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Snapped off end bolts

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On 9/30/2020 at 6:19 PM, d.elliott said:

 I have done both, the benefit of the 6BA is that it is inherently stronger, and you can have commercially available setscrews or bolts, remember to specify a fillister head, not a standard cap head. 


Any suggested website where I can get (to the UK) appropriate 6BA fillister head brass bolts? - the current ones seem to be 1 and 1/8 inch long (plus head).


If not, how about for M2.5 equivalents? Length is 29mm.


Also, are cheese head bolts OK if fillister head ones are scarce?

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As time goes by BA threads become less available.  There is a convention even (2,4,6,8) sizes are preferred and things can be more available in those sizes.  6BA is a good solid bolt but the heads of the bolts cannot be very large or they look out of place on a concertina. When bolt heads are about the right size it leaves very little shoulder under the head to bear down on the end. This will be OK if the holes are tightish to the shaft, but if anyone overdoes the torque on the bolt then the lack of square area under the head means it is bearing down with a lot of force and can impact on the wood beneath. 

 2.5m is close to the same shaft size as 7BA so much thinner; I have used first 7BA and now 2.5m and have managed never to break one and have not been asked for a replacement. 

Dave is absolutely right about fillister,  cheese heads look goofy on a concertina. Bought screws often look wrong even in fillister. They often have very broad slots in them, made so almost any screwdriver will fit. A nice narrow slot, around .5mm, is a lovely thing. 

The best source of bolts is to get them made to your design, they can be turned out very fast by a good machinist. If you know anyone who is involved in “live steam” this could be right in their field. 

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I know that they are in no way traditional, but I think that cap screws like these look OK and they certainly do not allow the screw driver to slip and gouge the wood like a slot head screw.  I had an Edgley that used these screws and if they are good enough for Frank then they are good enough for me!

SmartSelect_20201003-083444_Samsung Internet.jpg

Bolt Base in the UK sell M2.5 x 30mm versions of these screws.  They also have a 'cheese head' version but, IMO, that does not look so good.

Edited by Don Taylor
Add info about Bolt Base
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I usually find that bolts shear level with the captive plate nut, Irrespective of Lachenal or Wheatstone, it is quicker to split the chamois, and remove the nut, making good the bellows frame wall is straight forward, and there is less chance of spoiling the bellows leather end wrap.



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I agree that Tiposx's custom end-bolts look really good.


Here are some pics of what I have used:




This is an M2.5x30mm cap/Allen/socket head next to the end bolt it replaced.




Original end bolts.




Replacement end bolts.


These bolts are stainless steel.  If I wanted brass bolts then I would probably go with the ones that Springhub posted about.


A note about thread pitch.  The M2.5 bolts have a pitch of 0.45mm (56.44tpi) vs. the 6BA bolts which have a pitch of 0.53mm (47.92tpi) so not really a significant difference.  The big difference being that, in North America at least, 6BA and the taps and dies needed are practically unobtainium.




Edited by Don Taylor
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