Slipping collars

[Joel OF]

I've designed some fire dogs for a customer that have 3 x 20mm straight bars collared together to make a 60mm wide front. In imperial that's 3 x 25/32 inch bars collared together to make a 2" 23/64 front.

 

My concern is that the collars might loosen up from the heat of the fire and slide down the bars. That's an easy fix, I can just do away with the collars and rivet the bars together, but it's highlighted a more general concern about collaring straight bars together where there's no vertical resistance.

 

To help explain what I mean about vertical resistance I've attached a picture of a candleabra I made a while ago, it has four straight bars held together by 3 collars. I've always been slightly concerned that a heavy blow could cause one or all of the collars to slip out of position.

 

 

Collars are typically used to hold scrolls to something else, in such situations there is vertical resistance, like the pic below I've pulled off a Google search. The collar is unlikely to slide down the bar on the right, because the scroll is resisting on the left. (Chances are the scroll's also collared at the top out of shot, so then it's definitely not going anywhere).

 

 

So I guess I have 2 questions: would you be worried about the heat of the fire loosening the collars on the dogs? And, should collars only be used when there's resistance?

[Chinobi]

i dunno what the traditional solution would be, but you could install a blind pin somewhere in the system, probably drilled partially into the front of the middle vertical bar and countersunk into the inside of the collar to make it invisible. basically a shear pin to prevent it from slipping down if it does indeed expand too much when heated, much the same way a coat hook with a single screw would be fitted with a pin or spike on the back to prevent it from rotating around the screw.

Edit: or, nix the drill entirely and champher the outer 4 corners of the triple bar bundle for the same width as the collar material to create a recess in the edges. Install your collar into that recess so they will key into each other and lock together that way.

[Glenn]

It may not be traditional, but a small weld that would be covered by the collar would prevent any slippage. 

 

If the metal needs to move a little, I would go with Chinobi's method.

[Joel OF]

It may not be traditional, but a small weld that would be covered by the collar would prevent any slippage.

I mean the collars loosing grip and slipping, not the bars underneath slipping past each - which is what I think you're getting at, Glenn?

[ThomasPowers]

Nope for the collar: a small discrete tig weld someplace not easily visible.

 

I'd go with the pin and rivet the top and file it flush and then restore the surface with another go through the fire.

[Glenn]

Depending on the shape of the collar, you could tack one end then bend the collar around and cover the tack weld.

 

In your first photo, you could clamp the collar to the stock and slant drill a small hole in both the collar and the stock. Fill the hole with weld and file or grind to flush. Wrap the collar and it should butt up nicely or overlap as per the design.

[ianinsa]

Joel, in the past we have modified large bolt cutters to "crimp" collars(cheating I know) but it gives a cool look and you can get quite inventive? You then heat the whole shcemozzle  with an oxy-torch, sprinkle on some borax and crimp.... hey presto forge welded collar! Sorry to give the barbarian  solution but it's very effective!

 

Ian

[Frosty]

Am I wrong thinking all the collars are doing is holding their own weight against gravity? Another method I've read abut is using a chisel to to cut some teeth into the stock being collared. Raise the cuts in the direction  you're concerned it will slip. It wouldn't take much and will hold against considerable loading.

 

Another thought is to increase the friction surface by using wider collars, say 1" instead of 3/4" or 25mm instead if 18mm. (I know, I know, I just ciphered the conversion in my head)

 

I'm also thinking that unless you expect the customer to be bouncing heavy logs on it it'll be just fine with simple collars. There is a huge amount of force delivered as steel shrinks as it cools. I seriously doubt a hearth fire is going to bring the dogs up to even close to dangerous temps. It will also be heating the dogs themselves so they're expanding with the collars. It should be plenty secure.

 

Of course it isn't cheating to make a test piece, say a single upright and log dog for the outdoor fire pit. Build a roaring fire on it and abuse it with a long stout club.

 

Frosty The Lucky.

[billyO]

I agree with Mr Frosty, and if the collars are going to get hot enough to expand, how many thousandths are you talking about?  Could you draw an ever so slight taper where you collar?  That should minimize movement. 

[Joel OF]

Thanks folks, great ideas.

 

Putting the fire dogs to the side for a minute, what are people's general opinions about collars and their gripping abilities? Any situations where you would or wouldn't use them?

[Dogsoldat]

Uhmmm...  from what I remember from school its 6 millionths of an inch per degree Celsius temp change.  so it takes a few degrees to expand or contract a few thou

[anvil]

I was shown an example once a while back that convinced me. two half inch square bars with two collars about 4" apart. we hammered on one of the bars to get it to move. took a lot of hammering!

convinced me. even on two straight bars in a gate I would not worry.

on a railing same thoughts. say 36" railing. I'd put one near the top, one in the middle, one at the bottom and never worry.

or two at the top 4" apart, same at bottom and one in the center and worry even less and ya got a cool design as well.

[anvil]

however! make sure you know how to do a good collar. there's more than way to do good collars, but way more ways that won't work for more than decoration.

[John B]

Thanks folks, great ideas.

 

Putting the fire dogs to the side for a minute, what are people's general opinions about collars and their gripping abilities? Any situations where you would or wouldn't use them?

 

 

I have no problems with the secure gripping ability of collars, how I make and fit them. (and there are numerous types and sizes of collars, not just the wraparounds you are featuring. the key thing is they must have a solid core to secure to and be fit for purpose.

 

They are used where they are an appropriate method for the situation, and they should be designed for that situation

 

Not knowing your collar making method and how you fit them does not help in giving an opinion on how yours will perform..

 

You wonder about your candlestick and its potential to become loose, one thing that would have helped to secure it more effectively would be to not have all the collars' splits on one side of the column,  

 

How many types/methods of collar making are you aware of?

 

Each has its own place, method of manufacture and use. 

 

See you at the IBF, and we can discuss.

[Jim Coke]

Greetings Joel,

 

Now it is time for Jims hold a collar trick...  Drill a small hole in the element so that the bottom overlap just covers the hole..  Before setting down the collar create a dimple into the hole ... The top beveled end will cover the dimple..  No welding and still traditional

 

Forge on and make beautiful things

Jim

[Joel OF]

 

Not knowing your collar making method and how you fit them does not help in giving an opinion on how yours will perform..

 

How many types/methods of collar making are you aware of?

 

I know of two types - seamed like in my picture, and seamless which have tapered ends. There's also wraps, but they're slightly different.

 

I can think of a few methods according to stock size, shape, how many collars you want etc but for the minute I want to master them "by hammer and hand" before moving onto doing them in a more mechanized way so I do them the way you do them John, as per this old thread:

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Filling in a few stages you didn't mention/adding some things I do on top of what you do:

 

If the mandrel has an odd number of bars and doesn't have a seam line so you know where the middle is, gently centre punch on both sides of the mandrel where the middle is.

 

Gently centre punch half way along the length of the collar material so you know where middle of the collar is.

 

Open the vice a suitable amount and sink a U shape into the collar material, hammering on the centre punch mark.

 

Lock the mandrel stood up the vice, line up what remains of your centre punch mark with the centre punch mark on the back of the mandrel, flatten the back of the U shape against the back of the mandrel being careful not to draw out the length. (Depending on the collar width the U sinking stage might not be needed).

 

In another old thread about collars, Frank Turley highlighted how easy it is to lose where the middle of your collar is when you're sinking the U, the centre punching I do helps you know where you are.

[sfDuck]

Try crazy glue? or all the above