Calculate Helix Angle from Sample?

[Riverina]

On a large Helix angle and wide face, we measure the axial pitch and then calculate the Helix angle. With a small Helix angle and narrow gear it is not possible to measure the axial pitch. Does anyone know a way of measuring or calculating the Helix angle?

 

[EnglishMuffin]

The only method generally considered reliable is with a helix checking machine, because then you get a complete plot over the full length - extrapolating from point measurements is somewhat risky. These machines are common, but obviously you don't have one. If you are measuring a lot of gears, it's essential to get one. If you are only doing one or two, you could easily send them out to a local gear house.

 

[Riverina]

Thank you - do you have any information about these machines, brand and model etc? We have no access to a Gear Shop so need to do this in house.

 

[EnglishMuffin]

I find it hard to believe that you have no access to a gear shop. If you are in the business of making gears in any quantity, then I would have thought that you would surely already possess gear checking equipment. If on the other hand this is a purchased gear, most people who are not in the gear making business rely on certified inspection data from the manufacturer. However, if you are going to be inspecting large numbers of gears yourself, your best bet might be a used or reconditioned machine supplier, but since I don't know what country you live in, I can't be of much assistance. I am no expert on the subject - there are many makes wordwide, and many types of machines, most of which do other things as well as just measure helix angle. New, they are mostly very expensive. In the USA, makes that some shops use are Fellows, or Illitron. A lot of brands are no longer made - you will just have to do some searching for "Lead checking machine", "gear checking machine" etc.

 

[sacem1]

I think that people who work in very high industrialized cities think that everywhere there is always someone to turn to to buy, rent or give you a service I now for personal experience that that is not the case so here goes my way of solving the problem I think you are facing: Making a replacement part that is not availiable locally.
If thats the case we smear Prussia Blue paste on top of the gear teeth, then the gear is rolled aligned sideways by some kind of straight edge over a sheet of paper, from there with a simple protactor the aproximate angle can be read.
With that angle we set up the gear hobber and load the OLD gear then we fix a dial indicator with a magnetic base to the hob head, set up all parameters as if we are going to hob the new gear, possibly a very high speed for the cutting arbor which is not installed and put the work in motion you will find that if your angle was correct the dial indicator will only move from the starting point to both sides because of the roughness of the old gear. If you are of limits to just one side then you can use a little trigonometry to find the error and adjust the gearing of your helical advance, a new recheck and if you have been careful in your corrections you should be right on the requiered angle. We have found that even when the customer submits machinig plans its better to get hold of the used piece and recheck by this method because many times plan given are not original but drafted with mesurements taken from the piece in order that you can quote, and afterwards when the gears do not mesh well you are the only culprit.
Regards
SACEM1

 

[EnglishMuffin]

sacem1 : Yes, if you just want to check a gear against some other gear, perhaps even a master, that would work fine. But the guy specifically says he wants to measure the helix angle, and we must presume that he has no master of known accuracy. Where would it come from if they have no way of contacting a gear shop? And if they don't have "access to a gear shop", that suggests that they might not even have gear making equipment themselves. So actually I am a little mystified as to what their situation is, or was.

 

[Riverina]

SACEM1 - Thank you for telling us of your solution - unfortunately we don't have a hobber.
I can see in this instance why it helps to know a member's profile. Our business is a "Jobbing" shop in a small town (Pop 1000) four hours from a "Gear Shop". We have two Maag gear shapers (SH75 and SH150) and our work is replacing existing parts for Agricultural and Earthmoving industries. The Maag has an internal head and rack cutting attachment to auto feed and index that allows machining of internal splines with formed tools. The single tool feature enables all tooth forms to be machined. From previous experiences, I realize I need the mating gear and housing for center distance. It I can't measure axial pitch, I make both mating gears to suit housing supplied.
Regards - Riverina

 

[sacem1]

To EnglishMuffin:

You are right really he stated he wanted to know the exact angle not how to make a new one but you can also use this method as detailed before and from the resulting gear train that gave you your acceptable tolerance limits you can with simple math determine the angle, as I said if you don't have the special gear mesuaring devices, its a way out.
Have a Very Good 2004 to all of you
SACEM1