Myford Super 7

[John Wallett]

Hi Guys trying to help my son out I need to cut 25tpi on a gearbox Super 7 if it was a non gearbox model it would have been no problem any ideas or am I Kippered!

 

[Pete.]

Hi John,

What change gears do you have all together?

 

[John Wallett]

Hi Pete thanks for the reply, I have all the gears that were with the lathe before I fitted the gearbox about 5 years ago.

 

[Pete.]

Cool, then you need to set for 20tpi and add a 5/4 ratio in the end train. You should have a 50 and a 40 so stick them together as a compound and find somewhere in the end train to fit them in.

 

[John Wallett]

Hi Pete "thank you" I will try to get my head round the solution first time I have had to cut an odd number tpi!

 

[Pete.]

Well, ideally you would fit the 50/40 in place of an idler in the train but I'm not familiar with the end cluster so if you'd like to post a photo it would help. Because 25tpi is finer than 20tpi you would have the 50 tooth driven and the 40 tooth driving.

 

[John Wallett]

Thanks again Pete I will have a look in the morning and if need be I will send you a picture

 

[nick952]

You will need the quadrant that comes in the Metric Conversion Set, to mount the gears on. There's a PDF copy of the Myford Gearbox Manual here:- https://www.google.co.uk/search?q=m...ei=HK3VV8IIqcaABuzzgLgP#imgrc=ujjIgj5z6WCkqM:

 

[John Wallett]

Hi Pete I have a quadrant but? I cant see a download just some jpg's as you can see standard set up!

 

[nick952]

The problem with the standard gearbox quadrant is that the gear centre distance is fixed and you need them to be adjustable for the different gears.

I've put a PDF copy of the manual in my dropbox account for you here:- https://www.dropbox.com/s/oimiitgdt64fte8/Myford Super7 Gearbox.pdf?dl=0

Hope this helps.

Nick.

 

[John Wallett]

Hi Nick thank you for the help it is much appreciated! I gather I need the Metric Quadrant I have all the gears needed but as the cost of the quadrant would outweigh the use I would give it

John

 

[John Wallett]

Funnily enough I was looking at making something to do the job Nick

 

[Pete.]

I wonder if the original quadrant would do the trick?
Also I've been wondering what the application is because 25tpi is very close to 1mm pitch. If it's a one-off I could cut 25 or 1mm if you posted it to me .

 

[nick952]

Just in case you haven't seen it, there's a set of drawings for a fabricated quadrant here:- http://homews.co.uk/page348.html

 

[John Wallett]

Thanks Pete and Nick I was looking at the original quadrant and seeing how I could adapt it?

 

[nick952]

Just had a thought, if you set the gearbox to cut 20 tpi and then drive the gearbox 25% faster/more, then that should give you 25 tpi. The standard tumbler drive gear is 24 teeth, so if you swap this for a 30 tooth gear this might give you the extra 25% drive you need (I think).
Worth a try, as there's no need for another quadrant if it works.

Nick.

P.S. If it does work don't forget to put the 24 tothed gear back on after youre done, or there will be some head scratching when you come to cut some atandard threads later.

 

[Pete.]

The tumbler is an idler so it wouldn't make any difference Nick. Also 25tpi is finer than 20 so you need to slow the lead screw down rather than speed it up.

 

[nick952]

The tufnol tumbler gears are the idlers, the one I'm on about is the steel one that drives the gear train as it's a compound train (just checked and it's called the Tumbler Sleeve Gear in the Manual) and yes, you are right about slowing the box down

Myford do an 18 tooth gear, but I'm not certain about the bore size and it may not fit the stub http://www.myford.co.uk/acatalog/143.-18T-GEAR--A2304-18-977.html

Another thought, 30 tooth gear should give you 15 tpi in the origional case, so worth a try to see if the idea works or not.

 

[John Wallett]

Hi Nick and Pete that's worth a try thanks!

 

[Pete.]

The tufnol tumbler gears are the idlers, the one I'm on about is the steel one that drives the gear train as it's a compound train (just checked and it's called the Tumbler Sleeve Gear in the Manual) and yes, you are right about slowing the box down

Myford do an 18 tooth gear, but I'm not certain about the bore size and it may not fit the stub http://www.myford.co.uk/acatalog/143.-18T-GEAR--A2304-18-977.html

Another thought, 30 tooth gear should give you 15 tpi in the origional case, so worth a try to see if the idea works or not.

Ah yes I see it now in the image above, but I'm wondering if changing the small gear's tooth count by 25% will also change the compound's ratio by 25%, or some other factor?