Subject: Homemade dividing head??????

From: alan anganes <[email-masked]>
Date: 26 Jun 1996 23:51:45 GMT

Has anyone out there ever built a dividing head? I have been thinking 
that I ought to be able to build one around a standard right angle worm 
gear speed reducer, a few of which I happen to have. I have 20:1 and 30:1 
ratio gearboxes. It seems to me, that by adding a suitable center or 
chuck, and a method for attaching an indexing plate to the input shaft, I 
should end up with a servicable dividing head. 

  What are the flaws in this brilliant idea? I can't be the first to come 
up with this. Is there something magical about the 40:1 ratio used in a 
standard head? I don't see why any other ratio would not work. I sort of 
need a dividing head and am too poor/cheap to buy a real one. 

  How about some thoughts!!

                             Tahnks, AL

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From: PPIERCE <[email-masked]>
Date: Wed, 26 Jun 1996 17:53:03 -0700

>   How about some thoughts!!

Dave Gingery authored a book (order from Lindsay) on the construction of a
dividing head.  I've never looked ito it but suppose that 40 works out well 
as to the number of holes needed in the index plates.

In "The Shop Wisdom of Philip Duclos" (Village Press) on page two is a
construction article to make a dividing head, plates, sector arms, etc.  
Near the end of the article is a brief rundown of the math involved.

On page 10 of "Metalworking Two" Steve Wellcome has an article on the
mathematics of the dividing head.

Good Luck

Paul in AJ AZ
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From: [email-masked] (Ray Spinhirne)
Date: 27 Jun 1996 03:53:18 GMT

alan anganes ([email-masked]) wrote:
:   Has anyone out there ever built a dividing head? I have been thinking 
: that I ought to be able to build one around a standard right angle worm 
: gear speed reducer, a few of which I happen to have. I have 20:1 and 30:1 
: ratio gearboxes. It seems to me, that by adding a suitable center or 
: chuck, and a method for attaching an indexing plate to the input shaft, I 
: should end up with a servicable dividing head. 

:   What are the flaws in this brilliant idea? I can't be the first to come 
: up with this. Is there something magical about the 40:1 ratio used in a 
: standard head? I don't see why any other ratio would not work. I sort of 
: need a dividing head and am too poor/cheap to buy a real one. 

:   How about some thoughts!!

:                              Tahnks, AL

I built one using a 60 to 1 worm gear.  The body was two 4 x 6 x 1.5 plates
and the "spindle" was turned to match my lathe spindle so that it would
accecpt my chuck or face plate.  It was a fun exercise and I have used it
extensively as both a dividing head and a rotary table.  If you have a 
milling machine, lathe, and time, and not much money go for it.
Get the book mentioned in other posts to get some ideas, but remember
that you don't have to cast anything as long as you have solid material
and enough time.

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From: [email-masked] (Don Stauffer)
Date: 27 Jun 1996 08:00:11 CDT

>  How about some thoughts!!
I wanted something very small for my Sherline.  So commercial ones other 
than Sherline's own were out.  The combination of price, plus some lack 
of features I wanted, caused my to try to make my own.  I bought a 40:1 
worm and gear and designed it around that.

I am early in the construction, so cannot claim much about its success.  
But I do have the drawings, which are done in Autosketch, which can 
export DXF.

One thing I did unusual was the case material.  I had intended to make 
Delrin bushings, since I had a lot of scrap Delrin, and it makes good 
bearings.  Then it dawned on me- why machine an aluminum case and a 
Delrin bushing, when I can make the whole case out of the delrin.  I 
found I had a piece large enough to act as case, and another to act as 
cover, so that is what I am doing.  Of course, it will not be super 
strong, and may not be super accurate, but for my modeling activities 
these are not as important.

Don Stauffer in Minneapolis
[email-masked]

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From: [email-masked] (Paolo Zini)
Date: 27 Jun 1996 14:36:20 GMT

>should end up with a servicable dividing head. 

A friend of mine has done some similar, him has followed one rotating head approach
in place of a dividing head. I mean that him has placed one graduated disk in place
of indexing plate.
I tink that the true problems are:
1) backlash. The my friend has used a fairly good new unit and the play is limited.
2) indexing plates, You can buy it but....

>need a dividing head and am too poor/cheap to buy a real one. 

40:1 and 60:1 have nothing magical, have only a large number of prime number.
40 is 2*2*2*5 then any number that is a combination of those numbers can be
easy produced.
60 is 2*2*3*5 and has one more number.
if you want to produce any multiple of 3 on one 40:1 dividing head you must use one
plate that has a circle of holes that is one multiple of 3.
Obviously the larger the ratio more are reduced the plate errors.
If you have a 30:1 reduction unit the errors of the plate are divided by 30
if the unit is 60:1 are divided by 60.
I hope that all this is clear, is difficult for me to explain in english, but
no problem, i would find problem also to explain it in italian :-)

>  How about some thoughts!!

Ciao

Paolo

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From: [email-masked] (darylb)
Date: 27 Jun 1996 19:45:30 GMT

> as to the number of holes needed in the index plates.
snip....

I think the 40:1 ratio was for the pitch of the leadscrew when doing
spirals (I could be wrong).
1/4" per turn of the leadscrew tied in with the 40. I think it made the
math easier. But most people never use a dividing head for this and so you
could use any ratio. If you use a standard ratio plates could be bought &
existing dividing tables used.

Are you making a universal head or just a semi universal?

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From: [email-masked] (Russ Kepler)
Date: Thu, 27 Jun 1996 18:53:10 GMT

In article <[email-masked]>,
>need a dividing head and am too poor/cheap to buy a real one. 

Lots of DH kits out there, everything from Gingery's book on making
a DH from plate stock and parts to Geo. Thomas' "Versatile Dividing
Head" design.

As to ratio - all a high ratio does is to improve the chances that
you'll get a match between a plate and the number of divisions that
you want.  Even a small ratio such as the 4:1 on my Hardinge DH can
do most divisions up to 360 with a reasonable selection of plates (of
course the 75 hole plate look more like air than a indexing plate).

---

From: Steve Wellcome <[email-masked]>
Date: 1 Jul 1996 12:11:34 GMT

The only thing magical about 40:1 that I know of is that it has 
some nice factors so you don't need as many index plates to get 
a given number of divisions.  Other good ones would be, say, 
48:1 and 60:1.  Either 20;1 or 30:1 would be okay too.  You can
crank through the math, if you're so inclined, and figure out
the possibilities for each one.  In brief: 
  1. Decide which divisions you want to do.  Since you don't
     know in advance, for sure, you have to make an assumption.
     When I ran through it I assumed I wanted all divisions 2-50,
     all even divisions 52-100, 125, 200, and 360.
  2. For a given gear ratio, figure out what index plates you need 
     to do those divisions.  For instance, with a 30:1 ratio, to
     get 52 divisions you need to turn the crank 30/52, or 15/26,
     of a turn.  So you need a 26-hole index plate.
  3. When you have the list of all possible index plates, go through
     the list and knock out plates that are factors of others.
     You'll have a lot of cases where you need 1/2 a turn, probably,
     but you don't need a 2-hole index plate because we've already
     established that you need a 26-hole index plate and you can get
     1/2 a turn by doing every 13 holes.  Same for 1/3, 1/4, etc.
  4. You will end up with the minimum set of index plates you need
     *for the set of possible divisions you chose.*  Then you may want
     to go through and see if it makes sense to combine some.  You
     will probably end up needing a 6-hole and a 9-hole index plate,
     but it might make sense to combine those into a single 18-hole
     index plate, if you don't already need one.  Or a 36-hole plate.

Anyway, you can run through all that for 20:1 and 30:1, and it may
become apparent *for the set of possible divisions you chose* that one
ratio is better than the other.

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From: [email-masked] (Steven Malikoff)
Date: 2 Jul 1996 19:48:00 +1000

Yep, you've got the right idea. I built one about 15 years ago when I was
a kid from a scrapped worm gear arrangement and used it very successfully on
my dad's 6"x24" lathe. I welded up a bracket to attach the gearbox to the back
of the headstock, and machined a spigot that went into the headstock spindle.
This was fixed with an allen bolt through a hole drilled through the spindle.
The gearbox had a gear attached to the worm on the outside of the casing, so
I made another bracket to hold an allen bolt with the end turned to fit into
the gear teeth as a detent.
I used this to make all sorts of things such as homemade milling cutters and
other stuff I couldn't afford to buy from my pocket money.

Steve.
-- 
Steve Malikoff
[email-masked]
WW2 jeep page at http://phaedra.apana.org.au/ww2jeep.html