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Bolts & Screws using friction only to hold (or fluted)

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Richard Rogalewski01/01/2020 13:16:52
72 forum posts
14 photos

I have a need for a screw with a round head which uses friction only to hold it whilst the nut is tightened. So, the round head has no slot or anything, just plain round head. Or something similar which is partly fluted near the head. Do such things exist? Wanting M20-ish in stainless steel.Thanks.

EDIT: BTW, carriage bolts & screws not acceptable, well, I'd have to remove the square bit..

EDIT: Aaah, ribbed necked carriage bolts. Except ideally I'd need a screw of that type. I could use a spacer I guess, with a bolt.

Edited By Richard Rogalewski on 01/01/2020 13:32:31

old mart01/01/2020 13:39:15
1251 forum posts
116 photos

Car wheels used to be held on with headed studs with splines on the diameter just under the head. They didn't go as big as 20mm, but light commercial vehicles such as Transits might. Try a garage for wheel studs. 

A drawing would help.

Edited By old mart on 01/01/2020 13:39:41

Edited By old mart on 01/01/2020 13:41:02

bill ellis01/01/2020 13:46:54
71 forum posts
2 photos

Not sure if the round head without slot/hex is available, but if they are you could cut a slot across the threaded end and use a screwdriver to hold it whilst tightening. If you use a longer bolt than is required you can chop the slotted bit off afterwards (assuming you have access). I know you can get countersunk bolts that then have a smooth head cap screwed into them (usually used for mirror fixings and suchlike).

Richard Rogalewski01/01/2020 13:56:46
72 forum posts
14 photos

Actually, I'd need 3 for my needs. If I only made 3, best I just grind off the square part of M20 x 20mm stainless carriage screws. If I made a production run, I'd try to avoid having to grind off the square parts of carriage screws, and that suggests use of rib neck carriage bolts, or similar. But, I'd need a spacer with a bolt. As the screw or bolt is passing through 1mm thick sheet metal.

EDIT: Actually, in any case, I'd need to use a spacer given the thinness of the material the screw or bolt is passing thru.

Edited By Richard Rogalewski on 01/01/2020 14:07:05

daveb01/01/2020 15:10:24
621 forum posts
10 photos

Reshape the hex head of a M20 machine screw and cut a screwdriver slot in the threaded end so you can hold it to tighten the nut.

Howard Lewis01/01/2020 15:17:02
2927 forum posts
2 photos

If you are planning to make your own, make the diameter immediately below the head a tight fit in the hole, a fitted bolt, in fact. Once drawn into place, the slight interference between the shank and the hole should provide enough mgrip to allow the nut to be torqued up; especially with a dab of Loctite under the head and allowed to cure.

Howard

Martin Cargill01/01/2020 16:05:37
120 forum posts

For a machine we looked after we used a straight knurl on the shank of a 12mm socket head cap screw and machined the hex socket part off, leaving only a small part of the bolt head. The screws were then pulled into a tight fitting hole in the holding part using a 12mm nut and washers. They worked pretty well and were only ever removed (by punching the bolt out) if the screw snapped during use.

Martin

Richard Rogalewski01/01/2020 17:18:50
72 forum posts
14 photos

pin assy.jpg

Here is the item I'm wanting to make. I could use a M16 carriage bolt with square removed if I just made 3. But, if I made in production quantities maybe I'd need something else. Not easy to obtain 30mm M16 carriage bolt I imagine.. Would have to cut down a longer bolt/screw I suspect.. I would probably need a spacer between the nut and the 1mm thick sheet.

Ideally the screw/bolt head would be very hard - not susceptible to filing.

Edited By Richard Rogalewski on 01/01/2020 17:24:35

Phil P01/01/2020 17:43:54
592 forum posts
164 photos

Richard

I am curious as to what you are trying to make here, would you tell us what the purpose of the assembly is please.

Thanks

Phil

Richard Rogalewski01/01/2020 17:50:05
72 forum posts
14 photos

On the issue of production: Let's say a few hundred of these "pin assemblies" were to be made. Would it be perfectly reasonable, in terms of production efficiency (or whatever) to buy in carriage screws and use a lathe to remove the square features? As oppossed to getting someone else to produce the screws without the squares. I imagine buying in carriage bolts and modifying might be what most people would do.

Richard Rogalewski01/01/2020 17:52:17
72 forum posts
14 photos
Posted by Phil P on 01/01/2020 17:43:54:

Richard

I am curious as to what you are trying to make here, would you tell us what the purpose of the assembly is please.

Thanks

Phil

It's a "pin assembly" for a lock where a hooked bolt engages with said pin.

Tim Stevens01/01/2020 18:07:49
avatar
1143 forum posts

The problem you may face with a 'dead hard' bolt (pin, etc) is that extreme hardness comes at the expense of toughness. So, a firm tap with a decent hard-faced hammer is likely to knock the head clean off - rather defeating the excercise, I suspect. That is, if you could solve the problem of hardening the head while keeping the threads from being equally fragile. Or distorted.

Sometimes there is a good reason for not being able to find a novel part.

Sorry - Tim

Nimble01/01/2020 18:26:16
avatar
33 forum posts

Hi Richard,

Could you take a standard coach bolt and reduce the depth of the squqred part then counte-rbore a standard nut to fit over the square reducing its depth if necessary..

Regards, Neil

Jeff Dayman01/01/2020 19:11:50
1762 forum posts
45 photos

If you are making a lock and want cheap but strong construction, consider the design below. If the pin ends could be identical dia and length or at least the same dia, costs would be kept low due to minimal machining and simple workholding.

lock pin idea.jpg

JasonB01/01/2020 19:22:16
avatar
Moderator
17315 forum posts
1865 photos
1 articles

You are likely to need a spacer or counterbored nut anyway as almost impossible to thread right upto the underside of the head. Also having a dead square internal corner between head and shank will be a stress raiser

Keith Long01/01/2020 20:19:04
808 forum posts
10 photos

Richard have a search on the web for "rivbolt" or "clinch bolt". I think one of those would serve your purpose if they come in the sizes to suit.

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