Jump to content
I Forge Iron

Blowtorch capable of heating rivets?


Recommended Posts

I don't got an oxy setup, yet, but I remember having seen not rosebuds but smaller brazing nozzles for propane, they don't put out as concentrated a flame as a welding tip but not as large as a rosebud. The common design here for oxy-acetylene is injector based (AGA X11) and I've heard people say you can actually run propane with those tips, but not to welding heat. And I guess you could get something of a localized heating with the cutting torch and a propane tip, just don't hit the oxygen lever once it's up to temp...

Link to post
Share on other sites
  • Replies 56
  • Created
  • Last Reply

Top Posters In This Topic

Another bit of sign lore:  if you are driving through rural Arkansas and enter a small town---say a couple of hundred people and notice that they have interstate sized speed limit signs---SLOW WAY DOWN; often they are running a speed trap and making sure that "I didn't see the sign" where they change the speed every block isn't a defense.

Most of my cheap clamps are "road kill".  Used to be that a lot of the roadkill tools were Craftsman; now they tend to be "China".  You are right that it's handy to have a set of clamps that can be "abandoned in place".  Also having a selection of pipe lengths for your pipe clamps---it's surprising how handy very short lengths can be. I've used a 6" length through the hardy holes of my anvils at times.  A way to buy good clamps cheap is to find the ones that are ok but rusted and restore them.  Same as getting a blower working again...

Link to post
Share on other sites

Dennis, thanks for the added info. 

Another hint for cheap vise grips/c clamps. Many at flea markets and pawn shops are missing the spring or the adjusting nut at the rear. These parts are inexpensive and available at many tool supply stores.

Link to post
Share on other sites

I didn't pay much attention to signs before I went to work for road maintenance and worked on the sign crew. Nothing like working with and on a highway sign crew to pick up the basics. Believe it or not there are professional sign companies that install business signs just off the right of way facing the other side of the road. The ONLY way a driver could read one is by looking out the passenger window as they drive by. 

16 hours ago, anvil said:

Unless a propane setup had a fine welding type tip like this, that big rosebud flame is just too big for this kind of control.

Yes, it has tips too small to do what you describe you could almost solder electronics with the smallest one. It has IIRC 8 brazing tips, one rosebud and the cutting handle with 4 tips. All States and now Harris claim you can weld with oxy prop and you "CAN" but not well. 

I like to preheat the tenon if I can't bring it to peining temp before inserting it. It doesn't always work of course but that and a chisel notch in the mortise covers tight nicely. If I really want tight I warm up the mortise a couple hundred degrees and let it shrink on the peined tenon. 

Doesn't always work of course but nothing does.

Frosty The Lucky.  

Link to post
Share on other sites
20 hours ago, Frosty said:

I like to preheat the tenon

Thanks for the info on propane tips. I've used it in other shops and only for heating large or long pieces.

A few comments on using rivits and tenon's.

Preheating a tenon is many times pretty awkward in a one man shop. Setting tenon's etc is the last step and all parts already have a hot oil finish. Preheating a tenon is not a localized process and you lose your finish down the picket. The welding tip and a very small, hot flame minimizes immensely this problem of having to refinishing a couple of inches on each picket below the tenon. Small things like this are what add up to actually being able to make money on a job. With a small acetl welding tip, I minimize all that and a quick wipe with my thin, not paste, linseed, turps, beeswax finish on the rivit head and done. That area that "heat bleed" causes some really hard to get rid of colors in the finish. This is just my way of removing that problem quickly and efficiently.

Also, when a piece is put together and held by clamps, it's not possible to get the tenon in the fire to preheat. Imagine a 10' section of rail with pickets 4" I D. Even on smaller stuff, it's often not a one man job.

Concerning loose tenon's. Another problem for sure. I've used a notch in the mortise and it works, but it's time consuming when you have lots of tenon's. On small things like say a candle holder drip pan it's great, or use a square tenon. On a railing I rely on a well set rivit head to prevent this.

Lol, now it's duck and run time. Just joking. However, when you heat up the steel around a mortise, steel expands when it gets hot, correct? Thus the hole gets smaller, not larger when heated up, and gets larger when cooled.. The tenon expands when heated and shrinks in length when cooled. What keeps everything tight is the shaft shrinking in length when cooled and a structural head(1-1/2*shaft dia) is large enough to keep the picket tight and not loose. Many times new guys don't realize this and make their rivit heads far too small. Thus loose joints. This also eliminates the need for a mortise notch.

Thus, back to acetl vs prop, the small, intense and quick application of heat to the tenon minimizes the heat around the mortise which minimizes expansion/contraction of the mortise and keeps the loss of finish to a minimum. For what it's worth, I bring my tenon's up to a white heat, just below a sparking heat.

A lot of words to describe something as simple as heading a tenon/rivet.  ;)

Link to post
Share on other sites

Thomas, I wonder if the difference between expansion and contraction in the mortise examples is that with iron work, the mortise is generally surrounded by a larger mass than the brass ring, forcing the expansion into the mortise space, whereas hole in the brass ring in the video is allowed to expand outward freely making a larger hole?  

Link to post
Share on other sites

No, heating the mortise increases the hole diameter unless the metal surrounding the hole is say a ship deck. For the hole to shrink the metal would have to literally crush the metal surrounding the hole and it's expanding with temperature as well. Steel has a much greater crush strength than tensile. That's it for lay scienceyness. Next is personal experience.

Have you never sweated an interference fit? Sticking to terminology the tenon is made a couple few thousandths larger than the mortise. The mortised section is warmed, the tenon is inserted and the joint is finished when the temperatures equalize. This is also how warming up a seized nut helps break it loose. Think 4" peg in a 3" hole. (don't make me explain exaggeration for the purpose of illustration!)

I don't usually heat rivets or tenons in a forge, I use my torch. Sometimes you can drop a hot rivet in and set it but the torch is still easier. No tongs, no chance of burns, etc. Easy peasy.

Frosty The Lucky.

 

Link to post
Share on other sites

Frosty, I understand interference fitting. I've seen machinists use it to insert shafts into borings for a super tight fit.  However, quoting from anvil a few posts above here regarding his mortise and tenon work, the mortise hole shrinks, not expands.

"Lol, now it's duck and run time. Just joking. However, when you heat up the steel around a mortise, steel expands when it gets hot, correct? Thus the hole gets smaller, not larger when heated up, and gets larger when cooled.

Not to stir up a controversy here, but these are two opposite observations of heating a mortise hole.  Which is right??

Link to post
Share on other sites

I must admit, the reason I put that in, tongue in cheek, was to see if people actually did read these long windy posts we all seem to make. What happens with a mortise has been a long and sometimes heated discussion over a bottle of beer and the smoldering remains of a good day at the forge at a few conferences. I'll leave my belief a mystery for for another day. Hope it brought a smile to your faces. We need it with the crazy world we live in. And that was my intent.

The real point of my discussion is just why I use acetl instead of propane for what I call a localized heat. To recap, it's a very hot, small easily controlled source of heat. I minimize the heat on and around the mortise and maximize the heat where I want it on the tenon/rivit shaft. Because my iron already has it's finish when I do this function, the finish around the mortise never becomes that very ugly brown color that happens so easily with a hot oil finish and too much heat in that black heat range.. All I need to do is apply my liquid, not a paste, linseed oil, turps, and beeswax to the head of the rivit and as it smokes on, it also is wick'd down into the mortise which prevents rust. It's very quick and very precise. 

I haven't heated a rivit in any way other than this in a long time after working this process out. I make no claim to inventing this. It was more than likely absorbed by osmosis from those I have worked with as I evolved my own routines.

Not to mention that usually a rivit goes in from the bottom and the head sits in a bolster block. Back in the day with a couple of apprentices to lift a 100# of railing, or a complex chandler, no big deal. But not today. No hot rivits for me.  They have been replaced by a torch for a localized heat and a power hammer for a striker. Both of which fit nicely into my definition of what a modern day traditional smith is. (Couldn't resist.)  ;)

Link to post
Share on other sites
On 9/4/2020 at 4:54 PM, arkie said:

Not to stir up a controversy here, but these are two opposite observations of heating a mortise hole.  Which is right??

They're not opposing observations. The shrinkage Anvil is making use of is lengthwise in the tenon. Once headed the remainder of the tenon cools and shrinks drawing the head and joint more tight. 

My method uses shrinkage in a different manner and tightens the mortise around the tenon. Or does when I do it that way. 

I set rivets as Anvil describes to draw the joint more tight. Remember you do NOT want the rivet screaming hot or it will stretch as it shrinks and you won't have as tight a join. 

The only issue I was taking with Anvil's statement is that heating the mortise causes the hole to shrink. That is demonstrably incorrect.  Heck it's easy to test. Pick a piece of steel bar, 1/2" sq. is good, drill a hole in it say 1/4". Warn it up to say 500f. and insert the stem of the drill bit in the hole. If the hole shrinks it won't go. Wanna bet it'll rattle in the hole a little?

Frosty The Lucky.

Link to post
Share on other sites

Then when the bar cools it will be tight again.

My grandfather taught me about expansion & contraction. I was overhauling a motor cycle engine and the piston was stuck tight in the cylinder. No matter how much I bumped it with a wood block & hammer, it wouldn't move. He told me to go and get some ice cubes and I thought he was crazy or kidding. He dropped the ice cubes in the piston skirt, waited a few minutes and told me to push the piston out. I picked up the block of wood and hammer and he said, no use your fingers. I pushed on the top of the piston and it literally fell  out of the cylinder.

Link to post
Share on other sites

Dad used to put bearings in his spinning tools with an interference fit. The shaft went in a can of alcohol and dry ice and the roller went in the oven set on warm. The bearing went in the roller first, then got lined up with the yoke and the pin dropped through. They never slipped or moved and there are no set screws, pins, etc. The only way one would come apart is if the bearing broke or was broken up. The pic below are roller tools but not Dad's, his left hand tool looks nothing like the one on the right in the pic. 

Learned about interference fit from Dad on many scores.

Frosty The Lucky.

sctools.jpg.74f6afddf017df820b1c7c74078a0dbc.jpg

Link to post
Share on other sites

Frosty, your assessment matches what I have always heard about (but never had an opportunity to try) the method of interference fitting. I have seen machinist's videos showing the process.

Link to post
Share on other sites

It's a simple process and I imagine in use for millennia. Dad put on a show of being sad I hadn't figured it out myself but hey I was maybe 10. I DID get to ride my bike to the Piggly Wiggly and get the dry ice!

Just for giggle I'd like to polish both male and female pieces and see how long it'd take them to weld. Xrays would show. Hmmm, wonder what Xrays would cost. 

Frosty The Lucky.

Link to post
Share on other sites

I bring my rivits up to a yellow, just below a sparking heat. I want them hot. And note, the shaft too is hot because of the small concentrated and directed heat from the welding tip. This way when heading the rivit, the shaft too is upset. It continues to upset as the rivit head cools and contracts into the mortise. And that's what makes a hot rivit such a strong form of joinery. My technique just allows a one man shop to quickly and efficiently use rivits and tenon's, thus eliminating the need for apprentices.

As to what happens to the mortis, it does in most cases expand, then shrink as it cools. Let's not forget shrinking wagon tires onto wooden wheels.

However, here's a situation that is puzzling. 

A story, so bear with me. There used to be a large shop called Telluride Iron Works, Durango, Co. They delt with big iron for the gold and silver mining industries in this area, including Telluride for decades. They also did big iron jobs for the trains. They closed in relatively recent times. I have a friend about 10-15 years younger than me. His first job out of high school was in the train wheel shop at Telluride Iron. Their job was to replace wheels on axels for the trains, including drive wheels. The axels were removed with a press. He indicated the iron literally screamed as it was pressed out! Also, very dangerous. When putting on new wheels, the entire wheel was completely heated up to where it expanded,,, within the black heat range, I believe. Then slid on and shrunk to fit. Incredible. Imagine these engines with however long the train, filled with ore etc. Wheels spinning on the RR tracks til they grab and move forth! And the wheel does not spin on the axle! 

That's the background. Imagine a drive wheel, what? 4' high? And how thick? And the axle. Massive. Here's the hole shrink dilemma. Most likely a metals or structural engineer can answer this, but not me. To grab numbers, let's say the axle is 2" dia. So what would happen to the mortise if we heated a 2" wide donut around the mortise to the temp where expansion occurs? The mortise being the donut hole.  Now we have about 21" of basically cold iron surrounding that hotspot. When iron is heated, molecules move faster and move apart, thus expansion. Iron follows the path of least resistance. If the whole piece is hot, this path is outwards and thus the hole expands. If the whole piece is not heated up, just around the mortise, the path of least resistance changes. In this case will the mortise shrink? Perhaps the path of least resistance is up and out and down and out(horizontal wheel), and perhaps the hole shrinks.

as best I know, when we do a shrink to fit, we heat the whole piece as with Thomas's brass ring, Frosty's seized nut and bolt, and my iron wagon tire on a wooden wheel.

I'm sure there is an answer, but I don't know what it is and I'm curious if anyone knows. For what it's worth, at those after hours discussions at conferences, this is where the debate inevitably ended up,,, with no answer.

 

 

Link to post
Share on other sites

I have found when mounting wagon tyres that heating the entire wheel up to glowing precludes ever getting the iron tyre to fit properly!

Trying to figure out how the steel moves in a mass when heated using only the formula sounds like a basic calculus problem considering each layer individually and adding them up as the number of layers approaches infinity.  If you consider the disk as being composed of adjacent strings where each string out from the center is slightly longer then expansion is basically along the string and each adjacent string outward being slightly larger should not have an inward compression piece.  Yah; I used to have to do that sort of stuff; a pile of decades and a couple of concussions and I'm willing to accept empirical proofs!

Reading about Krupp once they mentioned shrinking steel tyres on cast iron railroad wheels. Theoretically you could repeat as the steel layer wore thin...

I've heat shrunk a war hammer head on a twisted sucker rod shaft---leaving extra so I could rivet it in place when it loosened up.  A lot of holes in refrigerators, stumps, car bodies, etc and it still doesn't even buzz!

 

 

Link to post
Share on other sites

I've done two jobs where I shrunk mild steel tires on wooden wheels. All for lighting. The first job was for an old guest ranch and the Carpenter built the wheels. He did the spokes/fellies joinery as a blind tenon, thus not a real working deal. They were 4'diameter. I turned the tires cold with bending forks and scrolling wrench. I was scared to death. I knew the diameter had to be slightly less than the outside wheel diameter, but had no idea how much less! My only source was Richardson's "Practical Blacksmithing. There were a number of articles saying the tire must be must be smaller, but none said how much smaller! Basically they all said "just a pinch smaller" like grandma baking cake! 

I made a guess. I didn't know if it was too small and might blow up the wheel! Or too big and fall off! Or would the darned wheel burn up before I could cool it!' talk about an adrenaline rush! It takes 16+' of steel to make a 4' tire. At that time a huge amount of work. Not to mention someone else's wooden wheel! I brought them to a black heat and hoped I got it hot enough to expand enough. The only helper I had was my right hand helping the left hand!

It worked! I did the 4 hub bands as well, lighting, chains and hangers and wiring. They hung it. They are still there. Fond memories of the sense of satisfaction at that job,,, especially the wheelwright part.

Link to post
Share on other sites
On 9/7/2020 at 12:00 AM, anvil said:

If the whole piece is hot, this path is outwards and thus the hole expands. If the whole piece is not heated up, just around the mortise, the path of least resistance changes. In this case will the mortise shrink?... 

... as best I know, when we do a shrink to fit, we heat the whole piece... 

I'm sure there is an answer, but I don't know what it is and I'm curious if anyone knows...

You've basically got it right, with a slight clarification being that the metal expands uniformly in all directions with increase in temperature, and shrinks uniformly in all directions with decrease in temperature. A coefficient of thermal expansion (CTE) is basically a length change per unit length per degree [length change/(unit length * degree)]. If you increase the temperature by one degree, then the metal expands by the length change for every unit length. For numbers, "mild steel" is listed by one reference as having a CTE of 5.9*10^-6in/(1in*1 degree F), or 0.0000059in/(1in*1F).  If you heat up an entire part uniformly, then that part will expand uniformly by 0.00059% per degree F. If you heat one side but not the other, then the heated side expands but the side that was not heated does not. The heated material wants to expand uniformly, but is constrained by the side that was not heated. Whether a particular feature expands or contracts locally depends on the balance of forces in the local region of the part. The variables include part geometry, the material(s), what the temperature(s) are, what the temperature gradients are, and whether there are other forces acting on the part. 

To your observations, there can be conditions where you can make a hole shrink by precise application of heat while the remainder of the part remains relatively cooler. This occurs when the balance of forces local to the hole prevent uniform expansion outward from the hole centerline but not inwards; the hotter material will expand somewhere, even if it has to crack itself to do so. 

Link to post
Share on other sites

Very cool, thanks. That's how I understand it.

I'm guessing why a ring, or iron tire, expands outward, thus the hole gets larger is because of the geometry. To compress a circle takes more force, thus all expansion is outward following the path of least resistance. My second example of a localized heat would tend to compress the hole and move inward and upward.

Thanks.

Link to post
Share on other sites

You're welcome. For the wagon tire, the hole gets bigger because the whole gets bigger.

If you were to measure the full part at room temperature and at fitting temperature, then the wheel (and all features!) would be scaled up proportionately according to the CTE.  The length (i.e., the circumference) would increase on I.D. and O.D. by the same proportion. If you make two wheels from two bars, and one bar is longer, then the wheel made (with no other differences) from the longer bar has the larger radius. 

There is one other slight difference that I need to point out for clarity. I previously said that the metal expands uniformly, but disregarded the increase in thickness and width in my example just now. Why? 

Simply put, there is far more length dimension than width or thickness dimension for the wagon tire. The thickness and width also expand, but nowhere close to as much as the length. 

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...