cutting spur gears on a mill

But how are you cutting the rack with a tap? Unless very short.

Well isnt the worm gear an endless rack?

Get creative, how about a spiral rack

Spur gear with round contour at edges, eg more tooth contact in the mesh

I am envisaging herringbone gear set , ie two spurs, one reversed against the other - no backlash

Waiting on mtl to start my modelling

After all who would ever dream up a pair of oval gears

https://www.radartutorial.eu/17.bauteile/bt08.en.html

By herringbone, do you mean helical? Why would that eliminate backlash?

.

I had presumed that Brian meant what he wrote

… but I could be wrong (it’s happened plenty of times before)

MichaelG.

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https://en.wikipedia.org/wiki/Herringbone_gear

Edited By Michael Gilligan on 21/08/2021 12:09:51

Sometimes I want to give up

https://en.wikipedia.org/wiki/Herringbone_gear

Yes, I know what they are thank you! It's just that though they have the great advantage of being quiet (as a derivative of a helical) and (unlike a helical) not creating a thrust force along the shaft axis, they do not have zero backlash. And making them is difficult. You could I suppose make two helical of opposite hands and mount on the same shaft, but how would you make those with a tap to mate with another similar pair?

Or maybe you don't mean herringbone but just have two straight gears with some angular offset to take up the backlash.

Whatever, I wait with interest to see the results.

Couple of videos for herringbone fans.

Don't blink for the second one.

https://www.youtube.com/watch?v=DFEN9_t150c
https://www.youtube.com/watch?v=9h7nn1v6D-E

John

The Anderton boat lift used 'herringbone' gears. Big ones. They were cast and then run in pairs in a sand bath to bed them in to my knowledge.

regards Martin

I have a cunning plan

I am making up gear blanks using hard wax. I will set up a jig so i can rotate the tap by hand and closely observe what is happening

I will also look at some 3d dynamic modelling s/w i used many years ago (my brian hurts already)

Well it beats lock down dunnit

Maybe he also has got a left hand tap but almost impossible to work into the middle of the chevron that way so would as you say John need two separate gears or opposite hand.

Pay attention at the back

Or maybe you don't mean herringbone but just have two straight gears with some angular offset to take up the backlash.

Does someone want to tell him he can come out now

:O)

Martin

Now I thought you could do something like that

The Anderton boat lift used 'herringbone' gears. Big ones. They were cast and then run in pairs in a sand bath to bed them in to my knowledge.

https://www.alamy.com/anderton-boat-lift-is-a-two-caisson-lift-lock-near-the-village-of-anderton-cheshire-in-north-west-england-image236836670.html

that should keep the back seat modellers quiet for a while

BTW have you all spotted the deliberate design error

see what you can do with a big enough tap

https://www.youtube.com/watch?v=mtV8Zu5EtUE

The hand of the tap or hob would have no influence on the
manufacture of left or right hand helical gears.
As here in the photo the hob is set over at the helix angle
and the work is set as here for right hand ,

and here for left hand.

John

I presume, Brian, that you are thinking along this line. However these are straight spur gears not helical or herringbone. The problem is that, as pointed out, for a herringbone effect you either need a matching left hand tap or else you need to have a large angular change in the relative position of the tap to the blank. Simply flipping a gear 180° will not change the angle of the teeth to give you a herringbone gear. The introduction of this angular relationship will change the tooth form produced quite substantially.

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Martin C

Thanks John P, a bit like screw cutting away from the chuck, something has to be reversed

OK say the tap/hob has a 6 degree helix angle. In order to cut a straight spur gear you angle the tap/hob at 6 degrees to the blank.( Or the blank to the tap/hob). If you increase the angle you get a helical gear of one hand and if you decrease it you get one of the opposite hand.

regards Martin

Changing the angle of the tap changes the pitch produced so they may be of opposite hand but they will have different pitches.

Martin C

No the pitch is set by the TPI of the tap. The approach angle of the cutting edge is set by the skew angle.

regards Martin