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Division Master (Stepper Motor Dividing)

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Emgee08/02/2019 22:25:12
1067 forum posts
197 photos

Andrew, does the mill have a powered knee or did you have to crank all of those cuts ?

Emgee

Andrew Johnston09/02/2019 08:26:06
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4498 forum posts
520 photos
Posted by Emgee on 08/02/2019 22:25:12:

Andrew, does the mill have a powered knee or did you have to crank all of those cuts ?

Nope, all done by hand. I actually cut six gears, four for my two engines and a mate who is building the same engine just 'happened' to have his two blanks ready at the same time. That makes 432 teeth; 12 turns down and 12 turns up for each tooth. That's a lot of handle w**king. I could do about half a gear at a time before needing tea and biscuits.

Andrew

Andy Carruthers09/02/2019 09:52:00
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200 forum posts
18 photos

Counts as exercise in my book, and lovely job well done too

Mark Simpson 111/02/2019 10:18:03
65 forum posts
20 photos

Andrew: Thank you, it's really good to know that someone with more experience has cut these large gears in the same way as I intend to... Horizontal RT, lock X and Y, and wind the table up and down... (good exercise!)

Also good to know that 5 thou backlash is a reasonable figure for TE gearing, I am less worried about the absolute accuracy of the thing now, but still want to do a good job.

On the division front I think I will have to do something more than "wind the handle to a spreadsheet"

  • My divisions are all awkward numbers as degrees... (76 teeth=4.737deg, 66 teeth=4.535deg, 55 = 6.455 deg
  • I work full time so I am unlikely to manage all the teeth on any gear at one sitting
  • I make mistakes and 55+66+76 is a lot of opportunity for Captain Cockup to pay a visit.

I do use my rotary table instead of a bigger lathe, so some way to drive the rotary table continuously would have additional benefits....

I've priced the stepper motor route at about £100 ( I have a suitable power supply already) and will have a go that way, building a whole division mechanism for the RT to cut 3 gears seems like too much effort

I do still like Jason's Idea to produce a large division plate and bolt it to the top of the gears then release the worm on the RT.... Easy, Cheap and I can check the accuracy of the division plate before cutting any teeth by measuring between the holes... I love a practical solution!

Many Thanks
Mark

Andrew Johnston11/02/2019 11:11:37
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4498 forum posts
520 photos
Posted by Mark Simpson 1 on 11/02/2019 10:18:03:

Also good to know that 5 thou backlash is a reasonable figure for TE gearing, I am less worried about the absolute accuracy of the thing now, but still want to do a good job.

These are not precision gears. As has been stated, in fullsize the final drive gears would have been as cast, with any lumps tidied up with a hammer and cold chisel.

Andrew

Mark Simpson 114/03/2019 11:10:39
65 forum posts
20 photos

Quick progress update...

I found that the dividing plates from a 6" table had a big enough bore (22mm), so made a mounting for them on my 14" table, made a new handle for it and it seems to work fine. Stepper motor route would perhaps have been better in the long run but I already had the plates for the 6" and decided to go for it (and not spend 100+quid)

20190314_085148.jpg

Then had to lift the gear blank off the table, and after investigating the price of 4 off 2" tall parallels I bought 3' of 2"x1" mild steel bar and added 5 thou of shim in 2 places (it's a one off setup after all). Added 6 clamps and a 1" whit stud and started cutting teeth
20190314_085158.jpg

It seems a very solid setup, and have been able to cut the 4DP, .539" deep teeth in one go

as Andrew mentioned, it's a lot of handle winding, but very satisfying

Thanks again for the advice, all useful

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