Another Westbury Seal 15cc

[doubletop]

While on the subject of gear cutting, a question. With MOD cutters how do you determine the depth of cut? Apparently cutters can be marked but mine are not.

From the data that Fusion gives me for my gears I get for 32 teeth Outer Dia 27.18mm and Base Dia 2.375mm so depth is 1.7145mm and for 16 teeth Outer Dia 14.38mm and Base Dia 10.95mm so depth is  also 1.7145mm

Whereas; I saw somewhere that for DP cutters the depth can be calculated as Depth of cut = 2.157/DP were 2.157 is a constant. As DP=25.4/Mod then depth of cut for Mod cutters would be  2.157 x Mod

So in my case Depth of cut for 0.8Mod would be 2.157 x 0.8 = 1.7256mm. Which is different to 1.7145mm OK only 0.011mm but I went looking for the answer expecting to find a table with the cut depth for all Mod cutters. I think I am right in assuming it should only be one value for each cutter but I can't find the info.

Any clues please?

Pete

[doubletop]

I realised that there is another source of information available - Copilot, so I asked it the same question

The constant  is 2.157 or 2.25 depending on the situation so the depth for a 0.8mod is either 1.725 mm or 1.8mm respectively. Using Outer Diameter and Base Diameter from Fusion is apparently incorrect

Answer attached - it is way too long to copy here as it runs to 11 pages!

All a bit academic really as my equipment isn't that accurate

Pete

[internal_fire]

I realised that there is another source of information available - Copilot, so I asked it the same question

I think you will be quite unhappy if you follow the Copilot advice. 

"you feed the cutter in by 2.25 m from the theoretical pitch circle."

You will have a better result by feeding 2.25 m from the OD.

Gene

[doubletop]

I realised that there is another source of information available - Copilot, so I asked it the same question

I think you will be quite unhappy if you follow the Copilot advice. 

"you feed the cutter in by 2.25 m from the theoretical pitch circle."

You will have a better result by feeding 2.25 m from the OD.

Gene

Gene

I missed that, but it was on page 1. I never really fully read their first answer as generally they get it wrong or have missed something, so I then follow up with further questions or point out the  error. At the very end the conclusion is

✔ 2.25 m - Used in rack type module systems (KHK, many textbooks). Not what Fusion is using.

✔ 2.157/DP - Used in AGMA/ISO full depth involute systems. Fusion’s geometry aligns with this family.

✔ Your 2.143 - A natural result of deriving a “constant” from base → outer instead of pitch → root, plus Fusion’s rounding and fillet geometry. Nothing is wrong — you were just measuring a different part of the tooth. If you want, I can compute Fusion’s actual whole depth constant precisely — I just need the root diameter from the same gear.


Pete

[petertha]

I posted about DOC elsewhere, more pertaining to any compensation required to cut small tooth count gears. For metric/module gears within the specified range of the cutter #, the formula is quite easy. So long as you made the correct gear blank OD. I'm not quite clear where DP enters the picture unless you are working off some other Imperial reference to sanity check?

[Jasonb]

.

[doubletop]

I posted about DOC elsewhere, more pertaining to any compensation required to cut small tooth count gears. For metric/module gears within the specified range of the cutter #, the formula is quite easy. So long as you made the correct gear blank OD. I'm not quite clear where DP enters the picture unless you are working off some other Imperial reference to sanity check?

Peter

I will come back to this tomorrow but I have done two examples today using 2.25 x mod 0.8 = 1.8mm and the teeth have sharp points and the OD is now undersized. After the first attempt I rechecked all my setups and re-made the gear with the same results.

I was considering trying a DOC  = 2.157 x 0.8 however, I note from the Copilot response "2.25 m - Used in rack type module systems (KHK, many textbooks). Not what Fusion is using" and the OD I'm using is the dimension Fusion gave me (14.38mm for a 16 tooth Mod 0.8 gear). Is that OD correct when using DOC = 2.25 x mod 0.8

Pete

[Jasonb]

Are you using the right number cutter, MOD are usually numbered the opposite way to DP.

OD is separate from Whole depth.

OD = NoT +2 x Mod

OD = 18 x 0.8

OD = 14.4

[doubletop]

Are you using the right number cutter, MOD are usually numbered the opposite way to DP.

Yes it is a set of M0.8

BTW I am just looking at another gear calculator and it is coming up with the same values for OD DOC etc so having the numbers confirmed it must be something I am doing. Fresh day tomorrow and I 'll try again.

I was have a conversation about this with a club member tonight. You try something new and it doesn't work, then it suddenly clicks and you wonder why you ever had a problem in the first place

Pete

[Jasonb]

Although a set of 0.8MMOD what cutter from the set are you using? are they just numbered or do they list the tooth range?

[petertha]

Assuming we are talking 32 teeth & 0.8 module and 20-deg pressure angle, here is evolvent calculator
https://evolventdesign.com/pages/blank-calc

I'm reluctant to post ondrives because they use slightly different terminology & 2 slightly different root diameters, but anyway similar results
https://ondrives.com/gear-calculator

And yes, selecting the correct cutter number corresponding to the range of teeth its designed for is critical

[petertha]

KHK for good measure

[petertha]

The (Chinese) module 20-deg PA numbered cutters I have have corresponding tooth ranges like so.

[doubletop]

Are you using the right number cutter, MOD are usually numbered the opposite way to DP.

OD is separate from Whole depth.

OD = NoT +2 x Mod

OD = 18 x 0.8

OD = 14.4

Jason

Yes 14.4 or 14.38 from Fusion or 14.44 from an external calculator. But I like the NoT + 2 * mod method for a sanity check

Pete

[doubletop]

The (Chinese) module 20-deg PA numbered cutters I have have corresponding tooth ranges like so.

Peter

Yes I am using #2 cutter

Pete