Myford ml7 21 tooth change gears

Back on topic:

There are many 'calculators' available, both on-line and off-line, but I rather like this one for its versatility: **LINK**

MichaelG.

Michael,

Thankyou for that link - its brilliant.

Allows user to input a target thread of 25.4 tpi whilst using a 8tpi leadscrew. and will then calculate closest gear combinations.

Bill

Did some looking around. ....... That web page gear calculator has been converted to an apk file that can be downloaded from here

http://mynewlathe.blogspot.co.uk/ - see post approx 1/4 way down the page.

My only problem is I dont know what to do with an apk file - do I simply copy it to my tablet or do I have to execute it somehow ?

And I think this link is relevant, useful and on topic if you want to generate templates to divide 21, 33, 34, 63 etc

http://www.cgtk.co.uk/metalwork/reference/divider

Bill

.

Bill,

I'm glad to see you found CGTK's 'Divider Wheel Generator'

I have posted that **LINK** several times on this forum, but [ref. my recent 'off-topic' discussion with Neil] people still seem to have difficulty finding it when they need it.

MichaelG.

.

Bill,

I haven't checked them yet, but these instructions look good.

MichaelG.

Many thanks for the info on this thread ........

So ........... I can "cheat" occassionally and use these dinky little timing pulleys and a toothed belt instead of meshing gears together ........... I imagine it would be easier to make these "flat" teeth than to make the cutter I've ground to match the profile of my current gears.

I was going to cut a pair of gears 47/37 = 1.27027027 and introduce that into my gear train but after reading this thread I think I can do

21 drives 40-30 drives 56 then gearbox

I think I can cut a 21 and a 30 and then use my gearbox ratios to produce metric threads .... and thats a lot less teeth to cut.

Will go and do some more playing with spreadsheets to check it out, have got a Hercus 9" lathe with a gearbox, Hercus is Australian equivalent of South Bend. Gearbox ratios probably different to Myford but the maths and ratios should still allow me a way through ............

Heres a picture of my lathe http://metalworkforums.com/attachment.php?attachmentid=308680&d=1395972160

Bill

I have enormous admiration for the people who calculated metric approximations by analytical means using translation gears but since it's it's a cold, damp, indoor afternoon here in Hampshire, I thought I'd have a go with the scattergun approach using my Excel/visual Basic calculator. Many older British lathes had a fairly basic changewheel set of 20-65 in steps of 5 and an 8tpi leadscrew (such as my old Zyto). Using only these I get the following table for all the usual metric coarse and fine threads that you might want to screwcut::

I'm not saying that you can get every combination to mesh on the banjo but I think it is quite interesting that no thread is more than a micron out! This is better than I got with a PET2000 some decades ago but I think that's because the calculations take a second, not overnight, and I'm letting them carry on to a smaller error.

Rod

Nicely done, Rod

Some very good results from a small collection of change-wheels.

MichaelG.

I think it's just an example that somewhere within all the combinations of changewheels is the required set for most threads to a practical accuracy. Even on the fairly small set mentioned above there are (I think) 4,200* unique combinations.

* 10C3 x 7C3 - is that correct?

Rod

Edited By Roderick Jenkins on 17/01/2016 16:15:28

From Issue 204 : These should be cut by thread milling, using the leadscrew to turn the mandrel with the lathe switched off. To dothis a toolpost milling spindle and a leadscrew handwheel such as that described by Alastair Sinclair (Model Engineer’s Workshop, issue 91, July 2003) will be needed.

Am curious ......... what would the milling cutter look like in the thread milling process described above ? Would it be a very skinny vee shaped end mill ? or a chunky slitting saw with a vee shaped cutting profile ?

From memory, you are referring to my comment on making threads with a pitch significantly greater than the leadscrew.

The usual cutter shape is like a gear cutter, (sort of like a chunky slitting saw but with about 10 or 12 teeth) obviously shaped to match the thread profile.

You can make and use a single point cutter but it's a lit slower.

In principle a shaped end mill would work, but you are talking a lot of effort to make one unless you need a square thread.

Neil

I've been pondering this 21 tooth pulley and the following photo posted by John S.

I found this link for different belt lengths - https://sdp-si.com/eStore/..%5Css%5CPDF%5C15501003.pdf - and I note one can buy the belt by the metre and make your own custom belt lengths, cannot find many different sized big wheels (found a few up to 36 teeth nothing bigger) to stick at the other end of the belt from the 21 tooth - have concluded that it would be a pain to make them. What should I search for please ? Are these standard items I would know more about if I was conversant with cnc machines and 3d printers ?

Bill

OK,

Please ignore previous post.

Found a heap of 1/5" timing wheels up to 72 teeth here http://www.globalindustrial.com/g/motors/timing-belts/aluminum-timing-belt-pulleys/XL-1-5-pitch

So as per Michael G's post can see how to run a hybrid sysem with a 21 drives XX joined onto a standard change wheel.

Thankyou Michael - good idea - have bought a 21 tooth for $5.47

Bill

Hi, I'm sorry for resurrecting an old 'thread', but would any of the combinations of gears be useable with a myford ML4 I have been told the lead screws are the same pitches, if not identical. Which would only leave the small gear wheel on the spindle as a variable? My lathe is pretty much still all imperial. Even after all these years.

For reference my lathe has a 20 tooth gear on the spindle and the available gears are, 20, 20, 25, 30, 40, 50, 55,, 60, 65, 65, 95, not including the back gears, or the two gears on a ML7 tumbler that I have.

I don't "approximate" threads, if it's right it's right, if not then it's wrong.

I know lots of people are happy with a very close approximation, God bless them for settling! 

Where else will they "Settle" ? 

Edited By Nick Hulme on 02/02/2018 01:28:48

My same-era Drummond M-type has the same gears as that, but no 95T. It will cut all metric threads using those standard gears, set up as compound gearing. My standard reference is the the charts in Martin Cleeve's book "Screwcutting in the Lathe". He gives all the needed combinations to cut metric threads with 8tpi leadscrew lathes, within about one thou per eight inches or so!

I think Rod's chart above and Michael's linked calculator will give the same result.

Sounds like what Martin Cleeve in his book "Screwcutting in the Lathe" refers to as the enthusiams of "overzealous amateurs".

In the real world, his "approximation" gearing is accurate to one thou in several inches. Mostly per eight inches or so, in other cases three inches.

How accurate is your lathe's leadscrew? Six thou per inch variation is not unheard of. Using "perfect gearing" on such a home hobby low-cost lathe (whether Myord etc or Chinese made) is perhaps something like waxing a dirt floor. The "approximate" gearing works just fine for anything one is likely to do at home, or in the average commercial machine shop for that matter.

I have the gears for a gear train that gives me the option to work without gearing errors in metric threads, and it's quicker to set up than the approximation options ;D

Do you introduce errors if you have the option not to?

The biggest fault in production engineering is to work to a greater tolerance than the job demands.

Working to higher than required precision is a luxury hobbyists can enjoy, but they shouldn't be scorned if they choose not too.

Neil