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Weld stops telescoping of barrel and plunger

  • This topic has 4 replies, 2 voices, and was last updated 2 years ago by Thor.
Thor digital-thor

Weld stops telescoping of barrel and plunger

18/07/2019 at 22:08

Hi.  I’ve been trying to build the injection machine, but am having problems.  Once, I weld the 2 mounting flat bars to the barrel, the plunger no longer telescopes.  (I did three small TIG welds on each mount.)  My first attempt ended with a stuck plunger.  My second attempt is also close to getting stuck, but I pulled the plunger out in time.

I sanded the plunger and tried to hone the barrel with a brake cylinder hone (along with cutting fluid), but I don’t think that the hone was coarse enough to increase the barrel diameter.

Any suggestions on how to bore the pipe out?  Worst case, I can buy a third barrel, but is there a trick to reducing the pipe distortion during welding?

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18/07/2019 at 22:15

TIG isn’t a great for this due to the massive heat; a better MIG welder will do fine if you make just very small welds and wait in between it should go fine.

19/07/2019 at 07:03

Thanks.  Actually, I don’t have a MIG welder.  I have a DC TIG/stick welder.  Is stick okay with electrode-positive for a cooler work piece?

19/07/2019 at 07:14

could work; now you have enough barrels to test it 🙂 most folks here use a stick welder

20/07/2019 at 06:28

Update: I tried once more with TIG.  I lowered the current by going to flat DC instead of pulsed.  Dropped the rod size, and did the welds in two shifts to allow cooling in between.  The plunger is working fine!  Lesson for me in welding distortion.  Thanks again.

PS. If anyone finds this in future, I used 100A with 3/32″ ER70S-2 rod and 3/32″ ceriated electrode with lens at 15 CFM pure argon.  Barrel is cold-rolled tube 1026 DOM 1.250″ x 0.120″.  Welder is Hitbox TIG 180A running on 240V.

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