Workshop stove repair

I have broken the glass on my ancient Coalbrookdale workshop stove. I've sourced replacement glass, but when I removed the four screws which fix the glass-retaining plate to the door:

one (there's always one!) sheared:

The 'screws' (bolts?) are 3/16 x 1/2 inch 32tpi fully threaded hex head, so BSF presumably. Two questions:

• Can anyone recommend a supplier for replacement screws? Searches so far have draw a blank.
• Any suggestions about dealing with the the sheared screw? It's pretty well corroded in place. The door comes off easily so could be mounted on a pillar drill.

Robin

2BA ?

Drill it out and re-tap 1/4"/ 6mm.

Weld a nut on top of the remaining screw, penetrating oil and they usually come out.

As Richard suggests, 2 ba will fit in 3/16 BSF, if you can't get it out without damaging the thread I'd drill right through and use a nut and bolt, appearances matter less in the workshop.

Hi , plenty of BSF bolts and screws on ebay.

Maurice

I used copperslip on the flue outlet adapter bolts on my multi fuel stove, they all unscrewed 4 years later when I needed to pull it out to finally tile the floor.

Tricky to get copperslip in between the threads of an already sheared bolt though.......

Lots of videos on Youtube about removing sheared bolts/screws. Most involve heat, or drilling, or both. And penetrating fluid. As an example; you could go to Abom79 and search his videos for seized bolt removal.

Edited By John Doe 2 on 11/10/2022 21:52:32

I did look on eBay, plenty of stuff 1/4" and above but I failed to find 3/16. Same thing with other suppliers.

Thanks for the 2BA suggestions - hadn't thought of that.

Duncan's suggestion of drilling through, nut and bolt, is probably the simplest solution for all four fixings though. I have a sort of taboo about badgering antique cast iron, but realistically when I replace it with something more modern/efficient it'll be 150kg of scrap cast iron. These things were built primarily as coal burners in the days when when coal was cheap and people didn't worry too much about how much energy/muck went up the flue.

Robin.

I once worked in a place that had a single central cast iron stove for heating. The usual technique for getting it going was paraffin soaked rags, kindling and coke, once the wood had caught, poking the cutting torch (oxygen only) into the ash pan and giving it a blast hurried it along. You'd be sacked for that nowadays, and rightly so

Edited By duncan webster on 12/10/2022 00:08:54

My "go-to" for broken screw removal after 50 years of restoring and maintaining vintage machinery is left-handed drill bits. Yes they are a real thing. You run the drill anti-clockwise and use a LH bit a little smaller diameter than the root diameter of the thread. So probably about 1/8" for a 3/16 screw to start with. Most often, the broken screw or stud remnants unscrew themselves while the drilling is in progress. The drilling seems to release the tension on the thread as the hole progresses and the anti-clockwise cutting forces do the rest. Sometimes you might need to go up a drill size and redrill closer to the thread roots before it breaks loose.

A pre-emptive soaking with your favourite penetrating helps maybe.

A Google search for "3/16 BSF screws" reveals some UK suppliers. Mostly machinery restoration specialists so I expect at specialist prices.

First port of call, every time these days, is my set of left-handed drills.

I start with a normal clockwise drill for the pilot (they are common and cheaper🙂 ), then change to larger left-handers progressively. Centring the pilot is quite important, but not generally a paramount requirement - more so on smaller diameters, I suppose.

That looks very much like chrysotile Asbestos rope seal around that !!!

Left handed dril bits were my first thought.

Possibly before you get to tapping size, the broken piece will come out.

+1 for inserting the 3/16 BSF screws with Copaslip, or Molyslip, Not that you hope to repeat the job too soon!

Howard

Surprised that they are BSF, normal would be BSW on cast iron.

Bob

I needed some 3/16 BSF hex set screws a month or two back. I found some easily, and still have a few.

Rob

Only 5/32” if 32TPI Whitworth….

Thanks for further replies.

Hopper: Thanks - I don't have a machine (drill press/mill) capable of drilling widdershins, but I guess I could centre clockwise (as suggested by ndiy) in a machine then go in with a LH drill by hand. Worth a try, if it goes horribly wrong I can always drill through and bolt. I had another look for 3/16 BSF x 1/2 - found capheads at £3.73 each - crazy, but not as crazy as paying £0.66 per kWh to heat the workshop electrically. What is the going rate down under? You have a lot of coal of course...

Juddy: Very likely chrysotile given the age of the stove!

Bob: That's what I thought, I spent some time with thread gauges trying to convince myself it was BSW, but definitely 3/16 x 32 TPI, so BSF or ME according to my researches. ME seems unlikely!

On penetrating oil - I remember reading ages ago that the best thing is a 50:50 mix of acetone and ... something. I think 'something' have been ATM fluid - can anyone confirm?

Robin.

Either a typo or difference in nomenclature.
ATF, as in the red auto transmission fluid.
That recommendation has been round for years, so I suspect Dexron type, rather than some of the more modern ones. That said, it's just a way of thinning the lubricant into a penetrating oil.

Soudal DeGrip-All, Plusgas, Oxim Ultra, and one occasionally available from Lidl are amongst my usual choices; I'm not sure that any one is head and shoulders above another, but all knock spots off the original WD40 formulation

Bill

There's also UNF 10-32, but that's unlikely too given the presumed age of your stove.

I expect the relative scarcity of 3/16" BSF is explained by the fact that the BSI encouraged the use of BA threads rather than BSF below 1/4" diameter.

I wish I could claim that it was a typo, but F and T too far apart on keyboard for that to be plausible - a brain rather than finger slip I'm afraid!

I made up this concoction and no joy, so I though I'd have a go with the 'welding a nut on' before resorting to drilling. To my surprise (I'm terrible at welding and there wasn't much of the sheared screw protruding) it worked! Maybe the heat had something to do with - it came out fairly easily.

As it would have been a couple of days before I could get down to my local supplier for 2BA screws I thought I'd have a go at faking them up myself, so made some bits of 3/16x32TPI stud on the lathe and welded on M6 nuts. Not pretty, but they worked. It'll be one of those stopgap fixes which never get 'done properly' I suspect. I have only 60 degree threading tools, so maybe not quite right, but the internal threads in the CI are pretty roomy and forgiving.

Anyway, thanks to all for advice - problem solved, and workshop is now running at a tolerable 17.5C.

Robin.

Edited By Robin Graham on 17/10/2022 21:52:51