finishing motorcycle exhaust pipe butt welds

hello, i am new to the forumn tonight. Glad i found you, and hope someone can help. i am not new to welding, but do not do it everyday. some days i weld like a pro, others i dont think i should be allowed to weld at all! i am making exhaust pipes for my bike, and am having a difficult time with the butt joints, and the size transitions. the pipes start at 2", step to 2-1/4" and end up at 2-1/2". i had a tubing company bend the specific radius of each size i was looking for, but when it comes to joining them at the size changes i am having to finish them by hand. the result is a smooth step, but not even in terms of around the pipe. keep in mind that not only are the pipes visible, they are a focal point, so perfection is the minimum. as far as the butt joints go, finishing them to a look as if no joint is even there is the goal, however, seems an impossible task. i have tried every different sanding device available to man, but by the time i grind / sand off the weld it is noticable in at least one spot or another. if i fill it in it only gets worse due to under cut from the new weld. any tips on filling pinholes? they usually grow into a nightmare also! the list of problems go on... PLEASE HELP! for equipment i have a Snap-On muscle-mig 250, arCo2 gas, i also have a spool gun for aluminum & stainless, and a tig setup for this welder, and get the same results. the pipes are .065" wall thickness. ANY AND ALL TIPS/TRICKS WILL BE APPRECIATED. THANKS

Why not get the ends of each pipe swaged out to the new diameter, that way you're welding the same size to each and the step will be perfectly round (unless the change is on a bend, in which case you need to redesign it) Just sit the two pipes in the V of a bit of angle iron to align them whilst you tack them up.

Cleaning off welds is an art in its self.

A flap disc will be one of the best bets. Using the pad, rough down the weld until you can only just see the edges of the weld. Then in a very light side to side motion take the rest off. The light touch is essential to prevent any dig in.

You will be left with some light sanding marks, but no deep digs.

The same on the bends, a very light touch, and keep the pad as flat as possible, by moving the grinder around the bend radius.

It comes with practice! Thin tubes are harder to do beceause any digs cant be polished out deeper.

PLEASE HELP! for equipment i have a Snap-On muscle-mig 250, arCo2 gas, i also have a spool gun for aluminum & stainless, and a tig setup for this welder,

You would be better using the TIG setup as it gives a much flatter, neater weld and, when done properly, actually adds appearance to the finished job; look at mountain bike frames etc. that have been nicely TIG welded. Forget about sanding/grinding off the weld; instead use some Pickling Paste to remove the thermal blueing & bingo!
weldequip

Being of the motorcycle building persuasion myself, you will only get nice looking welds with oxy-acetylene (if you're good and quick with it) or better still TIG it.

If you pre heat the area with a blow torch until the metal is straw yellow in colour, then MIG it you will get flatter neater welds also.

Guys, I have just used the browser and think have the same problem. But I found somethink like that

http://www.allegro.pl/item407154537_..._tasmowa_.html

quite nice but still expensive. I just thought... I could make such an adapter myself and add it to my milwaukee angle grinder... nice piece of stuff - what do you think?

Looks a useful tool, i'll add it to my list of must make one.

How good a joint fit do you have between the different size pipes?. If I understand correctly you are stepping up by a ¼ inch at a time with 1/16th inch wall tube, assuming you are inserting one inside the other, there must be gaps of 1/16th all around the tube, you could eliminate these gaps by rolling a band as a spacer this will centre up the joint and give you a nice fillet weld to make with the TIG, as weldequip says then just clean the weld with either pickling paste, or polish with a sisal mop and compound,

it's a mig section as I understand, so far I cannot affort TIG so I am trying to make my life easier in cheapo way..

ref pipes get yourself a welding rod take the flux off it
wrap around the smaller pipe till snug fit in the larger
pipe burn the lot together bit old school but simple
things often work well if not best and should always
be passed on