How to Wind a Coil Spring on the Metal Lathe

[Mayhem]

Wow - it is like being back in math class!

Should we pass on this info to Marv?

[arvidj]

I've sent Marv an email with the same information as in the thread. We'll wait and see where my thinking has gone astray.

[EdK]

Thank you Arvid! After reading the article yesterday, I stared at Marv's code and knew there was something wrong with it but could not put my finger on it. No wonder I keep getting a negative number for the mandrel diameter when I select phosphorus bronze with my program. It's curious that it's not the case when I run Marv's version of the program. I get the same results whether I select music or bronze wire.

Excellent analysis!

With your information I can now finish up the program.

Ed

[chucketn]

"k = mx + b

where m = -0.0124727272727273 and b = 0.980818181818182 for music and stainless steel wire

and m = -0.0109727272727273 and b = 0.984909090909091 for phosphor bronze wire.

and x is the Spring Index."

Arvidj, are thes values for m and b constants? Or are they just for the example in the article?

Chuck

[arvidj]

(07-03-2013, 09:33 AM)chucketn Wrote: "k = mx + b

where m = -0.0124727272727273 and b = 0.980818181818182 for music and stainless steel wire

and m = -0.0109727272727273 and b = 0.984909090909091 for phosphor bronze wire.

and x is the Spring Index."

Arvidj, are thes values for m and b constants? Or are they just for the example in the article?

Chuck

They are constants derived from the graph, not from the example.

I looked at the graph on page 20 and entered the data points into Excel ...

Music or Stainless Steel Wire

Code:

5     0.922
6     0.907
7     0.893
8     0.880
9     0.867
10    0.854
11    0.842
12    0.829
13    0.818
14    0.807
15    0.798

Phosphor Bronze Wire

Code:

5     0.933
6     0.920
7     0.908
8     0.896
9     0.884
10    0.874
11    0.863
12    0.851
13    0.842
14    0.833
15    0.823

I then ran a linest function on the data to determine the "best fit" straight line that fit the data ... i.e. a line that is defined by y = mx + b. The results are:

Music or Stainless Steel Wire

Code:

-0.0124727273          0.9808181818
0.0002209421           0.0023172607
0.9971838746           0.0023172607
3186.8803611737        9.0000000000
0.0171125818           0.0000483273

Phosphor Bronze Wire

Code:

-0.0109727273          0.9849090909
0.0001841018           0.0019308762
0.9974728525           0.0019308762
3552.3275535085        9.0000000000
0.0132440818           0.0000335545

The first row, first column is m and first row, second column is b.

The third row, first column the coefficient of determination ... a value between 0 and 1 that indicates how accurately the mx + b formula predicts the given y values for the data that was provided. A value of 1 means 'perfect fit' and 0 means 'not even close'.

In this case the values are so close to 1 that we are safe in assuming that "for any value of x [the spring index], the value of y [the elusive k] is ((-0.0124727273 * [spring index]) + 0.9808181818) for music and stainless wire and ((-0.0109727273 * [spring index]) + 0.9849090909) for phosphor bronze wire.

[arvidj]

(07-03-2013, 09:15 AM)EdK Wrote: ...
It's curious that it's not the case when I run Marv's version of the program. I get the same results whether I select music or bronze wire. ...

Ed

Very possibly a case where the code and the exe do not match. Developers love those types of challenges ...

[arvidj]

(07-03-2013, 08:54 AM)arvidj Wrote: I've sent Marv an email with the same information as in the thread. We'll wait and see where my thinking has gone astray.

I just got this from Marv ...

From: Marvin W. Klotz
Sent: Wednesday, July 03, 2013 11:04 AM
To: Arvid Jedlicka
Subject: Re: Possibly a bug in the mandrel application ...

Arvid,

Good catch. I don't think I've ever seen such a thorough analysis of a
suspected error. I'm convinced. I've incorporated all your constants
into the program and prepared a new version to go up on the website soon.

Thank you so much for taking the time to work through this and advise me
of the problem. I really appreciate your efforts.

Regards, Marv

Home Shop Freeware
http://www.myvirtualnetwork.com/mklotz

[EdK]

I got the Windose program running now with Arvid's new numbers. I'll upload it once I've done some more testing.

Ed


  done.jpg (Size: 56.86 KB / Downloads: 75)

[TomG]

Ed,

When you get all the details worked out, I'll give it a real world test drive.

Tom

[EdK]

(07-03-2013, 02:12 PM)TomG Wrote: Ed,

When you get all the details worked out, I'll give it a real world test drive.

Tom

That would be wonderful Tom! I'll have it uploaded this evening.

Thanks,
Ed