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Removing bang in self tappers

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Rik Shaw27/09/2020 17:30:28
1463 forum posts
396 photos

As you might see from the picture the satin chrome on the dial is being scored by debris collecting under the primitive indicator window. I have already replaced the cross slide dial which was heavily marked but it was quite pricey and in order to avoid further expense I intend designing a "window" with a bit more clearance.

So to remove the existing windows I need to remove the two bang in self tappers that hold them in place. So what is the best way - and by the way, are these screws hard? If not maybe I could drill them out with a HSS drill?

Lathe is WARCO BH600G so either Chinese or Taiwanese.



Steviegtr27/09/2020 17:38:19
2269 forum posts
313 photos

Most of those type of fasteners are of the spiral flute design. Usually clockwise. So in theory they need to be turned anticlockwise. I have a set of damaged nut / bolt removers which would, if you could get a small enough one, do the job. Those pins are usually made from a hard material.


nut removers.jpg

Edited By Steviegtr on 27/09/2020 17:39:19

Pete Rimmer27/09/2020 17:39:10
1094 forum posts
69 photos

They are called drive screws. I usually lift them by carefully tapping old feeler gauges under the plate they are holding down. Go slowly and you can raise the drive screw enough to get side cutters under the head.

J Hancock27/09/2020 17:42:19
773 forum posts

Or try to put a ultra thin Dremel cutting disc slot across each one and use a screwdriver on them.

Guess whether a RH or LH spiral.

mechman4827/09/2020 17:57:29
2935 forum posts
460 photos
Posted by J Hancock on 27/09/2020 17:42:19:

Or try to put a ultra thin Dremel cutting disc slot across each one and use a screwdriver on them.

Guess whether a RH or LH spiral.

Beat me too it as I was typing. Drill & retap for 2 / 2.5 / 3 mm socket cap screws or hex bolts


old mart27/09/2020 18:13:09
3392 forum posts
210 photos

Some careful tapping with a wedge with a similar profile to a wood chisel between the head and the plate, not just in one place, but at several positions. Then as the head starts to lift, a blunter wedge and finally they should be high enough to turn. I would expect them to have a right handed helix.

not done it yet27/09/2020 18:22:19
6430 forum posts
20 photos

Tried a pair of pliers? No need to mask the ‘window if you intend changing it. They usually unscrew easily, once started.

noel shelley27/09/2020 18:57:59
847 forum posts
19 photos

Gentle tapping in all directions will normally loosen them. A very small chisel is ideal for applying the tapping and pliers to unscrew them. plan B, grind 2 flats on opposite sides and mole wrench to unscrew.

Good luck Noel

Phil P27/09/2020 19:00:56
790 forum posts
194 photos

Slotting with the Dremel works very well.

I removed the engine number plate from my Morris Minor engine with that method.


Clive Brown 127/09/2020 20:00:02
720 forum posts
34 photos

My Warco 16B mill had nothing as sophisticated as hammer drive rivets holding the index marks. Just aluminium round head rivets seemingly banged in skew-whiff by the youngest apprentice. They were the worst feature on an otherwise well finished machine. When I decided to replace them they popped out easily with a small chisel. i drilled the holes deeper, tapped 7 BA, or M2.5 in new money, and retained the markers with small screws.

Looks much better.

Phil Whitley27/09/2020 20:28:35
1383 forum posts
147 photos

I tap a stanley blade under the head of the screw, or under the plate it is holding on, and they generally come loose quite easily!

Peter Krogh27/09/2020 21:59:17
219 forum posts
20 photos

The best tool I've found is a pair of well made toe nail clippers with edges that are truly flush and straight. The curved ones don't work as well. The edges can be gently worked under the head of the screw and will wedge the screw right out. With some care, drive screws can be removed without marking up the surface. If the flat sides of the edges are polished, and most clippers are, they won't mark.

I replace those things with screws or, on thin material like machinery cabinets, aluminum pop rivets.



Edited By Peter Krogh on 27/09/2020 22:01:08

CHAS LIPSCOMBE28/09/2020 03:38:05
23 forum posts
3 photos

I hope I am not taking this topic too far from the thread but these "Drive Screws" are of interest to me because they were used by Powell & Hanmer to secure their badge on motor cycle fittings, including their horns. I make replicas of these horns and have had difficulty in knowing what to buy. I have seen adverts for size 0, 1 etc but no indication anywhere of what dimensions these sizes are. Also ones that I have acquired from autojumbles are all too short or too large in diameter. Is there any convention covering the sizes of these screws or are they whatever size the manufacturer thinks will sell? Currently I use Aluminium rivets with the head diameter reduced for appearance sake and using rivets involves a whole lot of messing around


Michael Gilligan28/09/2020 07:55:33
19258 forum posts
959 photos


I have no idea whether this is a definitive list, but it looks a useful place to start: **LINK**

I remember, when my dad worked for GKN in the early 1960s, there was a wide variety available.


Chris Evans 628/09/2020 08:43:46
1973 forum posts

Memory is fading but I used to buy these to secure our nameplates. I think the brand name was "Titex" With 4 to a nameplate a box of 1000 lasted a long time.

Russell Eberhardt28/09/2020 11:53:24
2720 forum posts
86 photos

I found them easy to remove from vintage cast iron car engine blocks by filing flats on the edges and gripping with a mole wrench to twist them out.


Ady128/09/2020 13:17:08
4810 forum posts
717 photos

Must admit I struggled with the title for a couple of days, didn't know they existed

Removing bang in self tappers

Removing the bang in self tappers

...eventually twigged as...

Removing bang-in self tappers

and learnt something new

Brian Wood28/09/2020 15:27:13
2474 forum posts
39 photos

And to complete the information, they are right hand thread


Howard Lewis28/09/2020 18:07:28
5528 forum posts
13 photos

Hammer drive screws are HARD, and will fracture if the blow is sideways on

If it does not break when hammered sideways, it will enlarge the hole, reducing grip when replaced..

Being dome headed, they are difficult to grip, but with a good ole Grip, (Vise Grip etc ) they can, eventually be unscrewed. Patience and some strength is needed.

Can you manage to bend the "window" upwards a little, rather than remove?


CHAS LIPSCOMBE28/09/2020 23:23:29
23 forum posts
3 photos

Michael G,

Thanks for this info, just what I needed. I stand in awe of your internet searching capabilities


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