Knife tool Cut through not working

Will give it a try but i remember trying all sort of value for the clip start and it was still doing so.

The other reason i prefer centimeter is for easier spinning of numeric field since at default 1 meter unit the numeric field go way too fast making precision work a pain even while holding the shift key.

That’s weird. That is not what is supposed to happen.

Here i disable the z key for shading pie menu to see if z for cut trough in knife tool would work and it didn’t !

Like i have said this was fresh blender without addons with default settings so i am completely at lost but i saw a few post and thread on blender devs having a hard time with strange issues with knife tool.

It work correctly on one side but no way to have to cut trough it simply don’t want to do it correctly here.

I tried 0.01 in clip start and the result got a little better but still miss one edge here a picture;

I wonder if i should report this as a bug?

Did another test since the clipping make it work in perspective but the result is even worst regarding topology ;

I tried on a cylinder same issue ;

OK my latest test were to scale in edit mod 2 versions of the cube, one very small and another one gigantic and the result are always the same.

I thought about cutting half the cube and adding a mirror modifier on x as a workaround but the top and bottom are not getting cut.

So far my conclusion are that this tool function(cut trough is bugged) and this issue make that function unreliable.

Test it in 2.78 and it is working then i went back in all recent version and it is not working so something is certainly wrong here;

I just can’t believe i lost 5 hours trying to solved this issue that was not even documented or mention on stack exchange or any other thread i saw on the subject or maybe i miss one.

This is one of those obscure blender way to do thing that almost no one talk about! I had to dig really deep to find this one all by myself. I am seriously frustrated about that.

Make sure to activate it again if you only want to cut on front faces. Forget about holding z like many thread mention since it is a broken feature, sometime it will work if you only draw a straight cut but once you have a few cuts done it will screw up and cutting in any angle will not work at all.

Also if you want to cut only on selected face or edge just activate Only Selected.

Here the solution to anyone who stumble upon this thread ;

Edit : there is a better solution from John Malcom, the cut through option is indeed working but you have to do thing in the right order to make it work, first click once a little outside your object and you will see the bottom bar options for the knife tool then hit z and you should see the Cut Through option is now to ON finally proceed with cutting and there you have it.

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Yeah, with the new active tool system, you can’t toggle options by pressing a letter on the keyboard since they are on at all times. The z key still enables cut through when you use the command version of the knife tool though.

Hi zanzio,

Yes it’s still enable it but result are not correct for anything that goes beyond a straight cut and if you want to zig zag or overlap on new cuts it will go berserk like the image i post in thread beginning.

Even shift k that is suppose to activate Cut through doesn’t work and when you hit z in newest version you get the shading pie menu instead of the cut through even with knife tool activated!

I think a few features would need a little polish to become perfect.

Ah, i see what you mean now. I tried doing zig zags on a subdivided cube and it does mess up the geometry on the other side. Have you reported this as a bug?

Hi zanzio,

Not yet because i want to see if it is truly a bug or a limitation of the tool function.

Just came across this post,

hmmmm with ‘occlude geometry’ on it shouldn’t even touch the backfaces, so it is a bug to me.

Pressing Z won’t do anything useful if you are using the active tool Knife from the Toolbar. Z is only used for Knife related stuff if you are using the standard Knife command - by pressing K on your keyboard. Even then you don’t hold Z or anything.You press K, then Z then make your cuts. All the modifier keys like Z (for cut through) or C to constrain cuts to certain angles are shown at the bottom of the screen when using the Knife. They are on/off toggles mainly.

Hi John,

Well that’s what stack exchange was saying, to hold z while you are cutting not just hitting z once and then cut and after testing it for 5 hours you indeed have to hold z for cut through to work.

Just hitting z once do absolutely nothing and i tried it on many blender versions with the same result.

It’s flaky at best but at least i know how to have perfect cutting through with Occlude Geometry disable.

The name bring confusion since at first i also thought this was to avoid touching backfaces.

Press K. Look down at the bottom of the screen where the options are listed, as in my screenshot. Near the end of the line it will say ‘Z Cut Through (Off)’. Press Z once. It will now read ‘Z: Cut Through (On)’. It will now cut through.

Then try this: Press K. Look down at the options mentioned above and hold down K. You will see the text ‘Off’ rapidly alternating with the text ‘On’ as long as you have the button held down.

This may have caused your initial problem - where you showed some cuts cutting through and some not. Basically whatever state the tool was in when you made each section of the cut had a 50/50 chance of cutting through or not cutting through.

It’s a toggle. Press it once. Same with C to constrain. The only buttons that need held down while using the Knife tool are Shift and Ctrl (for midpoint snap and ignore snap)

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Yes, this is what it means.

Also, @JohnMalcolm1970 is right - Z is a toggle but doesn’t work in the tool version of the knife operator (like @zanzio said).

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John you are right it is indeed working but it was really not obvious since to see the bottom bar options you first have to click once on the screen and then hitting z put the cut through ON!

I swear i tried a lot of time to make it work last night and i was not able to make it work so i seriously think the documentation should be upgrade so other people are not having the same frustration i had.

You have the better solution so i will mark yours as the solution since even if my solution work it was not the right way to do it but it’s good to know these options are there.

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