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4-Participant

## HELP: units do not match

I am having difficulty figuring out what is wrong with my worksheet. This worksheet is a design calculation of spur gear. My problem is that addendum, dedendum, and clearance units are in 1/in, which is wrong. Why is it that the units are in reciprocal form? Is there any solution for this?. The goal is that the addendum, dedendum, and clearance must be in plain mm or in. Hoping someone can help me. Thanks

1 ACCEPTED SOLUTION

Accepted Solutions
23-Emerald II
(To:EL_9980860)

@EL_9980860 wrote:

Hi, it is from a textbook we are currently using for the Machine Elements subject by Myzka. Both the 1 and 1.25 are unitless, so how will I define it as unitless? My second question is, If there is a chance that both were defined as unitless, will the answer be in inches?

As Chris and Valery have mentioned, diametral pitch should have units of teeth per inch.   Your Mathcad expressions should then automatically calculate the correct units for the addendum and dedendum (inch).  I think the image below shows what you should get, but my knowledge of gear design is limited to what the internet showed me in a couple of minutes.

Stuart

(Revised Mathcad 7 Express worksheet attached)

9 REPLIES 9
23-Emerald II
(To:EL_9980860)

@EL_9980860 wrote:

I am having difficulty figuring out what is wrong with my worksheet. This worksheet is a design calculation of spur gear. My problem is that addendum, dedendum, and clearance units are in 1/in, which is wrong. Why is it that the units are in reciprocal form? Is there any solution for this?. The goal is that the addendum, dedendum, and clearance must be in plain mm or in. Hoping someone can help me. Thanks

Where do you get your addendum and dedendum definitions from?

Mathcad will generate the appropriate units for your expressions and if the units (dimensions) are wrong then there is something wrong with the expressions.  You have defined the addendum and dedendum as reciprocals of the diametrical pitch (in), so the units are bound to be 1/in.

Stuart

4-Participant
(To:StuartBruff)

Hi, it is from a textbook we are currently using for the Machine Elements subject by Myzka. Both the 1 and 1.25 are unitless, so how will I define it as unitless? My second question is, If there is a chance that both were defined as unitless, will the answer be in inches?

23-Emerald II
(To:EL_9980860)

@EL_9980860 wrote:

Hi, it is from a textbook we are currently using for the Machine Elements subject by Myzka. Both the 1 and 1.25 are unitless, so how will I define it as unitless? My second question is, If there is a chance that both were defined as unitless, will the answer be in inches?

As Chris and Valery have mentioned, diametral pitch should have units of teeth per inch.   Your Mathcad expressions should then automatically calculate the correct units for the addendum and dedendum (inch).  I think the image below shows what you should get, but my knowledge of gear design is limited to what the internet showed me in a couple of minutes.

Stuart

(Revised Mathcad 7 Express worksheet attached)

4-Participant
(To:StuartBruff)

The diametral pitch is where the solution is, I've learned a lot from this mistake. I overlooked the difference between diametral pitch and pitch diameter (gear diameter). Thank you Chris, Valery, and most of all Stuart for the help. Hoping for your help again, if I stumble into another mistake.

15-Moonstone
(To:EL_9980860)

Diametral pitch is a number representing how many teeth per inch (or mm) of pitch diameter you have in the gear (# teeth/pitch diameter). When you make this adjustment in your units (1/in), you will have the correct answers.

Cheers

4-Participant
(To:ChrisKaswer)

What are those adjustments, then? Can you show me those? Thanks!

24-Ruby IV
(To:EL_9980860)

There is a lot errors in print texts!

24-Ruby IV
(To:EL_9980860)

4-Participant
(To:ValeryOchkov)

Thanks for pointing it out. However, I am asking for a solution on the reciprocal form units of the addendum, dedendum, and clearance. Hoping you can help me.

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