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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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Making a plug for the broken end of an extension spring
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) |
#2
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Making a plug for the broken end of an extension spring
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) |
#3
Posted to rec.crafts.metalworking
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Making a plug for the broken end of an extension spring
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) |
#4
Posted to rec.crafts.metalworking
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Making a plug for the broken end of an extension spring
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. |
#5
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Making a plug for the broken end of an extension spring
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) |
#6
Posted to rec.crafts.metalworking
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Making a plug for the broken end of an extension spring
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 |
#7
Posted to rec.crafts.metalworking
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Making a plug for the broken end of an extension spring
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 |
#8
Posted to rec.crafts.metalworking
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Making a plug for the broken end of an extension spring
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 |
#9
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Making a plug for the broken end of an extension spring
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 |
#10
Posted to rec.crafts.metalworking
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Making a plug for the broken end of an extension spring
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. |
#11
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FOLLOWUP - Making a plug for the broken end of an extension spring
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 |
#12
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Making a plug for the broken end of an extension spring
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. |
#13
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Making a plug for the broken end of an extension spring
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. |
#14
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Making a plug for the broken end of an extension spring
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 |
#15
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Making a plug for the broken end of an extension spring
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. |
#16
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Making a plug for the broken end of an extension spring
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 --- Black Holes are where God is dividing by zero --- |
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