Can’t wrap my head around gear cutting, RE: Gear blank diameter.

[coleston pluzakParticipant @colestonpluzak68149]

Ladies and Gentlemen, hello! First let me say thank you so much everyone, I've been reading this forum for a couple years now since I bought a myford super 7, and all the threads have been so invaluable. I can't thank everyone enough. With help from reading posts from this forum I've brought this beautiful old lathe back to life and have been getting some basic turning done.

But I'm stuck. my lathe came with 6 gears, 20,50,30,60,25,75.

Which all together can be used to form one ratio on the chart. 120 TPI. Not the most useful amount of teeth.

I think the previous owner was trying to get the carriage to move quickly, but just from experimenting with the gears if you just use 3 gears instead of 6 you can get the carriage to fly.

So what I need are to make 2×21, 70,40,45,65 and if I get ambitious the mythical 127 toothed gear. As well the large back gear has a tooth broken off, so I need to either fix that or make a new gear.

Now I know the number of teeth, and I know the inside bore (5/8) and I know the pressure angle 14.5 degrees.

But what I don't know is the nominal diameter that I need to turn the gear blanks too. I have a 3" bar of some sort of tool steel which i intend to use to make all the smaller gears with, so I'm set there.

I feel like this is so simple, and I've been watching tons of youtube video's and reading all the threads about gear cutting on this site and it's just not clicking in.

Would anyone mind taking the time to point me in the direction of somewhere that clearly explains how to get the diameter of the gear blank to make new gears that mesh in with existing gears?

Thanks so much everyone and hello from Canada

PS Another question, the dials on all the slides go to 100, which according to the myford website makes the lathe a metric lathe. It says the dials would only goto 40 if it was an imperial lathe. But when I put a clock on the back of the cross slide and move the hand wheel 5 graduations, the clock moves .005" which makes me think it's an imperial lathe. Does anyone know why this would be like this?

PPS some friends of mine have a pretty good quality CNC mill, and I feel like it should be pretty easy to machine new feed nuts out of titanium or something exotic like that, is there a way to get the exact dimensions of the feednuts from somewhere without resorting to amateur measuring, I don't trust myself to get accurate results trying to measure something like that part.

Thanks for any input you can give me, and thanks so much for making all your combined knowledge available to the young guys starting out!

[coleston pluzakParticipant @colestonpluzak68149]

[Brian HParticipant @brianh50089]

Hello Coleston, for an all-round view of amature gear cutting I can recomend the Workshop Practice Series No 17, "Gears and Gear Cutting" by Ivan Law published by Special Interest Model Books.

I'm sorry I cannot give you the North America supplier but a search for the book should bring it up.

Brian

[JasonBModerator @jasonb]

Myford gears are 20DP. To get the Outside diameter add 2 to the number of teeth and then divide the answer by the DP

So for your 65T gear its 65+2 = 67. Then 67/20 = 3.350"

Depth of cut for 40-100T is 2.4/DP so 0.12" For the 21t you will want 2.25/DP so 0.1125

This PDF has the simple formulas

[Anonymous]

As far as I'm aware the Myford gears will be designed using diametric pitch (DP) although I can't remember the value. To find the outside diameter for a gear blank is easy. It's simply the number of teeth plus 2, and the sum divided by the diametric pitch. So to take an example from my traction engine (because I can remember it) a gear that is 5DP with 20 teeth requires a blank with an OD of (20+2)/5 = 4.4". Here's the gear being cut:

Andrew

[John HaineParticipant @johnhaine32865]

Also worth looking at Mike Cox's site which has tables for gear cutting which include the crest diameter, and useful information on making cutters. Mike can also provide a spreadsheet which allows to to construct the tables for any gear dimensions.

**LINK**

[Michael GilliganParticipant @michaelgilligan61133]

Posted by coleston pluzak on 25/04/2018 20:49:38:

PS Another question, the dials on all the slides go to 100, which according to the myford website makes the lathe a metric lathe. It says the dials would only goto 40 if it was an imperial lathe. But when I put a clock on the back of the cross slide and move the hand wheel 5 graduations, the clock moves .005" which makes me think it's an imperial lathe. Does anyone know why this would be like this?

.

Coleston,

BDH has given you an excellent response regarding the Gears; so I will try to address your concern about the dials for the slides.

Could you please let us have a link to the misleading information you have found on Myford's website ?

… So far as I can see; their information for the Super 7 items is stated correctly.

MichaelG.

.

https://www.myford.co.uk/acatalog/K15.-TOP-SLIDE-MICROMETER-DIAL—IMPERIAL–A2079-340.html

https://www.myford.co.uk/acatalog/K15.-TOP-SLIDE-MICROMETER-DIAL—METRIC–A3249-339.html

Edited By Michael Gilligan on 26/04/2018 07:58:25

I see a flurry of helpful posts appeared between BDH's and mine.

Edited By Michael Gilligan on 26/04/2018 08:01:34

[coleston pluzakParticipant @colestonpluzak68149]

Posted by Michael Gilligan on 26/04/2018 07:56:52:

Posted by coleston pluzak on 25/04/2018 20:49:38:

PS Another question, the dials on all the slides go to 100, which according to the myford website makes the lathe a metric lathe. It says the dials would only goto 40 if it was an imperial lathe. But when I put a clock on the back of the cross slide and move the hand wheel 5 graduations, the clock moves .005" which makes me think it's an imperial lathe. Does anyone know why this would be like this?

.

Coleston,

BDH has given you an excellent response regarding the Gears; so I will try to address your concern about the dials for the slides.

Could you please let us have a link to the misleading information you have found on Myford's website ?

… So far as I can see; their information for the Super 7 items is stated correctly.

MichaelG.

Found it in my history, was a dyslexic moment. Error was between the monitor and the chair.

-Coleston

[coleston pluzakParticipant @colestonpluzak68149]

Posted by BDH on 26/04/2018 07:34:52:

Hello Coleston, for an all-round view of amature gear cutting I can recomend the Workshop Practice Series No 17, "Gears and Gear Cutting" by Ivan Law published by Special Interest Model Books.

I'm sorry I cannot give you the North America supplier but a search for the book should bring it up.

Brian

I'm about 10 pages in, but this book is amazing. What a great resource!

Thank you so much for the recommendation.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by coleston pluzak on 26/04/2018 08:00:45:

Error was between the monitor and the chair.

-Coleston

.

… Quite a common problem.

All's well that ends well.

.

MichaelG.

[John HinkleyParticipant @johnhinkley26699]

Coleston,

You may find the program that I use to generate dxf files for gear drawings useful, not only to calculate the various dimensions, but help visualise the nomenclature used in gear production:

**LINK**

John

[Clive FosterParticipant @clivefoster55965]

Coleston

As a extra precaution against "wrong number in the calculator issues" consider looking at the HPC gears web site **LINK** too. They list the overall diameter of the gears and cover a wide range. I presume other catalogue gear suppliers have similar listings.

I'm always more comfortable when I have an independent verification of the sort of numbers I should be getting.

Clive.

[geoff walker 1Participant @geoffwalker1]

Hi Coleston

Now I know the number of teeth, and I know the inside bore (5/8) and I know the pressure angle 14.5 degrees.

If you have gears with a 5/8" bore and a P.A. of 14.5 degrees then they are not super 7 gears.

These gear sizes are the same as the ones for a myford m type lathe which are 14 d.p.

The gears you have listed are all standard for the m type except for the 25 and 75. Are you sure the 75 is not 73 which is one of the standard metric gears for the M type.

The m type has 2 X 20, 2 X 30, 35, 38, 40, 45, 46 (metric) 50, 55, 60, 65, 73 (metric).

The dial on the m type cross slide also has 100 divisions.

Sorry if this is a daft question but are you your lathe is a super 7?

Geoff

[coleston pluzakParticipant @colestonpluzak68149]

Hello Geoff, now that is an interesting question. I was under the impression that the gears for switching the lead screw direction had a pressure angle of 20, including the two fiber ones, while all the rest have a pressure angle of 14.5.

The bore I haven’t measured, that is just what I read whilst conducting research for this project. I’ll check with the callipers tomorrow.

As too being sure, I’m going off of three things, which I think are conclusive but myford sure made a lot of lathes, so who knows.

The three things being:

Super 7 embossed on the belt cover

The serial number matching up with super 7 lathes made from 1968-? On the myford website

And it has a rather lovely clutch, which I believe was one of the things that set it apart from the ml versions.

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by geoff walker 1 on 26/04/2018 10:09:37:

If you have gears with a 5/8" bore and a P.A. of 14.5 degrees then they are not super 7 gears.

Sorry to contradict you Geoff but Super 7 change gears ARE 20DP, 14.5 degrees PA and 5/8" bore.

Rod

[geoff walker 1Participant @geoffwalker1]

Sorry guys, silly me,

I'm confused, must be an age thing.

I thought the myford gears were the same as boxford 9/16" bore.

Geoff

[BazyleParticipant @bazyle]

You mentioned that you have a bar of 'tool steel' to make the gears. Hopefully it is just mild steel which is easily cut and filed. However you will find it is harder going and wear your cutter much more than the cast iron most of the gears are made from. However for larger gears look for a hard but tough plastic, like Delrin, tufnol, but not one that is brittle like perspex. This will be much easier to cut.
For the smaller gears consider brass or bronze. That is not so much for the strength of teeth but for the strength of the rim once you have cut the teeth and cut a hole in the middle there may not be much left.

[Phil PParticipant @philp]

Quote "I was under the impression that the gears for switching the lead screw direction had a pressure angle of 20, including the two fiber ones, while all the rest have a pressure angle of 14.5."

The above statement is correct, there are two different pressure angles in use on the Super 7.

I discovered this fact when making my Meek screwcutting clutch a few years ago, and it was confirmed by an ex Myford employee at the time. Graham Meek also updated his designs to show this.

Phil

[John PurdyParticipant @johnpurdy78347]

Coelston

Ivan Law's book is available here in Canada from "Busy Bee Tools" and is currently listed on their web site for $29.95, stock number BK170. That's where I got mine and I highly recommend it. Takes a lot of the mystery out of gears and gear cutting.

John

Edited By John Purdy on 26/04/2018 19:28:34

[Howard LewisParticipant @howardlewis46836]

Ivan Law's book is an invaluable aid. Would not be without it, has helped me to make a number of gears!

A definite "must have" for reference.

Howard

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