transformer rewind chalenge

So the other day in work we had in a large psu/charger for a forklift . Four bobbins on a multiKW core , one of the primaries cooked .
So we stripped off the flat wire wound pri. , calculated what two smaller round cores would be equivalent ,and wound er back up bifilar  . Anyway it comes to replacing the lams , as usual the first few lams to come out were  bashed up and a bit bent ,the boss issues a challenge , 200 euros each for me and the other guy working on it if we fit all the lams back in . I decided to trim the tongue of the E's that were mangled , all of a sudden the boss was really worried , we had it down to three lams remaining and bakelite spacers , before boss declared the trimming of lams wasnt part of the deal  ;D
We ended up leaving him off the hook in the end ,but Im certain with a little trim and the tap of a hammer we could have restuffed that core completely , oh well discretion is the better part of valour sometimes  :-X
Anyway job was a good one in the end , less than 5% difference in the dc resistance of the new and old half primaries , saved the owners thousands Im sure .

put the xfmr in the oven and you could have stuffed three more,

Yeah ,
stripping small edges  of varnish off the lams with razor blade made a big difference to how they settle back in to the stack , we could have done it ,but boss would have lost face ,ahahahahahah
running a file over the edge of the E lams central I made it do-able ,gotta be carefull when you bang the wedge back in not to break the bobbin though . Overenthusiasm bustin them lams back in could have ended up in a bum job easy too ,then we end up oweing the boss a few soverigns 

heating the transformer means the coil expands more than the core, thus allowing more clearance for lams

insulation also gets easier to stretch,



pound some Glastic blocking into the coil/core assy, put it in the oven, pull it out, remove Glastic wedges and you have room for lams

sometimes we would block the heck out of a coil , put it in the bakeout, come in the next day and the coil would be loose, requiring anoth 1/16 chunk  of Glastic.

Thanks for the tips Cj , will come in handy next week as I have another battery charger on the bench , smaller and more simple winding arrangement on this one , so I might get a shot at winding the coil myself this time . It probably makes sense to keep the lams stacked exactly in the order they come out as it seems to make it easier to fit them all back in in the end .