Dowding and Doll V-4 gear hobber

[roofman]

Just when i was starting to get my head around this machine to a very small degree, Pete then throws post 78 into the mix and i am back to square one

 

[minimutly]

I think this is some attempt to do that:

Find Differential Constant - Articles of Interest to Gear Manufacturers

www.meshingwithgears.us

It is a good site to skim through as there is some obscure stuff there.

Do you know the title of the Pfauter/Gleeson book?

Pretty much what I did to get to the gearset needed for my Cooper pinion. I still haven't back calculated to see why it didn't come out exactly according to the theoretical lead though, but I will.

 

[Pete.]

Do you know the title of the Pfauter/Gleeson book?

It's called "Change Gear Tables" by Becher and Koerner. There are other similar publications but this is the one I find most referenced.

 

[Johnnybravo]

Think that book is mentioned in here

 

[Pete.]

Think that book is mentioned in here

Yes it is. I am right now installing a program someone has made for the PC, which I hope will do the same job but with added functionality over a mere look-up table.

 

[Pete.]

Ok, thanks to a very clever guy called David Malphrus who has written software and made it freely available on his website:

https://bmmachineshop.com/

I have this calculator installed on my PC. It's super-simple, you just put in your list of changewheels, and your desired ratio, and it calculates numerous 4-gear trains to choose from along with calculated error and how many decimals of accuracy. For helical gears you are supposed to work to at least 5 decimals. I put in the number from the example given in the manual for the machine and it not only calculated 80 different 4 gear setups but the first 22 results were smaller error than the actual example given. The reason for this is because even though there are a huge range of combinations given in the traditional book tables there are literally millions of actual iterations which are too many to calculate and put into print. the power of computers removes this restriction by perfoming millions of calculations in an instant (the results actually update as you type in the number).

 

[Pete.]

By the way, anyone who operates a lathe with change-gears can make good use of that calculator, because the 4 gear train on a hobber is no different at all to the 4 gear train on the end of a lathe. So, with a simple bit of maths (basic TPI- inch or mm pitch conversions), putting in your list of gears and the decimal ratio you need to achieve, this calculator will give you all of the options of gear combinations you require to set up any lead required. It's true that the average gear set for a lathe doesn't lend itself to such a wide variety of ratios (they usually go up in fives) but if you threw in some extra wheels you could be cutting inch, millimeter, module, DP, BA threads down to a theoretical accuracy that is barely possible to measure. Or you could just do one good enough to screw a nut onto a bolt.

 

[Dr.Al]

By the way, anyone who operates a lathe with change-gears can make good use of that calculator, because the 4 gear train on a hobber is no different at all to the 4 gear train on the end of a lathe. So, with a simple bit of maths (basic TPI- inch or mm pitch conversions), putting in your list of gears and the decimal ratio you need to achieve, this calculator will give you all of the options of gear combinations you require to set up any lead required. It's true that the average gear set for a lathe doesn't lend itself to such a wide variety of ratios (they usually go up in fives) but if you threw in some extra wheels you could be cutting inch, millimeter, module, DP, BA threads down to a theoretical accuracy that is barely possible to measure. Or you could just do one good enough to screw a nut onto a bolt.

I used the same principle (just try every available combination) for the various change wheel calculators on my website.

There's a verified and published one for the M250 and the mini-lathe and some unverified and unpublished ones for an M300 and an LZ4P. The latter two were created after people got in touch to ask for them; they provided the required information & I made the calculators for them. I asked them to check they were right and never heard from them again. Ungrateful s*ds

Anyway, if anyone is interested, they're here:

CGTK - Mini-Lathe Change Gear Calculator

www.cgtk.co.uk

CGTK - Harrison M250 Change Gear Calculator

www.cgtk.co.uk

CGTK - Harrison M300 Change Gear Calculator

www.cgtk.co.uk

CGTK - Boley & Leinen LZ4P Change Gear Calculator

www.cgtk.co.uk

 

[Pete.]

I'm in awe of your mathematical and program writing skills Al. I wish I was as adpet I'm sure that it would be possible to plumb in the data for my particular hobber and have it spit out a soluton. I've been sitting here for several evenings just to get this far.

Now I've found the change gear program (which annoyingly won't save my gear selection) I'm going to try to get my head around the formula to get to that ratio number from the DP and helix angle. For that my challenge is going to be figuring out how to measure the helix angle of an existing gear accurately and then expressing it in a suitable manner for the calculation. the example above has it expressed in degress and minutes but I imagine it needs expressing in degrees decimal for this purpose. I need to figure out the best method for making actual measurements.

 

[Dr.Al]

Give me a shout if you need any help with the maths.

 

[Agroshield]

For that my challenge is going to be figuring out how to measure the helix angle of an existing gear accurately

There are a couple of methods to do this depending on what you have. Easiest is a mating pair of gears, where you can measure the centre distance. The formulas in 'Gear Design Simplified' then lead you to the helix angle (see: https://www.practicalmachinist.com/forum/threads/calculating-lead-for-a-helical-gear.383428/)

If you only have the one gear, there are ways of using span and overpin (overball) measurements. See attached.

Closely related to this is the overpin measurement stuff in the back of the Van Keuren Handbook. For identification (as opposed to inspection), you'd know the measurement and use it to calculate the helix angle. If inspecting, you would know the helix angle, use it to calculate the overpins measurement and then see how close the manufactured article was to that measurement.

 

[Pete.]

Thanks for that but the maths is too heavy for me.

On the plus side I find tables of natural sines from an old Brown & Sharpe publicationg long since downloaded right here in the literature folder on my PC (and this has reminded me to back this stuff up). That's one hurdle crossed, I can look up the sine/cosine of any angle in degrees and minutes.

 

[Seadog]

Thanks for that but the maths is too heavy for me.

I see what you mean, Pete.

 

[Seadog]

Low Budget Skills on Instagram: "Incredible Manufacturing Process of Double Helical Gear with 100yrs Old Technology"

59K likes, 166 comments - lowbudgetskills on October 16, 2023: "Incredible Manufacturing Process of Double Helical Gear with 100yrs Old Technology"

www.instagram.com

 

[awemawson]

Back in school in the 1960's we each had a light blue book of tables of all the trig functions, log, log / log, and anti log (Godfrey and Siddons iirc) - there must have been gazillions of them printed so surely they'll still be around in book shops?

Yes here you go:

Godfrey and Siddons - AbeBooks

Four - Figure Tables by Godfrey, C. And Siddons, A. W. and a great selection of related books, art and collectibles available now at AbeBooks.co.uk.

www.abebooks.co.uk

 

[Windy Miller]

Back in school in the 1960's we each had a light blue book of tables of all the trig functions, log, log / log, and anti log (Godfrey and Siddons iirc) - there must have been gazillions of them printed so surely they'll still be around in book shops?

Yes here you go:

Godfrey and Siddons - AbeBooks

Four - Figure Tables by Godfrey, C. And Siddons, A. W. and a great selection of related books, art and collectibles available now at AbeBooks.co.uk.

www.abebooks.co.uk

I still have mine. Used daily when I was at school before calculators!

 

[Brad93]

Back in school in the 1960's we each had a light blue book of tables of all the trig functions, log, log / log, and anti log (Godfrey and Siddons iirc) - there must have been gazillions of them printed so surely they'll still be around in book shops?

Yes here you go:

Godfrey and Siddons - AbeBooks

Four - Figure Tables by Godfrey, C. And Siddons, A. W. and a great selection of related books, art and collectibles available now at AbeBooks.co.uk.

www.abebooks.co.uk

I think we were shown excerpts of these types of books and it was quickly brushed aside.

Shame really, tremendous mathematical calculations used to be made with books like the aforementioned and slide rules.

 

[Pete.]

Well, she lives!

 

[Pete.]

Big thanks to @Dcal for coming round and helping me put this back together yesterday. Earlier in the day I had stripped out the oil pump and du-gunged the sump. There was no metal in it just the heavier elements of the ol cutting oil had settled out over 30+ years and formed a tar in the base.

With that all cleaned out I turned to the pump. I re-greased the grease caps after digging out all the old grease. I put some light oil in first to ttry to soften what was left of the dried out stuff then fresh grease. Stripped and cleaned the impellor housing and set the terminal box for 240v delta. Then I found a 8uf cap and a 4uf cap, cobbled up a steinmetz connection and tested it out.

That was pumping great (even going backwards) so I re-wired it to turn the other way and it pumped even greater.

By now Dcal was here so he set about re-assembling the gear trains whilst I wired in the VFD. The drive fitted on the back of the button plate after removing the old contactor and shifting a few wires so apart from losing the start and stop buttons in favour of an Estop switch and speed control pot, it all fits inside without spoiling the look of the machine.

So things left to do are:

Button up the electrical cover after fitting the speed pot
Re-fit the guards and covers
Re-make the arbor drawbar for the hob arbor, the original buckled under 4 tons of hydraulic press getting the arbor out
Make some other arbors for different bore hobs
Fit a light, and a magnifier on the hob head scale, coz I can't read it easily where it is.
Re-make a couple of bushes for the gear train which are the wrong type
Re-make the 5/16"BSF nuts for adjusting the hob angle, with intenal hex instead of nut flats, as they are the devil to use so tight against the housing (and you use them a lot)
See why thwheel is wobbling when it turns, and sort it out.
Find if there's a method of simplifying the index geartrain setting. I did this on my old hobber by making some new gears and fitting them so that setting the train was a simple matter of putting the same tooth count in the train as the gear you want to cut.

Finally, Find a permanent spot for it, coz it's a keeper.

 

[Seadog]

Back in school in the 1960's we each had a light blue book of tables of all the trig functions, log, log / log, and anti log (Godfrey and Siddons iirc) - there must have been gazillions of them printed so surely they'll still be around in book shops?

Yes here you go:

Godfrey and Siddons - AbeBooks

Four - Figure Tables by Godfrey, C. And Siddons, A. W. and a great selection of related books, art and collectibles available now at AbeBooks.co.uk.

www.abebooks.co.uk

I still have mine somewhere.