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View Full Version : What am I doing wrong? Dividing head.



The Artful Bodger
05-20-2012, 06:16 PM
I am trying to cut a 26 tooth gear but things are not going quite right!

Once around the blank and I find it has rotated too far, not much, but enough to be visibly out.

I am using the 39 hole range, one full turn plus 21 holes. i.e. I have 22 hole space between the sector arms of the dividing head. Is that right?

My technique is to rotate the handle and put the index pin back in the hole it came out of then turn the sector arms and advance the index pin to the new position of the sector arm.

???:confused:

John Stevenson
05-20-2012, 06:39 PM
you need 21 holes between arms.

Hopefuldave
05-20-2012, 06:41 PM
The maths sounds right, 40:1 worm and wheel?

so...
a turn (39) plus 21 = 60 holes
(39 x 40) / 60 = 26 alright!

Hmmm.... Are you coming up short (e.g. 26 and a bit teeth) or long (25 and a bit)? If short, you need to take an extra hole, if long one less - but it sounds like you're doing it right! Are you *certain* the sector arms aren't moving a bit as you crank the handle round?

Dave H. (the other one)

Hopefuldave
05-20-2012, 06:47 PM
you need 21 holes between arms.



No, 21 *spaces*, surely? that means 22 holes between - f'rinstance, if it was a turn-and-a-half on a 40-hole, you'd need to put on a full turn and 20 spaces, so 21 holes between the arms (you wouldn't count the starting hole)?

Just my ha'pennorth

Dave H. (the other one)

dp
05-20-2012, 06:59 PM
Assuming 40:1 on the drive,


40 / 26 = 1 14/26 if you have a 26 hole plate, or
1 7/13 if you have a 13 hole plate, or
1 21/39 turns for a 39 hole plate.

Don't count holes - count spaces. Or be sure you start your count at 0 for the zero'th hole.

The Artful Bodger
05-20-2012, 08:28 PM
Oh well, I guess I wasnt holding my mouth right or something! Second blank came out OK except some of the teeth are a bit tighter than others, not seriously and I am sure I can fix them.

Thanks for advice.

Forrest Addy
05-20-2012, 09:28 PM
This gadget it the bomb for indexing:

http://www.divisionmaster.com/divisionmaster.html

Make some parts bolt it on. Bye-bye index plates.

oldtiffie
05-20-2012, 09:37 PM
+1 Forrest Addy and the "Divisionmaster". It will cut or drill or what-ever any number - even 127 which no standard set of divider plates will.

I suspect that the "tight and loose" bit on the OP's gears is due to back-lash creeping in - ie it was not "taken up".

Always approach the arm in a clockwise direction and alway lock the table at each gear slot as its quite easy to move the table unless its locked.

bytewise
05-20-2012, 09:41 PM
Cranking is fussy! You must be sure to always take up slack in the same direction. If you accidentally go too far, you must back up a ways and come up to the end again. Depending on your machine, you might not be able to return the piece with the cutter in cut position. I have had to lower the knee during return and refeed for the next cut.
Hugh

Spin Doctor
05-20-2012, 10:02 PM
First what is the number of turns of the input shaft for one revolution of the work holding shaft. If it's 5-1 then for a 39 hole plate you have 195 holes. 195/26=7.5. So if you go 15 holes an index that should work. It'll take two full turns of the work to get what you need so you won't be cutting adjacebt teeth until you get to your second revolution of the work. One sector arm aganst the trailing side of the index pin. the other 15 hole away from the index pin. Lock the sector arms. Pull the index pin and rotate to the arm. Insert pin. Unlock sector arms and bring the trailing arm up to the pin. Lock in place. Repeat as required.

oldtiffie
05-20-2012, 11:12 PM
My bet is that its a 40:1 "Vertex".

The Artful Bodger
05-20-2012, 11:49 PM
My bet is that its a 40:1 "Vertex".


Maybe a clone, Homge BS-1 semi universal dividing head. 40:1 handle.

The Artful Bodger
05-22-2012, 01:10 AM
P.S. Always ensure chuck is firmly screwed onto dividing head...:o :eek: :eek:

oldtiffie
05-22-2012, 03:25 AM
Having your head as well as your chuck screwed on tight is always an advantage.