Test run of the Stevo Eee-lec-tronik hobber.
Managed to get the stepper driven head mounted on the horizontal mill table in between customers calling and ringing up and generally being a pain. Finished tidying the wiring for the driver box and connected this to the head and the arbor driven encoder.
Found some scrap brass blanks and a decent 12 DP gear hob so I turned three blanks up all the same. Fitted the blanks to the stepper head and set the table over by 3 degrees 20 minutes which is the lead angle of the hob.
Set the depth, wound clear and started this up, amazing to see it start cutting and all the while you are expecting this to run all the teeth off.
First one off had wavy teeth because I'd forgotten to tighten the blank up.
I won't mention what happened to the second one After all this is ONLY a test run, isn't it ?
Turned all three blanks down to get rid of the mistakes and restarted using fewer teeth No problems this time.
I've put some pics on my web space, 10 in all
[Edit - now 19 at this point ]
Just keep changing the last number from 1 thru to 10
Pics 1 and 2 are the head being built up and there is no pic 3 - gone missing somewhere
Pic 4 is an overall view of the setup on the Victoria mill.
Pic 5 is a close up of a 12DP 21 tooth gear being cut.
Pic 6 is a close up of the finished driver box with plugs fitted but before painting.
Pic 7 is similar to pic 4.
Pic 8 is a nice one. It shows three gears I cut tonight, all the same size OD but they have 20, 21 and 22 teeth on them and they all mesh together perfectly, only the 21T is the correct standard. These are 12 DP cut in brass.
Pic 9 is a close up of the finish obtained.
Pic 10 is a 20DP nylon gear of 52 teeth. Ironically I cut this for a friend with a Micron hobber who's missing a 52 tooth gear and he needs a 52 tooth to make one !!
Got around to doing a bit more thinking and playing tonight.
Next step from doing spur gears are helicals.
Thought this one was easy, just add the helix angle of the hob to the helix angle of the gear and spin the table that amount.
WRONG - mucho ripped up teeth. Go back to reading the book and it appears you need a differential feed between the blank and the table. Well if you need gears this does away with all this He - Lec- Tronik gismo's although you at least can cut your own special spur gears without a master.
Two nights sleep, long bath and a read of a 1913 gear book and all becomes apparent.
Spin the table to the helix angle of the hob, this to all intents and purposes straightens the hob up so it's neutral cutting. Then spin the DH over to the helix angle of the gear.
Quick test run and Da-Da:-
One helix, shaken not stirred.
Shows it cutting, ignore the funny hob as my digital can't stop moving objects.
Final proof is to spin the DH over the other way by the same amount and cut the opposite hand. If these are correct they will lie together on a level plane.
Further playing and you get this:-
Herringbone gears to remove the side thrust associated with helicals.
Last play was some course gears to show the effects of undercutting on low number pinions.
The two outer gears are 8 DP 14.5 pressure angle and 10 teeth, note the heavy undercutting that occurs. The centre gear is done with the same cutter, same blank but decreased from 10 to 9 teeth, note the heavy strong tooth shape produced. All these gears will run together in any order perfectly.