Will flux core tack weld on 4130 steel affect the finish weld?

by Rob
(Connecticut)

Hi,
I'm new to welding, and am working on a 4130 steel engine mount for an airplane. I've elected to try and tackweld the mount while in the jig and have a professional finish-weld the mount with TIG. I've been contemplating using flux-core wire welding to do the tacks (obviously less $ investment), but I am concerned that the tacks may contaminate the joints of the finish-weld. Do I need to worry about this in 4130 steel?

Also, most of the mount is 0.75" diameter 0.049" walled tubing (see fishmouthed tube angled up and off to the left in the photo) but a few of these connect with some beefier 0.75" x 0.3125" walled pipe pieces (vertical piece with the bolt going through it, in the photo) that actually accept the bolts that attaches the mount to the firewall. It is these latter joints that have proven to be very challenging with the ox/acetylene gas apparatus I have. I was hoping a cheap ~100 watt flux-core wire apparatus would be adequate to tack the 0.049" tubing to the 0.3125" material....would this work? (n.b. I have an aluminum 'shield' under the pieces to protect the wood table).

Many thanks,
Rob

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Rob,

the professional tig welder will hate it if you use flux core for tack welding. it spits and ends up with porosity .

bare wire mig would be better but there are some considerations because mig cools pretty quick for tack welding 4130.