I doubt you will get enough EVEN heat to achieve decent forge welds with that type of setup. If it's all you have, you can give it a try, but I would suggest letting it "warm up" for some time....like an hour or so. Depending on the material the rasp is made of, you're going to need between 2200F-2350F to get solid forge welds. Often times with temps below 2200F, folks will think they have thing forge welded, but it's usually just what I call a "glue job"..... very small "spots" will stick, but as soon as any impacts or stress takes place, those spots will pop apart.