3d engrave with a flat bottom?

I am using Alphacam 2014R2 essentials router. I have to make a sign for a guy at work that is retiring. They want it to be cut with a 90 degree V-bit .500" deep. The problem is the that the sign is 75"x30"x1" made out of some pretty expensive wood. There will only be one shot to cut it so it has to be right the first time. With the 45 degree bit it will cut the inside of all the letters with the 3d engrave but then it leaves sections in the middle of the letters that are not cut. They want those sections to have a flat bottom. This is my first time doing any 3d engraving or lettering at all. Everything else I cut is pretty basic. I have tried pocketing with the V-bit and it doesn't work. Nor does pocketing with a 1/8" end mill leaving .500" material for the V-bit. It cuts off parts where the V-bit should be cutting.

Attached is a DXF of what I am trying to cut. Any ideas on how to program this sign?

The end mills I have are 1/2, 3/8, 1/4, 3/16, 1/8 all 2 flute flat bottom and a 90 degree Vbit

Material top 1"
Final depth .500"

Hi - it's quite easy - if you attach the AlphaCAM Drawing you have made, with the tools inside (doesn't matter that it's not correct programmed - just to work further on this) Then I can make a small video of what to do... -I don't want to confuse You, with an example with my tools etc. as I work in Metric - not in Inches :-)

Answer sent :-)

This can be a bit tricky - because AC can have some problems when running around sharp internal corners, it loves to round them.. therefore I do an offset, so I can decide where it must go.

And the "M" has a loop in the Geometry - this I remove.. Then a big tool - and a smaller to remove the small bits.. and finally the 3D engraving..

There is some small parts left to remove with a smaller tool the same way as nr.2 operation, or by hand

A link to a small Video here: 2014-12-10_1754 - Lisbeth_B's library

Hope this helps You out a bit - or just ask..

This is my tried and tested method.. it's really easy. You can get tools with flats on from 0.1mm upwards I usually use one with about a 0.3mm flat on depending on the size of lettering. So no tool change needed!

VIDEO

I just but 0.1 stock on the pocket make sure there are no scuff marks from the pocket operation.

Have fun!

Sorry to put this down...
But - what about the internal corners? Not sharp - They look awful.. and this was one of the problems from the start..
- and cutting the flat parts with the 45 deg. Engrave Tool - is ok in Simulation - but not in real life... (not even if it's 0,3 flat) - You need to do some rough cutting first

It came out looking great. Thanks for your help camnerd. The fonts were not my choice at all. The graphics girl thinks our CNC machines are magic and can cut anything she can think up. She sent me a dxf once with a bunch of rectangles .254mm wide, 76.2mm long, spaced .127mm apart and wanted me to cut them 15.875mm deep....... One of the biggest issues from the start is the fact that I had one shot to do it and I am using Alphacam essentials so I can't view solid simulations. I'll try to get a picture of the finished product. It was made from strips of red oak, white oak, and cumaru.

Just trying to give some advice.... I must say as I was never sign writing in my 15 years as CNC operator programmer so the round corners never bothered me :)
I like your method it is a very good solution !

Yes, I see your point.. but people designing signs etc. are VERY sensitive.. ;-)

AlphaCAM is very good to make this kind of things (and for the price for an Essential version, there is very much power) - but sometimes we need to tweak it a bit anyway...

But I think when making signs / special jobs etc. I would be sad, not to have the simulation - I would then go for the Standard version instead.