Making a threading gear for an SB lathe - alternate idea:

[Alan J. Richer]

Now, I realize that the traditional way to do these is by gashing the blank and then using a hob for the cut, but what would prevent me from using a flycutter ground to the shape of an Acme thread and cutting the threads in my horizontal mill with an indexing fixture?

Reason I ask is less-than-stellar skill set in making things like hobs, but little trouble doing odd bits like this in my horizontal mill with my rotary table.

Discuss... ;D

Thanks, Alan

 

[steamer]

Hi Alan,
For a single gear you could just buy one, as they are available.

If you NEED to make one, I would buy the appropriate gear cutter. You will need an indexing head or equivalent.

I Believe SB's are 18 pitch which is a bit odd ball....You will need to check exactly what DP and pressure angle you will need.
And tooth count to choose the proper cutter ( numbering 1-8 normally)
The setup in the horizontal mill to cut a gear looks like this

Hope that helps!

Lindsay has a book I believe by Colvin on "Gear Cutting Practice" that would be very informative

Dave

PS....I have some articles on Making form relieved Involute gear cutters......though doable, HSS cutters are something like $20 US and the best a HSM can do usually is carbon tool steel....so unless the form or DP are truly "Unobtainium" I would suggest buying the right numbered cutter for the DP and pressure angle required.

 

[John S]

Alan,
None at all.
By threading gear I presume you meant the thread dial indicator, Steamer seems to think you mean change wheels.

The thread dial indicator gear has to do very little work and any close interpretation of a gear with 32 teeth will work.

I have even seen it where people have used just a slitting saw and rubbed the sharp edges off.
I have also seen it where they have hobbed them with an 8tpi tap.

Do what you are most comfortable with - it can't fail to work.

JS.

 

[Alan J. Richer]

Re: Threading gear: Yes, I did mean the thread dial engagement for the leadscrew - I have a very nice full set of change gears for my SB 405, thank you very much...

I thought as much on the manufacturing technique - it's just that I tend to think within the available tools and materials rather than making something new to make something new...a bit too recursive for my tastes.

Thanks!

 

[Holescreek]

I do it all the time. Fly cutting works well. -Mike

 

[steamer]

John..your right.I think my age is starting to show :big:

As Mike has demonstrated so aptly with his 4th axis conversion ( read the thread...its nice)....you could fly cut just fine...... :bow:

Dave

PS On the other hand...if you can match the pitch decently, you could also just buy a gear and put the indicator on the helix angle of the thread.......but thats no fun....

 

[John S]

Pitch is a problem because it's a 8 tpi screw so 8 x Pi is 25.13

However thats damn close to a 1 MOD of 25.4 and thos 1 MOD gears are very common on the import lathes but then the problem is getting a 32 tooth from one of them.

HPC gears in Chesterfield will stock 32 teeth 1 mod gears.

.

 

[Alan J. Richer]

Holescreek:

Showoff... :bow:

I thought it would work well - just wanted a sanity check before I started tooling the little monster up. This is a when-i-get-to-it project - at present doing a small production run of shear pins for old Land-Rover capstan winches and want to get themout of the way before i pursue anything else.

As opposed to the vertical setup you're using, I'm going to be doing this trick on my horizontal mill. This actually makes it a lot easier to work with, as everything will get done right up top and quite visible. Works for me.

John: MOD 1 gears? I assume that is a metric pitch? Do enlighten the Colonial, please... My uncle in Loughborough would be shocked to hear one named Stevenson going on about metric anything!

Thanks, folks - the input is much appreciated.

 

[Holescreek]

Holescreek: Showoff...

Sorry, I really am trying to hold back. I did learn a valuable lesson with regard to single pointing helical gears. Because the cutter is spinning while both the X and A axis are moving, the cutter must be oddly shaped to even come close to the proper tooth form. -Mike