V-carve first or pocket first for raised letters?

[blackhawk]

When you guys create raised letters inside a pocket, do you machine the pocket first and then V carve or vice versa?

I have been doing the V-carve first, but when I go back to clean the pocket area, I sometimes have chunks of material break off before it is machined. I suppose that when the pocketing endmill gets near the V-carve areas, the material left is real thin and breaks off. Sound like a good theory?

[signtist]

You should have a bold enough outline around the letter so this isn't a problem. Looks better too!
John www.signgraphics1.com (http://www.signgraphics1.com)

[eaglesplsh]

This issue came up when I started playing around with the V-carved inlay method that's often discussed on the forum. The Male half of the inlay is made up of raised V-carved letters/pictures.

I noticed that PartWorks handles things funny when you include a larger bit to speed up the flat area clearing in a V-carve operation. PW puts the large bit moves before the V-carve bit moves. But, the V-carve tool path cuts the letters first, and then does any remaining flat clearing.

I did a small amount of testing and my results seemed to show that you were better off cutting the V-carve tool path first. That maintains an even cutting load on the bit and seems to cut down on the potential for chipout. The V-carve toolpath will automatically follow this initial cut with area clearance using the V-bit. Then your large cutter tool path can hog out the remainder.

I was cutting maple for my tests. It sounds like you're describing different results. What kind of wood/material are you using? Anyone else have experience to give advice?

[blackhawk]

Russ - I have seen my problem on HDU and MDF mostly. I don't have a tool changer, so I have always been doing the V carve first. My thoughts were that by doing the V carve first, the V bit would not lead off because there would be solid material on both sides. I doubt now that the loads are really that significant.

Back on subject, when the V carve bit finishes, it of course leaves an open area around the lettering. When the endmill does the pocketing it starts in the center of an area and spirals its way out. Once the endmill gets close to the V carved areas, chunks of material will start to break off before the final pass of the endmill. When the material tears off, it will sometimes leave a gouge.

[widgetworks_unlimited]

Brad - I used a downcut spiral for clearing between letters. That may be why I didn't get the gouging that you're seeing.

I usually set me stepover to 40% - seems to give me a cleaner finish on the bottoms of pockets.

[hardak]

I've found a same problem cutting acrylic. Pocketing should be done from the outside in. when i start on the inside out I get to the thin strips and they break off before the bit gets there. it hasn't wrecked anything yet when pocketing try adding some raster allowance

[Gary Campbell]

Brad...
I've done this in the past, using pointed roundover bits and V bits. If you do your outline around the letter about .015 to .020 deeper than the area clearance it helps to eliminate chipping. The extra depth border is barely noticeable, and may even add to the aesthetics.

The pic below shows lettering outlined with a .1875 pointed roundover and the area clearance was done with a 1/4 and 1/16 EM's. The oval border was cut .025 lower than the surrounding area clearance.

5531
Gary

[blackhawk]

I tried a raster toolpath in cedar and it cut much much better. The raster toolpath eliminated about 80% of my toolmarks. The raster pattern would also tear out strips of wood. This actually happened several places away from the letters. With raster, your cutter goes back and forth, so you have one pass in climb and then the next pass in conventional cut. The climb cut never tore out any strips of wood. The conventional cut would do so about half the time. It makes senses if you imagine how the cutter is pushing into the wood during a conventional cut. I think that two things could have helped to lesssen the tear out. First, I had about a 60% stepover, so backing that down to 40% probably would help, although a slower cut time. Second, I used a straight bit, a down spiral may not tear as bad.