Myford 33t and 34t gears for metric threads

I’ve just read the article in MEW August 2018 on metric overlays for the Myford gearbox. This uses 33 and 34 tooth gears to replace the existing gear, to enable most of the common metric thread pitches.

Can anyone tell me how this compares with using the metric conversion set, as it certainly seems simpler and cheaper.

Can anyone tell me where I can source the 33t and 34t gears?

Many thanks, Mike

Mike

A google search for Myford 33T, Myford 34T comes up with lots of links.

Read this past thread for more information as well

https://www.model-engineer.co.uk/forums/postings.asp?th=125630

Norm

Edited to add that the John Stevenson mentioned in that thread is now no longer with us. But the gears are now made by others.

Edited By norm norton on 27/01/2019 09:58:32

Edited By norm norton on 27/01/2019 10:00:52

Hi Mike,

It seems the 33T is available from RDG.

Thor

Mike,

The results are almost equivalent to the values you would get using the expensive conversion set, in practice you will see no sensibly measurable errors. However, the metric and BA pitches you can get with just these two gears is rather limited in extent.

Regards

Brian

That's great Thor - I'll buy a 33T from RDG.

Does anyone know where I can get the 34T?

Mike

Widely advertised on eBay.

Brian Wood's book Gearing of Lathes for Screwcutting is a good read.

Can't see any on ebay at the moment.
Try HPC Gears, who offer 34t 20dp in metal and Delrin.
OK would need modifying to fit, but probably easier than making from scratch.

Bill

Mike,

Just for interest I calculated the actual pitch achieved using the official Myford metric conversion set for the gear box. The actual figures are in the right hand column:

A similar calculation for the 33/34 option is shown below

So, the official set is an order of magnitude more accurate but for practical purposes the difference is negligible. For the finer metric threads some additional gears to the 33 and 34 are useful. I have the metric conversion set, it came withe my S/H lathe but when I needed to cut a 16mm x 2 thread last week I broke out the 34T gear. Much more convenient.

HTH,

Rod

Hi

I bought both 33 and 34T gears from the present Myford brand owner last year at one of the shows. I don't have any information about current stocks.

Rod

Take care if buying gears from HPC. Most of their standard gears are 20 degree pressure angle, whereas Myford change gears are 14.5 degree pressure angle.

We need to be a little careful here, Myford change gears are 14.5 degrees pressure angle.

Rod

Roderick Jenkins:

Thanks for the comparison; I regularly consult your stud gear table.

Some of those Myford errors are pretty huge, approaching the wavelength of light...

And one of the other lot is almost six microns out!

Lean on the lathe while you are screwcutting and it may introduce a bigger error

Neil

Hmm, was thinking of going this route but 33T and 34T changewheels not on the Myford or RDG site anymore.

At £263 for the metric conversion kit I wonder why 🤔

The 33T seems to be available.

Thor

Edited By Thor on 28/01/2019 05:12:40

When this subject came up in the past(10/2016) I bought a pair of gears from the late John Stevenson for £25 inclusive of UK postage. I'm sure John would have produced a "stick" of gears and parted them off to width. Maybe worth an email to Adam to see if he can lay his hands on any.

Hi Ian,

Is Adam related to John? How can I contact him?

Many thanks,

Mike

I don't think 33 and 34 tooth gears were ever part of the old Myford inventory. I got mine from the late, great John Stevenson. Shortly before his sad demise Sir John mentioned on this forum that he was making a batch of gears - I wonder if these were for RGD Myford? If so it seems that they are running out. Perhaps there is an opportunity for a little entrepreneurship here.

Rod

Mike,

No lathe with an imperial lead screw can cut a truly accurate metric thread unless a 127 tooth gear is used. Despite this fact both the official Myford conversion set and the 33, 34 toothed input gear method are capable of producing metric threads accurate enough for all practical purposes.

The Myford conversion kit is both very expensive, is inconvenient and time-consuming to set up and then take down. The 33, 34 method only takes a few moment to set up.

I cannot understand why anyone would find the need to screw cut BA threads as a good set of taps and dies together with a tailstock die holder will do a very good and accurate job. In almost 60 years of model (and full size ) engineering I have never known anyone screw cut a BA thread.

Eric

Adam runs the homeworkshop.org.uk website. A request on there for 33 and 34 tooth Myford change gears might do the trick.