Author Topic: Press fit Trunnions? (Read 1140 times)

Powder keg · « **on:** January 25, 2006, 05:56:47 PM »

Hello All, I am working on a couple of new projects and have been thinking of pressing the trunnions in. Is there a recomended amount of interference? I'm thinking .002" - .003" or so? Coments are apretiated.

Thanks, Wes

Cannonmaker · « **Reply #1 on:** January 25, 2006, 06:11:33 PM »

Wes, what is the Dia. of the rimbase. You will want it tight but yet be able to press them in.

Powder keg · « **Reply #2 on:** January 25, 2006, 06:28:40 PM »

The rim bases are 1" in diameter on the test model. I'm building a 1/4 scale model. I don't have a press at home (yet :grin: ) So I might have to use my vice. I made some pushers to go around the trunions and press against the rimbases.

freddo · « **Reply #3 on:** January 25, 2006, 08:39:52 PM »

Will a press fit distort the tube to any degree?

freddo · « **Reply #4 on:** January 25, 2006, 08:43:27 PM »

Sorry about the double post, but if one decides on a press fit for trunnions of this diameter, how deep should they be seated?

GGaskill · « **Reply #5 on:** January 25, 2006, 09:43:38 PM »

The normal allowance for a press fit is .001" interference for each 1" of diameter. Since the trunnion should be welded to keep it from being brought out by repeated recoil (assuming a firing gun here), the press fit really doesn't buy anything. If for a non-firing gun, the above is appropriate. Depth is as much as you can get without compromising bore wall thickness. I try to leave at least a half inch bore wall for 1/3 scale Parrotts, Napoleons, etc.

Hope you have a strong vise. (-:

Double D · « **Reply #6 on:** January 26, 2006, 12:35:37 AM »

To repeat what George said...WELD

Powder keg · « **Reply #7 on:** January 26, 2006, 01:44:36 AM »

If they are going to be welded why go to the trouble to press them in? What about Brazing them in. I can do this and make it look pretty clean. This barrel is going to be painted. I just want to maintain the clean lines and still have a sturdy little gun.

Thanks for the input, Wes

GGaskill · « **Reply #8 on:** January 26, 2006, 12:00:27 PM »

I don't see why you can't weld it without any filler material (I am assuming [a bad thing to do] that you weld it using the TIG process.) Obviously it's not possible to not use a filler if you are stick or wire welding.

Double D · « **Reply #9 on:** January 26, 2006, 12:23:54 PM »

Weld---Grind---File---Bondo---Sand---Paint!

Powder keg · « **Reply #10 on:** January 26, 2006, 12:38:27 PM »

I don't have a tig

I have a friend that will do it though. So they need to be Pressed and tigged or just tiged? What about Brazing? Is it acceptable? or not?

Later,

GGaskill · « **Reply #11 on:** January 26, 2006, 12:43:15 PM »

I brazed the trunnions on my 24 pounder but you have to remember that the joining strength is the brazing filler only which is not as strong as a weld where the base metals are fused in addition to the extra filler metal. If the tube is not going to fire heavy shot, I would not be concerned. If the shot is heavy in proportion to the barrel, I would have some concern because I have no experience.

Powder keg · « **Reply #12 on:** January 26, 2006, 12:51:55 PM »

It's settled then. I'll weld them in after a press fit.

Thanks, Wes

Double D · « **Reply #13 on:** January 26, 2006, 01:10:20 PM »

Press fit---Weld---Grind---File---Bondo---Sand---Paint!

dominick · « **Reply #14 on:** January 26, 2006, 01:54:36 PM »

Wes, If the metal is 4130 or 4140 then you do not want to braze it. If you weld these alloys you should watch your heat. Slow heat and cool. Tig weld if possible. My trunions are slide fit and tig welded and they have held up well after much use.

Powder keg · « **Reply #15 on:** January 26, 2006, 03:02:16 PM »

My test piece is 1018. The 1/2 scale version will be 4340. I plan on having them welded. I am going to use my burner for my foundry settup to preheat and then weld them.

Thanks,

kappullen · « **Reply #16 on:** January 26, 2006, 04:34:03 PM »

Wes,

Ocasionaly when welding a loosly fitted parts togather, a crack will develop because the inner will pull from the cooling stress on the other side from the arc, and a crack will follow you right around the job.

In that situation, you have a real mess because another bead will likely crack too.

Some engineers recommended several heavy "tacks" around a job.
If one weld cracks, the crack will stop there.

I would recomend at least "size to size" fit.

To each his own, good luck.

Kap

GGaskill · « **Reply #17 on:** January 26, 2006, 06:07:47 PM »

I agree they should be a tight fit but you shouldn't rely on the shrink only to resist the forces of recoil.

Powder keg · « **Reply #18 on:** January 26, 2006, 06:23:23 PM »

It took 9.5 wacks with a 3 pound hammer to install the trunnions on my 1/4 scale pack parrott. I am going to have my friend tig weld them on. I'll put a large clamp on them to help hold them while being welded. Wish I knew how to tig.

Later, Wes

GGaskill · « **Reply #19 on:** January 27, 2006, 07:12:16 AM »

TIG welding is very similar to OA welding except for the lack of extended flame. See if your community college has some TIG (also known as GTAW) classes.

kappullen · « **Reply #20 on:** January 27, 2006, 05:04:26 PM »

I ment to say size to size fit, and weld, but didn't type it.

I'm with you. I like a nice bead, that can be ground to a clean fillet.

Some of those tig guys can make the weld look like a ring of shiney dimes.

Not me, with old sparky, they need the 4.5" disc sander treatment.

Kap