non slotted screws

Hi, can anybody please give me some advice on how to screw in threaded non slotted counter sunk screws. I want to use these so that they look like rivets, but I can't seem to figure out how to get the last turn nice and tight.

Thanks

Garry

Could you slot or make flats on the threaded end and tighten the screws from the other side, with a screwdriver or wrench? Just an idea.

Thanks for that, but no, they are going into blind holes.

Try a matching rivet punch, pushed down firmly.

They are best used with nuts, though.

Neil

Why bother with a thread, drill the holes for an interference fit and drive the screws in.

Emgee

Edited By Emgee on 28/09/2018 20:50:34

I don't think you will ever pull a threaded one down tight enough for it to look like a hammered rivit which should be all but invisible once filed flush.

If you want to screw them in then don't make then with a head, just turn a length of your rod and leave a 45deg shoulder then thread the smaller diameter. You now have the whole length of rod to hold so you can screw it in then cut off just above the surface and finish by filing smooth

"Shear Screws" are often used in applications where fasteners are not meant to be unscrewed - areas prone to vandalism, for example. A countersunk screw can be turned from hexagon bar, with the plain head you require, but with a deep groove formed between the head of the screw and a short length of hexagon. When you tighten the screw fully, using a spanner on the hexagon, the hexagon shears off at the groove, leaving you with a small pip on the now blind head of the screw. A stroke with a file will get rid of it. It's usual to turn the groove with a tapered bottom, such that the smallest diameter is adjacent to the screw head, thus provoking it to keep the majority of the pip with the hexagon, and not sticking out of the screw head.

Some experimentation is needed to determine the groove diameter - it depends on the screw material and the torque needed to tighten the screw. Tiny variations in groove diameter will give big variations in shearing torque!

Perhaps Garry wants to avoid the filing part of the operation. Maybe high strength loctite could hold a temporary head on for a strong enough action before shearing off.

How about soft soldering a nut on top of the flat top of the head ? This could be tedious if you have a lot to do and a non starter if the job cannot be heated to remove the nut.

Mike

Use Technifast drive pins of they are not to be removed . Trevor.

Thanks for all the different ideas but I forgot to mention that these are 5BA X 3/8 by two hundred of the little buggers.

Cheers Garry

What is the application? do they take any load, are they holding two items together or just cosmetic, will they be painted?

I can't think what bit of a traction engine you would want to do his on

Edited By JasonB on 29/09/2018 07:42:48

They are for the strakes. I don't want to rivet them from the inside with round head steel rivets. So I thought that I could use c/s non slotted screws from the outside into blind threaded holes. And no they will not be painted.

I would have thought that the lateral forces on the strakes together with the constant pounding would be likely to loosen the screws even if you did manage to get them reasonably tight! Another thought, the round head rivets on the inside of the wheel rim is a characteristic of most engines that I have seen, a plain rim might look a bit odd.

John

Edited By Journeyman on 29/09/2018 10:07:20

Cant you just buy some csk steel rivets, size the hole for a light interference fit or sized for Loctite retainer. Countersink the holes to leave the head just proud and clean back to flush. Would save one hell of a lot of work if you have 200 to do.

p.s.Forgot to say I am assuming they are cosmetic, if not then its a different story.

Ron

Edited By Ron Laden on 29/09/2018 10:08:31

Edited By Ron Laden on 29/09/2018 10:12:12

I'd agree, seems like the wrong solution. What's wrong with riveting? I'll definitely be riveting the strakes on my rear wheels.

Andrew

The problem with strakes is it is almost impossible to roll/twist them to the true helix so that they lay completely flat on the rim, you need the closing force of riviting to pull the strake hard down onto the rim. Also a rivit expands sideways when set and takes up any play in the holes, you can't do that with a screw so they will soon start fretting and the strake will loosen. As siad by John you run the risk of the screws loosening too.

The strake rivits are some of the easiest to do on a model, trick is to use a ctr drill as you don't need the usual 90deg CSK. Put the factory formed head on the inside of the rim and then it is just a few good blows to expand the outside end into the CSK hole, you don't even need to flush them off as the full size never were. Also they are a prominent feature of a Traction Engine wheel. Also if you are not used to riviting they are good ones to practice on before the snap heads need to be formed.

Count your self lucky that you only have 200 to do if and when I get round to doing my ploughing engine there will be 14 rivits per spoke, 36 spokes per wheel = 1008 rivits.

Edited By JasonB on 29/09/2018 10:18:20

Using countersunk screws in shear is not good practice. For starters for shear you should have a non threaded length through the hole so that the bit in shear is full diameter and the sideways force is passed from the hole to a close fitting full diameter shank. Second if relying on the countersunk head to transmit shear you will find it comes loose as Journeyman says. As others have said, hammering 1/8 rivets into a countersunk hole is not all that taxing. It makes it easier if the snap supporting the round head is mounted on something heavy so that all the hammer blow goes into deforming the rivet, not deflecting the support

Ok thanks everybody for the tech input. I will now go ahead and use round head rivets right through the rim and hammer them into the counter sink.

Thanks

Garry

Instead of hammering them you could squeeze them which would give a tighter fit. Getting the strakes to the correct helix is quite easy if you set your rollers up correctly.