View Full Version : Shortening one ton truck frame.

04-28-2009, 06:44 PM
http://photos-h.ak.fbcdn.net/hphotos-ak-snc1/hs010.snc1/2885_1053108890133_1298124187_30116231_7662862_n.j pg

Laid a tri-square on the mark, traced it with the plasma cutter, made another mark 27" up the flat part of frame, clamped tri square there, traced it with the plasma cutter.

Did other side exactly the same. Pulled the two halves back together and the miter cuts fit perfectly. Welded with a root pass from the backside kinda hot, then a pass on the front kinda hot. Beat the "tab" over on the bottom and welded it in. That's the cut out piece laying on top of the frame.

Capped the outside with a 3/32nd 7018 at 125 amps on the Synchrowave 200 in stick mode.

Now have winched it in front of the wrecker body under a Aframe outside, going to slide in under it tomorrow after I doctor my sunburn.
I'll probably add in a fish-plate, but have to see where the wrecker body tabs hang down since they will interfere with the alignment. There are tabs in front of this weld, and behind it. The two channel frames will support each other.

Re: why I angle cut it.. a angle has more surface length, a 45 degree side of the tri square has 1.5 the 10" distance, so I ended up with over 15" of weld instead of the 10" if I had cut it straight across. A HOT root pass walking back and forth stitches the sides together and the metals all flow together.

I was going to tig weld it all, changed my mind. Took longer to clean it all up with a grinder than to do it. The truck is stripped, no engine, transmission or driveshaft in the way.

04-28-2009, 07:48 PM
almost looks like you know what your doing. . . . . :D

04-28-2009, 08:02 PM
David its called fishplating. that is how frame truck shops make up extensiond and just like youre train of Logic. The extra length of weld gives it increased strength BUUT you DO NOT weld the ends.. Nice Job when you coming up North to Bear Country for some good home cooking??

04-29-2009, 11:25 AM
Can you explain about not welding the ends?

04-29-2009, 07:28 PM
Welding across lines of stress?

04-30-2009, 01:40 AM
I am lost too...


On Ibeams patched a diamond shaped piece put across the seam is fully welded in. A gusset if you will or "fish plate" ie: it's namesake since it being diamond shaped it looks like a fish.

04-30-2009, 01:56 AM
He knows what he is talking about.. just never considered the torsional stress. IE: twist..

Next to any weld will be what is termed the heat affected zone and it can be a stress riser causing a crack to develop . On a box section frame the upper plane is under a compression load , the lower under tension .The web or side plane is under the same loads with the center of the web as a neutral loaded member . To weld an overlay plate it is best to shape it as a diamond <=> or >=< on the vertical so a crack can't run across the web in a straight line .Most welders refer to this as a "fish" plate , it can be welded fully . We routinely use this method on heavy truck frames when shortening or lengthening wheelbase .Hope this helps .

04-30-2009, 11:04 AM
He knows what he is talking about.. just never considered the torsional stress. IE: twist..

Who were you quoting?

04-30-2009, 11:21 AM
Hi David..

Well Mike didn't answer, so I googled till I come up with a response.

I was taught to put diamond shaped plates on Ibeam, those were mostly cut straight across so they could drop out, then go back.

I cut one in a big C once.. got cursed out.. I thought lapping the top and bottom would make it stronger.

I did lap the bottom edge of this truck frame. THE other frame, the one with the dump truck bed now, it has a flat bar up the length of the frame bottom edge.

I'm sunburnt, poison ivy'ed, saw briar scratched, dug metal, thorns from my feet, sore throat, itchy.. vision blurred, and full of bisquits and gravy.. My dog has been in a coma all morning from the plate I gave him.

Not got anything done on the truck in two days now. I got more than I can work on right now.. probably stick this one up on Hamb.

05-10-2009, 05:43 AM
Just a suggestion. This is how I would layout the section on a frame.


and the oppossite on the other side. Still looks good though with the fishplates

05-10-2009, 09:07 AM
IMO you're still going to get stress risers at the corners. A scarff joint is still going to be the stronger joint.