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jontwo13
05-13-2006, 02:06 PM
Are the button holders on John Stevenson form tool ajustable for center to center? I can't tell from the pictures. They have a grub screw to lock button.
Could anyone give me any information on making an adjustable one or if it is possible. I need to cut several 16 DP 14 1/2 degree gears for a 1940 clausing.
sol

JCHannum
05-13-2006, 03:02 PM
They are not adjustable, and it would be a little difficult to do for as small a gear as 16DP.

Since involute cutters are a compromise for size any way, you might be able to span the range you need to cut by making a cutter that falls between the normal cutter range. For instance a "3-1/2" that would span around 30 to 45 teeth.

jontwo13
05-13-2006, 04:19 PM
I was looking at making the button's and useing one holder for all of them. Like Tiny T-nuts or a locked dovetail with small bolts through the buttons. I hate to make 6 different botton holders.
sol

John Stevenson
05-13-2006, 07:19 PM
Sol,
There is an easy way which entails making just one single holder for one button but you will have to do some maths from the tables.

Lets take a 30 tooth gear at 14-1/2 PA in 16 DP
The table tells us that the button diameter is 8.22 / 16 = 0.514"
The centre distance of the buttons is 9.42 / 16 = 0.589"
Infeed is 2.98 / 16 = 0.186" for a given blank size of 4 / 16 = 0.250"

Lets look at that.

http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/30T_14.5.BMP

The drawing on the left shows the geometrically correct layout with the buttons just touching the blank.
The one on the right shows the buttons after infeeding 0.186" to form the cutter shape.

Now if you just have one button mounted in a single holder if you centre the button on the blank, wind 0.295" to the left, just touch the blank then infeed 0.186" you will generate one side of the cutter.
Do the same on the right and you have a finished cutter.

You just need to offset by half the centre distance to use one button.

HTH.

.

George Seal
05-13-2006, 11:05 PM
Sir John,

What table are you using?????????????

jontwo13
05-13-2006, 11:17 PM
John Stevenson has a table for 14 1/2 degree and 20 degree angle gears and it is different for the number of the cutter or number of teeth.The 30 tooth is a number 4 cutter 26-34 teeth.
sol Del Rio TN

J Tiers
05-14-2006, 02:12 AM
I'll bet that form tool is a pig for chatter, with about 0.4" of cutting face in contact with the work...... at least if you don't have something like his TOS....

It did occur to me that if you did want an adjustable one, a sort of scissor tool on its side with the buttons on the arm ends could be made to take the different diameter buttons and do different spacings by adjusting a screw somewhat like that on a pair of dividers.

John Stevenson
05-14-2006, 08:04 AM
George,
Here's the table for 14-1/2 degree to go with the article on the Metal web new group.

http://homepage.ntlworld.com/stevenson.engineers/lsteve/hidden/14.5degree.jpg

These are not as easy to do in the smaller tooth sizes due to undercutting. The best way I found using home made cutters was to take a second cut with a slitting type saw.
Commercial ones have multiple curves but only approximate the true shape as the dedenium is always wider than the shape at the pitch circle line and can't be cut by a rotating cutter, only a planer type cutter or hob can get this undercutting.

This was one reason that the change to 20 degrees was made, however that doesn't help if you are having to make gear to fit an outstanding application.

.