DIN 3967 2

[spigor]

I have seen some drawings where gear quality is specified as 8fs DIN 3967. I browsed through this standard only to find that it should be specified with something like 8f25. The standard says nothing about "fs", if anyone knows what "fs" means, your input would be highly appreciated.

 

[Occupant]

I can only guess since I don't have the standard, but it seems to me that the eight signifies the ISO tolerance quality (8 is better than e.g. 11 and depends on the size of the tooth (module). Then "fs" should be Flankenspiel - backlash.

 

[TVP]

I looked through DIN 367, and I agree with Occupant that this designation is almost certainly referring to backlash (Flankenspiel) with a quality class of 8. Keep in mind that many times people improperly use standards, or are only interested in a portion of the standard, rather than using the full capability, designations, etc.

 

[juergenwt]

Spigor- Occupant is probably right on. Fs (Flankenspiel ?/F) is configured by combining many factors. One would be the change of play due to heat, another factor is the tolerance between shafts, another the out of parallel condition of shafts and the deviations of other components of the gear like tooth profile, dividing variations etc.
The basic values for quality 8 in µ for module:
over 1 to 2 = 34
over 2 to 3.55 = 36
over 3.55 to 6 = 40
over 6 to 10 = 51
over 10 to 16 = 59
over 16 to 25 = 75
over 25 to 40 = 94

I would recommend for you to go to "Beuth Verlag (google) and order the English translation for DIN 3967 and DIN 5480
T 14. It contains all the formulas for obtaining Max and Min Fs depending on the tolerances used in your project.
Good luck - you want to be sure on this one.

 

[spigor]

Juergenwt, how should I know what backlash tolerances were used in the project by the designer, as all I have is "fs" in the drawing?

If "fs" means only "Flankenspiel" (german for "backlash") it should be written "Fs", not "fs", right? But if it means "Flankenspiel", then it also would mean no backlash was specified by the designer and the manufacturer should choose some standard values acc. to his experience. Fair enough for me, assuming "fs" really means Flankenspiel. Could somebody confirm?

 

[juergenwt]

Spigor - scroll down to 10.4.1 Quality

http://abeg.gwj.de/help/de/Handbuchch10.html#x11-27000010.1

Scroll down to 2.6 Genauigkeitsstufe

http://www.mitcalc.com/doc/gear1/help/de/gear1txt.htm

I think you are just looking at a gear grade 8 - medium fine milled. The tables also give you max speed for the gear.
To give you all the deviations on grade 8 I would need more info such as the pitch dia and modul. Could you post the print?
I hope your German is good enough.The"fs" could stand for "fräsen" milling.
Hope this helps you.

 

[Occupant]

If "fs" means only "Flankenspiel" (german for "backlash") it should be written "Fs", not "fs", right? But if it means "Flankenspiel", then it also would mean no backlash

You may be right. As I said, I was only guessing. But "DIN 3967 8fs" is common, I've seen it lots of times. In that case, though, the "8" still stands for the quality of the fit and the "f" for the location in the table i.e. not as loose as "e", but as not as tight as "g". That leaves the "s" - your guess is as good as mine.

 

[juergenwt]

Spigor - I should have known "s". 8 is the quality, f=individual error (Fehler) and s = tooth thickness (Stärke).
So "fs" stands for "tooth thickness error". This designation is in use in Germany but has been replaced with the new symbol "Rs" (tooth thickness variation).
So the new designation should be 8Rs.DIN 3961
For the RS values on quality 8 I would need : Type of gear,
modul and pitch dia.
Part of DIN 3967 has been replaced by DIN 3962 T2.
Everything is covered under the quality number 8. That includes "fine milling" as a production method.

 

[spigor]

Occupant, if it was "8f" than OK, somebody just forgot to specify the tolerance field. But "8fs" ruins everything, because "s" does not match here at all, so it leads to a conclusion it must mean something different instead. I don't think somebody would just use a part of a designation and change the rest. Since you have also seen this designation lots of times, it is widespread and must mean something.

Juergenwt, I have checked all the sources you mentioned. I found no references to "fs". I now believe the "tooth thickness error" or "tooth thickness variation" is a part of a gear quality class rating, e.g. quality class 8 tells us all about it. We take the DIN 3961 and DIN 3962 standards and find what profile error, angle error, pitch error, runout is allowed for our given gear. It is all in the class 8. What we lack is the backlash w/tolerance, which is specified by DIN 3967. But the designation does not match, and we're right where we started.

Correct me if I'm wrong, but I still think "fs" means something, probably connected to backlash or cutting method (maybe reference profile), but as for now we didn't get any closer to the correct solution.

If anybody is able to help us here, your input would be highly apprecited.

 

[juergenwt]

Spigor - "fs" would be related to backlash or play since it gives you the allowable deviation for tooth thickness. A separate value for backlash would require a second gear and would also be determined by many other factors such as center distance between gears. Here is a direct translation from "Klingenberg": "The size of the tooth thickness deviation has no relation to the quality of the gear and governs only it's part of the whole tooth play in a transmission".
Clk. on below and scroll down to page 6. You will find "fs" = Zahndickfehler (Tooth thickness error). I know this is for a spur gear from Polyacetal and quality 12 but I believe the system is the same for metal.
I would still go to "Beuth Verlag". Talk to them and I am sure they can supply a pocket book that will give you all you need in English.
You could also google "Zahnraeder" and find the US location of a German Gear manufacturer. They may be able to help you.
Good luck.

http://www.produktinfo.conrad.com/d...9/219568-da-01-de-Kegelrad_aus_Azetalharz.pdf

 

[Occupant]

I don't know if anybody is still interested in this, but I contacted a company that advertised selling bevel gears based on DIN 3967 (8fs). At first they didn't believe me, but after I send them the URL for their ad, I got a reply stating that this was an error and it should have been (8f24)

 

[spigor]

Thanks Occupant for posting this. They must have not known what it means, probably took it from some old drawing.

But still, that "fs" is used on far too many drawings to be an error in all cases.