Gear Alignment Question
Gear Alignment Question
(OP)
Hello,
I have designed my first gear/pinion set for a rotary table. I have a large 350 mm pitch diameter 0.4 Mod ring gear and and an 88 tooth antibacklash pinion will be driving it. My question concerns alignment. I am designing a mounting assembly and would like to know what type of tolerance would be appropriate for alignment of the centers, pitch, yaw, etc for proper funtioning. This will help me design for a properly stiff frame. Thanks for your help!
Shelby
I have designed my first gear/pinion set for a rotary table. I have a large 350 mm pitch diameter 0.4 Mod ring gear and and an 88 tooth antibacklash pinion will be driving it. My question concerns alignment. I am designing a mounting assembly and would like to know what type of tolerance would be appropriate for alignment of the centers, pitch, yaw, etc for proper funtioning. This will help me design for a properly stiff frame. Thanks for your help!
Shelby





RE: Gear Alignment Question
You are using an 88 tooth anti backlash
pinion with an 875 tooth gear. You should
state the gear face and pinion face widths
as well as the materials. Obviously the
more exacting you can set these up, the
better life you can expect. I assume these
are metal parts and lightly loaded. Sounds
like an interesting application.
RE: Gear Alignment Question
Thanks for the advice.
RE: Gear Alignment Question
Second, calculating the pinion using Lewis gear strength formula show that the tooth bending stresses are almost equal to the yield strength which is way too high and there is no safety factor even if we assume 7 mm pinion width. More than that, if the anti-backlash gear is a split gear (meaning two adjacent gears of 3.5mm width each) the situation is much more severe because, only half the pinion width actually carry the torque load.
Third, I do not know of any split anti-backlash gear that the springs between the two halves of the pinion can carry 30N-m therefore, actally you will have backlash. Those types of anti-backlash gears are not designed to take load and the are used to rotate sensors such as potentiometers resolves etc where there almost no rotating resistance.
RE: Gear Alignment Question
Good catch and thanks for the feedback. The 30 N-m move is a conservative estimate that includes a fudge factor for the inertia values when I designed the gear. The masses are actually considerably lower, and the effective torque to achieve the desired move profile is around half of this.
A matching face width for the pinion is all that I have room for, but I will re-check the bending and Hertzian stress calculations to ensure that I still have an effective margin of safety.
As for the third point, I am aware of the limitations of an antibacklash pinion. I am not using a convenitonal spring,or a spring at all for that matter :) The design will have the ability to modulate the spring rate of the antibacklash pinion. In reality, I am not as concerned with backlash on the large force moves so long as I have the ability to settle in and fine tune the position to within a micron without backlash.
Do you have any advice on my original query concerning alignment?
Thanks again!
RE: Gear Alignment Question
RE: Gear Alignment Question
RE: Gear Alignment Question
One more issue is that as the AGMA number goes up the hobbing process will no longer fit and the gear should be grounded, polished etc. However, small module grounding is a problem if not impossible.
RE: Gear Alignment Question
RE: Gear Alignment Question
RE: Gear Alignment Question
I hear you loud and clear. We have a fast tool servo driven by a voice coil that weighs 6 lb. and runs at 15 G.
You can reduce the motor rotor inertia significantly over conventional designs by
1) Making the interior out of aluminum.
2) High pole count motors can have quite thin magnets thus reducing peripheral weight.
3)The thin magnets do not need much back iron so the iron rim under the magnets can be reasonably thin.
RE: Gear Alignment Question
To control center distance accurately, you could go to a toolmaking shop that has a jig-boring machine. This will hold tolerance of +-0.0002" if a jig-grinding attachment is used on the spindle.
This still leaves you with what israelkk brought up "...However, small module grounding is a problem if not impossible." What about hand scraping and lapping? This would undoubtedly be expensive but if you really need it, cost might have to take a back seat.