End Bolts and Inserts

[Cathasach]

One of my concertinas is on the more affordable end of the spectrum in terms of quality, to put it nicely, and I end up having to open it up fairly often. It only has wood screws and I worry that in the long term it will be a problem so I'm going to put some inserts in and use end bolts instead of screws.

 

My biggest hurdle now is finding inserts that will fit M2.5 bolts. I've found brass inserts but no brass bolts that will fit. I suppose I could use steel bolts with brass inserts but it makes me nervous about stripping the insets.

 

Any recommendations?

[Tiposx]

I have made a few inserts with 2.5 mm internal thread, and a helical knurling on the outside. The o/d is 3.1mm. I tap them (with a tack hammer and threaded drift) into 3mm holes and they grip very well. I have only used them on Anglo concertinas to accept the wrist strap screws.

if I was going to use them for end plate screws, I would want to be sure that there was enough wood to support the inserts without breaking out the sides of the bellow frames as they were fitted.

[Howard Mitchell]

Are these cheese head brass machine screws any good https://www.modelfixings.co.uk/brass_cheese_heads.htm

 

[Cathasach]

They m2.5 aren't long enough. That seems to be the most common problem.

[alex_holden]

I wouldn't worry that steel bolts are more likely to strip a brass insert than brass bolts. M2.5 should be strong enough to not strip as long as you don't overtighten them. Most vintage instruments have brass bolts that are about 2.2mm diameter with 2mm thick nut plates.

 

I know some makers use knurled cylindrical inserts for end bolts, but the one time I tried it, the installation went wrong and I quickly went back to traditional flat nut plates. The problem I had was that the drill bit drifted slightly as I was drilling the holes for the inserts, so when I glued the inserts in they were all randomly slightly out of position and the tapped holes didn't line up properly with the clearance holes in the action box walls.

[Tiposx]

-cathasatch

I make my own bolts from brass. I find 2.5mm is strong enough with a brass insert.

 

Regarding Alex’ post and the issue of accuracy, that would be the challenge. I would imagine that fitting an insert into an existing hole in the correct position, would work out out ok, so long as the hole wasn’t already worn out. I haven’t tried it though.

Edited February 3 by Tiposx
Clarity

[Stephen Chambers]

 

3 hours ago, Cathasach said:

They m2.5 aren't long enough. That seems to be the most common problem.

 

Unfortunately, nobody seems to manufacture M2.5 x 30mm screws in brass, and those are what are needed.

 

So I bought a bag of 500 M2.5 x 30mm ones (a lifetime's supply!) in stainless steel, which have proved to be very successful as replacements for rusted mild-steel endbolts, and used them to replace long woodscrews too (by using screw-in inserts) in some cheaper (mostly Jones) models.

 

With an M2.5 tap you can rethread the original receiver plates.

[Cathasach]

11 hours ago, alex_holden said:

I wouldn't worry that steel bolts are more likely to strip a brass insert than brass bolts. M2.5 should be strong enough to not strip as long as you don't overtighten them. Most vintage instruments have brass bolts that are about 2.2mm diameter with 2mm thick nut plates.

 

I know some makers use knurled cylindrical inserts for end bolts, but the one time I tried it, the installation went wrong and I quickly went back to traditional flat nut plates. The problem I had was that the drill bit drifted slightly as I was drilling the holes for the inserts, so when I glued the inserts in they were all randomly slightly out of position and the tapped holes didn't line up properly with the clearance holes in the action box walls.

Yeah, I think my plan is to just use steel bolts with brass inserts and since I'm the only one using the instrument I'll just know not to tighten it too much. Not that I haven't been doing that anyway.

[Fanie]

If you have time to wait for delivery you can order these from Aliexpress:

 

https://www.aliexpress.com/item/4001307378488.html?spm=a2g0o.order_detail.order_detail_item.7.6e1df19ccmUDGQ