Selecting the right cutter for a Helical gear .
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# Thread: Selecting the right cutter for a Helical gear .

1. ## Selecting the right cutter for a Helical gear .

Hello guys again

While I'm reading some pages from "The Machinery's Handbook" I found this formula N′ = NK +QK′ the one I know and always find in the net and other places is this N′ = N ÷ cos3 α .

My Question is , is there a table helps on how to find Q in metric mode or a formula to do that ?

2. Thumbnail from 1916 Treatise on Milling and Milling Machines by Cincinnati. His example needed to cut 19 and 38 teeth.

Originally Posted by NzNacer
Hello guys again

While I'm reading some pages from "The Machinery's Handbook" I found this formula N′ = NK +QK′ the one I know and always find in the net and other places is this N′ = N ÷ cos3 α .

My Question is , is there a table helps on how to find Q in metric mode or a formula to do that ?

3. Thanks Johnoder ,So I should forget the other two formulas and stick with this one from Cincinati ?

Another question if you don't mind please , by your experience what is the best way the measure the helix angle of a damaged helical gear to make another one

4. I have the info I posted, not the other. Feel free to use what suits you. The Cincinnati info shows the work of just where the results come from. A way to check helix angle will be the same Universal Milling machine set up that will mill that helix angle. You vary change gears(or electronic relationships as the case may be) until the damaged gear no longer moves an indicator touching the pitch diameter area on the flank of a non damaged tooth being ,moved by the set up past the indicator

Here is the link to the Cincinnati info. See both pages 298 and 303

https://archive.org/stream/treatiseo...ge/n5/mode/2up

Originally Posted by NzNacer
Thanks Johnoder ,So I should forget the other two formulas and stick with this one from Cincinati ?

Another question if you don't mind please , by your experience what is the best way the measure the helix angle of a damaged helical gear to make another one

5. Originally Posted by NzNacer
Another question if you don't mind please , by your experience what is the best way the measure the helix angle of a damaged helical gear to make another one
Originally Posted by johnoder
A way to check helix angle will be the same Universal Milling machine set up that will mill that helix angle. You vary change gears(or electronic relationships as the case may be) until the damaged gear no longer moves an indicator touching the pitch diameter area on the flank of a non damaged tooth being ,moved by the set up past the indicator
A very important point to bear in mind is that everything is made to a tolerance and you have no real guarantee that it was made correctly to begin with. As such, it is folly to depend on what results from its interrogation. It is a much better practice to let the actual need of the design envelope dictate what angle you endeavor to make it to now. All you need is the Pitch, the Center Distance, and the Tooth Counts to derive the necessary Helix Angle. At least then, one can be reasonably assured that it would be correct. Good luck.

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Originally Posted by NzNacer
Hello guys again

While I'm reading some pages from "The Machinery's Handbook" I found this formula N′ = NK +QK′ the one I know and always find in the net and other places is this N′ = N ÷ cos3 α .

My Question is , is there a table helps on how to find Q in metric mode or a formula to do that ?
Module or DP makes no difference to that formula, since it only calls for tooth number and helix angle to get a result.

7. Originally Posted by HuFlungDung
Module or DP makes no difference to that formula, since it only calls for tooth number and helix angle to get a result.
Are you sure ? I think the Q value contain thz cutter dimensions in inch

8. Hey guys , I'm reading an article on the net , After he calcul the lead (lead = PCD * pi / tan(helix angle)) then he dvided it by pitch of leadscrew and then by 40 and call it R , what is R and why we need it ? if i'm not asking too mach

9. You are talking helical gear but you need to back up and find out how a helix or spiral can be milled. The 40 represents the normal ratio in a driven-from-the-table-screw dividing head. A certain ratio between the table screw and the input to dividing head produces a certain LEAD. As for instance, a 4 pitch table screw geared 1:1 to input to dividing head will generate a LEAD of 10.000" for every single turn of dividing head output or chuck or dog driver. Your helix will require an exact LEAD to generate the appropriate helix angle. If this is new to you, you have some home work to do.

Cincinnati's Tables of Leads has about 2800 choices of four gear ratios - and each one makes some SPECIFIC length of lead.

Don't forget that gear cutter you asked about selecting HAS TO address the work at the HELIX angle - no ifs, ands or buts. See page 54 and 55 in the above linked Treatise. 54 shows a UNIVERSAL mill on which the table can be swiveled. 55 shows a PLAIN mill equipped with a Spiral Milling attachment - two means of allowing the cutter to address the work at the helix angle

Originally Posted by NzNacer
Hey guys , I'm reading an article on the net , After he calcul the lead (lead = PCD * pi / tan(helix angle)) then he dvided it by pitch of leadscrew and then by 40 and call it R , what is R and why we need it ? if i'm not asking too mach

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