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centring for gear cutting

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ady19/01/2011 09:40:24
612 forum posts
50 photos
I was having a go at a spur gear last night where the workpiece was held in the lathe between centres and the milling unit was doing the work with a cutter at right angles, coming down from above while mounted on a milling slide to cut the slots.
 
While the job was o-kay it wasn't exactly what I would call precision stuff, having to line things up from above purely by eyeball seemed a bit hit and miss.
If you had to do say a more precise/complicated gear for a critical job and you needed it as spot on as you could, like with parallel turning between centres for example.
 
I've read a few books now...becoming a bit of a lathe anorak now actually lol...but I've read nothing on lining up externally mounted cutters to any degree of precision.
 
I'll be mulling it over myself over the next few days because a simple system would be pretty darned handy.
 
Anybody got any pointers?
 
I suppose it could be a watchmakers question...but engineers need precision as well

Edited By ady on 19/01/2011 09:42:04

ady19/01/2011 09:48:19
612 forum posts
50 photos
Line the cutter up between dead centres...but how would you be happy that it was spot on, like if you used a dial indicator and you now knew you had achieved a thousandth or two before the job kicked off.
Gray6219/01/2011 17:03:44
1058 forum posts
16 photos
One way to achieve this, measure the thickness of the gear cutter at the cutting tip, then using a center height gauge set one face of the cutter (top or bottom) at center height, using a DTI or the mill vertical DRO, move the cutter in the appropriate direction, half the thickness of the cutter tooth. This will set the centre of the cutter tooth at exactly centre height.
It may sound a little long winded but I have used this method many times with excellent results.
Bowber19/01/2011 18:01:43
169 forum posts
24 photos
I normally use the half cutter width and shim (paper) up to the side of the job, then move half the cutter width + half the blank width + shim thickness, when I'm being a bit fussy I also check from the other side as well just to make sure.
I suppose you could try a flat steel rule under the cutter tip and judge when it's level, same as you can do while setting the tool height, but the cutter tip must not be flat to do this.
If your wondering what I mean then try a steel rule between the tool tip and some round bar in the chuck, if the tool height is right the rule will be vertical.
I'm normally working with a milling machine, rotary table and centre but it's essentially the same.
Steve

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