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Involute Gear Cutter Question

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MozamPete

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#1
When I look a references to involute gear cutter set they always refer to eight cutter to cover the range of sizes, and normally list them from a #1 being 135 teeth to a rack to #8 being 12-13 teeth.

When I look at the gear cutter sets out of China on ebay they number them the other way around (#1 being 12-13 teeth to #8 being 135 teeth to a rack ).

Involute-Gear-Cutters-DP20_zpsf6db5c44.jpg

What is the convention? Is this an English vs American difference or a Module vs DP difference?

Immediate reason is I wanted to cut a 33 and a 34 tooth gear so ordered a #5, but now I'm not sure if what is going to arrive is for 21 to 25 teeth or for 26 to 34 teeth.

As a secondary question how important is it to use the correct cutter? Can you get away with using the cutter number above or below in a pinch?
 

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Karl_T

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#2
Well, I've bought several different made in USA brands over the years all using the same numbering system...

What do you think the chances are of all the USA manufactures being wrong and China being right :)
 

Wreck™Wreck

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#4
Buy them by the numbers, DP, pressure angle and tooth range that they will produce, the tools in the picture are well marked (until used) , for instance the tool in the lower right corner is marked , 20 DP, 14 1/2 Deg. PA, 55-134. What could be simpler than that? Naming conventions are meaningless if there is no governing body to enforce them.
 

Bill Gruby

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#5
One last time, those cutters are marked wrong. The ones in the pic will not cut the teeth as marked. They are marked bass akwards. Below is the correct marking for Involute Cutters.

#1 = 135 to Rack Teeth
#2= 55 to 134 Teeth
#3 = 35 to 54 Teeth
#4 = 26 to 34 Teeth
#5 = 21 to 25 Teeth
#6 = 17 to 20 Teeth
#7 = 14 to 16 Teeth
#8 = 12 to 13 Teeth

"Billy G"
 
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4gsr

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#6
Listen to Bill, they are numbered backwards.

If you look at them closely, they are marked correctly for the range of number of teeth they will cut. But are not numbered correctly.

the gear cutter for cutting 12 to 13 teeth is marked as a number 1 cutter. Should be marked number 8. And so on.
 

terrywerm

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#7
This seems to be a common problem with the gear cutters coming from China. Every set that I looked at on eBay had them backwards.
 

MozamPete

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#10
Those Chinese numbers are backwards. Try to cut 134 teeth with that #7 and you will find out in a real hurry.

"Billy G"
So are you saying looking at the cutters in the picture the number appears correct but the tooth range is incorrect? i.e the #7 in the picture looks more like a 14-16 tooth cutter than a 55 to 134 cutter?
 

MozamPete

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#11
Buy them by the numbers, DP, pressure angle and tooth range that they will produce, the tools in the picture are well marked (until used) , for instance the tool in the lower right corner is marked , 20 DP, 14 1/2 Deg. PA, 55-134. What could be simpler than that? Naming conventions are meaningless if there is no governing body to enforce them.
Problem was the one I brought was only sold as 20 DP, 14,5 PA, #5. Can't see a tooth count on the cutter from the picture provided but it does appear to have 'Detroit' written on it so I'm now expecting it to be 21 to 25 teeth - not actually what I wanted.
 

Bill Gruby

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#12
If you go by the picture, yes the #7 looks like it will cut 14 to 16 Teeth. It looks heavy whereas the #8 in that picture looks lighter at the cutting edge. The only way to really tell is to have one in my hands and that won't happen in my lifetime. I wouldn't touch mismarked tooling with a 10 ft. pole. I also won't buy imported cutters either, been burnt before. The seller of those cutters appears to know squat about the standard or he would have caught that obvious mistake.

"Billy G"
 
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MozamPete

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#13
Glade I didn't buy them then. The one that I have ordered may not actually be the one I currently need but at least it does appear to be American made.
Not a problem, I'm not opposed to having excess tooling on hand just in case I find I need for it in the future.
 

Baithog

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#14
The gear set in the original picture appears to be for the US diametrical pitch system. The #1 cutter also appears to be smaller than the #8 cutter. It is appropriate that the higher tooth count cutter be smaller, so the gears are marked correctly for the cutter standard they were made to. The problem a lot of North Americans have in these situations is that they do not take into account that the rest of the world works in metric. The metric module standard numbers their cutters in reverse order and they IIRC they also cut different numbers of teeth per cutter than the diametrical pitch system. Using Ebay as a reference is iffy at best because someone ignorant of how the two systems work can come to incorrect conclusions.

Personally, I would not buy a cutter without the full set of markings, including cutter number and number of teeth cut.
 

Bill Gruby

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#15
The #1 and the #8 cutters are side by side in that picture. The #1 says it cuts 12 to 13 teeth, #8 says it cuts 135 to rack. That is just the opposite of what it should be so please, take a moment to tell me how they are marked right. I listed the correct numbers, those on the cutters clearly do not match.
"Billy G"
 
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Bill Gruby

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#16
CONCLUSION --- Both numbering systems are correct. The ones in the first picture are Module. They number them backwards so as not to get them mixed up with DP cutters.


"Billy G"
 

Reeltor

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#17
I have to agree with what others have posted about imperial involute sets from China. I recently bought a "China" set of cutters, 14-1/2 degree 16 pitch. In my opinion they are marked backwards, they are direct opposite from what my Machinery's Handbook list how they should be marked and other very old American made set of cutters.
 

Bill Gruby

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#18
As I stated, they are marked opposite on purpose, they are Module not DP. To mark them the same would be a fatal mistake. Module will not cut DP gears and vice versa. A #1 in DP cuts 136 to rack. A 31 in Module cuts 12 & 13 teeth.

"Billy G"
 
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Reeltor

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#19
As I stated, they are marked opposite on purpose, they are Module not DP. To mark them the same would be a fatal mistake. Module will not cut DP gears and vice versa. A #1 in DP cuts 136 to rack. A 31 in Module cuts 12 & 13 teeth.

"Billy G"
Billy,
My cutters are marked 16 DP 14.5° pressure angle. Am I mistaken, I thought Module cutters are to cut metric gears not imperial
 

Bill Gruby

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#20
Yes, you are correct, module cutters cut metric gears. That's why the numbers are backwards so they are not confused.

"Billy G"
 

MarkM

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#21
Module cutters are also only 20 degrees where dp can be either 14.5 degrees and 20 degrees.
 

CarlosA

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#22
I have purchased several sets of these from Russia and China. The module gear cutters are always the opposite of the DP gear cutters. This is also true for Chinese cutters in DP sizes. In other words, a metric country made DP gear cutters using their own metric dimensions.
 

BROCKWOOD

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#23
If you can get past the naming convention on foreign made DP style cutters, & have a 7/8" arbor, you can save a lot of money on cutters. USA made DP cutters for a 1" arbor are $500 for a set of 8 if a common size is sought.
 
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