Where There Is No Nylock (Locknut)
Intro: Where There Is No Nylock (Locknut)
This is an explanation of two methods of creating multi-use steel locknuts for threaded bolts, and a reminder of a few other methods that you may already use.
Nylon Locknuts work well, but sometimes they are not available, and after several times on and off a bolt they lose much of their locknut properties as the nylon shapes to the threads of the bolt. Twice in my work traveling, I have needed locknuts and been unable to find them.
Methods:
1. “Cut and Crush”—distort the threads on a nut by cutting out a narrow section of threads and crushing the remaining threads into that gap.
2. Ovalized nut –distort threads into an oval
3. Reminders They nylock. and other commercially available locking nuts, 2 nuts tightened against each other, Loctite, etc.
**The “cut and crush” and “ovalize” methods were taught to me by Ralf Hotchkiss, my colleague at Whirlwind Wheelchair. Ralf travels and works extensively in places with limited access to modern manufacturing technology and supply chain, and has been learning and designing tricks for “low tech” manufacture for the past 40 years.
These methods can be replicated pretty much anywhere—but I made these locknuts at Techshop SF (amid the whir of CNC machine tools).
Links:
where i made it: http://techshop.ws/
where i learned how to make it: http://www.whirlwindwheelchair.org/
Nylon Locknuts work well, but sometimes they are not available, and after several times on and off a bolt they lose much of their locknut properties as the nylon shapes to the threads of the bolt. Twice in my work traveling, I have needed locknuts and been unable to find them.
Methods:
1. “Cut and Crush”—distort the threads on a nut by cutting out a narrow section of threads and crushing the remaining threads into that gap.
2. Ovalized nut –distort threads into an oval
3. Reminders They nylock. and other commercially available locking nuts, 2 nuts tightened against each other, Loctite, etc.
**The “cut and crush” and “ovalize” methods were taught to me by Ralf Hotchkiss, my colleague at Whirlwind Wheelchair. Ralf travels and works extensively in places with limited access to modern manufacturing technology and supply chain, and has been learning and designing tricks for “low tech” manufacture for the past 40 years.
These methods can be replicated pretty much anywhere—but I made these locknuts at Techshop SF (amid the whir of CNC machine tools).
Links:
where i made it: http://techshop.ws/
where i learned how to make it: http://www.whirlwindwheelchair.org/
STEP 1: Split and Crush a Nut (Thread Interference)
1. Cut and Crush: (For steel nuts)
This locknut works by distorting the threads of a nut, so that threading it onto a bolt will spring the nut to its original position. This method does weaken the nut somewhat so use with caution. First, cut into the nut with a hacksaw blade as shown, approximately 1/3 of the way through the inside hole. This will remove a width of approximately 0.8mm .
Then crush the nut in a vice to bend the two split sections of the nut to touch. The nut will deform into this shape. When threaded onto a bolt, the thread pattern forces the nut to spring back into shape, remaining under spring tension until it is unthreaded.
Don’t cut farther than halfway through the nut, in order to retain strength, but if you don’t cut far enough into the threaded are it won’t be possible to crush the two sides inward enough to get a good thread interference for locking. I recommend cutting 1/3 of the way though the hole in the center of the nut.
With a ½”-20 nut made with this method, I measured a torque of 8 foot-pounds at both the first and tenth time tightening the nut.
This locknut works by distorting the threads of a nut, so that threading it onto a bolt will spring the nut to its original position. This method does weaken the nut somewhat so use with caution. First, cut into the nut with a hacksaw blade as shown, approximately 1/3 of the way through the inside hole. This will remove a width of approximately 0.8mm .
Then crush the nut in a vice to bend the two split sections of the nut to touch. The nut will deform into this shape. When threaded onto a bolt, the thread pattern forces the nut to spring back into shape, remaining under spring tension until it is unthreaded.
Don’t cut farther than halfway through the nut, in order to retain strength, but if you don’t cut far enough into the threaded are it won’t be possible to crush the two sides inward enough to get a good thread interference for locking. I recommend cutting 1/3 of the way though the hole in the center of the nut.
With a ½”-20 nut made with this method, I measured a torque of 8 foot-pounds at both the first and tenth time tightening the nut.
STEP 2: Ovalized Nut
2. Ovalize nut
(These are commercially available as Elliptical offset nuts.)
Crush a nut in a vice to deform the round threads into an oval. Threading this nut onto a bolt will force the nut to become more circular, under spring tension. You could also crush the nut with a blow from a hammer, but the results would be less consistent without a jig.
There is a relatively narrow range of amount of ovalization that leads to a good locknut. To make more than a few of these nuts, you could make a jig that has a calibrated hard stop for the crushing force (vice or hammer).
This 1/2"-20 nut moved with a torque of 20 ft-lbs at the first and tenth time tightening it onto the bolt.
(These are commercially available as Elliptical offset nuts.)
Crush a nut in a vice to deform the round threads into an oval. Threading this nut onto a bolt will force the nut to become more circular, under spring tension. You could also crush the nut with a blow from a hammer, but the results would be less consistent without a jig.
There is a relatively narrow range of amount of ovalization that leads to a good locknut. To make more than a few of these nuts, you could make a jig that has a calibrated hard stop for the crushing force (vice or hammer).
This 1/2"-20 nut moved with a torque of 20 ft-lbs at the first and tenth time tightening it onto the bolt.
STEP 3: Other Locknut Reminders
Reminders
A) Nyloc
B) Castle nut (with cotter pin)
C) Flex-Top Expanding Hex Locknuts
D)2 nuts tightened against each other
E) Loctite
F) Spring Washers
McMaster-Carr is a good source of locknuts, and information about commercial options.
http://www.mcmaster.com/#hex-locknuts
A) Nyloc
B) Castle nut (with cotter pin)
C) Flex-Top Expanding Hex Locknuts
D)2 nuts tightened against each other
E) Loctite
F) Spring Washers
McMaster-Carr is a good source of locknuts, and information about commercial options.
http://www.mcmaster.com/#hex-locknuts
12 Comments
ralfhotchkiss 12 years ago
So here is a simple jig: Take a short bolt of the same size as the nut that you want to ovalize. File just a little off one face of the head of this bolt. Put a washer and a nut on this bolt so that you can hang the head of this bolt down between the jaws of your vise. Put the nut you want to ovalize next to the head of the bolt, and squeeze hard. The bolt head will stop the vise from closing too far, but not until the nut is ovalized a little. Now take the nut and screw it on a bolt. Matt, is this how you did it in the Philippines?
With a torque wrench (or a fish scale and any wrench), measure the torque that it takes to turn the nut onto the shaft of the bolt. If this nut is twice as hard to turn as a nylon locknut, you have made a good jig...but probably you will need to file some more steel off the head of the bolt, crush the bolt head and the nut, side by side in the vise, then test the nut again and again until the torque is enough.
I found that a 12mm diameter bolt, which has a 19mm head (measured 18.9mm) worked as a vise stop when i filed it to 18mm wide. After each nut was squeezed to 18mm wide and taken out of the vise, it sprung back to 18.5mm across. This deformation was enough to create 2 to 3 ft-lbs of resistance when i screwed the nuts onto new bolts. After 10 times on and off, these nuts - like AAron's - are still just as tight.
I lubricated each bolt with a drop of 90+ weight gear oil - my favorite to prevent rusting and seizing after years of riding in the mud and rain. Any suggestions for better oils or greases - for all the rustable or movong parts of a wheelchair - that are available in small towns worldwide?
Generic nylon locknuts, some bought in South Africa and some bought in the U.S., resisted twisting with about 1 ft-lb of friction when new. All had a drop of oil.
Assuming that this amount of friction is adequate, our starting - and staying - with 2-3 ft-lbs of resistance to unscrewing should be better yet.
matt.mccambridge 12 years ago
You may know that Freedom Tech (small wheelchair shop in the Philippines) used the oval ones for a while. The bummer about the oval ones is that they aren't visibly different from regular nuts ie no simple visual inspection (compared to say the cut nuts and the nylocks which are visibly distinct). I think it was you who suggested that if you set up a jig to produce the oval ones in batches for anything but immediate use, painting/dyeing/stamping/notching them is a good additional step.
AlanS14 8 years ago
ok idea but a meaningless test- 'I measured a torque of 8 foot-pounds at both the first and tenth time tightening the nut.'
What you should do is apply a particular torque then measure the release torque, but even then your evaluation method seems numbers for the sake of numbers rather that have any sound scientific basis.
LynxSys 10 years ago
This is a very helpful Instructable with some great comments! Commercially made distorted-thread locknuts can be expensive and hard to find, so I'll certainly be using this method soon.
Does anyone have a good formula for how much to ovalize a nut? I imagine that there's a fairly simple relationship between fastener diameter and how much you need to crush a nut to reach a useful amount of resistance. If that relationship (maybe it's as simple as a percentage?) were known (and you know how much your vise closes with one turn of the screw), it would be very easy to consistently make oval locknuts in whatever size you needed.
Also, I know that most commercial elliptical offset locknuts are only distorted at one end or in the middle, to make initially threading the nut easier. Has anyone who has used this method found that threading a DIY ovalized nut becomes unacceptably difficult?
Finally, what range of sizes have people used the cut and crush method for? It seems that the kerf of a hacksaw might be too wide to use this for smaller nuts, and might even be too narrow for particularly large nuts (although, if you're using giant nuts, you're probably building something structural and are hopefully using properly rated fasteners). An interesting side-note: the cut and crush method appears to create nuts that are a close cousin of some commercially available Philidas locknuts.
buddie1st 11 years ago
rimar2000 12 years ago
If you have access to the place, you can use a center punch to deform the threads of both, nut and bolt. It is effective, make sure the position is the correct before make that.
pfred2 12 years ago
Robot Lover 12 years ago
pfred2 12 years ago
Robot Lover 12 years ago
pfred2 12 years ago
Orngrimm 12 years ago
Thanks! This finds its way to my notebook of "Improvising stuff you need but dont have at hand"