Tapped Holes vs Bolt an Nut

[SerpentEagle]

Can anyone shed some knowledge based on experience on whether it's safe to use tapped holes instead of locknuts?

Lets say you wanted to attach some square tubing to the side of another piece of tubing like this:



Is it safe to just tap and screw a bolt into the block that I have between the two tubes, or would it be better to just run a bolt through the whole thing and use a lock nut on the end of the bolt? The block is ~.5 inches thick in the middle.

If I'm not being clear enough please tell me.

[jman4747]

I guess you could tap it. It depends on what that bar is holding up though. If doing a through hole isn't a hindrance to some other part of the system then it more than likely would be safer.

[MaGiC_PiKaChU]

our 2014 canon as well as our 2015 frame were folded aluminium tapped together... saves some weight on the nuts and it's solid enough with some locktight

[GeeTwo]

I can't see the picture, so it's hard to be specific.

If the block is made of steel or another hard metal, and you have five threads engaged, you're getting as much holding power by tapping as you would by using a through bolt. Your block is 1/2" thick, so if you're using 1/4-20 bolts, the bolts would touch when each engaged 5 threads; this would not be optimal. If you're using finer thread bolts, it would just be a matter of trimming the bolts to the right length: no less than 5 threads engage, but less than 1/4" will enter the block. If using an aluminum block, definitely go with the through bolt.

Depending on how much vibration and variation of load you have, you may want to use lock washers on the bolts; I prefer the ones with the interior teeth, as the grip is at least as good and there are no sharp edges exposed. Given that you were going to use lock nuts originally, this is probably the case.

Another solution if you have an aluminum block might be to use a coupling nut within the aluminum block, which has even better strength than a tapped hole in steel.

[AdamHeard]

It looks like your designing parts far more complicated than necessary, as a design exercise you should see if you can get this done with purely 2d plates.

[jman4747]

Originally Posted by GeeTwo

I can't see the picture, so it's hard to be specific.

If the block is made of steel or another hard metal, and you have five threads engaged, you're getting as much holding power by tapping as you would by using a through bolt. Your block is 1/2" thick, so if you're using 1/4-20 bolts, the bolts would touch when each engaged 5 threads; this would not be optimal. If you're using finer thread bolts, it would just be a matter of trimming the bolts to the right length: no less than 5 threads engage, but less than 1/4" will enter the block. If using an aluminum block, definitely go with the through bolt.

That's what we don't know.

Are you using 1/4-20, 1/4-28, 10-32, 10-24, 8-32, etc ?

Also to Adams point, if you went with through holes that block could just be a spacer and wouldn't need the extra flanges on the top and bottom with the holes in them.

[Mr V]

The general rule of thumb when tapping is that if the 2 materials are the same you need the thickness of the material that is being tapped to be 1x the diameter of the bolt that it will be used with. Coarse/fine thread it doesn't matter.

Now if you are using a hard/strong bolt into a hole tapped into a soft/weaker material, say a steel bolt into a piece that is made of aluminum the thickness of the tapped material needs to be 2x the diameter of the bolt. Again it doesn't matter if they are coarse of fine threads and there is no rule that says you need X threads.

Both of those cases are based on achieving a strength the same or substantially similar to what would be obtained by using a nut. If you don't need the ultimate strength of the bolt then you can get away with tapping into thinner material but you'll need to use a lower torque to avoid stripping the tapped material.

If you look at bolts and their corresponding standard nut (not nylocks, or jam nuts) you'll find that the height of the nut is equal to the diameter of the bolt.

Things get more complicated when you are going through a tube. The problem is that when you go through both walls of a tube you usually end up with a situation where the tube starts to crush before you reach the ultimate clamping strength of the fastener. Again it does depend on whether you need the ultimate strength of the fastener being used. But if you go through both walls of a tube then you will need to use a lower torque when tightening the fastener in some cases.


I would look at how to make that connection without a bracket and without the need for a spacer, ie move one of the components if possible so that you could attach the two pieces directly. Another option that I would consider is the use of two pieces of angle and rivets to attach them. It would again be best without a spacer but it would increase the number of fasteners and distribute the load over a greater area. Net weight should be lower and the strength should be greater, with high strength rivets.

[Travis Covington]

Originally Posted by SerpentEagle

Can anyone shed some knowledge based on experience on whether it's safe to use tapped holes instead of locknuts?

Lets say you wanted to attach some square tubing to the side of another piece of tubing like this:



Is it safe to just tap and screw a bolt into the block that I have between the two tubes, or would it be better to just run a bolt through the whole thing and use a lock nut on the end of the bolt? The block is ~.5 inches thick in the middle.

If I'm not being clear enough please tell me.

If you are trying to duplicate what we did on 254, I would heed Adam's advice and simplify things greatly. We make a lot of complicated parts seem easy because we do some unique 3D milling and tabbed machining and have extensive experience doing so. You have changed some of the parts in our design to actually make them more complicated than they were originally. We also do a lot of things design wise on our robot purely from an aesthetics perspective. We could do them simpler, but chose to make them more complicated because we feel that looks cleaner and more elegant. Take a step back to analyze the problem and your chosen solution to decide if you need the complexity you have in there.

Regarding your original question - We tend to use nylon lock nuts in locations where we absolutely do not want something to come loose and do not have a piece of material behind it which we can tap to 1-2x thread diameter. We never use non-locking nuts except for jam nuts on cylinders. 1D (D = thread Diameter) thread depth is about the smallest I would feel comfortable with. We prefer to go thicker where we can. 1/4" thread depth is about as thin as we tolerate for #10 screws, for example.

[SerpentEagle]

Real quick, this is the reason for the spacer:

[AdamHeard]

Originally Posted by SerpentEagle

Real quick, this is the reason for the spacer:

I'll reiterate you can probably reach your top level design goals with making all of these parts simpler 2d parts. They are much easier to get made, and allow much faster iteration.

[R.C.]

Originally Posted by AdamHeard

I'll reiterate you can probably reach your top level design goals with making all of these parts simpler 2d parts. They are much easier to get made, and allow much faster iteration.

I agree with Adam. 2d stuff will also be easier/cheaper to get outsourced or made by sponsors.

[SerpentEagle]

Originally Posted by MaGiC_PiKaChU

our 2014 canon as well as our 2015 frame were folded aluminium tapped together... saves some weight on the nuts and it's solid enough with some locktight

When you say tapped do you mean bolted together? How thick was the aluminum?

[SerpentEagle]

Originally Posted by GeeTwo

I can't see the picture, so it's hard to be specific.

If the block is made of steel or another hard metal, and you have five threads engaged, you're getting as much holding power by tapping as you would by using a through bolt. Your block is 1/2" thick, so if you're using 1/4-20 bolts, the bolts would touch when each engaged 5 threads; this would not be optimal. If you're using finer thread bolts, it would just be a matter of trimming the bolts to the right length: no less than 5 threads engage, but less than 1/4" will enter the block. If using an aluminum block, definitely go with the through bolt.

Depending on how much vibration and variation of load you have, you may want to use lock washers on the bolts; I prefer the ones with the interior teeth, as the grip is at least as good and there are no sharp edges exposed. Given that you were going to use lock nuts originally, this is probably the case.

Another solution if you have an aluminum block might be to use a coupling nut within the aluminum block, which has even better strength than a tapped hole in steel.

I am using an aluminum block. Is it really that bad with aluminum? I've seen teams use aluminum blocks with threads before, and we've done it before ourselves without many problems.

The coupling nut in the block is an interesting idea. Have you guys tried it before?

[SerpentEagle]

Originally Posted by AdamHeard

It looks like your designing parts far more complicated than necessary, as a design exercise you should see if you can get this done with purely 2d plates.

The only way I could see this being done is just using a solid block with holes; I need the tube to be offset. Maybe angle brackets? I'm not sure on how to do this purely 2d.

By the way, I love your RAMP videos. They really helped me out.

[Travis Covington]

Originally Posted by SerpentEagle

I am using an aluminum block. Is it really that bad with aluminum? I've seen teams use aluminum blocks with threads before, and we've done it before ourselves without many problems.

The coupling nut in the block is an interesting idea. Have you guys tried it before?

Aluminum blocks hold threads fine. See the numerous posts others have already replied with.

If doing what you have above with #10 or smaller screws, threads in the blocks will be more than sufficient.