Cutting Threads

[Geoff_S]

I've built a new front door and now I want to fix the original door knocker, but I have a problem.

The bolt welded to the knocker extended all the way through the old door secured by an ugly nut on the inside. Not nice. So what I wanted
to do was cut the bolt down, embed an insert in the front of the door and fix it that way. So it screws into the insert but doesn't then
protrude on the other side.

The problem I have is that I cannot find an insert that fits, and the bolt isn't threaded all the way. So I want to cut a new thread. I've looked at some videos and understand the tap & die tools but will it work on brass?

It's one of those things that I have never done before, will probably only ever do once and I want to get it right. Is there anything I should watch out for or any tips please?

Cheers

 

[sunnybob]

Brass is nowhere near as strong as iron. If you fix a heavy knocker with small brass threads, and you get a few heavy handed people using the knocker, it might strip.
But cutting a thread is easy, just make sure you have some lubricant (tallow is best, but even butter or lard. I dont like using the "normal" wd40 as it runs off too quick) as brass tends to shred. For every 3/4 turn down, back up a 1/4 turn to clear the dies of swarf.

 

[CHJ]

Is the knocker shaft fixed in orientation to the threaded boss, if it is, one serious problem you may have in trying to mount it into a fixed threaded insert is that when tight it may not be aligned vertically, you may be able to negate this with a thin veneer or brass washer the same size diameter as the boss.

If the insert mounting method is viable, then selecting a more modern metric thread form nearest your stud diameter would give you a better chance of finding a threaded nut insert to suit.

 

[Yojevol]

Or you could drill the hole in the door and glue the bolt in with Araldite. The only problem is that you'll never get it out again.
Brian

 

[AES]

Perhaps I'm making this too complicated, but if you're thinking of extending the thread on the bolt shown and don't already have a die to fit the thread, how do you know what size/thread die to buy?

If you do know what size die, then that will tell you the size of the threaded insert you need (99% chance the size and thread will be stamped/etched into the face of the die).

If you don't know the size/thread of the die you need, what about trying to find a bolt (any old bolt) to fit that ugly nut? That bolt may well be easier for you to find out what the thread is, especially if it's marked.

If, as seems likely, the thread on that original bolt & nut is old and therefore probably BSF or BSW, then CHJ is right, it will be much easier to find a modern Metric equivalent threaded insert. But as above, the first step is to find out exactly what that thread is. AFAIKS, before you know that you can't proceed further. Any mates/family who have a set of thread gauges that they could put in the post to you for example?

Agree with sunnybob, if you are going to extend the thread on the existing bolt then extending the thread in brass is "easy-peasy". Just as he says, use a lubricant (just about anything will do, I do like WD40 or paraffin), and just as he says after 1 turn MAX, rotate the die back again half turn MIN. And keep on doing that - brass is pretty easy to thread, but by the same token, it's pretty easy to damage a thread while cutting it too (mainly by not clearing the swarf properly, which is what all the forward one turn/back half a turn is all about).

Hard to tell from you pic, but also just as sunnybob says, if the knocker is a big heavy thing and if your visitors are likely to "swing on it" too much, the existing brass bolt may be a bit weedy, but again, if the knocker is pretty old the hardware manufacturers often knew exactly what they were doing back in the day.

Also, agree with CHJ about getting a new threaded insert in to the door at exactly the right depth to match the length of the bolt while ensuring the threaded insert is "blind" from the inside. If it were me I'd probably saw the old bolt off the knocker and start again, but's that's easy to say 'cos when it comes to metalworking my shop's fairly well equipped.

 

[loftyhermes]

How about using something along the lines of these connector caps. https://www.fastenright.com/general-fix ... -caps/ff08

 

[AndyT]

As already said, to get it lined up you need the bolt part in a clearance hole and a nut on the inside.

If you can measure the diameter and threads per inch accurately, someone here will identify it. It's almost certainly a Whitworth thread.

Decorative dome nuts in Whitworth sizes are available eg on eBay, which would give you a tidier arrangement once you know the size. There are also snap on white plastic covers eg these

https://www.ebay.co.uk/itm/184068148658

which would fit ok, probably even using the nut you already have.

 

[Lons]

Re threading isn't difficult but perhaps a different approach?

Fix the knocker as intended right through the door but recess the nut and stud flush or slightly below the inside face then stick on a brass disk with hot glue or if you have a lathe turn a matching domed button. That way the knocker can be securely fixed, correctly orientated and be removable if required.

 

[novocaine]

Thats a machine rolled thread rather than a die cut thread (the major diameter is bigger than the shaft diameter), so it can't be that old but it doesn't mean it isn't some odd ball thread, hardware manufacturers love to chuck a curve ball in.

how much meat is there in the backplate (of the knocker itself, the bit that the shaft is braised to), if there is maybe 10mm of brass there I'd cut off the current "bolt", drill and tap an M6 (you'll need a blind tap to cut to the bottom of the hole that only needs to be 6-8mm deep) in it and fit it with a bolt from the other side.
if there isn't I'd cut it off still but braise a nut to the back of it and drill a clearance hole in the door to do the same thing.
on the back of the door I'd drill a counter bore and plug it to cover the bolt head.

 

[toolsntat]

Or you could drill the hole in the door and glue the bolt in with Araldite. The only problem is that you'll never get it out again.
Brian

Better than gluing, just cut the bolt short of door thickness and drill stub hole same size as unthreaded portion and proceed to screw thread into the door.
This will cut a thread in the timber with hopefully enough grip to render a good enough job.
You made the door? Perhaps try on an offcut first even without cutting bolt :idea:
If it really struggles, a chamfer to the start of the thread may help and if still not satisfactory a groove or two filed into the edge of the thread may help.

The spanner in this could be orientation when tight but application of a bit of candle wax works wonders to tease a bit of extra rotation.
Want to pack it out a bit?, maybe the diameter is close to a Yale lock rose/surround/ring?

If unsuccessful you can fall back on threaded insert and matching die :wink:

Cheers Andy

 

[Geoff_S]

How about using something along the lines of these connector caps. https://www.fastenright.com/general-fix ... -caps/ff08

Thanks, I've looked at these but I want to avoid any fittings showing on the inside of the door.

 

[Geoff_S]

Or you could drill the hole in the door and glue the bolt in with Araldite. The only problem is that you'll never get it out again.
Brian

Better than gluing, just cut the bolt short of door thickness and drill stub hole same size as unthreaded portion and proceed to screw thread into the door.
This will cut a thread in the timber with hopefully enough grip to render a good enough job.
You made the door? Perhaps try on an offcut first even without cutting bolt :idea:
If it really struggles, a chamfer to the start of the thread may help and if still not satisfactory a groove or two filed into the edge of the thread may help.

The spanner in this could be orientation when tight but application of a bit of candle wax works wonders to tease a bit of extra rotation.
Want to pack it out a bit?, maybe the diameter is close to a Yale lock rose/surround/ring?

If unsuccessful you can fall back on threaded insert and matching die :wink:

Cheers Andy

Andy mate, that's so weird, because that is exactly what I have tried as an option, almost to the letter, even to testing the process in a lump of offcut that I had left

It can work with the knocker as I can get leverage on that. The issue is with what I think is called the plate, the other bit that the knocker knocks on. It' s just a circular lump of brass and I can get no leverage or grip on that to turn it.

I think I'm leaning towards a hybrid solution of shortening the bolt, drill holes as suggested but a little bit larger and then using epoxy to set it in the door as Brian suggested, or maybe even a little expanding foam?. It was in the last door for 140 years (we think) so another 140 before someone wants to remove it should be OK

And thanks to everyone that helped me out here. Cheers

 

[AndyT]

One more option without glueing it in. Take novocaine's suggestion of swapping to a bit of metric thread studding. Combine that with the expanding cone part of a Rawlbolt of the same size. Insert cone end into hole, rotate knocker, as it tightens, align a quarter turn shy, knock it down flush, give it a final twist so it tightens in the right position.