cutting spur gears on a mill

[SillyOldDufferModerator @sillyoldduffer]

Posted by John Haine on 03/10/2021 20:02:47:

But surely if the cutter is triangular it should cut an involute tooth?

I don't think it's possible to predict the form because the shape depends on how much the blank slips during the cut. And because it slips, I think the form will be different on each side of the same tooth. For the same reason all the teeth will be different. The problem is fixed by indexing the blank, but that's not Brian's way.

How good free-formed teeth will be in terms of meshing with other gears is difficult to foretell. Be interesting to see some close-up macro photographs of several examples. Jason's simulations illustrate a likely problem: gears that have to be backed off to turn without jambing at the price of excessive backlash.

Dave

[Dave SParticipant @daves59043]

Over on homeshopmachinist there is a thread where a chaps leadscrew appears to be the wrong pitch.

In the middle of that is :Plastic gear making

Spur gears free moulded install a lathe…

[Nomex Donned]
Dave

Edited By Dave S on 07/10/2021 19:25:29

[brian jones 11Participant @brianjones11]

yes indeed Dave , thats one for the Numpty's gear making tool box. Fits the bill of being cheap and cheerful, course as said you do need to select the OD of the blank correctly ca PCD so that the right desired number of teeth fit on the circumference

Myford gears might well do the job nicely

I am working on it but got bogged down with Carbide insert problems not cutting properly on another thread (since shut down cos comments got up the Mods nose)

 

OBTW Dave looks like you link has been disabled

Edited By brian jones 11 on 07/10/2021 21:40:51

[Michael GilliganParticipant @michaelgilligan61133]

Posted by brian jones 11 on 07/10/2021 21:36:50:

.

OBTW Dave looks like you link has been disabled

Edited By brian jones 11 on 07/10/2021 21:40:51

.

It’s just a typo, Brian … The link should be : **LINK**

https://bbs.homeshopmachinist.net/forum/general/1963293-threading-problem-threads-to-long/page5#post1963737

MichaelG.

[brian jones 11Participant @brianjones11]

Great stuff Batman, you saved Gotham City

An intriguing link must try it out perhaps on bits of acrylic glued together to get suitable thickness

I wonder what DP Myford gears were made to? They look crude and square CI to me at first glance must examine one closely. I stole a spotty neighbours kids USB microscope (Bresser

https://www.ebay.co.uk/itm/114910256604?chn=ps&norover=1&mkevt=1&mkcid=2&itemid=114910256604&targetid=1280441980681&device=c&mktype=pla&googleloc=9045025&poi=&campaignid=12126077997&mkgroupid=123467436475&rlsatarget=pla-1280441980681&abcId=9300480&merchantid=114999425

) and it provides very usable pix at 20X on my PC screen, at 80x I can even see little living amoeba in our pond water, maybe grow some tardigrads

but I must not get swerved (again) from my noble purpose

Bring gears to the masses – Meccano did it

There might be more gems from across the pond, there are a lot of valuable opinions available from the Cousins

Just look at their contributions to the development of machine tools (spurred on by gun smithing and the auto industry between the wars)

[brian jones 11Participant @brianjones11]

Indeed MG that site has a long thread devoted to free hobbing (not a rude word from anyone btw)

stats started 8/7/20 last 14/7/20

views 2134. comments 109

Our little thread

stats started 19/8/21 last 8/8/21

views 19,317 comments 378

All that excitement just to be put in a barrel

[JasonBModerator @jasonb]

Brian Wrote

"I wonder what DP Myford gears were made to? They look crude and square CI to me at first glance must examine one closely. I stole a spotty neighbours kids USB microscope (Bresser) and it provides very usable pix at 20X on my PC screen, at 80x I can even see little living amoeba in our pond water, maybe grow some tardigrads"

 

Why on earth would you need to go to the trouble of using a microscope to find out the DP of Myford gears?

With all the links to various gear calculation charts in this thread etc You should have no difficulty in working it out all you need is OD and number of teeth which should be easy enough to see and in most cases give you a usable answer. PA has also been mentioned here and probably DP too. This is the way a beginner with limited resorces can work out gear sizes I would have thought that would be right up your street.

Hopefully beginners have learnt from this thread but from your methods to work out the DP of Myford gears you certainly have not picked up much useful information and it is no wonder you have not been able to come up with 2:1 gears yet as it's these every things that need to be understood to be able to design simple gears.

 

Edited By JasonB on 08/10/2021 08:07:40

[John HaineParticipant @johnhaine32865]

Um, 20 dp?

[John PParticipant @johnp77052]

Posted by Jason B 8 10 2021 07:15:50

Brian Wrote

"I wonder what DP Myford gears were made to? They look crude and square CI to me at first glance must examine one closely. I stole a spotty neighbours kids USB microscope (Bresser) and it provides very usable pix at 20X on my PC screen, at 80x I can even see little living amoeba in our pond water, maybe grow some tardigrads"

Why on earth would you need to go to the trouble of using a microscope to find out the DP of Myford gears?

With all the links to various gear calculation charts in this thread etc You should have no difficulty in working it out all you need is OD and number of teeth which should be easy enough to see and in most cases give you a usable answer. PA has also been mentioned here and probably DP too. This is the way a beginner with limited resorces can work out gear sizes I would have thought that would be right up your street.

Hopefully beginners have learnt from this thread but from your methods to work out the DP of Myford gears you certainly have not picked up much useful information and it is no wonder you have not been able to come up with 2:1 gears yet as it's these every things that need to be understood to be able to design simple gears.

Edited By JasonB on 08/10/2021 08:07:40

================================================

I just wonder who that this reply was aimed at as all of Brian Jones 11 's postings seemed to have disappeared from this thread ,shades of Barrie Lever .I thought that the posting that you put up in Home cnc the other day here

"From Previous posts on here the Wabeco machines seem to perform well, have a look back for posts by barrie Lever. "

was bit daft as all of his postings have been removed and is only referred to as Former member.

John

[brian jones 11Participant @brianjones11]

Well some cousins made a success of Free Hobbing as I suspected

[speelwerkParticipant @speelwerk]

Gave up following this thread but do admire the patients responders hat with Brian.

Niko.

[brian jones 11Participant @brianjones11]

The best is yet to come, Elvis has not left the building and he will shortly be presenting the debut of the Anti-gravity Grinder – hold that thought. Is it a way to create extended spiral turns (as in pulling a spring apart) on a lathe without a CNC in sight.

[Dave HalfordParticipant @davehalford22513]

Odd how this thread only appears in 'latest forum posts' on the righthand side and not in the larger 'latest posts' and opens on the last page.

 

Seems to work now ????

Edited By Dave Halford on 09/10/2021 11:29:19

[duncan webster 1Participant @duncanwebster1]

It's the shape shifting lizards from the AGMA

[brian jones 11Participant @brianjones11]

Stand back from success

I made a predictable gear

OD 27.1mm got 28 teeth as I pre-calculated

Then I had a happyfanny moment and found a solution to the clearance backlash criticism

It has blown me away

I need to make a proper jig to mount spindles to test out pairs of gears more accurately and make vids

My desktop kids microscope (recently pooh pooh'd by the little modeller) has shown up some remarkable shots of Carbide tips and why PRC stuff my not cut mustard

PM me for details if you are interested

The worm turns

WaM

[John HaineParticipant @johnhaine32865]

Another phantom post at 2205!

[brian jones 11Participant @brianjones11]

Another tedious naysayer at 23:03

What value does he think he has to this thread

[Nigel Graham 2Participant @nigelgraham2]

Going back a bit nearer topic I am fairly sure the Myford manuals tell you the gear standards, so you don't need resort to measuring etc.

I must admit I have never thought the headstock gears and the change-wheels on my ML7 either "crude" or "square"; whatever those were meant to mean. If my screw-cutting comes out ragged, I blame the operator not the machine!

Or stray tardigrades….

[SillyOldDufferModerator @sillyoldduffer]

Posted by Nigel Graham 2 on 10/10/2021 00:01:52:

…

I must admit I have never thought the headstock gears and the change-wheels on my ML7 either "crude" or "square"; whatever those were meant to mean. If my screw-cutting comes out ragged, I blame the operator not the machine!

…

Myford and most other lathe gears are 'good enough' rather than well made. The main disadvantage of their relative crudeness and imperfect curves is noise. Vintage car gearboxes use basic gears and the whine is all too obvious, but lathe gears don't work that hard. Backlash is also evident, but doesn't matter when screw-cutting or anything else lathe related.

Putting the best possible gearing into a lathe is a waste of money unless the machine needs to be as quiet as possible or is exceptionally powerful. Myford lathes, bless 'em, aren't powerful!

Dave

[John HaineParticipant @johnhaine32865]

Though I doubt that they made especially crude gear cutters just for Myford! However they are 14.5* PA which I think will make them look squarer. This from the late great Sir John in 2012:

"Jim,

I can't comment on the rack or it's mating pinion as I don't have any details on these but could get them if I wanted.

However as regards the screw cuting gears they are all 14 1/2 degrees PA with the exception of the first 4 on the Super 7 and like family.

The first 4 being spindle gear, the two tumblers and the gear the tumbler drives. These are 20 degrees PA.

Outboard of this they are all 14.5 degrees.

The ML7 are all 14.5 including back gear but the backgear on the S7's is special and requires a special hob as the tooth form is modified.

 

John S."

Edited By John Haine on 10/10/2021 11:05:39

Edited By John Haine on 10/10/2021 11:06:08

[DC31kParticipant @dc31k]

Posted by Nigel Graham 2 on 10/10/2021 00:01:52:

Going back a bit nearer topic I am fairly sure the Myford manuals tell you the gear standards…

It is a strange thing. Of every manual for every machine tool that I have ever come across, the gear specification is never mentioned.

As a few examples: Myford 7-series; Colchester Bantam, Chipmaster, Student; Harrison L5, 140, M-xxx class; Boxford. Look at every Asian-sourced lathe available new from UK suppliers – how many of them mention the change gear spec.?

You might also explore mills that use change gears (e.g. Harrison, Deckel, Alexander, early Beaver).

It is notable that change gear specs. are hard to find on lathes,co.uk, perhaps the most comprehensive resource available.

Also surprising is that in the many years since the web has been part of our life, no-one has produced a compendium of this information.

[brian jones 11Participant @brianjones11]

I guess if unkown gears seem to conform and mesh ok with std forms then you can guess what the spec was (all thanx to AGMA of course)

but if its a modified form, how do you measure it without resorting to sophisticated optical equipment?

let alone say you have to make a replacement to mesh with an existing gear

If its CI then you cant just TIG weld some new teeth and re machine AFAIK

I did some welding once using Nickel electrodes – I gues its akin to brazing which works

So Maureen's back gears are a challenge – how strange.

WaM

[BazyleParticipant @bazyle]

Interesting to hear the Myford back gear are 'modified'. Another odd one is the RanDa lathe back gears (not their changewheels) as was brought up on a thread last year. Info to store in the little grey cells.

As for quality of teeth I have some changewheels from a Britannia that are cast as 'pegs' straight sides and round top and not then machined. Minimum cost. I find when I pair a 60 with a 30 the ratio is somehow still 2:1 despite the crude teeth. How come?

Spec? I swear some people on this forum would need a fully dimensioned drawing with tolerances to BS blahblah to make a tommy bar.

[Tony Pratt 1Participant @tonypratt1]

I can't see any reason why the gear spec would be mentioned in the manual.

Tony

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Bazyle on 10/10/2021 11:43:57:

[…]

As for quality of teeth I have some changewheels from a Britannia that are cast as 'pegs' straight sides and round top and not then machined. Minimum cost. I find when I pair a 60 with a 30 the ratio is somehow still 2:1 despite the crude teeth. How come?

 

.

I know you are kidding, Bazyle … but just in case some innocent takes your comment seriously: Let’s just note that the the velocity ratio will vary whilst they are running [which does not bode well for accuracy of screw-cutting].

… The relevance of that will of course depend on the job that the resulting screw will be doing.

MichaelG.

.

Edit: __ Jumping from the ridiculous to the sublime : Feast your eyes on this:

http://lathes.co.uk/bryantsymons/

Edited By Michael Gilligan on 10/10/2021 12:16:37

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