Tools - Spring Making

[Last edit 7/25/2015 - spreadsheet update to version 3]

THIS PAGE IS A WORK IN PROGRESS. (But note that working spreadsheets are available)

WARNING:

When winding springs on the lathe, be advised that spring wire is sharp and can behave unpredictably. Further, wound springs can contain a large amount of energy and can unwind with a great deal of force. Observe all normal safety precautions when using the lathe, in particular:

• Wear eye protection when handling spring wire (a full face shield is even better).

• Turn the lathe chuck manually, NOT under power (switch lathe off and unplug to be sure).

• After a spring is would on the mandrel, revers the chuck rotation to remove any tension before cutting the spring wire, or before attempting to remove from the mandrel.

Spring Making

The basic process of spring making is conceptually very simple: Wind spring wire on a mandrel of suitable size, and then heat treat the spring to temper it. In practice, however, there are numerous variables to consider:

• size of wire to use

• type of wire to use

• number of coils

• length of spring

• size of mandrel

Let's start with the last item first - the size of the mandrel; seems like it should be simple, just use a mandrel with the same diameter as the inner diameter of the spring you want to make. But in practice, when a spring is wound around a mandrel it will "spring back" when removed from the mandrel, so the actual spring size turns out to be a bit larger than the mandrel size. Further, heat treating the spring to temper it will also change the size, making it a bit larger or a bit smaller depending upon the type of wire used.

This web page will include a method for estimating the required mandrel size, as well as some tools for winding springs on the lathe.

For links to more information on spring making, see References below.

Determining Mandrel Size

Design and Wind Your Helical Springs by Kozo Hiraoko (Part 1 page 20 Home Shop Machinist 1987 May-Jun, part 2 page 30 Home Shop Machinist 1987 Jul-Aug) provided a method of estimating the required mandrel size for a spring based on experimental data. While the results of this method may not provide an exact solution, they do provide an acceptable approximation, or a starting point for exact results.

Using this information, and data from other sources, I have created a spreadsheet which you can download a copy from the References section at the bottom of this page.

Spring Making Tools

 WORK In PROGRESS

References

Spreadsheet for spring making calculations:

This spreadsheet enables calculation of mandrel sizes for spring winding, and also for duplicating equivalent springs with alternate spring wire types, spring diameter, etc.

WARNING: While I believe the spreadsheet to be correct, it has not yet been independently tested - use at your risk.

How this spreadsheet was created:

The article on which this spreadsheet is based includes a graph for determining k values for different types of spring wire (the k value is essentially the experimentally determined  parameter which determines the mandrel size for a given finished spring size). I measured a series of points on this graph to create data sets for the two lines on the graph, and then used the CorePolyGUI extension for LibreOffice (see References section below) to calculate the polynomial equation which best fits the data. The polynomial equation is then used to calculate any needed k value, which can then be used to calculate mandrel size.

Note that the CorePolyGUI extension for LibreOffice must be added to your LibreOffice installation if you want to re-create the calculations using this extension; however, this is not necessary to use the spreadsheet for making spring calculations. Something similar would need to done with Excel, but as I do not use Excel I cannot further advise on this.

To download a copy of the spreadsheet: 

LibreOffice format Version 3: https://drive.google.com/file/d/12PsbkNMGGn1h4vu2Fznn2jz6Ddcwgnf_/view?usp=sharing

Excel Format Version 3: https://docs.google.com/spreadsheets/d/16ugOJyV_xpLtL6SijtasstlqUeUqkPca/edit?usp=sharing&ouid=106113331597260614243&rtpof=true&sd=true

Online version : https://docs.google.com/spreadsheets/d/1MGq_rMhGs1BuGvD80oTjyQPVgwPIuEuB7QjhD0Qm40U/edit?usp=sharing

Note :  To use the online version, make a copy in your own Google Drive account.

Please note the version numbers; the most recent version will always be linked to above. It is advised to always get the most recent version, as this will include any error corrections or new features.

Version 1 (4/16/2015):

• Included only spring mandrel calculations.

Version 2 (4/16/2015):

• Added spring index calculation, with warning flag if outside recommended range..

• Increased number of decimal places for wire diameter from 3 to 4

• Added table from Machinery's Handbook 28th  Ed.

• Re-arranged sheets

• Added additional calculations and illustrations

Version 3 (7/25/2015):

• • Revised file name from “mandrel-adjustment” to “spring calculations”

  • Added sheet to calculate spring equivalent

  • Added warning re active coils must be less than or equal to total coils

  • Corrected formatting errors

  • Added warning if spring length is <= solid height

  • Reorganized cells to simplify data entry

  • Added sheet protections to prevent accidental changes (there are no passwords so you can turn this off if you want to make modifications)

For additional links on spring making, go to the link below and scroll down to "springs":

https://sites.google.com/site/lagadoacademy/useful-links#info-other

To get the LibreOffice extension for calculating polynomial line fits to data:

CorelPolyGUI : http://extensions.libreoffice.org/extension-center/improved-trend-lines

"CorelPolyGUI plots extra trend lines such as linear and polynomial with forced intercept option, or moving average."