Bolts & Setscrews Help Needed

[Clive B 1Participant @cliveb1]

Hi Guys

Is there a name for a bolt or setscrew where the first 4mm of it has no thread, in other words the first 4mm is slightly less than the root diameter and what is the purpose for it?

Thanks for your help

Clive

[Clive B 1Participant @cliveb1]

[Ian ParkinParticipant @ianparkin39383]

Dogtooth. Used for locating into a hole in a shaft or. For toolpost bolts so the ends dont get burred over

[EmgeeParticipant @emgee]

Clive

Sounds like a rolled thread bolt to me,

Emgee

[Neil WyattModerator @neilwyatt]

+1 for a dogged or dogtooth screw.

[fishy-steveParticipant @fishy-steve]

Dog point screw.

[JonParticipant @jon]

Definately Dog Point and applies to any type of screw fixing whether cap head, grub screw, hex head or pan head etc.

[VicParticipant @vic]

Yes, Dog point set screw.

**LINK**

[Jeff DaymanParticipant @jeffdayman43397]

Careful how you use them. The dog tip is OK to provide compressive force on things as for holding pulleys on a shaft or behind another setscrew to prevent it backing out. One useful feature is that if the thread is overtightened it is less likely to bulge out at the end and jam in the hole as it could if there was no dog point. The dog point can be engaged in a drilled hole in the part being secured, stopping rotation. There's a catch to this though – if things move in use and the hole gets deformed, it may be very difficult to get the hub off the shaft. If the dog engages a groove in a shaft to stop end play, the same thing can happen if things move and the groove gets mashed up.

If the dog point is applied as a precision locating feature,say a hub to shaft hole tight fit for precision timing a sprocket, there can be big trouble. The dog point may not be concentric to the thread, and you can't locate anything with a thread. Two dowels one hole one slot in plate work, or a taper or spring pin through a hub and shaft, yes, these will locate things together precisely but threads will not.

For holding things on shafts I prefer to cut two flats on the shaft 90 deg apart and use cup point setscrews. The OD angle of the cup point will prevent thread bulge and the cup point will bite into the flats to hold the item well (assuming unhardened shafts or flats in soft shaft material under a hard outer layer). The flat allows the cup to bite into the shaft raising a volcano shaped dimple. If the flats were not present it would be awful to get the shaft out of the hub, with the raised dimples interfering with the hub ID. With the flats, the dimples clear the hub ID.

Simple stuff but can save a lot of headaches.

[Clive B 1Participant @cliveb1]

Thanks for the lowdown fellas, not that I’ve managed to find any of these screws yet but at least I now know what they are called.

Just to put you in the picture not exactly model engineering I know, I’ve just removed a 3.5mm thick steel plate from under my car, the plate protects the front axle and it’s bolted to the chassis using hexagon head screws which have a very short shank with a plain and spring washer encapsuled on them and as I’ve just found out from yourselves a dogpoint at the end of the thread.

The car chassis is a rectangular box type section with nuts which are welded to the inside of the boxing, they are not caged nuts but welded on as I say.

I don’t suppose the world would come to an end if I used ordinary setscrews of which the thread size is metric fine M10 x 1.25 pitch.

I don’t have a metal turning lathe but I guess I could put a couple of nuts on the screws using them as a register and file a dogpoint on them if I had to.

I had to use a blowlamp and keep heating the screws up in order to screw them out and even then the creaked like hell coming out, but If I hadn't have heated them I guess they would have sheared off.

What is the opinion on using ordinary setscrews, obviously with the correct size thread? and Jeff you blew me away with what you have said, so I sure would like to hear what you have to say concerning my application.

Thanks again fellas

[Brian Sweeting 2Participant @briansweeting2]

I believe in your case that the dogtooth is simply to aid the installation of the bolt in a production line. It guides the bolt into the hole for a faster fit.

[Gordon WParticipant @gordonw]

I've similar problem on my fiat 4×4. Use standard screws and spring washer, plenty of copper grease on screw, you will need them off again. Check the thread in chassis is still there ! If worried about them loosening drill the heads and use locking wire.

[Clive FosterParticipant @clivefoster55965]

Clive B 1

As Brian says the dogtooth is almost certainly there to help align things on the production line. However as you clearly had a corrosion problem in the threads a dogtooth reduces the amount of corroded thread that has to be wound back through the nut. I'd be unsurprised to discover that the manufacturer designed things so that the actual thread projection beyond the nut was minimal making it easier to get the bolt out should it have corroded. The aligning action of the dogpoint is still valuable during removal as it stops the bolt cocking over on the last thread or two potentially damaging the first thread. Naturally with a plain bolt sticking out the other side of the nut the last thread or two will always be most corroded.

Something to consider perhaps when wearing your Mr Fixit hat. I've made a dogtooth end a time or three for that very reason.

If you anticipate corrosion issues with a bolt in a steel bush consider if a fully threaded set-screw will suffice. The thread points leave much less area for the rust to grab and any bulk rust turns into a fairly respectable thread so things wind out pretty well. My Range Rover P38 uses such on the rear damper mounts which are both extremely inaccessible and almost invisible. Probably body off job if they jam up. Expecting the usual difficulties with getting a plain bolt shank out of the steel bush inside the rubber damper mount I was more than delighted to discover that they just wound out after the usual impact gun "burrrp – burrp" to take off the initial nip. Frankly the first one got a second go with the impact gun 'cos it came off so easily that I thought the socket had bounced off the head. Actually it had come fully undone.

Clive.

 

Edited By Clive Foster on 15/10/2017 14:58:08

[Jeff DaymanParticipant @jeffdayman43397]

Posted by Clive B 1 on 15/10/2017 12:11:34:

Thanks for the lowdown fellas, not that I’ve managed to find any of these screws yet but at least I now know what they are called.

Just to put you in the picture not exactly model engineering I know, I’ve just removed a 3.5mm thick steel plate from under my car, the plate protects the front axle and it’s bolted to the chassis using hexagon head screws which have a very short shank with a plain and spring washer encapsuled on them and as I’ve just found out from yourselves a dogpoint at the end of the thread.

The car chassis is a rectangular box type section with nuts which are welded to the inside of the boxing, they are not caged nuts but welded on as I say.

I don’t suppose the world would come to an end if I used ordinary setscrews of which the thread size is metric fine M10 x 1.25 pitch.

I don’t have a metal turning lathe but I guess I could put a couple of nuts on the screws using them as a register and file a dogpoint on them if I had to.

I had to use a blowlamp and keep heating the screws up in order to screw them out and even then the creaked like hell coming out, but If I hadn't have heated them I guess they would have sheared off.

What is the opinion on using ordinary setscrews, obviously with the correct size thread? and Jeff you blew me away with what you have said, so I sure would like to hear what you have to say concerning my application.

Thanks again fellas

Clive it sounds like what you are looking for is a SEMS hex head body bolt with a dog point and captive washers. These are available at most car parts stores here in north America but not sure about the UK. You could call a dealer for your make of car, describe the year and make and where the screws go, and they can probably provide some. Failing that you could contact a manufacturer of these bolts like the one in the pic below and they will likely send you a few.

I would not mess around rigging up some other sort of fastener to hold such a heavy 3.5 mm plate on a car. Chances are this plate carries some significant loads if it is that thick, so it is wise to use OEM spec screws as originally fitted. If your rigged up screws ever broke while driving on a highway, there would be a big chunk of metal flying about under the car that could be a major hazard to your car and others.

[Mike PooleParticipant @mikepoole82104]

In automotive applications these type of fasteners are widely used to aid assembly, many fasteners are installed by non seeing non feeling machines so to avoid crossed threads the plain end helps locate the bolt and start cleanly. Some nut runners are just a windy tool used by an operator but very sophisticated nut runners measure the torque and the rotation angle so crossed threads can be detected and faulty nuts identified.

Mike

[Neil WyattModerator @neilwyatt]

Some recommend them for 3D printing as the end threads are less likely to distort. the dog can be very short.

Neil

[Clive B 1Participant @cliveb1]

Thanks for all the info guys,

I’ve had a quick look on the net but not found any screws, well certainly not M10 x 1.25 pitch with an hexagon head and in the UK.

I know I could try the main agents but no doubt they will be at some silly price even if they have any, so I'll just get some 8.8 steel ones and for what it’s worth bung a couple of nuts on the thread as a register and file a dog point on them plus make sure there’s not a load of screw sticking up beyond the nut. when they are in place.

I noticed when undoing them they were very stiff to turn at the beginning even after putting heat on them and then they freed up until they were nearly out only to go as tight as hell again, no doubt corrosion on the thread which was sticking up beyond the nut even though they had a dog point on them.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Clive B 1, these people have M10 x 1.25 hex head, **LINK** no dog point on them though.

Regards Nick.

[Mike PooleParticipant @mikepoole82104]

Copaslip is very useful on fasteners if you would like to disassemble at some point in the future, the dog type point in your application is purely an assembly aid, I don't think manufacturers worry too much about how you are going to get something apart after the warranty period so just use whatever you have handy, the tensile strength is worth bearing in mind in an automotive application as they do tend to be very important in some areas, if your number plate falls off it's not a big deal but you would tend to notice a suspension or steering failure or if the engine fell out!

Mike

[Clive B 1Participant @cliveb1]

Thanks for the link Nick, I'll make a note of that for future.

Mike I will be putting some Copaslip on them, hopefully it will save getting the blowlamp out should I need to remove them in the future.

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