If undoing like 70% or more, I would start fresh. If something went wrong, you can try opening the backup file if you are backing up stuff. I have mines set at 30 minute interval. I'm more worry about a crash then not able to undo.

Sounds like you can split the U-shape into an L using a plane in the middle or create a rectangle big enough to cut off the long leg off the U. Not sure which direction would be your L. Once cut, you can extend the short leg of the L further if cutting through the middle. It is much easier to manipulate the solid than start from scratch.

Hi Bill,
Yes so if I had used N sided polygon this would work, but in this instance I had used lines.

Rockyroad, so the L shape was generate by removing one upright section, and keeping the whole length across the bottom part of the L. I could do so much with a sketch and then do more with the solid modelling, push/pull or whatever but why can't I go back?

Earlier I was doing more surface work, I did a surface join, then wanted to go back and remove the join and do a fillet instead, and there is no option when you right click the surface join to remove surface. So here do we need to add more features to the history?

Seems a little odd to me?

Hi,

OK so I've made up a tester part to demonstrate this. Apart from every other time I select something in the tree, I sometimes get an option, then if I reselect it, I get a different option. I've basically made something that will have a few levels to the history. Now I know it's not an idea build up, that's the point! so please don't be saying well you should of done this, should of done that, this is the point I'm making.

So in the attached, I have split a solid. Put a cut out in it and then added them together, from the opposite end towards the end that is split. Then added chamfers.
First issue - change the chamfer from 1mm to 0.5. start with chamfer 1041, then 1063 then 1087 and tell me what you see. What I see is it won't edit 1041 or 1063 but will edit 1087. Why? And again, please don't say you should've done the chamfers in one go by holding shift, sometimes you don't want too.
Second issue - go into the split in the union, and change the profile of the cut out from the 4 lines to a circle. You can't. Here it is, it's at a point where you need to undo a bunch of stuff, to change the profile to the do it all again.
Third issue - right click and remove chamfer 1041. tell me what happens. All of a sudden you have a new end piece? Why? I've only removed a chamfer? You may say, well at least remove the last chamfer put in first? Well ok then, lets remove 1113 chamfer. Nope still get an extra piece. At this stage this is where you can very quickly and easily run in to a dumb solid situation. You get a new bit, don't understand it, or know why it's there, hit delete and before you know it you're screwed.

Now I have no idea why after removing a chamfer you get an extra body, with history? I have no idea, why I can't edit the size on half the chamfers, and half of them I can. I would say being able to edit that cut out should be possible? It's not reliant on anything. Yet it'll happily let me edit the length of the extrude that has been split so it sticks out everywhere?

No, what I described works with extrusions built from any lines with the exception of arcs. With arcs you can move the whole arc but not individual ends.

The only think to be aware of is that the extrusion will fail if lines cross and form negative spaces.

Very true, then you rely on the undo, but you need to be able to see in to the future to know whether you'll ever need to change the part. I had a situation where I hit undo and the entire model disappeared! No idea what the hell happened there, but luckily I had saved it prior to doing it. It's just not smooth, this then takes more time, checking and double checking what's happened, why, how and so on.

I mentioned surfaces earlier. If for example you work on one half of the surface. Mirror it, or do a slightly different other half, join then,/add them, then for whatever reason you want to undo the join, you just can not undo it. so if you have done a load of other stuff in the mean time, undo is not going to be your friend.
There may be a load of reasons for doing something a certain way, but the only option you have with a surface is replace, or simply delete it all and start again. Time, time time!

Thanks for the comments so far @rockyroad, hopefully things will be looked at? I can deal with a few work around options, but when you simply shouldn't need them I think it starts to take the biscuit a little.