Posted by Rick Bromley on December 30, 2001 at 08:18:09:
In Reply to: Can you cut worm gears wiithout a hob? posted by Bob M on January 14, 2001 at 20:12:29:
I have done this operation in a Ferranti toolroom in the UK. You need the following.
1 Universal milling machine with dividing head ( universal mean that the table can swing so you can cut a helix)
2 A gashing cutter which is the same form as the worm i.e. 29deg inc but a single thread
3 A finishing cutter which is screw cut to the same for as the worm but longer. This will need teeth milling into them and clearance putting on the backs of each tooth. Teeth should be spiral milled square to the helix of the worm the clearance can be filed or hand ground with a pencil grinder. This will then need to be harded and temp, we used HSS.
4 Set the wormwheel on a mandrill between centres in the dividing head with a drive.
5 Swing table to the correct helix angle of the worm. Then gash out the teeth using the dividing head to index each tooth. Go to a depth just short of full size. This was set with slips from the C/L of the machine spindle to C/L of the dividing head i.e. centre distance of the worm and worm wheel.
6 Remove the drive from the gashed worm wheel so that it runs free on the centres.
7 Swing the machine table back to zero.
8 Put the finishing cutter in and re centre it to the wormwheel.
9 The depth is still set from the roughing operation.
10 Move the table up to the roughed wormwheel moving it till the teeth mesh keep moving till it scratches the sides of the roughed wormwheel. This will be near the top.
11 Switch on the machine this will start to drive the wormwheel round. Slowly raise the table .005 per rev of the wormwheel. Till it reaches the zero you have set before when gashing with the slips.
You have now produced a wormwheel with generated side so that the worm and wheel roll and slide together.
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