverter on this machine.

Any help or advice appreciated. Regards James Quinn (Glasgow UK)

Edited By JasonB on 20/07/2023 06:44:31

There is a Colchester-specific group at groups.io . That could be a second port of call if you cannot obtain photos or drawings from here.

The exploded diagrams in the manual can help a lot. Based on the size of known, adjacent parts in the diagram, enlarge the missing part on a photocopier to full size and make a test item.

Colchester Spares (https://www.colchesterspares.com/) might be a last resort if you have to resort to chequebook engineering.

Hi James

Colchester group on iO Groups has manual in the Files section, Apron switch control is in pt 3 of 7 PDF docs.
join at the Homepage and follow the link below.

**LINK**

Emgee

Hello James, welcome to the forum, I can't help with your problem but I'm sure someone on here will be able to help. Good luck. Noel.

Hi friends and thanks for the prompt replies. I have already tried all my known sources for Colchester parts in Colchester Spares.com , nobilla.co.uk , Fairclough Machine Services, and the modern Colchester company in Yorkshire , but as yet to no avail so far. I already have an original copy of the “Colchester Bantam 2000 Instruction and Spare Parts Manual” from Nov 1978 and my machine dates from Sept 1978. I will try the iO group route at the location helpfully suggested. They may perhaps have an original company service manual for the machine or perhaps an alternative tried and tested safe and economic solution. Thank you all for all the suggestions and advice. James

Hi James

I worked in School workshop and we had two Bantams, though they were the early 800 speed models. The mechanical switches with lever on the side of the apron always gave troubles and were unreliable so, as kids were using them, the mechanical switch gear and operating levers were removed and replaced with an electrical forward/ reverse switch and a push button on/ off switch. I can’t say that I really liked the arrangement but they never gave any trouble thereafter and were still working when I retired

Effective though it is when in proper working order I always felt that Colchester motor control system was a little too clever for its own good.

I appreciate the probable operational advantages over a simple three push button system. Especially when used by an operator under pressure to meet production targets as it is clear which way the motor is running. It also eliminates any possible wrong button pushes going direct from forward to reverse without passing stop. That said my Smart & Brown 1024 with its three button system does the same thing electrically at, I think, the cost of extra contactors.

Given the known long term fragility of the mechanism I'd junk the whole thing. Options then are :-

1) Do a standard 3 button set-up with the usual microswitch train for safety turning the motor off or inhibiting re-start when covers are open et al. Requires a button box on the front instead of the lever which maybe aesthetically unacceptable.

2) Re-work the lever mechanism to have sprung detents at the nominal Forward-Stop-Reverse positions with over travel against a respectably strong spring to operate microswitches selecting run direction. Naturally the stop position actuates a third microswitch permanently interrupting the contactor coil supply when Stop is selected. Aesthetically and operationally invisible. Personally I'm in favour of a really positive action being needed to start a motor.

Whilst you are at it I'd replace all the contactors with modern DIN rail versions. They aren't silly expensive these days and are much easier to handle. Aged overload switches are notorious for occasionally being fracticous. Probably a combination of dust, workshop air stuff and never moving for years at a time.

I'd also shell out a few extra drinking vouchers for box on the back to hold the contactors so you can easily get at things when connecting up. My patience with neat, tucked away connections with screws you can't quite get a driver on dead straight ran out about 40 years ago! When it comes to electrics accessibility beats aesthetics any day. Not to mention that it's much easier to make a mistake when you cannot clearly see what you are doing.

Clive

Hi folks, I can readily appreciate the need for safety with kids using it but I would prefer to retain the original lever control. I note with interest the suggested detants or indented cam with micro switches solutions. So far I have already fitted a Din rail mounting and replaced both contactors with new old stock next generation Klockner-Moeller Moeller contactors and overloads and I have also fitted new replacement modern equivalent rotary switches from Eaton Moeller. As I have already got most of the way there and spent some money I am still looking at the original “as built” method by Colchester and presently, I have a usable working machine (albeit not completely safe) solely used by me. I have also discovered a new Colchester parts source in Millhill Supplies in Basildon and they are now on the case today. Later tonight I will try the iO group when I have had time to study it and join.
Thanks again everyone. James

Hi folks, I managed to get a complete used switch mechanism and used switch from Simon at Nobilla Eng Ltd. I stripped ,cleaned and inspected the switch and found contacts in good shape. Reassembled and lubricated the tumbler cam mechanism. Discovered I had misunderstood the operating philosophy of the switch as it is basically a three way switch with a fwd / O / rev position with the top two contacts (110V)11 & 12 made in the O position thus powering the (110V) contactor coil with the apron handle in stop whilst the contactor is additionally latched closed via the parallel (110V) supply via the Aux contacts 13 & 14 on the contactor. Operation of the handle to the fwd or rev position away from the O position reduces coil supply to only one 110V supply thus giving safe tripping of the motor with no restart of the motor without having carried out a safe reset by moving the apron lever back to the O position. Found that my unsafe restating problem had come about because someone previously replaced original KM reversing switch with a normal fwd/stop/rev reversing switch that did make 11&12 in the Off position. In addition they had butchered the old switch tumbler mechanism to get it to fit the different type of reversing switch, thankfully I now have a fully and smooth operating 1978 Bantam Mk2 2000 lathe.

I have purchased a modern Eaton T0-3-20/E which is the operating equivalent of the original Klocknerr-Moeller T2b-3-20 as Eaton took over KM, however the modern switch is off a much lighter and less robust construction than the original KM one and if needed in future, will require an adaptor to convert the plastic profiled shaft to a square drive and will also require some additional rotating restraints to mount and locate the new switch so as to prevent the torque effect from the fairly heavy and substantial lever tumbler mechanism. I have got there in the end and thanks to you all for all the helpful suggestions and advice! James Quinnis

Sorry folks important typo error in last thread !!
should read:

“ someone had previously replaced original KM reversing switch with a normal fwd / stop / rev reversing switch that did “ not​​​​​​​​​ “ make 11&12 in the Off position.

regards James Quinn