The same neighbor with the broken recip saw has a broken 7" angle
grinder that he'd like me to fix for him.

It's the switch on the grinder that's broken - the return spring on the
trigger has a broken end (it's an extension spring with hook ends).
I've checked the usual sources & can't find this one, but I have a good
repair, I think.

The repair is to make a plug with threads to match the coiled spring
profile. The plug would just thread into the broken end & have the
needed hook. The spring has a very high spring rate & extends very
little, so there would be little chance of the plug escaping during
extension.

As far as turning the threads on the plug, how closely do I have to
match the profile? Can I just use a standard 60 degree thread (with the
same pitch, of course), or do I have to use a form tool to get a
semicircular thread?

This will a small plug: the ID will be 3/32 & the pitch 24 tpi.

Anybody ever done this?

Thanks,
Bob

BTW - the spring is 3/16 OD, 1-9/16 OAL, .044 wire, preloaded - if
someone has a REALLY good source for springs (i.e., much better than McM-C)

I like your idea, You might consider making the screw a tad bit larger than
the id of the existing spring so it will be nice and snug.



If it doesn't work you could always roll your own spring. Just get music
wire the right diameter and make yourself a mandrel for the lathe. With
back gears go slow and make a test run. The loops can be formed by hand.

The spring will tend to get bigger once the tension is off so the ID will be
a bit smaller when winding than when it relaxes.

Alternatively if it is only the hook that is broken you can sometimes make a
new hook from an existing loop and go with that. If the pull is a bit too
stiff, you can stretch it out a little.

Also if you can find a longer expansion spring you can shorten it.

Good luck and be sure to report back on your results.


--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
they come up with this striped stuff.
"Bob Engelhardt" wrote in message
...
The same neighbor with the broken recip saw has a broken 7" angle
grinder that he'd like me to fix for him.

It's the switch on the grinder that's broken - the return spring on the
trigger has a broken end (it's an extension spring with hook ends).
I've checked the usual sources & can't find this one, but I have a good
repair, I think.

The repair is to make a plug with threads to match the coiled spring
profile. The plug would just thread into the broken end & have the
needed hook. The spring has a very high spring rate & extends very
little, so there would be little chance of the plug escaping during
extension.

As far as turning the threads on the plug, how closely do I have to
match the profile? Can I just use a standard 60 degree thread (with the
same pitch, of course), or do I have to use a form tool to get a
semicircular thread?

This will a small plug: the ID will be 3/32 & the pitch 24 tpi.

Anybody ever done this?

Thanks,
Bob

BTW - the spring is 3/16 OD, 1-9/16 OAL, .044 wire, preloaded - if
someone has a REALLY good source for springs (i.e., much better than
McM-C)

On Mon, 03 May 2010 22:48:52 -0400, Bob Engelhardt
wrote:

The same neighbor with the broken recip saw has a broken 7" angle
grinder that he'd like me to fix for him.

It's the switch on the grinder that's broken - the return spring on the
trigger has a broken end (it's an extension spring with hook ends).
I've checked the usual sources & can't find this one, but I have a good
repair, I think.

The repair is to make a plug with threads to match the coiled spring
profile. The plug would just thread into the broken end & have the
needed hook. The spring has a very high spring rate & extends very
little, so there would be little chance of the plug escaping during
extension.

As far as turning the threads on the plug, how closely do I have to
match the profile? Can I just use a standard 60 degree thread (with the
same pitch, of course), or do I have to use a form tool to get a
semicircular thread?

This will a small plug: the ID will be 3/32 & the pitch 24 tpi.

Anybody ever done this?

Thanks,
Bob
I've made spring ends with Cerrobend and Cerrosafe, alloys that melt
at temperatures well below what would affect heat-treat of a spring.
Think boiling water temp.

Drill hole in bit of scrap same as OD of spring. Insert spring into
hole. You could also have a center hole housing a hook. Pour in a
little molten alloy. It forms a plug that grabs a couple of turns of
spring, and in your case a hook. Or, you could drill the plug after
the fact and then insert the hook.

BTW - the spring is 3/16 OD, 1-9/16 OAL, .044 wire, preloaded - if
someone has a REALLY good source for springs (i.e., much better than McM-C)

Bob Engelhardt wrote:
...
BTW - the spring is 3/16 OD, 1-9/16 OAL, .044 wire, preloaded - if
someone has a REALLY good source for springs (i.e., much better than McM-C)

I want to know how springs are manufactured "preloaded", that's all.
Completely collapsed, coil-bound, under tension even at rest? I'm
guessing they were first compression springs that were somehow flipped
inside out, end to end.

Improvising a fix (not actually a repair) on a switch that insures that a
grinder will turn off the instant that finger pressure is released, doesn't
seem wise.

If the spring fails again, the switch could close if the trigger is resting
on something, just from the weight of the handle end.

There are numerous tool parts dealers, and some other sources that
specialize in new vintage-style switches, like the ones used in all-metal
power tools, if the grinder switch is assumed to be obsolete/NLA.

--
WB
..........


"Bob Engelhardt" wrote in message
...
The same neighbor with the broken recip saw has a broken 7" angle grinder
that he'd like me to fix for him.

It's the switch on the grinder that's broken - the return spring on the
trigger has a broken end (it's an extension spring with hook ends). I've
checked the usual sources & can't find this one, but I have a good repair,
I think.

The repair is to make a plug with threads to match the coiled spring
profile. The plug would just thread into the broken end & have the needed
hook. The spring has a very high spring rate & extends very little, so
there would be little chance of the plug escaping during extension.

As far as turning the threads on the plug, how closely do I have to match
the profile? Can I just use a standard 60 degree thread (with the same
pitch, of course), or do I have to use a form tool to get a semicircular
thread?

This will a small plug: the ID will be 3/32 & the pitch 24 tpi.

Anybody ever done this?

Thanks,
Bob

BTW - the spring is 3/16 OD, 1-9/16 OAL, .044 wire, preloaded - if someone
has a REALLY good source for springs (i.e., much better than McM-C)

Roger Shoaf wrote:
..., You might consider making the screw a tad bit larger than
the id of the existing spring so it will be nice and snug.

Right - in fact, the coil direction of the spring is such that friction
while inserting the plug will tend to open the spring, making a tight
fit easier.

If it doesn't work you could always roll your own spring. Just get music
wire the right diameter and make yourself a mandrel for the lathe. With
back gears go slow and make a test run. The loops can be formed by hand.

The spring will tend to get bigger once the tension is off so the ID will be
a bit smaller when winding than when it relaxes.

I've heard of doing that & have it bookmarked in case. But this spring
is so stiff & small that I'd never try it. Visualize this: the ID is
1/2 the OD - that's a very tight spring. Also, it's preloaded & I
haven't a clue as to how I'd do that.

Alternatively if it is only the hook that is broken you can sometimes make a
new hook from an existing loop and go with that. If the pull is a bit too
stiff, you can stretch it out a little.

I was expecting that I was going to have to do that, until I ran across
the plug idea in the Google group archives. But I figured that by the
time I annealed, re-bent, hardened, and tempered it, I was sure to have
ruined it.

Also if you can find a longer expansion spring you can shorten it.

Good luck and be sure to report back on your results.

You bet.

Bob

Don Foreman wrote:
I've made spring ends with Cerrobend and Cerrosafe, alloys that melt
at temperatures well below what would affect heat-treat of a spring.
Think boiling water temp.

Drill hole in bit of scrap same as OD of spring. Insert spring into
hole. You could also have a center hole housing a hook. Pour in a
little molten alloy. It forms a plug that grabs a couple of turns of
spring, and in your case a hook. Or, you could drill the plug after
the fact and then insert the hook.

That's a great idea! I have some Cerro-something just waiting for a use
like this. Do you think that the inserted hook would need some kind of
tooth to it, for the Cerro-x to grab? Or would it bond like solder?

Thanks,
Bob

Beryl wrote:
I want to know how springs are manufactured "preloaded", that's all.
Completely collapsed, coil-bound, under tension even at rest? I'm
guessing they were first compression springs that were somehow flipped
inside out, end to end.

I know! A HSM'er can wind his own springs, but preloading them? How DO
they do that? The inside-out compression spring is a better explanation
than anything that I can think of.

Bob

Wild_Bill wrote:
Improvising a fix (not actually a repair) on a switch that insures that
a grinder will turn off the instant that finger pressure is released,
doesn't seem wise.

Good point. The broken spring means that the switch & grinder stay on.
But the neighbor has been using it that way, so maybe he'll chance it.
I'll ask though.

If the spring fails again, the switch could close if the trigger is
resting on something, just from the weight of the handle end.

It's almost certain that if it fails it will do it when the trigger is
pulled & give feedback that it's happened (release of pressure on finger).


There are numerous tool parts dealers, and some other sources that
specialize in new vintage-style switches, like the ones used in
all-metal power tools, if the grinder switch is assumed to be obsolete/NLA.

The neighbor's tried the tool-part replacement route, but not the
generic-switch one. I'll look into it.

Thanks,
Bob

What's that Lassie? You say that Beryl fell down the old
rec.crafts.metalworking mine and will die if we don't mount a rescue
by Mon, 03 May 2010 23:34:42 -0700:

Bob Engelhardt wrote:
...
BTW - the spring is 3/16 OD, 1-9/16 OAL, .044 wire, preloaded - if
someone has a REALLY good source for springs (i.e., much better than McM-C)

I want to know how springs are manufactured "preloaded", that's all.
Completely collapsed, coil-bound, under tension even at rest? I'm
guessing they were first compression springs that were somehow flipped
inside out, end to end.

When the wire is being wound on the mandrel, it's held at the 'wrong'
angle. That is, the wire is rubbing on the previous turn on wire.

Imagine if you wanted to wind a spring that was a compression spring.
You would feed the wire ahead of the wound coils.
With a pre loaded spring you're doing the opposite.
--

Dan H.
northshore MA.

Bob Engelhardt wrote:
snip
make a plug with threads to match the coiled spring profile.
snip

I made the plug - it went off without a hitch & works a treat, as they say.

I made 60 degree threads, kind of. The profile is:

__/\__/\__/\__

The minor diameter is just the ID of the spring and the major diameter
is the ID + .73 * D. Where D is the diameter of the spring wire and the
..73 comes from some geometry & trig.

In this case, making the plug had a huge advantage over reforming a coil
into a new hook. After the plug was turned I didn't cut it off from the
stock it was made from. This left that stock as a handle to manipulate
the spring as I reassembled the switch. Which involved putting about 15
lbs tension on the spring.

Thanks for the comments,
Bob

On Mon, 03 May 2010 23:34:42 -0700, Beryl wrote:

Bob Engelhardt wrote:
...
BTW - the spring is 3/16 OD, 1-9/16 OAL, .044 wire, preloaded - if
someone has a REALLY good source for springs (i.e., much better than McM-C)

I want to know how springs are manufactured "preloaded", that's all.
Completely collapsed, coil-bound, under tension even at rest? I'm
guessing they were first compression springs that were somehow flipped
inside out, end to end.

It's determined by the angle of the wire relative to the mandrel -- or
at least that's how I do it. If the wire is fed at the helix angle of
the spring then it's neutral. If it's fed in tension at less than the
helix angle of the spring but advancing at the spring's closed pitch
rate, then it'll have preload.

Bob Engelhardt wrote:
Beryl wrote:
I want to know how springs are manufactured "preloaded", that's all.
Completely collapsed, coil-bound, under tension even at rest? I'm
guessing they were first compression springs that were somehow flipped
inside out, end to end.

I know! A HSM'er can wind his own springs, but preloading them? How DO
they do that? The inside-out compression spring is a better explanation
than anything that I can think of.

Bob

dan and Don gave the same good explanation. I suppose...
Except the wire would need to already be a tempered springy wire before
winding.
My garden hose got me thinking about this. I hate pulling the end of it
out of the wrong side of the coil and then fighting with 50 feet of
preloaded hose.

On Tue, 04 May 2010 21:20:40 -0700, Beryl wrote:


dan and Don gave the same good explanation. I suppose...
Except the wire would need to already be a tempered springy wire before
winding.

Small commodity springs are wound from hard wire and receive a low
temperature heat treat after winding that improves stability and
fatigue life.

http://www.spring-makers-resource.net/spring-steel.html

--
Ned Simmons

Ned Simmons wrote:
On Tue, 04 May 2010 21:20:40 -0700, Beryl wrote:

dan and Don gave the same good explanation. I suppose...
Except the wire would need to already be a tempered springy wire before
winding.

Small commodity springs are wound from hard wire and receive a low
temperature heat treat after winding that improves stability and
fatigue life.

http://www.spring-makers-resource.net/spring-steel.html


Nice site.
http://www.spring-makers-resource.ne...n-springs.html says "In
some cases the coils could be wound so tightly that it requires an
effort just to pull them apart." which is close enough to what I wish
they'd explained.
The page also shows a *Drawbar Spring* which Bob might try if his plug
repair ever fails.

On 2010-05-05, Ned Simmons wrote:
On Tue, 04 May 2010 21:20:40 -0700, Beryl wrote:


dan and Don gave the same good explanation. I suppose...
Except the wire would need to already be a tempered springy wire before
winding.

Small commodity springs are wound from hard wire and receive a low
temperature heat treat after winding that improves stability and
fatigue life.

http://www.spring-makers-resource.net/spring-steel.html

Here is another good site which has been around for a while.


http://home.earthlink.net/~bazillion/intro.html

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
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