Need help drawing up a gear...

[charliekeller]

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.

 

[mrpi]

Are you going to have the gear wire-EDM cut or something? If you don't need to actually specify exact geometry of the gear profile, I would contact whoever is going to make the gear for you.

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.

 

[drawoh]

charliekeller,

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?

JHG

 

[charliekeller]

I will be having the gears wired out so I need the actual profile.

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)?

 

[Occupant]

If you need the profile, let me know. BTW what ball?

 

[CPosner]

Try this yet? You can get the CAD drawings for a MOD 1.5, 16 tooth 20deg gear here:

http://www.qtcgears.com/RFQ/default.asp?Page=../KHK/newgears/KHK046.html

 

[charliekeller]

Occupant - On the rack print there is a 2.7mm dia circle drawn in between two teeth. Referencing the gear print there is a 'Ball Diameter' in the info box that is left empty. Am I correct in assuming the 2.7mm circle is what the 'Ball Diameter' is referring to? Is it for determining tooth thickness? If you look at the attached picture you can see the circle drawn in.

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.

 

[charliekeller]

Doesn't look like my last picture uploaded. Here it is again.

 

[charliekeller]

http://i224.photobucket.com/albums/dd274/charlie_keller/Misc/gearrackassembly.jpg

 

[Occupant]

I have simply overlaid the rack per your specifications over the tooth profile I already had and found a profile shift of 0.25mm per attached. Please keep in mind that, given this dimension, there is no clearance between the gear and the rack.

 

[charliekeller]

Is there suggested minimum clearance? I have placed a 0.5 profile shift on the rack for 0.25 clearance and it seams to work.

 

[Medeski]

Hi, I may be able to translate the missing pieces for you, but I can't seem to download (either) of the files you posted. Perhaps the "_" at the end of the file name is messing things up? If you could email a PDF that would be fine too.

 

[charliekeller]

Did you try to use the photobucket one? i know the first two didn't work but the photobucket one does.

 

[Medeski]

The photobucket picture is a closeup of the gear assy and has no writing. If you want me to look at the writing, email me a pdf at zactacular (at) gmail (dot) com

 

[mfgenggear]

charliekeller

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.

 

[mfgenggear]

The circular tooth thickness if correct of your loose gear will control the backlash required after assembly.

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.

 

[dinjin]

If you draw a gear without some undercut, it probably will interfere with the rack. You have to know how a rack meshes with a 16 tooth pinion to be able to provide the proper profile from the point of start of active profile and provide the proper trochoid fillet radius to ensure that you will not have interference.

 

[mfgenggear]

Dinjin is correct, however if the gears are designed correctly to the center distance required, the start of the true involute form(TIF) of each mating gear must then allow for clearance.