Ernest

T handle box spanners in 7/16" from Smith & Francis here :- **LINK** . Site has an "expensive" look tho'.

Probably plenty of suppliers if you knew what to search for without getting umpteen million results for square drive sockets.

As Brian says easily made by welding or brazing if you have the kit.

Clive

Call me a heathen, but I have always used a 13mm ring spanner for this function. A bit of a loose fit, but given that not much pressure is required to lock the saddle, it works well enough for me.

My Chippie has dual dials, does that count

Continental units have a different screwcutting gearbox as well the leadscrew. Mine is imperial, but does have the dual dials. which i have been told is quite rare. Very useful though.

And strangely enough, although the Continental model has an impressive range of imperial threading abilities, I believe the dual dials only work on imperial feedscrews. Hence, you could have imperial threads on a Continental but could not have imperial dials.

The only serious thing an imperial machine cannot do is M12 (x 1.75) threads. However, with 36t and 63t change gears from an ancient Drummond, it can.

Let's start slightly at a tangent: Chipmaster gears are 14DP, 14.5 degree PA, same as a Drummond or Myford M-type or Harrison L5 or 140 (and possibly an older Colchester Student or Master). The six-spline centre detail is discussed here: https://www.model-engineer.co.uk/forums/postings.asp?th=84252&p=1

There is someone on eBay called you_engraving who will cut these gears in delrin, including the centre detail, for what I consider a very good price.

Standard gears on a Chipmaster are 66t and 33t, giving 2:1 or 1:2 ratio. This does not change when you put the (55t/65t) metric translation gear into the train.

The theory behind it is: the relationship between 1.75mm and 1mm is 7:4 so if you put the location bar in 9, which gives multiples of 1mm pitch, alter the 2:1 (66/33) or 1:2 (33/66) ratios to 7:4 (63/36) or 4:7 (36/63) and flip the other lever between A, B, and C, one of the six possible combinations will give 1.75mm and another will give 3.5mm.

That ends the factual bit. Now everything that follows is potentially incorrect. It is a long time since I did the experiment so details are hazy and there might be a mistake below.

My pencil note in the handbook says 63/36 9C for 1.75mm and 63/36 9B for 3.5mm. What I cannot recall is if this was my initial calculation or is the final, correct result. I do remember that the first time I tried the gears, I did not get the expected pitch. I then either swapped the gears around or moved the A,B,C lever and it eventually worked. So what is written in my book may be correct or incorrect, but there are only six possibilities so it will not take long to find out which two are correct.

I happen to have a Continental Chipmaster.

If anyone should stumble over a set of changewheels to cut imperial threads,

please let me know. I know a thread dial indicator is out of the question.

While the imperial version has it integrated in the apron – lucky you…

Cheers

Erik

PS: If your Chippie has a working variator – take care of it. Ask, if you don't know how.

Well I'll be….

Just bought a Myford M type with set of change gears, but the 36 and 63 are not here. The here are

65, 60, 40, 35, 30 and 20.

But thanks anyway, good to know that someone can make it from delrin , although I would make my own from steel or cast iron.

Howard Lewis, the saddle lock, mine is 7/16 square and the spanner says 7/16 on the star end, and 1/2 on the open end.

Erik Werner Hansen, mine still has the original variator. I change oil quite often, installed an hour counter on two of the motor's wiring. I keep a chart with oild changes and workimg hours. How do you take care of your variator?

Tiger