Need help drawing up a gear...
Need help drawing up a gear...
(OP)
I have a print for a gear that I need to draw up and make. Most of the print in is Japanese. This is a project that has been handed over to me and the previous engineer didn't draw them up correctly so this is round 2 for making them. My experience with gears is pretty limited and this one doesn't seem to match any profiles if can find, and of coarse this project needed to be done yesterday.
Profile - F.D.S (Full-Depth System maybe??)
Module - 1.5
Pressure Angle - 20deg
Number of Teeth - 16
Base Pitch Dia - 24
Overall Dia - 27
SPAN - 6.978
SPAN Teeth - 2
Ball Dia - ?
So my problem is when I draw up the gear, it does not match the mating rack. One thing I thought of on the way home today was if the center-center distance may be incorrect. I'll have to check in the morning.
Does anyone have any links to information on the F.D.S profile and determining lead in radius for it?
Is it OK that the SPAN measures over 2 teeth and not 3? All references I have seen cover 3 teeth.
Profile - F.D.S (Full-Depth System maybe??)
Module - 1.5
Pressure Angle - 20deg
Number of Teeth - 16
Base Pitch Dia - 24
Overall Dia - 27
SPAN - 6.978
SPAN Teeth - 2
Ball Dia - ?
So my problem is when I draw up the gear, it does not match the mating rack. One thing I thought of on the way home today was if the center-center distance may be incorrect. I'll have to check in the morning.
Does anyone have any links to information on the F.D.S profile and determining lead in radius for it?
Is it OK that the SPAN measures over 2 teeth and not 3? All references I have seen cover 3 teeth.





RE: Need help drawing up a gear...
Tell them what you need, supply a reduced-dimension drawing that shows bore/hub dimensions etc and include the info you listed above for the tooth specs. Have them provide a quote and an engineering drawing to sign off on.
The gear manufacturers have software for generating gear profiles, not to mention they have the cutters that will actually hob the gear. No sense in re-inventing the wheel just to have the print 100% dimensionally correct.
Beat to fit, paint to match.
RE: Need help drawing up a gear...
Your pitch diameter sounds correct to me. The two pin span makes sense to me given you have an even number of teeth. With an odd number of teeth, you would use three pins. I don't have a handbook here, so I cannot verify your span diameter.
Your rack should have a pitch of 4.712mm. Are you modeling it correctly?
RE: Need help drawing up a gear...
The 4.712mm gear pitch is correct and is called out on the rack print.
Does the ball dia (2.7mm)given on the rack print need to be centered with the base pitch dia (24mm)?
RE: Need help drawing up a gear...
RE: Need help drawing up a gear...
RE: Need help drawing up a gear...
CPosner - Thanks for the link! I was able to download a 3D gear model matching the specifications. It is the one used in the attached picture. It looks like it may works with the rack that I have but only if I change the distance between the rack and gear. I also found this link to help explain drawing the involute on the tooth profile:
http://www.ul.ie/~nolk/gears.htm
Now for the next question, what do I do to determine the distance between the gear and the rack? My calculations using working depth make the gear/rack crash and so does mating the pitch diameters. Could my rack profile be drawn incorrectly?
How do I know if my method for drawing the rack is correct?
The rack profile is cut on the side of a shaft. I am given a distance of 9.5mm from the center of the shaft the top of the teeth and from the center of the shaft to the top of the 2.7mm diameter circle is 10.31.
Pitch 4.712
Pressure Angle - 20
Addendum - 1.5
Dedendum - 1.75
There are also two numbers given in which I do not know what they are due to it being in Japanese. One is 16 (also the number of teeth on the gear) and 20.000 (located just under the 16).
Deducting the 1.5 addendum from the 9.5mm would give me the location of the pitch diameter line. Using the 2.7mm circle at the specified 10.31mm distance sets my tooth thickness.
I greatly appreciate all the help given so far! I am learning a good deal about gears from this experience and although frustrating due to the time crunch it is always fun to learn.
RE: Need help drawing up a gear...
RE: Need help drawing up a gear...
RE: Need help drawing up a gear...
RE: Need help drawing up a gear...
RE: Need help drawing up a gear...
RE: Need help drawing up a gear...
RE: Need help drawing up a gear...
RE: Need help drawing up a gear...
mrpi is correct, even if you draw the correct profile, after manufacture it needs to be inspected for the profile, lead, & tooth tooth error.
wire cut does a good job however inspection is required to verify there is correct geometry.
RE: Need help drawing up a gear...
the tooth thickness is based on the center distance required.
the span measurement or wire measurement over teeth will control the tooth thickness required.
spur gear teeth only require two wires.
the EDM house will need the the actual geometry of the gear tooth profile. I like to give them the the entire geometry
of a full compliment of gear teeth.
RE: Need help drawing up a gear...
RE: Need help drawing up a gear...