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View Full Version : How to keep a compression spring in a hole?



Jimno2506
08-15-2007, 03:34 PM
Machinists,
I have the need to keep a compression spring (.25" dia x 1" long) in a 3/4" deep hole while another piece of metal comes up and hits the spring, the pieces then is held in place by a sear, and when the sear is released the spring pushes the metal away.

My question is how do I keep the spring in place inside the hole so it doesn't spring or fall out?

I suppose friction fit would work, but looking for other ideas.

Regards,
Jimno

Joel
08-15-2007, 03:42 PM
An easy solution might be a .255 or so plug of fairly still rubber, pressed to the bottom of the hole.

Rusty Marlin
08-15-2007, 04:23 PM
assuming the part with the spring has clearance and isn't much thicker than the spring is long.

Make an internal spring guide shaped like a nail with a snap ring groove at the far end. The spring bore would be a deep c'bore with a clearance hole through, that will control the spring guide.
The guide goes through the core diameter of the spring and out the backside of the part and the snap ring groove is set at the max length the spring is allowed to expand.

http://i61.photobucket.com/albums/h45/rusty_marlin/srpingguideasm.jpg
http://i61.photobucket.com/albums/h45/rusty_marlin/srpingguideasm-1.jpg

topct
08-15-2007, 04:31 PM
How about some very stiff grease?

hitnmiss
08-15-2007, 05:13 PM
Maybe an O-ring "threaded" onto the 1st helix of the spring and pressed fit into the hole?

demerrill
08-15-2007, 05:40 PM
Remember that a compression spring expands slightly when compressed and size clearance hole accordingly to prevent binding.

Also if the L/D ratio of a compression spring is too large the spring will try to buckle and bind in a hole or over a rod when compressed. Guide well and accept increased friction or substitute multiple shorter springs of suitably small L/D with ends closed and ground and separate them by washers.

David Merrill

Frank Ford
08-15-2007, 05:56 PM
I've made and sold about 500 of these little brass thingies that fit between two hooks on banjos:
http://store01.prostores.com/gryphonstrings/catalog/Banjo4Small.jpg

It works like a toilet paper roll holder, with an internal spring that's captured by friction at both ends so the parts don't separate when you take it off. On the part that receives the spring, I simply drill a stepped hole so the spring jams by friction only at the bottom 1/8" inch. That accommodates the compression/diameter change.

Cheers,

Frank Ford
FRETS.COM (http://www.frets.com)
Gryphon Stringed Instruments (http://www.gryphonstrings.com)
My Home Shop Pages (http://www.frets.com/FRETSPages/Machining/index.html)

topct
08-15-2007, 06:07 PM
Reread the question.

You need to have the spring compressed.

Can you drill a small hole across the bore to insert a piece of wire that would hold the spring compressed for assembly, then pulled out to let the spring expand?

Alan Smith
08-15-2007, 06:41 PM
Frank, what's the purpose of your brass thingie for the banjo?

Sorry to hijack the thread.

Frank Ford
08-16-2007, 02:58 AM
Alan -

It's a little bracket that holds a small electronic tuner. The banjo teacher at our shop asked me to make him a gizmo to hold his tuner, and, well, things got a bit out of hand.

itís spring loaded and squeezes in between two hooks on the banjo rim. Itís the right diameter for the small clip that comes with the Korg AW-1 tuner, so it holds the tuner at just the right angle for easy viewing as you play. Because the tuner is held in close to the rim, your banjo can go in and out of its case without removing the tuner. This adapter fits most open back banjos that have 1 1/4" to 1 1/2" of space in between the brackets. It also fits most resonator banjos with a cast flange that have 1 1/4" to 1 1/2" of space in between the brackets. NOTE: some resonator banjos with two piece or other bulkier flange designs may not fit or may require some modification of the tuner clip. To use the holder, you need to attach the clip first, install the holder on the banjo, and then slide the tuner onto the clip.

Here's the tuner installed:
http://store01.prostores.com/gryphonstrings/catalog/BanjoTunerB.jpg

Cheers,

Frank Ford
FRETS.COM (http://www.frets.com)
Gryphon Stringed Instruments (http://www.gryphonstrings.com)
My Home Shop Pages (http://www.frets.com/FRETSPages/Machining/index.html)

Jimno2506
08-16-2007, 02:50 PM
A whole website dedicated to spring plungers. I'm sure one of these will work.

Thanks to all.

Jimno

Scishopguy
08-16-2007, 03:33 PM
Rusty hit the nail on the head. This is a common solution in tool and die and is used as a stripper to keep the part from sticking in the bottom of a form die. The shoulder bolt from the back side of the bolster will limit the travel as well as retain the spring.



assuming the part with the spring has clearance and isn't much thicker than the spring is long.

Make an internal spring guide shaped like a nail with a snap ring groove at the far end. The spring bore would be a deep c'bore with a clearance hole through, that will control the spring guide.
The guide goes through the core diameter of the spring and out the backside of the part and the snap ring groove is set at the max length the spring is allowed to expand.

http://i61.photobucket.com/albums/h45/rusty_marlin/srpingguideasm.jpg
http://i61.photobucket.com/albums/h45/rusty_marlin/srpingguideasm-1.jpg

kevindsingleton
08-16-2007, 04:08 PM
Frank,

That's pretty neat. I didn't know people were tuning banjos! :D

Kevin

Paul Alciatore
08-17-2007, 02:54 AM
How about a small drop of epoxy in the bottom of the hole?

Frank Ford
08-17-2007, 04:13 AM
Kevin -

Strange as it may seem, banjo players actually believe they are making a substance called "music."

Now, at the extreme risk of posting an off-topic item, let me clue you into just about the coolest T-shirt ever:

http://elderly.com/images/accessories/TEE/TMUTE-BLUE-M.jpg

Cheers,

Frank Ford
FRETS.COM (http://www.frets.com)
Gryphon Stringed Instruments (http://www.gryphonstrings.com)
My Home Shop Pages (http://www.frets.com/FRETSPages/Machining/index.html)

Jimno2506
08-17-2007, 10:54 AM
How about a small drop of epoxy in the bottom of the hole?

Simple and effective...should work great!

Thanks Paul!

Jimno

A.K. Boomer
08-17-2007, 11:22 AM
Fan out (increase coil diameter) the last (deepest) coil on the spring and install spring all the way in, Now you have all the travel because your spring is still smaller diameter than the rest of the bore and you have a spring that has a friction fit in the bottom of the hole, this will keep spring from popping out...

kevindsingleton
08-17-2007, 05:09 PM
Frank,

I love the t-shirt! Banjo players probably have one for guitarists, too. :rolleyes: You do great work, even on something as distasteful as a banjo!

I like A.K. Boomer's spread coil idea. Seems the simplest.

Kevin