[machinedude]

if you would have made that from solid it would have most likely moved some after you machined the bulk of the material away. something like that you would have to be pretty careful machining to keep it from moving. you would have to rough most of the material release everything and finish machining it by holding on to the piece in a manor that would not throw stress back into the part.

since you welded the piece and have some movement from welding you can work it back to being flat the same as you would after roughing from solid you would have just needed to have some thicker stock than needed so you have some material to straighten things back out after welding. stress relief after welding would make this process easier but that is not always needed if your careful in your approach machining things.

[JakeInCharlotte]

since you welded the piece and have some movement from welding you can work it back to being flat the same as you would after roughing from solid you would have just needed to have some thicker stock than needed so you have some material to straighten things back out after welding. stress relief after welding would make this process easier but that is not always needed if your careful in your approach machining things.

I left an extra .125" on the linear guide blocks for rough milling and scraping flat. Hopefully I won't have to take too much off the front and compromise the stiffness. The upside is I get to use my homemade table vise again. Do you have any opinions on soft jaws? Will they help grip the part better?

[machinedude]

soft jaws are not needed here. they work if you want to hold onto something irregular in shape or not mark a part up if it cosmetic. since this is just a basic rectangle steel jaws will work just fine.

most of the time soft jaws are used in a secondary operation on a contoured shape done on a CNC in the first operation. flat stock would be over sized mostly on thickness so you have a work holding hub to grip onto and the contour work is done above the vise jaws. once the first operation is done then a set of soft jaws are machined to match the contour so the work holding hub can be machines off and any additional work can be machined on that surface. this would be something typical where soft jaws come into play. for what your doing they would not offer any benefit.

when you flatten your part by resurfacing the faces watch your vise does not flex the part when you tighten it. you want just enough force to hold things but not so much it distorts the part. small light cuts to work the bow out is what your after on the first side and you don't want to hit the part down on this side. once you get one side flat in a free state then you can tap the part down on the second side but you still what just enough force on the vise to hold the part but not so much it flexes the part here too.

[machinedude]

i would probably approach the flatness something like this. take small light cuts with light force on the vise to take a little of the high spot out of the center. use a long straight edge so you can see where the bow is on the part. the bow is most likely to be across the long side and have a convex and concave side to it. i would put the convex side up and the concave side down since this will be the most stable position to hold the part. the first material to get removed will be in the center area, once you get the first side flat then you can flip the part and tap it down so you can hold the thickness close. i made a quick sketch for reference nothing fancy Attachment 434150