Startrite Mercury MkI nutset threads

I'm renovating a Startrite Mercury MkI - 5 speed (age before 1965), it came without the on/off switch on left side and a different external switch/fuse arrangement. I may put an on/off switch there or a blanking plate. There were no screws in the nutsets, but the serial number plate screws fit, so I measured it up:

Outside thread: 3.47mm, 40 TPI (counted over 1/4''.

This rules out M3.5 since the thread count do not fit either normal (pitch 0.6) or fine (pitch 0.35) and the diameter do not fit the wiki BSW or BSF tables.

I could be UNF #6, but I have another screw that measure 3.50mm, 40 TPI, but that do not fit. The screw that fit is not tight, so I guess it is not the 0.03mm difference but thread geometry?

If anyone know the what the thread is it would be appreciated.

British, and associated with electrical fittings, have you eliminated the possibility of 4BA?

Chronos sell a BA thread pitch gauge should you need one.

I grew up metric and have lived happily so far........so new for me to try to work out any inchy threads bar UNC.

I checked again over 1/4'' and get ~9.5 threads, so ~38 TPI. I cant get closer with only a caliper and magnifer.

The 4BA is a likely candidate, thanks.

And if it turns out to be a BA thread, you can continue to do so.

BA _is_ a metric thread.

Please see: http://www.stubmandrel.co.uk/workshop/18-reference-information/23-are-ba-screws-metric-or-imperial

Jon

I have a similar machine to yours, mine was new to me in about 1970, though it may have been in the dealers showroom a long time. It is serial number 57645, only a few different from yours..

I have just taken one of the screws out of the switch plate on mine and tried a 4BA screw from the little plastic drawer I call my stock and it fits perfectly. No question, it's 4 BA. If you can't get any locally let the forum know and one of us will send you some, they are plentiful in UK.

Rod

Thanks Rod and DC31k. Good info on the BA thread history. BA thread gauge on the way.

The guy who sold me the drill said it was originally in a factory where he started working in 1964/65.

I alo have a Startrite Mercury, mine developed a motor starting issue and I stripped the electrics out and cleaned out the motor - capacitor had failed - no marking so I made a judgement on size and it works currently !

In doing so I replaced the original rotary switch with a contactor box type - so if you are interested in an original switch with very clean plate and original pvc insulation 'boot' PM me.

Richard.

Hi Richard,

Thank you for the offer, I PM'ed you a few days back but don't know if it worked.

The motor is 3 phase and as off this week runs of an inverter that give the options of: forward, revers (requires an external switch), and variable speed via potentiometer on the inverter or use an external one.

I intend to use the variable speed control on the inverter and put a rotary switch in the original position to get a REW-OFF-FWD operation. I would like to keep an original look and feel if possible. This requires a 1 pole 3 position switch but it will only be switching low voltage control signals. What I can see from the pictures on lathes.co.uk it looks like an ON-OFF-ON-OFF switch that would probably not do this directly. It may be possible to add some small electronic switches and just use the mechanical positions.

Jon

Hi Jon,

No PM received - I think there is a minimum number of posts required and as I just joined that may be the problem ? I will try and PM you.

Had another look at the switch - its made by TOK switches Ltd. marked P13/1 15A 200v, 7A 440v, AC only.

Yes the switch is On/Off in two positions in rotation.

I've just taken the really heavy PVC insulation 'boot' off it to see the wiring - the earth is looped through and not wired into switch. it has three contacts marked 1,2and 3 and another three marked !A,2A and 3A - only the 1 and 2 /1A and 2A are used -. the 3 /3A also makes and breaks with the switch action.

Not sure if its any good to you - electrics are not my best subject !!!

I'll post a couple of pics in my album.

R.

Forgot to mention my drill motor is the low speed (930 rpm) single phase.

R.

Hi Richard,

I got your PM and replied to it, don't know if it got to you.

I was in the workshop looking at mouting the inverter, no obvious place, so I will probably have to cut and weld up a bracket.

I may just place it away from the drill and use an ON-OFF switch on either the 1 phase input for the inverter or work out some control on/off. In either case it would be great to have a switch that fit. Btw I am an electronics engineer, so that part is not a problem.

Edited By Jon Halland on 01/10/2021 07:33:43

Hi Jon,

Found out where your PM's reside ! have replied.

Not sure I'd bother with reverse on a heavy drill.

I mounted my new contactor box on a wide aluminium bracket bent to less than 90deg to the left side of the base on my machine so it falls easily to hand with nice big buttons !

I could have use an electronics engineer when the new contactor box turned up - Chinese - no instructions/wiring diagram and set up to fit a thermal overload which was not supplied (or required) so loose tails to sort.

R.

I've decided to skip the reverse run for now and focus on getting the drill finished. I can always program the reverse on the inverter when needed. This will hopefully prevent all the bits from complete amalgamation with the disc sander project, which started when I got fed up hand sanding OZ redwood for a pepper grinder (it has not been seen lately.....).

Thank you so much for the switch it will make that part easy.

Just give me a shout if you need help with how to wire things up next time.

You have mail - switch soon to be in the post complete with 4BA set screws,

R.

Switch in perfect condition arrived yesterday. A huge thank you to Richard.