Author Topic: Trunnion attachment (Read 1810 times)

freddo · « **on:** October 29, 2005, 02:33:58 AM »

I have been advised to shrink the trunnions onto my barrel.
I was myself considering the possibility of tinning the contact surfaces and then shrinking the trunnions on.
Does anybody have an opinion on this?Has anybody tried this method?

Edited - trk - added the T to runnion in the subject line

Double D · « **Reply #1 on:** October 29, 2005, 03:42:25 AM »

Freddo,

If you are going to fire your cannon, I strongly urge you to weld your trunnions after you get them in. The trunnions are the recoil lugs and bear all the forces of firing and must be securely and strongly attached.

Powder keg · « **Reply #2 on:** October 29, 2005, 04:41:01 AM »

How big is the barrel? What is it made out of?

Cat Whisperer · « **Reply #3 on:** October 29, 2005, 05:23:17 AM »

Quote from: freddo

I have been advised to shrink the trunnions onto my barrel.
I was myself considering the possibility of tinning the contact surfaces and then shrinking the trunnions on.
Does anybody have an opinion on this?Has anybody tried this method?

Hmmm. Two methods compared here.

Shrinking - I assume this indicates making one piece larger by heating and assembling letting it cool and shrink down onto the inserted piece. This could be done in two ways - cutting a pocket for the trunnion and heating the barrel inserting the cold trunnion. Problematic to say the least at those temperatures. The other way would be to have the trunnions attached to a band which would be heated and slid down the barrel shrinking onto it - secure, but also problematic to assemble.

Tinning the contact surfaces might be easier to do (simply matching curves of trunnion to barrel with no pocket). But the result would be the shear stresses would be along that surface - through a material that would be much weaker than the material of the trunnions or barrel.

Cutting the pocket and inserting a close-fitting trunnion provides great resistance to shear stresses. SO much so that it then takes very little to secure the trunnion into the pocket.

Several methods of attaching the trunnion when inserted into the pocket - welding is of course the strongest, then silver soldering/brazing. These will bond and seal from any corrosion. Then you could use an adhesive, JB weld being one of many. Entirely satisfactory as the stresses are going to be shear of the trunnion/barrel and the JB weld merely fills in a very thin gap and is compressed between the two (where shear is involved). This is a common industrial process that has been successful for some number of years. Lastly, one could thread a stud concealed inside and under the trunnion.

Choice is yours. there are folks here that have done each of these methods - they will pitch in on their experiences and the finer nuances of doing them.

freddo · « **Reply #4 on:** October 29, 2005, 05:37:36 AM »

The barrel is about 54.5 mm diam @ the trunnions.The bore is 19 mm=a bit over 2 inches and 3/4 inch .he material is S1214.
I note your comments Douglas and make the following obsevations,
1 The bore is drilled,Welding may distort the tube and may create a heat affected zone of steel with altered characteristics ?
2. Recoil forces are at right angles to the axis of the trunnions and I am at a loss to see how they may force the trunnions out of the barrel without tearing the steel.
3 The bore is 12 guage and I anticipate a loading such as one might use for a twelve guage shotgun in BP.With some windage the pressures would be less than those in a shot gun,Are the lumps on a shotgun not soldered to the barrels?
.In asking these questions please do not think that I am questionino your jugement.I know you to be a very prudent and safety aware shooter.
I am totally new to this game and I ask them with the intention of gaining knowledge through discussion
Regards Freddo

freddo · « **Reply #5 on:** October 29, 2005, 05:53:38 AM »

Cat whisperer I am sorry I did not make myself clear [Interesting how that happens on these forums I suppose its because there are so many possibilities that I am unaware of ]
I had only thought of boring pockets for the trunnions,heating the barrel,freezing the trunnions after tinning and assembling.
Silver soldering has a strong appeal alhough I wonder about the effect of the amount of heat required.It would certainly look better than welding I think a modern weld looks quite out of place on a reproduction early 19 century cannon and I don't think I could clean up and grind the weld with such skill as to conceal it.

freddo · « **Reply #6 on:** October 29, 2005, 06:05:28 AM »

Bye the way I have succeeded in shrinking the tyres onto the wheels I used 14 inch diameter pipe sections 1 inch wide and about 3]16 thick They are a bit overscale but look good,
A very hot hot hot burn ya fingers and suck em sort of exercise but it was very interesting to hear the wheel talk to me as the metal shrank[shrunk?]
And they are now tight and solid.
I am planning to show some photos of the wheels and the methods that I used to make them I must confess I am quite proud of them for a first attempt

Cat Whisperer · « **Reply #7 on:** October 29, 2005, 06:47:34 AM »

freddo -

You've made some very good observations and raised some very good questions.

The recoil lugs for shotguns (if not mig/tig welded) are often silver soldered. Silver solder, as you know, melts at a lower temperature than brazing and is quite strong. Getting the whole thing up to temperature will be a chore.

Consider the stresses placed on the barrel if you have an interferance fit (shrink fit). I don't have a clue as to whether they'd be significant.

Double D · « **Reply #8 on:** October 29, 2005, 07:46:55 AM »

The linear direction of the recoil force may indeed be 90 degrees to the axis of the trunnion, but that is not a solid axis. Rather the axis is interrupted. The recoil force doesn't pass through the axis but past the end. The Trunnions are levers.

When fired the rear side of the end of the trunnion on the carriage provides resistance to the recoil. Force of recoil is applied to the front if the trunnion inside the barrel and the outside edge of the barrel where it bears against the center of the the trunnion is the fulcrum.

Since the exposed trunnion is longer the portion inserted it transmits more force.

Yes you will get some resistance from levering by the mass of the rear of the pocket. But you still get levering.

I use to do trunnions as William Green suggested with a heavy threaded stud. I would make them interference fit and turn them in tight with a barrel wrench.

I went to a cannon shoot one time and had to have my barrel inspected before shooting. The barrel was pulled from the truck and the first thing that was noted was the trunnions on both sides were loose. They would not turn all the way out but would turn a little. When I got home I had to use the barrel wrench to get the trunnions all the way out.

The trunnion had a peen mark at the front where it bore against the outer surface of the barrel. It also had a peen mark at the bottom back of the trunnion where it bore on the back bottom of the trunnion pocket. The screw stud was also bent.

I got with a fellow that was a connon maker and long time millwright and talked the problem over with him. My idea was also to shrink fit. His idea was to just weld them. He said that is what he had been doing for years.

I expressed concern about heat affects of welding. He told me that using the proper welding techniques would minimize those effects.

To demonstrate we built a trunnion pocket in a piece of scrap steel and shrink fit the trunnion in. We put the piece of steel in a vise and smacked the trunnion with a hand sledge. The trunnion went flying across the shop. We put the trunnion back in the pocket with a press and he arc welded the trunnion in place. Thenm we smack the trunnion with the sledge. We dinged up the end of the trunnion pretty good and finally bent it a little, but we did not break the weld or pull it out of the pocket.

He explained to me that the heat affected zone was in and adjacent to the weld and not through the entire barrel. He did tell me that he welds the trunnion before he does the final finish or ream of the bore.

After he welded my trunnions in for me I ran the reamer back it and could not detect any distortion or scaling from the weld. I suspect now, thinking back that I got no scaling or distrotion because the type of weld used was one that minimized the the heat and size of weld plus the mass of the metal being welded localized heat dispersion.

This is the cannon, my very first made after my first semester of Machine shop practice out of 4140 20 years ago.

GGaskill · « **Reply #9 on:** October 29, 2005, 09:01:42 AM »

I am a firm believer in welding trunnions; however, in your case, silver solder would likely be adequate if a good job was done. But in my experience, you need to reach red heat for silver solder to flow, and you need it to wick into the joint between the trunnions and the barrel to get strong joint.

A friend of mine built a 25 mm rifled cannon from a piece of 25 mm automatic cannon barrel. He made the trunnions on a ring and heat shrunk the ring in place, on the taper, I think. It is still in place after many firings with more powder than should be used.

Double D · « **Reply #10 on:** October 30, 2005, 05:16:59 AM »

Quote from: freddo

It would certainly look better than welding I think a modern weld looks quite out of place on a reproduction early 19 century cannon and I don't think I could clean up and grind the weld with such skill as to conceal it.

Agreed. But you can grind it and fill it with Bondo- epoxy car body filler to blend it.

I left my welds visable so I could shoot.

kappullen · « **Reply #11 on:** November 01, 2005, 05:28:08 AM »

I feel that press fits need to be 1/ 1/2 to 2 times the depth of the diameter of the pin.

That is pretty much the accepted rule on threaded holes as well.

You would have to bore the tube right into the bore to achieve that.

One cannon maker I have met, bores trunnion holes clean thru the barrel, below center, and loctites in a trunnion with a scallop machined into it to clear the bore.

This is a well known established gun maker in the business for years.
He has had no problems with this design.

These guns only shoot 10 gauge blanks so the load probably is not that great.

I wouldn't recommend that procedure for any blackpowder gun.

It is important to preheat a barrel, or anneal it, if you don't know what the material is after welding.

Tool steel can get as hard (and brittle) as glass when welded.

I prefer a welded trunnion with a large trunnion base and good bevels for welding.

Thats my thoughts on that matter.

Kap

Cat Whisperer · « **Reply #12 on:** November 01, 2005, 09:51:32 AM »

Quote from: kappullen

....
Tool steel can get as hard (and brittle) as glass when welded.
....

Let me echo that! We had a die (made of what was supposed to be D2) heat treated (by a very reputable firm). Since the steel was a bad batch it cracked on the first use - within minutes of being heated in the press.

The company that did the machine work and supplied the steel stood behind it and replaced it, and fortunately there was no damage nor injury.

Amazing to see a 6" diameter of tool steel (with a pocket in it for pressing together a disk-brake pad) with cracks running all through i!