Making A Spring

[EdK]

I made the mandrel today that I'll need to make the spring I want to make. I'm going to make a clone of the spring I bought for my pump center project as practice in making springs. Thanks to Tom's excellent video, I think I can do this without too much trouble. One thing I'm going to try differently is to try making the compression spring using the TPI threading capabilities of the lathe to duplicate the spring coil spacing. The spacing on the coils for this spring are about .075" which translates to roughly 13 TPI. Tomorrow morning I plan on making a video of my attempt at making my first spring. Those of you that can't handle the sight of blood should probably refrain from watching the video. To be continued.

Ed

   

[oldgoaly]

my music wire arrived today, now to make a couple of mandrels and a wire feed guide..... it's in the 70's for a high in July!!!! so spending a bit of time outside!!! rain Tuesday, sounds like a plan!

[EdK]

I screwed up the first spring but it wound nicely. I miscalculated the spacing and used 13 TPI instead of 5.75TPI. The second ended up with the correct spacing of the coils but the ID is .020" oversize. In my application it's not going to matter since this 5/16" OD spring is put into a .375" hole. According to the spring calculator the mandrel should be .207" and mine ended up .210" but that certainly wouldn't account for a .020" oversized ID. I think I'll make another mandrel out of some 3/16" CRS and see if that gets me closer to the target ID.

The top spring in the picture is the store bought spring.
The middle one is my attempt at duplicating that spring.
The bottom one is the first one I made that I screwed up the TPI on.

Ed

   

[Highpower]

How do you guys figure out the TPI you need to use when you need a specific length with a specific number of coils? I need to make one of these:

Quote:Spring length - .675"
Spring EXT. Diameter - .15"
Spring INT. Diameter - .08"
1/16" drill bit mandrel
10 coils of .032" wire

[TomG]

I cheat by winding them all close. Then I just stretching them out to whatever pitch I happen to need and clip to length. It works for me.

Nice job on the spring Ed. There are a lot of variables in calculating the mandrel diameter, so I'm not surprised that it's off a bit. I always expect to do a couple trial runs.

Tom

[oldgoaly]

Ed
looks good to me! what size wire did you use? getting closer, got derailed cleaning up today!

[EdK]

(08-02-2013, 04:14 PM)Highpower Wrote:

How do you guys figure out the TPI you need to use when you need a specific length with a specific number of coils? I need to make one of these:

Quote:Spring length - .675"
Spring EXT. Diameter - .15"
Spring INT. Diameter - .08"
1/16" drill bit mandrel
10 coils of .032" wire

Willie,

Take the length of the spring and subtract the diameter of the wire times the number of coils. Divide the answer by the number of coils minus one. Add to the result the diameter of the wire. Take the reciprocal of that number and you'll have the TPI to set your lathe to. In your case:

.675 - (10 x .032) = .355
.355 / 9 = .03944444444
.03944444 + .032 = .071444444
1 / .0714444444 = 13.99

So you need to set your lathe to 14 TPI, or whatever is close to that.

Hopefully I didn't make any math errors, but highly likely.

Ed

[EdK]

(08-02-2013, 04:57 PM)oldgoaly Wrote: Ed
looks good to me! what size wire did you use? getting closer, got derailed cleaning up today!

oldgoaly,

I used the same size wire as the store bought spring which is .033".

Ed

[Mayhem]

Nice job there Ed

[dallen]

number 19 in the workshop practice series is one the design and manufacture of springs, full of info on how to make and design springs.