Help with reverse engineer spur gear

[[Ma...]]

Hi,

i have here an old spur gear ( not made by milling ) and i am strugling with getting some numbers.
With some help of online generators i came to these numbers:

• num. teeths: 17
• module: 12.5
• angle: 25°
• profile shift: -0.03
• clearance: 2.25

I am getting deviations on edges about 0.2mm - this is as close as i can get with try-error.

Can anyone help me to clarify numbers? I have to measure this gear and then present data to recreate documentation - we need to send order for new piece.

Thx for reading

Edit - graphic deviations.

[[Ch...]]

Martin,

Well done for getting this far. Reverse Engineering a gear can be challenging. Especially when it is non-standard.

I'm curious how you found the profile shift.

At any rate, I may be able to help. Do you have Gear Pro?

If so, I would punch in your #Teeth, Module, & Pressure Angle, and check pitch, lead and profile to see if the data is plausible.

You will also need things like root radii minimum, etc. How many more pieces of this do you plan on developing? If it is high quantities, it may be worth sending to a gear supplier in your area that can help gather the data - for best accuracy.

[[Ma...]]

Thanks for compliment Chris.

No we don't have Gear Pro.
I went to "Free Gear Generator" ( evolventdesign.com ) where i tried some settings.
For profile shift i played with module, angle and shift to get outer diameter similar to what i measured. Then with help of solidworks i compared measured curve ( spline ) with generated DXF.

I think that it should have 26° angle, then it would be better - but i don't have such knownledge - too long from school, and i did just basic drawings at school - machinist since then.

We have old machine LKO 315 - weaker press, not used for forging and this gear is broken/worn out. So we got to make new - no chance to buy from original company.

[[Ch...]]

Martin,

Gear Pro manual has a short guide for 'reverse engineering' gear data.

I can share some points, however that being said I personally would not start cutting chips on a new gear until I inspected this gear with a gear analyzer or gear software, etc. to confirm results.

It's a bit of a stretch but (After aligning a tooth in Calypso), you could try to generate a 25/26° involute 2d curve, and try to plot that as a straight line to mimic how profile would be checked. Lead would be similar, but I'm pretty sure this is based on straight spur gear.

Tooth thickness should be fairly easy, measuring points at PD, or calculating a pin size based on your original numbers and measure an actual/average M.O.W. and convert to CTT.

[[Ma...]]

I think i got it now. Still trying on Solidworks

• angle 27°
• module: 12.7
• profile shift: -0.18
• clearence: 1.75

Tomorrow i'll try it in Calypso to get deviations - but it looks promising.

Edit:
Now it looks promising 🙂
Used mm not inch.

lko315_tooth.png

[[Ow...]]

Martin, did this work out for you?
Common pressure angles used in spur gears are usually 14.5°, 20° & 25°, with 20° being the most common.
In America, you have to order special involute gear cutters that are not made to the common pressure angle sizes and they are not cheap.
The picture shows the gear has some significant wear in the addendum and while I'm no gear expert, I bet you were closer with the 25° pressure angle and with some tip relief added in by design or wear?
In the automotive industry using non-standard pressure angles happens often in my experience but, in older machinery, the common pressure angles are almost always used.

[[Ma...]]

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Hi Owen,

this gear is brand new 🤣 But made before y2k i would say. This is not made by gear cutter - it's made by old way, this explains grooves and scratches on surface ( basicaly knive goes up and down and part is moving to make tooth profile )

With 25° will tooth have more material then original.

Edit: this gear is for weaker press - aprox. press force is about 30 tons. 3090kN
https://www.exapro.cz/smeral-lko-315-p01124091/

[[Ch...]]

Owen is correct , those are common Pressure Angles,

however depending on load, tooth strength required, they may be higher. A lot of ours are between 25° + 29.5° for heavy loads.

If you have the wrong pressure angle on 30 ton equipment there is a high chance of tooth fracture / failure.

At a minimum - if you do not have Gear Pro or other gear software to inspect actual gear - you may be able to generate a gear involute curve based on your calculation in NX/ Solidworks whatever you use, and export that curve to Calypso. to check for deviations. This is what I would do if I had no gear software, I would say total profile/involute curve error should be under 0.001" at the correct pressure angle.

Have you tried reaching out to the manufacturer for support? Perhaps they will be generous and share the info, and let you make your own. Also be advised that some manufacturers have been known to purposely make oddball pitch and pressure angle size gears so they cannot be easily reproduced (looking at you Gleason...).

Good luck!

[[Ma...]]

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Thanks Chris,

we did reach manufacturer for new part - nothing came from them - no price, no drawings.
Letting other companies to make documentation is much more costly.

As i posted - i have max deviations about 0,05mm ( .002 inch ) i would say - fair enough for this size of gear.
I don't know exact position and presures at this gear.

After recalculations - this machine should make 315 ton force.
Because i don't have access to SW to make try-outs ( from sketch to model -> curve check ) it's far more complicated.
If i would know how to construct this type of tooth, then i would create nominal curve using formula.

As far as I know, i would rather have new tooth smaller than wider. Perhaps it would be better with bigger angle to cover a little from existing deviations.