Calculating Feed Rate using Myford G-box

[Anna JablonskaParticipant @annajablonska79888]

Dear All.,

 

Perhaps it is just one of those days, but I’ve been unsuccesful in resolving an issue – so am turning to you for some advice.

 

What I would like to understand, is how to calculate feed rates on the Myford, when using a gearbox set up for metric screw cutting.

 

Eg. Assume I have set up to cut a metric thread of say 1mm pitch. Using of course the change wheels / quadrant & gearbox.

 

If I now want to leave the set up in place, but perhaps need a different feed rate how could I define / calculate to where I should reposition the gear selector or the three position lever ?

 

Looking forward to any replies.

 

Kindest Anna

[Anna JablonskaParticipant @annajablonska79888]

[Roderick JenkinsParticipant @roderickjenkins93242]

Anna,

 

I’ve been investigating this with a view to using the gearbox/changewheel combination to produce some long leads for helical gears. My understanding is that the set up gives 2 ratios, one for the gearbox setting and one for the changewheels. When the set up for screw cutting is in imperial mode the gear ratio (from mandrel to gearbox input shaft ) is 1:1 and the gear box in effect gives you a variable pitch leadscrew, 8tpi, 9tpi etc to 56tpi. With the metric quadrant in place then you can work out the gear ratio from drivers / drivens and then divide by the gearbox setting as if it was the leadscrew tpi to give you the lead. For example: from the metric conversion chart, the gear settings for 0.2mm pitch are: 28/60, 63/50, 45/60 = 0.441. If you now set the gearbox to position C8 for 56 threads per inch you get a feed or lead of 0.441/56 =0.008″ per rev. If you multiply that by 25.4 you end up with 0.2mm, as from the chart. To get a finer feed you will need to make the drivers as small as possible and the drivens as big as possible. So, in theory, the finest feed you can get with the metric conversion set is 60,60,63 as drivens with 28,30,35 as drivers and a gear box setting of 56, which gives 0.002″ which (just by coincidence I think) is the same as the finest feed from the imperial set up using the reversible threads/fine-feed gear.

 

I hope this makes sense,

 

cheers,

 

Rod

Edited By David Clark 1 on 04/09/2011 14:09:25

[David Clark 13Participant @davidclark13]

Hi John

Anna was banned.

Now reinstated.

She posted a glamour photo and I thought we were headed for another husband wanted scenario.

regards David

[John Stevenson 1Participant @johnstevenson1]

Repost the photo – sod the Myford.

[JasonBModerator @jasonb]

“She posted a glamour photo and I thought we were headed for another husband wanted scenario.”

 

I thought that maybe you had answered Anna’a add for a husband and that was why you are selling up your workshop and house, then moving in with her and her Myford.

 

Hope your recent Ill health has not forced the sale.

 

J

[_Paul_Participant @_paul_]

Posted by John Stevenson on 04/09/2011 15:42:59:
Repost the photo – sod the Myford.

ROFL

[chris stephensParticipant @chrisstephens63393]

What John said, got to be better than some photos.

chriStephens

[Anna JablonskaParticipant @annajablonska79888]

Not quite sure why I should be banned Mr. Clark. This is my photo, and I’m proud of the way I look. If anyone feels it is inappropriate, please do let me know.

 

Kindest regards

 

Anna

[Anna JablonskaParticipant @annajablonska79888]

Dear Rod et al.,

Thank you very much for taking the time to reply.

 

I will read in detail what you have written, and if I may I will get back to you soon.

 

Kindest Anna

[John Stevenson 1Participant @johnstevenson1]

Anna,

Long post so go get a coffee.

I used to have an ML7, bought new from Myfords and it served me well for many years.

I always wanted a screwcutting gearbox but they were too expensive for me at the time. Years later I came across one quite reasonable so bought it and fitted it to my lathe.

 

I wanted one to save the hassle of keep changing gears for the wide variety of jobs I was doing

 

I then had to buy the new banjo and conversion gears from Myfords for doing metric threads, as there were no cheap rubber Indian copies I had to pay full price.

 

After doing a few imperial threads then metric threads I realised I had made a big mistake in doing this conversion. Let me explain.

 

When in imperial mode provided that the ration needed is in the box then there is no problem. You have quickly selectable ratios and a quickly selectable fine feed arrangement by just turning the gear over which requires no tools, after all this is what it was designed for in 1953 when metric was well into the future.

 

The problem comes about when you swap to metric screwcutting. Instead of having to replace a few change wheels on a banjo yo now had to strip the original banjo, replace it with a new one and then populate this with the gears needed. Far, far more work than swapping gears on a non- gearbox lathe.

 

Added to this you lost the fine feed arrangement when in metric mode and if needed entailed the whole job lot to be swapped over again.

 

It was this constant swapping that made me realise that I had made a bad decision in fitting the gearbox. Shortly after this I sold the lathe as room was needed for a far larger lathe.

 

In hindsight and knowing what I now know IF I still had the lathe I would keep the gearbox and the default original drive and purchase just two additional gears to enable the standard box to cut metric AND still have the default fine feed arrangement.

 

The gearbox machines have a 24 tooth input gear on the tumbler shaft as standard.

 

 

If this gear is replaced with a 33 tooth or 34 tooth, depending, then the standard box will cut all the common metric threads from 0.45 to 4.5mm pitch and BA sizes from 0 to 8 although a 20 and 21 is also needed for some of these sizes.

It is far easier to replace one gear than swap a load or the whole banjo.

 

Now if David will allow me a small plug these gears with a laminated chart can be bought here

 

Metric Screwcutting Gears

 

John S.

Edited By John Stevenson on 04/09/2011 20:40:48

[Anna JablonskaParticipant @annajablonska79888]

Dear John.,

 

Thank you very much for that informed response.

 

As with Rod’s, I’ll mull it over a cup of coffee as you so rightly suggest, and get back to you as soon as I can.

 

Kindest regards.,

 

Anna

[John McNamaraParticipant @johnmcnamara74883]

Hi All

Should I or should I not express a view on this? Well here goes…….

There is a very basic tenet in British law, the presumption of innocence. And the possible guilt in this case was a presumption that a post by a female person on an engineering related site; created a prima facie case for the presumption of guilt, based on the reasoning that it is extremely unlikely that a female person would be interested in engineering. And therefore that person must have an ulterior motive.

Let’s look at the facts on this issue. Female Engineers are on the increase.

Women are taking an increasing role in the sciences and that includes engineering, a couple of Google searches confirmed this.

 

General Google search: Increase in Female Engineers…….

 

More specifically in the UK……

 

As the second post above also suggests that in spite of their scholastic achievements they still face poor employment prospects; why?

Because (some) of the broader Engineering community particularly the more senior or for want of a better word older men are still trapped in the mire of the past.

Fortunately the world is evolving and times do change.

It is also worth considering the perilous state of model engineering, we need every member we can get, Not just for the ME site but as members of the model engineering, I prefer to say Engineering community, it is in all our interests to recruit new members whenever we can.

Cheers
John

[Ian PParticipant @ianp]

I fully agree with John’s reply (& John Stevensons too!) but whilst it is very nice of Anna to put her picture up, so Anna, please leave it there.

 

As engineers though, what we really need to see is her workshop

 

Ian P

[David Clark 13Participant @davidclark13]

Hi There

A woman joined the Model Engineer website.

She posted a glamour photo of herself.

Not a problem.

She was based in Poland.

Alarm bells rang so I suspended her temporarily.

 

I don’t see a problem.

 

regards David

 

[DMBParticipant @dmb]

How about if Anna shows us all what she`s got, in terms of a workshop, that is!

[blowlampParticipant @blowlamp]

In my opinion, David’s glamour shot is much more provocative.

 

Martin.

[JasonBModerator @jasonb]

I can see why david did it, there is a lot of similar spam about – eastern European ladies looking for husbands etc. I expect she was temporarily suspended while David confirmed Anna was a genuine member. Perfectly acceptable moderation in my view.

 

Now Where is that Avitar of Diane’s

 

J

[NJHParticipant @njh]

Hi Anna

 

Welcome to the talking shop that is the ME forum – although at times Colosseum might be a more suitable name than Forum ! As far as David’s categorisation of your Avitar as a “glamour” ‘photo well I think he should get out more – it seems perfectly OK to me – but he IS the boss so we must accept his point.

 

So to the point of your question – I’m very pleased that you asked it. I had been vaguely considering adding the metric conversion set to my S7 and I’m glad now that I did not.

John S’s answer is just the way to go for me so thanks to you both for this flash of insight!

 

As far as having the woman’s touch on this site I say welcome – please continue to contribute. It may be that it will encourage some better manners and more polite exchanges – but I wouldn’t bet on it!

 

Cheers

 

Norman

 

 

[Diane CarneyModerator @dianecarney30678]

Jako jedyna kobieta na tym forum, że byłoby miło mieć jakieś firmy! Anna, wyślij zdjęcie kilku rzeczy, które dokonały lub modele robisz właśnie teraz. Następnie cynicy tutaj będzie wiedział, gdzie stoją.

Diane

 

ps JasonB – Diane don’t do glam

[NJHParticipant @njh]

Diane !!!!!!!!!

 

That’s quite out of order!

Alright quite often I can’t fully understand what my wife is on about but your post well……..

 

Please translate so that we all may share the joke (?)

 

Regards

Norman

[Roderick JenkinsParticipant @roderickjenkins93242]

From the Polish/English translater web site:

 

As sole woman on this forum, that would be some
(certain) firms nicely have! Anna, it send photo several thing, they
have performed which (who) or now you make models exactly. Here it will
know next cynicy, where they stand.

 

Google translate does rather better:

 

As the only woman on this board, it would be nice to have some company! Anna, send a photo of a few things that have made or models do right now. Then cynics here will know where they stand.

 

Anyway, well said.

[Roderick JenkinsParticipant @roderickjenkins93242]

Whoops… We’ve done it now. Google adsense has started offering opportunities to meet Polish singles in the banner ad above Or is it just me. How am i going to explain this to Mrs J?

[John Stevenson 1Participant @johnstevenson1]

Dunno about the only woman on the board but there are certainly some old maids.

Actually I believe we have had some posts from Julie who also inhabits the traction forum.

 

John S.

[Diane CarneyModerator @dianecarney30678]

I’m sure there are one or two but most women don’t have time to post on forums, do they? It really is a man’s thing isn’t it? Haven’t seen Julie’s name for a while. I expect she’s busy.

 

I was laughing at the “that would be some firms nicely have”… ha ha. Hmmmmm

 

 

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