Author Topic: Gear parameters  (Read 1894 times)

Offline John Rudd

  • Hero Member
  • *****
  • Posts: 2456
  • Country: gb
Gear parameters
« on: September 04, 2020, 03:28:32 PM »
Unfortunately my 11x27 lathe has an issue with the power feed...
The worm drive gear is wearing...not suprising made from brass....

A new one,if I think its the right one, is around £25..but is an a 12 week lead time.

I'm sure I can make a new one....
So, I know its diameter, teeth count is 17 ( seems an odd number..)
What I dont know is the DP and the angle of the teeth...

How would I determine these ?

eccentric millionaire financed by 'er indoors
Location:  Backworth Newcastle

Skype: chippiejnr

Offline tom osselton

  • Hero Member
  • *****
  • Posts: 1141
  • Country: ca
Re: Gear parameters
« Reply #1 on: September 04, 2020, 05:28:27 PM »
Iíve heard roll it on plastercene then measure the angle.

Offline Lew_Merrick_PE

  • Hero Member
  • *****
  • Posts: 690
  • Country: us
Re: Gear parameters
« Reply #2 on: September 04, 2020, 05:50:11 PM »
Unfortunately my 11x27 lathe has an issue with the power feed...
The worm drive gear is wearing...not suprising made from brass....
Hi John  --  The real is the Diametral Pitch (or Module) of the gear.  I assume it is a Drive Gear rather than a pure Spur Gear.  That information plus OD and ID measurements would help identify it.  --  Lew

Offline John Rudd

  • Hero Member
  • *****
  • Posts: 2456
  • Country: gb
Re: Gear parameters
« Reply #3 on: September 05, 2020, 02:29:09 AM »
Sorry, I seem to have written in haste....

The feed drive shaft passes through a worm gear at the rear of the apron, this in turn drives the brass gear in question which is placed at right angles to the worm, thus providing the drive for the carriage and powered cross feed.

I guess  the brass gear is probably MOD being a Chinese made lathe, but there is a chance it could be DP....

So armed with the gear's od and teeth count should aid identifying DP or MOD?
eccentric millionaire financed by 'er indoors
Location:  Backworth Newcastle

Skype: chippiejnr

Offline chipenter

  • Hero Member
  • *****
  • Posts: 900
  • Country: gb
Re: Gear parameters
« Reply #4 on: September 05, 2020, 02:36:20 AM »
The worm will be the same pressure angle and is straight , cut a paper template and measure that .
Jeff

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5827
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Gear parameters
« Reply #5 on: September 05, 2020, 08:19:46 AM »
A set of pitch gauges is what I use. As chipenter says, they are just straight sided rack form, so you could make a template and measure that. The worm is a straight rack at any axial profile. If you make your pitch gauge accurately out of tin sheet stock, and cut it out with tin snips, you can use it to check your cutter grind (for making the hob). The pitch gauge is handy to have in future.

To make a really accurate template, do a rough one first, get its measurements, which will point to one standard pitch and angle (one hopes). Then lay out the proper measurements in CAD for that pitch, and print it. Paste that onto your tin sheet and cut out with snips to give you a gauge.

If you then duplicate the worm on the lathe in drill rod (silver steel) and gash and harden you can make it into a hob to cut the gear.

Making a tap is similar -- I did that in my new lathe build project, though I used Acme threaded rod, gashed, and hardened with Kasenit.
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5827
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Gear parameters
« Reply #6 on: September 05, 2020, 08:58:00 AM »
Actually, there's an even easier way.

With a scriber just lay out a doubled 14-1/2 degree (29 degree) angle on a piece of sheet tin, and cut it out to make a 14-1/2 deg pressure angle gauge. Since it comes to a sharp point, trim/grind that back until it just fits into your worm. If it's right, that's your gauge for making a lathe tool.

If the angle looks wrong, do the same thing to make a 20 degree pressure angle (doubled) gauge. Now you have two useful gauges.

Since you now need only the TPI  (or metric equiv). to set your lathe for cutting the hob, just count the worm's threads per unit length, and Bob's yer aunt!

« Last Edit: September 05, 2020, 09:27:34 AM by vtsteam »
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline John Rudd

  • Hero Member
  • *****
  • Posts: 2456
  • Country: gb
Re: Gear parameters
« Reply #7 on: September 05, 2020, 09:55:29 AM »
Guys, I appreciate all the help here, I appreciate the DP and or MOD are the same for the gear and worm, but I am completely lost from then on...... :scratch:

.........Just read Steve's 2nd post....I'm off to play and see what trasnpires....
eccentric millionaire financed by 'er indoors
Location:  Backworth Newcastle

Skype: chippiejnr

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5827
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Gear parameters
« Reply #8 on: September 05, 2020, 10:43:08 AM »
Also, your hob needs to be the same diameter as your worm. So no need to calculate or look that up, either. Just measure it.
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline John Rudd

  • Hero Member
  • *****
  • Posts: 2456
  • Country: gb
Re: Gear parameters
« Reply #9 on: September 05, 2020, 11:35:26 AM »
Steve,
The gear mates at right angles to the worm, the teeth are cut at an angle so its not just a straight cut gear...( which I could handle...) so I need to determine the angle at which the teeth are cut...,is that easy to do?
eccentric millionaire financed by 'er indoors
Location:  Backworth Newcastle

Skype: chippiejnr

Offline Sea.dog

  • Full Member
  • ***
  • Posts: 182
  • Country: gb
Re: Gear parameters
« Reply #10 on: September 05, 2020, 11:49:30 AM »

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5827
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Gear parameters
« Reply #11 on: September 05, 2020, 11:51:51 AM »
No John, it's easy. The gear blank and hob rotate together, so the hob naturally cuts that correct helix angle automatically. Just line them up perpendicular, the same as they are on the lathe.

If you think about it you're just making a toothed worm, exactly the same as the existing worm in shape and size and position, and it is gradually cutting its way into the blank by rotating together, the same as the original gear train meshes. This results in exactly the proper form teeth for the gear to fit the hob (and worm).

Another analogy is that this is very similar to how a tap works. Yes the threads are at an angle, but you drive the tap vertical to the work, and by rotating it cuts the angle automatically.

In fact a rotating tap can be used, in a suitable fixture with a gear blank, to create a worm gear that fits a threaded rod of the tap's pitch and diameter. Then, a piece of threaded rod, end turned down to a journal, can be used as a worm for that gear.

If an Acme tap and threaded stock is used, the gears are very similar in tooth form to standard worms and wheels.
« Last Edit: September 05, 2020, 12:50:39 PM by vtsteam »
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5827
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Gear parameters
« Reply #12 on: September 05, 2020, 12:48:40 PM »
Here's a pretty good video. He gashes the wheel with a spin indexer on the mill with a fly cutter, and for that operation he does pack it up to the helix angle.

But on the lathe,  the hob cuts straight perpendicular to the wheel.



I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline John Rudd

  • Hero Member
  • *****
  • Posts: 2456
  • Country: gb
Re: Gear parameters
« Reply #13 on: September 05, 2020, 01:07:31 PM »
Well that looked easy..... :bow: :bow:

The only bit of info I am missing is the packing angle....

I guess the hob was made from Silver Steel and hardened?
eccentric millionaire financed by 'er indoors
Location:  Backworth Newcastle

Skype: chippiejnr

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5827
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Gear parameters
« Reply #14 on: September 05, 2020, 04:33:19 PM »
It would be the helix angle, which is the angle that the worm has when looking dead on if you hold it vertically in front of your face. You could probably approximate this, if you don't want to calculate or look it up. The reason it doesn't have to be spot on is that you don't gash the gear blank very deep. Just enough to help the hob find its way, and then the hob modifies the tooth space anyway. So "close enough" is probably good enough.

But if you want to calculate it (i'm still Imperial here so forgive me these units) and you have your TPI from counting the worm teeth per measured length (let's say it's 10 TPI), and let's say your worm is 3/4" in diameter. Let's say that the length of the base of the collet spinner you want to shim is 8". Then shim height = Base length divided by (TPI X Diameter X Pi) or:

Shim height= 8" / (10 X .75 X 3.14)
Shim height = 0.34"

This isn't using the technically correct definition of the worm helix angle, I believe, but I think it's close enough for gashing.

Uh, also people, check me on this -- I just made it up. If you know how to properly calculate (or look up in a table) the helix angle of the above worm, do that, and then multiply the sine of that angle times 8" and tell me how close I got for the shim height. Thanks.....!  :smart:
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5827
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Gear parameters
« Reply #15 on: September 05, 2020, 04:50:31 PM »
ps. all of your setups including the mill gashing will be "handed". Be careful about this, or you might make a left handed worm and wheel (assuming you want right). Or worse, one of each.  :bang:
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline djc

  • Jr. Member
  • **
  • Posts: 73
Re: Gear parameters
« Reply #16 on: September 06, 2020, 03:55:55 AM »
Also, your hob needs to be the same diameter as your worm.

AIUI, that is only the case if you want to make an enveloping gear.

The splash screen on this video seems to show the three examples of worm-wheel combinations that I am aware of:


Offline vtsteam

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5827
  • Country: us
  • Republic of Vermont
    • www. sredmond.com
Re: Gear parameters
« Reply #17 on: September 06, 2020, 11:01:14 AM »
Nope, I said the same size as the worm.

And the wheel width should be the same width as the present wheel.

We're duplicating existing parts, yes?
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline John Rudd

  • Hero Member
  • *****
  • Posts: 2456
  • Country: gb
Re: Gear parameters
« Reply #18 on: September 06, 2020, 11:12:44 AM »
Yep,I got all that.....

What I'm now unsure of is the material for the hob....I'm thinking silver steel?

But at the diameter needed, there arent  many suppliers that do ss at diameters bigger than inch....
Tool steel as an alternative maybe....
Thn the next dilemma, the existing driven gear is brass....should I use something a bit better wearing, like phos bronze? Assuming the worm is hardened... :Doh:
eccentric millionaire financed by 'er indoors
Location:  Backworth Newcastle

Skype: chippiejnr

Offline Pete.

  • Hero Member
  • *****
  • Posts: 1067
  • Country: gb
Re: Gear parameters
« Reply #19 on: September 06, 2020, 12:29:15 PM »
Unfortunately my 11x27 lathe has an issue with the power feed...
The worm drive gear is wearing...not suprising made from brass....

A new one,if I think its the right one, is around £25..but is an a 12 week lead time.

I'm sure I can make a new one....
So, I know its diameter, teeth count is 17 ( seems an odd number..)
What I dont know is the DP and the angle of the teeth...

How would I determine these ?

The angle of the teeth will be the helix angle of the worm at the pitch diameter (not at the OD). Helix angle increases as diameter decreases on all screws so use the pitch diameter for a happy medium.

So, what is your worm TPI and diameter? From those you can work out the helix angle. Also look here for a very good source of info:

http://103.71.168.43:81/mis/files/coursefiles/AY2018%20-%202019/Mech/ME6601/cf~pdf%C3%A2%E2%82%AC%E2%80%9C%20WORM%20GEARS~63~ME66011542615387-1.pdf

Offline Lew_Merrick_PE

  • Hero Member
  • *****
  • Posts: 690
  • Country: us
Re: Gear parameters
« Reply #20 on: September 06, 2020, 04:19:14 PM »
What I'm now unsure of is the material for the hob....I'm thinking silver steel?

But at the diameter needed, there arent  many suppliers that do ss at diameters bigger than inch....
Tool steel as an alternative maybe....
Hi John -- from the other side of the pond  --  Where we call silver steel tool steel.  What size are you looking for (as I have a moderately large "surplus heap").  Irrational minds want to know ;-)  --  Lew

Offline Bee

  • Jr. Member
  • **
  • Posts: 41
  • Country: gb
Re: Gear parameters
« Reply #21 on: September 12, 2020, 05:56:04 PM »
I think silver steel in UK translates to drill rod in the USA not tool steel which is HSS in most countries except China where it is cheese.
Instead of a large diameter rod just use a piece guage plate (flat equivalent of siver steel ie a high carbon hardenable steel) 3/8 thick as a disc. Cut it as only a single turn worm to make the cutter. You will have to feed it in slower depthwise but if just > one turn it can still even rotate the blank as it cuts. You could even double it up pinning two pates together for a bit longer worm.

Offline Lew_Merrick_PE

  • Hero Member
  • *****
  • Posts: 690
  • Country: us
Re: Gear parameters
« Reply #22 on: September 12, 2020, 10:11:53 PM »
I think silver steel in UK translates to drill rod in the USA not tool steel which is HSS in most countries except China where it is cheese.
Bee  --  At least here in the U.S. "tool steel" is any hardenable steel.  Drill Rod is merely round bar Tool Steel.  --  Lew

Offline John Rudd

  • Hero Member
  • *****
  • Posts: 2456
  • Country: gb
Re: Gear parameters
« Reply #23 on: September 13, 2020, 07:24:00 AM »
From'this side of the pond to the other'..... :)
I havent measured directly the worm size diameter yet, but reckon on it being around 1-3/4"....
I'll get an exact measurement when I strip it out which wont be anytime soon as the lathe is working quite well at the moment....

As soon as I know the diameter I will post it up...... :dremel:
eccentric millionaire financed by 'er indoors
Location:  Backworth Newcastle

Skype: chippiejnr